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String-pulling is among the most widespread cognitive tasks used to test problem-solving skills in mammals and birds. The task requires animals to comprehend that pulling on a non-valuable string moves an otherwise inaccessible food reward to within their reach. Although at least 90 avian species have been administered the string-pull test, all but five of them were perching birds (passeriformes) or parrots (psittaciformes). Waterbirds (Aequorlitornithes) are poorly represented in the cognitive literature, yet are known to engage in complex foraging behaviours. In this study, we tested whether free-living ring-billed gulls (Larus delawarensis), a species known for their behavioural flexibility and foraging innovativeness, could solve a horizontal string-pull test. Here, we show that 25% (26/104) of the ring-billed gulls that attempted to solve the test at least once over a maximum of three trials were successful, and that 21% of them (22/104) succeeded during their first attempt. Ring-billed gulls are thus the first waterbird known to solve a horizontal single-string-rewarded string-pull test. Since innovation rate and problem-solving are associated with species' ability to endure environmental alterations, we suggest that testing the problem-solving skills of other species facing environmental challenges will inform us of their vulnerability in a rapidly changing world.

Interactions between parasite species may influence their distribution and abundance within communities. Experimental single-species infections of Diplostomum spp. in the gut of the definitive host, the Ringed-billed Gull (Larus delawarensis Ord, 1815), were compared with mixed-species infections to explore interactions among parasites. Three species of Diplostomum von Nordmann, 1832 (Digenea), designated as Diplostomum sp. 1, Diplostomum sp. 4, and Diplostomum baeri Dubois, 1937, were examined for intestinal distribution and fecundity in single and mixed infections. In single-species infections, most specimens of Diplostomum sp. 1 and D. baeri were recovered from the mid-region of the intestine, whereas Diplostomum sp. 4 were mainly present in the anterior region. Significant spatial displacement was observed only for D. baeri when Diplostomum sp. 1 was also present. Intensity was directly correlated to the number of occupied intestinal segments, and there was no significant difference in mean linear span for each species between single-species and mixed-species infections. Diplostomum sp. 4 had the highest mean number of eggs per worm in utero in single-species infections. In mixed-species infections, the fecundity of Diplostomum sp. 4 declined dramatically in the presence of Diplostomum sp. 1, whereas fecundity of Diplostomum sp. 1 increased in the presence of D. baeri. These results highlight interspecific interactions that may play a role in population dynamics of Diplostomum spp. and community structure.

Larus delawarensis (Ring-billed Gull) populations have increased >4% annually in the Great Lakes region since 2003. Gull–human interactions and conflicts have similarly increased, particularly concerning human health and safety issues related to gull feces deposited at recreational beaches. During June–August 2013, we conducted a radiotelemetry study of Ring-billed Gulls in a Lake Michigan coastal region to determine patterns of habitat use and movement between recreational beaches and human infrastructure by gulls. Of 14 individuals relocated, we found Ring-billed Gulls selected recreational beaches and landfill sites and avoided agricultural fields. We found 5 of 14 gulls made a minimum of 2 roundtrips between beaches and landfills over the study period. Gulls may serve as transport vectors for bacteria and other pathogens from human-waste sites to areas of probable human contact and concentration, such as public recreational beaches. As such, pathogen distribution and connectivity within a landscape could be established, maintained, and enhanced by gull movements. Managers may need to implement exclusion tools for gulls at both of these sites to maintain human-health standards.

Do birds detect and respond to forces acting on feathers through filoplumes, which appear to be unique mechanosensory feathers? If filoplumes function as sensors, their morphology should covary with the morphology of their companion feather to better detect feather movements and position. We explore covariation in filoplumes and primaries across 5 species of birds that vary in body size, molt strategy, and the functional life span of their primaries (Green-winged Teal [Anas crecca], Ring-billed Gull [Larus delawarensis], Turkey Vulture [Cathartes aura], Red-tailed Hawk [Buteo jamaicensis], and Red-winged Blackbird [Agelaius phoeniceus]). Filoplumes never extended beyond the coverts and inserted immediately adjacent to the base of their companion primaries, positioning them to detect subtle changes in feather vibration or movement. Far more variation in filoplume number and morphology was due to species differences than to individuals or position in the wing. Across species, filoplume length and number increased with calamus length of primaries. In the 2 species with growing primaries, the number and length of filoplumes were only weakly associated with molting primaries, suggesting that filoplumes were not replaced when their companion primary was replaced. Further, filoplumes associated with a growing primary were not replaced synchronously, leaving others to sense primary position and movement. Finally, filoplume number and length were greatest in Red-tailed Hawks, a species that carries individual feathers for multiple years, but links between filoplume morphology and molt strategy await broader comparative studies. Taken together, the morphology of filoplumes and their replacement schedule relative to their associated primary suggests that they are sensors, capable of detecting subtle differences in the position and movement of their companion feathers.LAY SUMMARYHow do birds detect and respond to forces acting on feathers, which have no nerves? One idea is through unique mechanosensory feathers called filoplumes.Filoplumes resemble hairs with downy tufts at their tips. They are found immediately adjacent to every contour and flight feather and are thought to transmit information about feather position and movements.We explore links between filoplume morphology and flight feathers in five species of birds. We find that, across species, filoplume morphology matches feather morphology as expected if they function as effective sensors. We also find that the replacement of filoplumes is staggered and not strongly tied to their companion feather, which would allow for the overall sensory function to be maintained.Our findings support the idea that filoplumes may function as sensors of feather position and condition. If these suppositions hold, we predict strong associations between flight ecology, molt strategy, and filoplume morphology.

Landfills represent important sources of local emissions of organic contaminants, including halogenated (HFR) and organophosphate ester (OPE) flame retardants used in a large variety of consumer products. Gulls foraging in landfills may be exposed to elevated atmospheric concentrations of HFRs and OPEs that may vary spatially and temporally within a landfill site, thus modulating their exposure. The objective of the present study was to investigate the spatial and temporal variability of HFR and OPE concentrations in air samples collected from a major landfill in the Montreal area (QC, Canada) that is frequently visited by gulls for foraging. Miniature stationary passive air samplers (PASs) and high-volume active air samplers (AASs) were deployed in six different areas within this landfill site for 34 days to collect HFRs and OPEs in air. During the same period, wild-caught ring-billed gulls (Larus delawarensis) were equipped on their back with a similar miniature PAS that was deployed in the landfill along with a GPS datalogger to monitor their movements for ten days. Elevated concentrations of certain OPEs (e.g., tris(2-chloroethyl) phosphate and tris(2-chloroisopropyl) phosphate) and brominated diphenyl ether (BDE)-209 were measured in stationary PASs and AASs, although they were homogenously distributed within this landfill site. Temporal variability was observed for concentrations of BDE-209, -99 and -47 measured in AASs as well as tributyl phosphate during the 34-day deployment period. Moreover, air concentrations of BDE-209, -207 and -206 and selected OPEs (tris(1,3-dichloro-2-propyl) phosphate and tris(methylphenyl) phosphate) determined using AASs were positively correlated with ambient air temperatures. Gulls that visited a landfill at least once exhibited significantly greater concentrations of BDE-47 measured in PASs they carried on their back, suggesting that landfill air may represent a source of exposure to PBDEs for these birds, and potentially other urban-adapted wildlife using these sites for foraging.

A 20-year-old female mute swan (Cygnus olor) originally in a flock of free-living swans on a Long Island, New York, lake, was presented for facial swelling and decreased appetite. An adult male ring-billed gull (Larus delawarensis) was also presented to the same wildlife rescue center for bilateral lameness of 1-week duration. Once referred for veterinary evaluation and care, both species were diagnosed with septic arthritis and osteomyelitis caused by Chryseobacterium indologenes and treated with orbifloxacin until complete recovery. Chryseobacterium indologenes is infrequently diagnosed as an opportunistic pathogen in human medicine, and less so in veterinary medicine. In human patients, this bacterium is the cause of various infections, including meningitis, pneumonia, and implant failure. However, in veterinary medicine its pathogenicity has only been reported in fish, and sporadically mentioned as a culture result in tree frogs and turtles, where it was generally considered insignificant. In this report a clinical presentation, diagnosis, treatment, and outcome of osteomyelitis and septic arthritis caused by C indologenes is described in 1 anseriforme and in 1 charadriiforme species.

Birds may act as biovectors of nutrients and contaminants at the regional scale and potentially increase the exposure to such substances in ecosystems frequented by these birds. However, no study has estimated biotransport of contaminants by individual birds through their feces (guano). Elevated concentrations of halogenated flame retardants (HFRs) have been reported in ring-billed gulls (Larus delawarensis) breeding near Montreal (QC, Canada)- a known hotspot for HFRs. The objective of the present study was to investigate the concentrations of polybrominated diphenyl ethers (PBDEs) and selected emerging HFRs (e.g., Dechlorane-related compounds) in guano of individual ring-billed gulls, and to assess the relative accumulation of these HFRs by comparing concentrations in plasma (absorbed) versus guano (excreted). A second objective was to determine the importance of one of the largest ring-billed gull colony (Deslauriers Island) in North America located near Montreal as a vector of HFR biotransport at the regional scale. Elevated concentrations of PBDEs and Dechlorane plus were determined in guano and plasma of ring-billed gulls, although in general no difference was found between males and females. However, plasma to guano concentration ratios were significantly greater in females for the highly hydrophobic BDE-209 and Dechlorane plus compared to males. Overall, for both sexes combined, the total amount of HFRs (sum of the 16 major PBDEs and five emerging HFRs) deposited by this entire colony (64,980 gulls) in the Montreal area through guano during the 28-days incubation period was estimated to 1 g. This study showed that urban-adapted ring-billed gulls from this large colony represent an underestimated biovector of HFRs, which may contribute to augment exposure to these toxic compounds in nearby ecosystems.

Nesting localities of extant birds and reptiles may provide taphonomic models for interpreting nesting sites of ancient archosaurs. Here we describe assemblages of nesting gulls (Larus delawarensis...

Studies have shown that debromination of the major component in the deca-brominated diphenyl ether mixture (deca-BDE), BDE-209, occurs in vivo in birds. Recent work from our laboratory on breeding ring-billed gulls (Larus delawarensis) exposed to elevated PBDE concentrations in the densely-populated metropolis of Montreal (Canada) further suggests that BDE-209 debromination is potentially catalyzed by deiodinases in liver microsomes. The first objective of this study was to determine if type 1 deiodinase (D1) was involved in the in vitro debromination of BDE-209 in liver microsomes of ring-billed gulls. The second objective was to determine if there was an interaction between D1 and BDE-209 using an in vitro D1 activity assay. No depletion of BDE-209 was observed in gull liver microsomes. A significant 42% increase in total D1 activity was found in gull liver microsomes at the medium BDE-209 concentration (1.0 nM), although not at the low (0.5 nM) or high (2.5 nM) concentrations, suggesting potential non-dose related interaction with D1. Moreover, no correlation was found between total D1 activity in liver microsomes and plasma thyroid hormone levels, although there was a negative relationship between plasma BDE-209 concentrations and FT3 levels. Results from this study suggest that debromination of BDE-209 did not occur using present in vitro assay conditions, although indicated potential interaction with D1 that may have implication on circulating thyroid hormone status.

Impacts of large-scale oil spills on avian species are far-reaching. While media attention often focuses on lethal impacts, sub-lethal effects and the impacts of rehabilitation receive less attention. The objective of our study was to characterize effects of moderate external oiling and subsequent rehabilitation on feather structure and thermoregulation in gulls. We captured 30 wild ring-billed gulls (Larus delawarensis) and randomly assigned each individual to an experimental group: 1) controls, 2) rehabilitated birds (externally oiled, rehabilitated by washing), or 3) oiled birds (externally oiled, not rehabilitated). We externally oiled birds with weathered MC252 Deepwater Horizon oil (water for controls) and collected feathers and thermography imagery (FLIR) approximately weekly for four weeks to investigate feather structure (quantified using a barbule clumping index) and thermoregulatory ability (characterized by internal body temperature and external surface temperature). Post-oiling feather clumping was significantly higher in oiled and rehabilitated birds compared to controls, but steadily declined over time in both groups. However, feather microstructure in rehabilitated birds was indistinguishable from controls within three weeks of washing whereas the feathers of oiled birds were still significantly clumped a month post oiling. Internal body temperatures didn't differ in any of the groups, suggesting birds maintain thermoregulatory homeostasis in spite of moderate external oiling. External temperatures for rehabilitated birds didn't differ from controls within a week of rehabilitation. Overall, rehabilitation procedures were effective and washed birds were in better condition compared to non-rehabilitated, oiled birds. This study provides evidence that the benefits of rehabilitation for moderately oiled birds likely outweigh the costs with regard to feather structure and thermoregulation. While feather preening and time were insufficient to reestablish baseline fine scale feather structure in moderately oiled birds, the significant clumping reduction over time may indicate that rehabilitation of lightly oiled birds may not be necessary and deserves further study.

Avian species experience extensive morbidity and mortality following large-scale oil spills, often resulting in oiled birds being rescued, and admitted to rehabilitation. Our objective was to experimentally establish time-specific, descriptive blood analyte data following sublethal oil exposure and subsequent rehabilitation. Thirty wild Ring-billed Gulls (Larus delawarensis) were randomly allocated to three treatment groups of 10 birds each. One treatment group served as controls and two treatment groups were externally oiled daily for 3 days with weathered MC252 oil collected from the Deepwater Horizon oil spill, mimicking the upper threshold of the US Fish and Wildlife Service's moderate oiling classification. Following external oiling, one oiled treatment group was cleaned via standard rehabilitation practices. Serial venous blood samples were collected for a month to measure packed cell volume, total solids, blood gas and select plasma biochemistry analytes, total white blood cell estimates and differentials, and reticulocyte estimates. We found that both sublethal oil exposure and aspects of captivity were associated with a mild non-regenerative anemia. No other differences in venous blood gas and biochemical analytes as well as white blood cell concentrations were observed among the three groups. These findings suggest that the mild anemia seen in oiled birds undergoing rehabilitation is possibly multifactorial and that moderately oiled gulls have subtle, but potentially not insignificant clinicopathological abnormalities following sublethal oil exposure. Oiled gulls did not develop any clinicopathological derangements post-rehabilitation, suggesting current standard practices for rehabilitation cause minimal morbidity in clinically stable, moderately oiled gulls.

Deca-brominated diphenyl ether (deca-BDE), composed mainly of BDE-209, is subject to usage restrictions in North America and Europe, although global action on its continued use has yet to be undertaken. Relatively large concentrations of polybrominated diphenyl ethers (PBDEs), especially BDE-209 and its higher brominated degradation products, have been reported in tissues of ring-billed gulls (Larus delawarensis) breeding near the densely populated city of Montreal (QC, Canada). There is limited knowledge of BDE-209 biotransformation and toxicokinetics in birds. Deiodinases, a class of enzymes catalyzing thyroid hormone conversion, have been suggested to be involved in BDE-209 debromination in birds. The objective of the present study was to investigate the relationships between PBDE concentrations and type 1 deiodinase (D1) transcription and in vitro activity (microsomes) in livers of Montreal-breeding ring-billed gulls. The ring-billed gulls exhibiting the highest D1 activity in liver microsomes accumulated the greatest liver concentrations of hepta-BDEs and octa-BDEs. Activity of D1 was inversely related to concentration ratios of BDE-209 to octa-BDEs and ∑hepta-BDE. An even stronger inverse relation was found between D1 activity and BDE-209 to ∑nona + octa + hepta-BDE concentration ratios. The messenger ribonucleic acid (mRNA) levels of D1 in gull livers were inversely associated with liver concentrations of ∑octa-BDE. The present study's findings suggest that D1 is potentially involved in BDE-209 biotransformation and accumulation of higher brominated PBDEs in livers of ring-billed gulls. Environ Toxicol Chem 2016;35:2215-2222. © 2016 SETAC.

Ring-billed Gulls (Larus delawarensis) were rare at the beginning of the 20th century, possibly because of intensive exploitation. Once they became protected in 1916, their numbers increased throughout eastern North America, reaching a maximum of 875,000 breeding pairs around 1990. Since then, an overall decline of 19% has been recorded in the Great Lakes and the St. Lawrence River while their numbers tripled in Atlantic Canada. The largest concentrations are still found on the Great Lakes with 38% and 42% of the birds breeding in Canada and the USA, respectively. The remaining individuals breed along the St. Lawrence River (15%), on Lake Champlain (2%), and in the Gulf of St. Lawrence including the Atlantic Provinces and Saint-Pierre-et-Miquelon (3%). In 2009, a study was undertaken in the largest colony located on Ile Deslauriers near Montreal, Quebec, to determine the factors that regulate the number of breeding birds. This colony supported 52,000 pairs in 2000 and 44,000 in 2012. Ring-billed...

While the breeding ecology of gulls (Laridae) has been well studied, their movements and spatial organization during the non-breeding season is poorly understood. The seasonal movements, winter-site fidelity, and site persistence of Ring-billed (Larus delawarensis) and Herring (L. argentatus) gulls to wintering areas were studied from 2008–2012. Satellite transmitters were deployed on Ring-billed Gulls (n = 21) and Herring Gulls (n = 14). Ten Ring-billed and six Herring gulls were tracked over multiple winters and > 300 wing-tagged Ring-billed Gulls were followed to determine winter-site fidelity and persistence. Home range overlap for individuals between years ranged between 0–1.0 (95% minimum convex polygon) and 0.31–0.79 (kernel utilization distributions). Ringbilled and Herring gulls remained at local wintering sites during the non-breeding season from 20–167 days and 74–161 days, respectively. The probability of a tagged Ring-billed Gull returning to the same site in subsequent winters was ...

Ring-billed Gull (Larus delawarensis) populations have dramatically increased throughout their geographic range with the largest concentrations in the Great Lakes region of Canada and the United States. Large populations of gulls cause conflict with humans at recreational beaches, where their effects on human health and safety include bacteria contamination from gull feces. We used border collies to harass and exclude gulls from beaches in summer 2012 and 2013, then measured gull numbers and Escherichia coli. Dogs were effective at reducing gull numbers by 56–76% during continuous and noncontinuous dog treatment periods. Levels of E. coli were lower on dog-treated beaches, but only during the first half of the summer. Mixed modeling analysis showed presence of dogs was a strong predictor of gull numbers and E. coli levels, with variation among dogs, possibly related to age. Noncontinuous use of dogs, applied within an integrated beach management framework, can provide a nonlethal method for reducing gull use and E. coli levels at recreational beaches.

Concentrations of trace elements vary naturally between geological environments and as a result of emissions from anthropogenic activities. Habitat use strategy is an important determinant of trace element concentrations in tissues and eggs of wild birds. However, a scarcity of studies have documented the relationships between individual bird movements related to foraging activities and exposure to contaminants including trace elements. The objective of the present study was to investigate the influence of habitat use strategy, determined using GPS-based telemetry, on the liver concentrations of selected trace elements including rare earth elements (REEs) as well as lead (Pb) isotope ratios in an urban-adapted omnivorous bird, the ring-billed gull (Larus delawarensis). Male (n = 20) and female (n = 18) ring-billed gulls breeding near Montreal (QC, Canada) in one of the largest colony in North America were tracked using miniature GPS devices to characterize their movements over a 10-days period. The time spent foraging by both male and female gulls in landfills and wastewater basins positively correlated with liver Pb concentrations. A positive correlation was also found between the time spent foraging in agricultural fields and liver concentrations of yttrium (Y) in male and female ring-billed gulls. Heavy REE concentrations were significantly greater in female gull liver relative to those of males, although this was not associated with the time spent in any foraging habitats. Pb isotope ratios (208Pb/206Pb and 206Pb/207Pb) in the liver of male ring-billed gulls tended to be lower in individuals that foraged in landfills, thus indicating that they may have been exposed to different Pb sources relative to birds that visited other sites. This study provided valuable information on the potential sources of trace elements at the landscape level in free-ranging birds spanning urbanized environments.

Gulls (Larus spp.) commonly roost in large numbers on inland and coastal waters, yet there is little information on how or where gulls choose sites for roosting. Roost site selection can lead to water quality degradation or aviation hazards when roosts are formed on water supply reservoirs or are close to airports. Harassment programs are frequently initiated to move or relocate roosting gulls but often have mixed results because gulls are reluctant to leave or keep returning. As such, knowledge of gull roost site selection and roosting ecology has applied and ecological importance. We used satellite telemetry and an information-theoretic approach to model seasonal roost selection of ring-billed (L. delawarensis) and herring gulls (L. argentatus) in Massachusetts, USA. Our results indicated that ring-billed gulls preferred freshwater roosts and will use a variety of rivers, lakes, and reservoirs. Herring gulls regularly roosted on fresh water but used salt water roosts more often than ring-billed gulls and also roosted on a variety of land habitats. Roost modeling showed that herring and ring-billed gulls selected inland fresh water roosts based on size of the water body and proximity to their last daytime location; they selected the largest roost closest to where they ended the day. Management strategies to reduce or eliminate roosting gulls could identify and try to eliminate other habitat variables (e.g., close-by foraging sites) that are attracting gulls before attempting to relocate or redistribute (e.g., through hazing programs) roosting birds. © 2016 The Wildlife Society.

Avian bornaviruses, recently de- scribed members of the family Bornaviridae, have been isolated from captive parrots and passerines as well as wild waterfowl in which they may cause lethal neurologic disease. We report detection of avian bornavirus RNA in the brains of apparently healthy gulls. We tested 439 gull brain samples from 18 states, primarily in the northeastern US, using a reverse- transcriptase PCR assay with primers designed to detect a conserved region of the bornavirus M gene. Nine birds yielded a PCR product of appropriate size. Sequencing of PCR products indicated that the virus was closely related to aquatic bird bornavirus 1 (ABBV-1). Viral RNA was detected in Herring Gulls (Larus argenta- tus), Ring-billed Gulls (Larus delawarensis), and Laughing Gulls (Leucophaeus atricilla). Eight of the nine positive birds came from the New York/New Jersey area. One positive Herring Gull came from New Hampshire. Histopathologic examination of one well-pre- served brain from a Herring Gull from Union County New Jersey, showed a lymphocytic encephalitis similar to that observed in borna- virus-infected parrots and geese. Bornavirus N protein was confirmed in two Herring Gull brains by immunohistochemistry. Thus ABBV- 1 can infect gulls and cause encephalitic brain lesions similar to those observed in other birds.

Wellfleet Bay virus (WFBV) is a recently described orthomyxovirus isolated from the tissues of Common Eiders (Somateria mollissima) collected during recurrent mortality events on Cape Cod, Massachusetts, US. Coastal Massachusetts is the only location where disease or mortality associated with this virus has been detected in wild birds, and a previous seroprevalence study found a significantly higher frequency of viral exposure in eiders from this location than from other areas sampled in North America. This suggests that coastal Massachusetts is an epicenter of WFBV exposure, but the reason for this is unknown. Opportunistic sampling of sympatric species and testing of banked serum was used to investigate potential host range and spatiotemporal patterns of WFBV exposure. Antibodies were detected in Herring Gulls (Larus argentatus), Ring-billed Gulls (Larus delawarensis), a White-winged Scoter (Melanitta fusca), and a Black Scoter (Melanitta nigra). These findings demonstrate the likely occurrence of fall/winter transmission, expand our understanding of the host range of the virus, and provide further insight into the epidemiology of WFBV in the northeastern US.

Benthic substrate has a large impact on aquatic plant and invertebrate assemblages and likely directly or indirectly influences waterbird distributions. The association of birds with various substrates can be important in survey design or habitat management. Northern Shoveler (Anas clypeata), Common Goldeneye (Bucephala clangula), Eared Grebe (Podiceps nigricollis), Ring-billed Gull (Larus delawarensis) and California Gull (L. californicus) densities on the hypersaline Great Salt Lake, Utah, were estimated to determine the association of bird distributions with benthic substrates. Three of the four groups of species monitored had densities that varied by benthic substrate; gulls were the exception. Eared Grebes occurred at the highest densities over calcareous reef-like structures known as bioherms, either as a result of ideal water depths for foraging or greater prey densities, than over other substrates. The highest densities of Northern Shovelers and Common Goldeneyes were observed over mud s...

Regular surveys of waterbird colonies are needed to identify changes in abundance and distribution. Consistent surveys have been maintained in some regions, but one area where updated surveys were needed was southern Manitoba, where Lakes Winnipeg, Winnipegosis and Manitoba had not been jointly surveyed since 1979. In mid-June, 2012, an aerial survey of the region was conducted using digital photography to estimate abundance of six colonial waterbird species that are regular breeders on these lakes. Breeding by at least one of the six species was confirmed at 131 locations. Double-crested Cormorant (Phalacrocorax auritus) was the most abundant breeder (43,388 pairs, 47 colonies), followed by Ring-billed Gull (Larus delawarensis, 41,819 pairs, 67 colonies), American White Pelican (Pelecanus erythrorhynchos, 12,680 pairs, 20 colonies), Common Tern (Sterna hirundo, 7,950 pairs, 31 colonies), Herring Gull (L. argentatus, 4,013 pairs, 90 colonies) and Caspian Tern (Hydroprogne caspia, 3,207 pairs, 14...

With urbanization, anthropogenic foods have grown in importance for several species. A shift away from natural foods is likely to affect trophically transmitted parasites, although this has received limited attention in urban-adapted avian omnivores. We examined the effect of habitat use and diet on gastrointestinal parasite assemblages of Ring-billed Gulls (Larus delawarensis Ord, 1815) breeding in an urbanized region (Montréal, Quebec, Canada) using three approaches depicting different temporal scales. Birds were fitted with global positioning system data loggers to determine habitat-use patterns during a 2–3 day period. Stomach contents were examined, providing dietary information during the preceding hours. Liver carbon (δ13C) and nitrogen (δ15N) stable isotope signatures served as proxy of nutrient assimilation during the preceding 10 days. Endoparasite community variations were best explained by δ13C and δ15N ratios. Individuals with lower δ15N had lower parasite abundance, while δ13C was enriched in birds with less diverse parasites (fewer helminth genera). Tissue depletion in15N in Ring-billed Gulls from this colony has previously been associated with predominant consumption of human-related foods. The present study supports the hypothesis that Ring-billed Gulls exhibiting preference for anthropogenic food sources encounter fewer trophically transmitted parasites, which may have contributed, in part, to their population expansion during the last century.

The capture of birds is a common part of many avian studies but often requires large investments of time and resources. We developed a novel technique for capturing gulls during the non-breeding season using a net launcher that was effective and efficient. The technique can be used in a variety of habitats and situations, including urban areas. Using this technique, we captured 1,326 gulls in 125 capture events from 2008 to 2012 in Massachusetts, USA. On average, 10 ring-billed gulls (Larus delawarensis; range = 1–37) were captured per trapping event. Capture rate (the number of birds captured per trapping event) was influenced by the type of bait used and also the time of the year (greatest in autumn, lowest in winter). Our capture technique could be adapted to catch a variety of urban or suburban birds and mammals that are attracted to bait. © 2014 The Wildlife Society.

West Nile virus (WNV) emerged in the Americas with its introduction in 1999 and now is considered endemic across the continent. In 2002, WNV was detected in Mexico, where its occurrence and mortality are considerably lower compared with the US. However, continuous national surveillance programs in Mexico are nonexistent. Birds are considered the primary hosts and primary geographic dispersers of this pathogen. A total of 200 cloacal and tracheal samples from wild migratory or resident birds were retrospectively analyzed using reverse transcription PCR to detect WNV from birds collected in Mexico from 2008 to 2009. The overall prevalence was 8% (16/200), and positive samples were from Oaxaca, Chiapas, and Tamaulipas in Ruby-throated Hummingbird ( Archilochus colubris), Double-crested Cormorant ( Phalacrocorax auritus), Ring-billed Gull ( Larus delawarensis), and Mourning Dove ( Zenaida macroura). Analysis of the partial sequence of the envelope gene from one of the samples from Oaxaca provided evidence that the virus belonged to the WN99 genotype. Taken together, these results demonstrated that WNV circulated in wild birds from northern and southern Mexico during the 2008-09 season, providing further information about the presence of WNV in Mexico.

Type E Botulism is an important source of mortality for waterbirds on the lower Great Lakes. The purpose of this study was to determine: 1) the spatial distribution of waterbird mortality and 2) if that mortality possibly impacted the breeding colonial waterbird populations in eastern Lake Ontario. Six islands in eastern Lake Ontario, Canada, were searched, July–November, 2004–2009, for dead/moribund waterbirds. Over 6600 dead/dying birds were located; five species accounted for > 98% of the birds found: double-crested cormorant ( Phalacrocorax auritus ), herring, ring-billed and great black-backed gulls ( Larus argentatus , Larus delawarensis , Larus marinus , respectively) and Caspian tern ( Hydroprogne caspia ). Cormorants accounted for 65–78% of all birds annually. Mortality was greatest in 2005 (7.5%). Most carcasses (91%) were documented on four islands. Most necropsied carcasses (58%, N = 95) were confirmed/suspected to have died from Type E Botulism; it was the only mortality factor identified in all years and in all five main species. These results produced a different guild of affected birds from previous beached bird surveys; virtually no birds that roost on water (loons and waterfowl) were found. Deaths reported here had minimal impact to herring and ring-billed gull, double-crested cormorant and Caspian tern populations nesting in eastern Lake Ontario. However, they accounted for > 100% of the great black-backed gulls breeding there. The species was extirpated from Lake Ontario during the study period. When assessing mortality in aquatic birds, it is crucial to examine off-shore islands, where birds roost, to fully document this critical demographic parameter.

The aim of the present study was to investigate the feeding ecology of an omnivorous bird, the Ring-billed Gull (Larus delawarensis Ord, 1815), breeding in a highly urbanized and heterogeneous landscape (Montréal area, Quebec, Canada). We used gastrointestinal (G.I.) tract content analysis, GPS-based tracking information, and stable isotope profiles of carbon (δ13C) and nitrogen (δ15N) in selected tissues and major food items. Based on GPS tracking data (1–3 days), Ring-billed Gulls were categorized according to their use of three main foraging habitats: agricultural, St. Lawrence River, and anthropogenic (comprising urban areas, landfills, and wastewater treatment plant basins). Ring-billed Gulls that foraged predominantly in anthropogenic habitats exhibited significantly lower δ15N in blood cells and higher total C to N ratios (C:N) in liver. These lower δ15N and higher C:N ratios were characteristic of profiles determined in food items consumed by Ring-billed Gulls at these urbanized sites (e.g., processed foods). The strong positive correlations between δ13C and δ15N in Ring-billed Gull tissues (plasma, blood cells, and liver) that differed in isotopic turnover times, as well as the strong positive correlations in both δ13C and δ15N between tissue pairs, indicated that Ring-billed Gulls exhibited conserved dietary habits throughout the nesting period. This study demonstrates that combining conventional dietary examination, tissue stable isotope analysis, and fine-scale GPS tracking information may improve our understanding of the large intrapopulation variations in foraging behaviour (and isotopic profiles) commonly observed in omnivorous birds.

This paper describes the interspecific fostering of two Ring-billed Gull chicks (Larus delawarensis) following natural adoption by a pair of Caspian Terns (Hydroprogne caspia) at Gull Island, Presqu'ile Provincial Park, Ontario, Canada, in 2011. Naturally-occurring, interspecific adoptions among waterbirds are rare and those between distantly-related species have not been confirmed to produce fledglings. The observation of one Ring-billed Gull chick being raised by Caspian Terns beyond fledging (approximately 46 days of age) appears to be the first record of successful adoption between different taxonomic families of waterbirds. Behavior, provisioning rate, and growth of chicks were recorded to document this adoption. During linear growth, the mass of the adopted Ring-billed Gull chicks were close to, or even exceeding, maximum mass of Ring-billed Gull chicks raised by their natural parents. After this period, however, the adoptive Caspian Tern parents reduced provisioning rates below those reco...

Synchrotron radiation analysis is a powerful tool for identifying pollutants. Here, we explore the distribution of elements in the flight feathers of ring-billed gulls, Larus delawarensis, to identify potential pollutants and their distribution throughout the feather. Our analysis using Synchrotron Radiation Analysis and Environmental Scanning Electron Microscopy has identified a variety of metals that are integral parts of the feather structure including: calcium (Ca), strontium (Sr), zinc (Zn) and iron (Fe). The darker portions of the flight feather were enriched with Zn and Fe, which supports the suggestion that feather melanins are efficient ligands of some metals found in the environment, sequestering potentially harmful particles away from the body. However, trace lead (Pb) acquired from the regional pollution was detected only in females, and it was distributed across both the melanized and non-melanized portions of the feather suggesting that only some metals are efficiently sequestered by melanins. Overall this study highlights a potential method for identifying pollutants using bird feathers, which has broader implications on environmental sensing as well as avian and human health. Copyright © 2013 John Wiley & Sons, Ltd.

Daily energy expenditure (DEE) in animals is influenced by many factors although the impact of stressors remains largely unknown. The objective of this study was to determine how multiple physiological stressors (parasite infection and contaminant exposure) and natural challenges (energy-demanding activities and weather conditions) may affect DEE in nesting ring-billed gulls (Larus delawarensis) exposed to high concentrations of persistent organic contaminants (POPs). Physical activity, temperature, gastrointestinal parasitic worm abundance, relative spleen mass, plasma thyroid hormone levels and liver concentrations of POPs were determined; field metabolic rate (FMR) was used as a measure of DEE. For females, FMR was best explained by the percent of time spent in nest-site attendance and exposure to temperatures below their lower critical limit (65% of variation); 32% was also explained by relative spleen mass. In males, FMR was best explained by the number of hours spent in nest site attendance and either relative spleen mass or liver concentrations of tetra-brominated diphenyl ethers (tetra-BDEs) (55% of variation). Relative spleen mass, as an important factor relating to FMR, was best explained by models with a combination of parasite abundance (Diplostomum for females and Eucoleus for males) in a negative relationship, and liver POP concentrations (p,p'-DDE for females and tetra-BDEs for males) in a positive relationship (34%, 55% of variation for females and males, respectively). This study demonstrates that immune activity may be an important factor affecting energy expenditure in ring-billed gulls, and that contaminants and parasite abundance may have both a direct and/or indirect influence on FMR.

The population of ring-billed gulls in the upper Midwest has increased exponentially in recent decades leading to a variety of conflicts including property damage, negative economic impacts, threats to human safety, and potential threats to human health. Some studies have suggested a link between gull fecal droppings and elevated Escherichia coli levels in water, which result in swim advisories on public beaches. The objectives of the Chicago ring-billed gull damage management project were to reduce the local production of ring-billed gulls, to evaluate the affects that limiting gull production has on the use of beaches by gulls, and to reduce the severity of conflicts with gulls including the issuance of swim advisories. Between 2007 and 2014, we applied corn oil to 52 - 80% of nests in several gull colonies in Chicago and successfully reduced hatching success and subsequent fledging. It is estimated that we prevented the production of between 77,314 and 183,621 ring-billed gulls since initiation of the project. The number of hatch year gulls observed on Chicago’s beaches during 2008 through 2014 has consistently been less than during the initial year of egg oiling, 2007. The reduction in the number of gulls using Chicago beaches has contributed to a reduction in conflicts with gulls, including a decrease in the frequency of swim advisories on Chicago’s beaches in comparison to 2006.

Landfill managers often need to implement scaring programmes to deter gulls from feeding at their sites because the birds can be a significant nuisance for both site employees and residents of the surrounding area. Our objective was to assess the efficiency of firing rubber shots, a method assumed to be non-lethal but never tested in a bird deterrence context. This method was compared to selective culling, a well-known lethal technique that some people find ethically unacceptable. Both methods were employed in combination with the use of pyrotechnics. Our study was conducted at the Ste-Sophie landfill site near Montreal (Canada) located 37 km from a Ring-billed gull (Larus delawarensis) colony supporting 48,000 pairs. Daily counts and behavioural observations were conducted throughout the breeding and post-breeding periods. Firing rubber shots was ineffective in deterring gulls as we observed the same number of birds at the landfill during periods with and without deterrence (P = 0.949). However, we counted 38% less birds during the culling periods than during the rubber shot treatment (P = 0.014). We detected no sign of habituation during the 7-day culling trials. Culling was also more effective in getting the gulls to leave the site than was rubber shots (47 vs. 11%; P

Sex-biased resource allocation in eggs is increasingly recognized as one strategy oviparous mothers can employ to invest diff erentially in one sex, depending on nutritional requirements. Previous studies have used egg size as an index of nutrient allocation, but few have examined egg contents directly. We used molecular sexing of early-stage ring-billed gull Larus delawarensis embryos, a species with sexual size dimorphism, to test whether sex-specifi c nutrient allocation occurs in ovo. Despite no sex diff erence in size, eggs with male embryos contained more albumen, while eggs with female embryos contained more yolk, lipid and non-lipid (protein and carbohydrate). It is unclear why such sex-biased resource allocation in ovo is utilized by ring-billed gulls. However, our data indicate that a cursive examination of egg mass or size may not necessarily refl ect nutrient allocation strategies mothers use in ovo, and that sex-biased investment in ovo may be more widespread than currently appreciated.

Bird colonies are potentially rich sources of social information that can be used to compensate for the numerous disadvantages of communal life. This information can reduce uncertainty about nest locations, mates or food sources. However, there is little empirical evidence that colonies can actually serve as an information exchange point. We asked whether a large nesting colony of ring-billed gulls, Larus delawarensis, could provide its members with social information about the quality and location of food resources during the chick-rearing period. We first determined whether social information was available in the colony, then whether it was signalled by some reliable cue, and finally, whether the birds used it by following knowledgeable individuals. We combined observations of flight departure bearings at the colony with flight tracks obtained from birds fitted with global positioning system (GPS) data loggers. We found that reliable information about feeding site locations could be obtained by observing the vanishing bearings of gulls leaving their nest. Birds nesting in different parts of the colony flew in different directions to reach their feeding grounds, but this did not influence the type of food brought to the chicks. To test whether gulls actually followed departing individuals, we searched for temporal clumping of departures and bearings for different time intervals during a day. We found that departures of gulls nesting in the same neighbourhood were not temporally clustered, nor did the gulls tend to leave in the same direction as their previously departing neighbours. We conclude that ring-billed gulls do not appear to use social information at the nest site to locate foraging opportunities. However, stopovers on nearby water or along the colony edge after a short flight from the nest could allow exchange of information that we could not document.

Little is known about whether chewing lice (Insecta: Phthiraptera) suppress or activate immunity in birds. Here, relationships between lice (Quadraceps punctatus, Saemundsonnia lari and Austromenopon transversum) and immune parameters were evaluated in Ring-billed Gull (Larus delawarensis) chicks. Eosinophils made up greater proportions of leukocytes in chicks with more lice (partial r = 0.64, P < 0.001), suggesting louse-induced immunoactivation via either eosinophil production or redistribution to peripheral blood. However, there were no significant relationships between lice and other immune parameters (proportion heterophils, proportion lymphocytes, heterophil:lymphocyte ratio, response to injection with phytohaemagglutinin). Collectively, results suggest only minor immune responses to lice, but experimental manipulations of louse infestations are needed to better quantify these responses and evaluate their potential consequences for fitness.

The similarity of parasite communities often decays with increasing geographic distance. Here, geographic distance decay is evaluated in parasite communities of 145 ring-billed gulls from six localities in Quebec, Canada, among both individual gulls and gull populations. Spatial decay in similarity is compared to temporal decay, using host age differences as a distance measure. The similarity of parasite communities of individual gulls from localities spanning 300 km within Quebec is more strongly associated with host age differences than with geographic distance. Among gull populations in Quebec, only geographic distance is significantly related to parasite community similarity. The explanatory power of geographic distance is higher still when data from Quebec are combined with those from a study conducted 3000 km away, indicating an effect of spatial scale on geographic distance decay. The rate at which parasite community similarity decays with distance in gulls is compared with that of 17 other host species using data from published studies. Spatial scale explains two thirds of the variance in distance decay rates, and some of the remaining variance is explained by latitude. The rate of decay in parasite community similarity with distance is greater in larger scale studies and further away from the equator. Traits of host species traits such as vagility, body weight and trophic level have little or no effect on distance decay rates.

Heart rate is a useful physiological index for studies of stress, locomotion, and activity patterns. Measuring heart rates of birds without the need to handle individuals is desirable when trapping is problematic or may cause unwanted disturbance. Heart-rate recorders housed in dummy eggs offer an effective solution, but the usefulness of previously described devices is limited by their size, complex construction, and reliance on analog media. We constructed egg-based, heart-rate monitors through simple modifications of inexpensive, commercially available MP3 players and Bluetooth headsets. We compared the merits of each device during tests in the laboratory, an aviary, and the field in 2008. Field testing was undertaken at Presqu'ile Provincial Park, Ontario, Canada, where we recorded heart rates of Common Terns (Sterna hirundo), Caspian Terns (Hydroprogne caspia), and Ring-billed Gulls (Larus delawarensis). Birds incubated dummy eggs normally, with no differences in behavior (all P > 0.05) when incubating either wired (MP3 players) or wireless (Bluetooth) devices. MP3 devices were more reliable in the field. Bluetooth devices often lost pairing with laptop computers (33% of files analyzed contained no signal), produced files with more obscuring noise, and only two could be deployed simultaneously with a single computer; there was no limit on how many MP3 devices could be deployed simultaneously. Common Terns, the smallest of our three focal species, had significantly higher (P < 0.001) mean heart rates (268.6 ± 9.3 beats per min (bpm)) than either Ring-billed Gulls (198.0 ± 7.1 bpm) or Caspian Terns (204.2 ± 8.0 bpm). Heart rates of all three species were consistent with those reported or predicted from previous studies. The MP3 devices we describe provide investigators with a simple, inexpensive, and minimally invasive way to digitally record heart rates of birds of almost any size.

After near extirpation in the early 20th century, Ring-billed Gulls (Larus delawarensis) are currently (2009) the most abundant colonial waterbird nesting on the Great Lakes. Nest count data are reported from four decadal censuses (1976–2009) conducted by the Canadian Wildlife Service and the U.S. Fish and Wildlife Service. Numbers increased from 305,790 nests (1976–80) to a peak of 718,887 nests (1989–90), then decreased to 652,664 (1997–2000) and to 585,984 nests (2007–09). Changes varied spatially after the second census with greatest losses (-38.6%) at North Channel, Georgian Bay and northern Lake Huron colonies, and greatest gains (+324.2%) at Lake Michigan colonies. A total of 472 sites had nests in at least one census (Canada N = 319; U.S. N = 153). Eighteen (3.8%) colonies had >2,000 nests in all four censuses, and had 37.5–41.9% of all nests in each census. Site occupancy was fluid. A high proportion (56.8%, N = 268) of sites contained nests in only one of the four censuses, and few (N ...

The possible role of tag color in mediating behaviors that could bias resighting rate has not been examined. In a study that began in 2007, we marked 725 ring-billed gulls (Larus delawarensis) with Bondcote royal blue, green, yellow, or orange patagial tags. Report sw e gathered over 2 years indicated approximately a 3.4:1 bias in resighting rate toward yellow or orange tags. The observed bias is inconsistent with color-associated visibility bias or differential mortality among color-tagged breeding adults. Potential behavioral effects of tag color on individuals and conspecifics should be considered by biologists when planning marking studies.

Birds within the orders Charadriiformes (shorebirds, gulls) and Anseriformes (waterfowl) are reservoir hosts for avian influenza (AI) viruses, but their role in the transmission dynamics of AI viruses is unclear. To date, waterfowl have been the predominant focal species for most surveillance and epidemiological studies, yet gulls, in particular, have been shown to harbor reassortant AI viruses of both North American and Eurasian lineages and are underrepresented in North American surveillance efforts. To address this gap in surveillance, 1346 ring-billed gulls (Larus delawarensis) were sampled during spring and fall migrations and at three breeding sites in 2017 across Minnesota. Results indicate noticeable age-cohort dynamics in AI virus prevalence within ring-billed gulls in Minnesota. Immunologically naive juveniles represented the cohort with the highest prevalence rate (57.8%). Regardless of age, more gulls had AI virus detected in oropharyngeal (OP) than in cloacal (CL) swabs. The high AI virus prevalence within ring-billed gulls, particularly in immunologically naive birds, warrants further targeted surveillance efforts of ring-billed gulls and other closely related species.

Avian influenza virus (AIV) was studied in ring-billed gulls (Larus delawarensis) in one breeding colony on Lake Erie in 2000, and two on Lake Ontario in both 2000 and 2004. Antibodies to H13 AIV were detected in 92% of adults in 2000 and 82% in 2004. Antibody prevalence in 3-wk-old chicks was 5%-30% (overall 15%) in 2000 and 21% and 76% (overall 48%) in 2004. In 5-wk-old chicks, antibody prevalence was 23%-75% (overall 53%) in 2000 and 53% and 79% (overall 66%) in 2004. Geometric mean antibody titers at 3 and 5 wk did not differ in 2000, but increased significantly at one colony in 2004. In 2000, overall prevalence of AIV isolation from cloaca in embryonated chicken eggs was 32% (3 wk old), 13% (5 wk old), and 0 (adults), but AIV was also isolated from kidney and lung in a high proportion of tissues cultured from 3-wk-old birds in one colony. Isolates from cloaca were characterized as subtype H13 by serology; all 15 tested for neuraminidase were H13N6. However, three AIV detections considered on the basis of nucleotide sequence to be subtype H16 were among the 28 detected retrospectively by PCR in archived cloacal swabs; the remainder were subtype H13. Outcome of virus isolation was not related to presence of antibody titers in chicks. The presence of antibody to AIV in chicks was associated significantly with inflammation in heart, kidney, pancreas, and liver. AIV was not isolated in 2004. AIV infected chicks annually within the first 3 wk of life, ultimately infecting the majority of birds in most colonies, but did not appear to cause clinical disease.

Beginning in the 1960s, Ring-billed Gulls' (Larus delawarensis) historic breeding range expanded from inland habitats and freshwater wetlands to marine sites in Atlantic North America. Adults winter on salt water but salt tolerance may entail costs (e.g. maintenance of salt glands) and favor reduced parental use of marine resources for feeding chicks. Diets of Ring-billed Gull chicks nesting on a marine island off Prince Edward Island, Canada, were investigated using soft regurgitant collection and stable isotope (δ13C and δ15N) analysis of both regurgitants and blood samples. Isotopic signatures in blood of chicks of Ring-billed and sympatrically-nesting Herring (L. argentatus) and Great Black-backed Gulls (L. marinus) were also compared. Regurgitants of Ring-billed Gull chicks contained freshwater/ terrestrial and marine invertebrates and fish. A stable isotope mixing model incorporating both δ13C and δ15N in chick regurgitants and blood estimated that 42.2% of Ring-billed Gull chick diet came...

Investigators often find it necessary to determine the volumes of bird eggs (Hoyt 1979). As direct measurement is usually difficult under field conditions, volume is usually calculated from length and breadth measurements of eggs (e.g., Coulson 1963, Ryder 1975, Mills 1979). However, this technique is not without difficulties. Preston (1 974) discussed the calculation of egg volume from linear measurements and concluded that the use of just two parameters such as length and breadth suffered from significant inaccuracy. However, Coulson (1 963) showed that the prediction of volume from length and breadth of Black-legged Kittiwake Rissa tridactyla eggs produced a maximum error of only 4%, an amount the author found acceptable. We recently required precise, field-determined measurements of the volume of Ring-billed Gull Larus delawarensis and Common Tern Sterna hirundo eggs. Whilst devices for the direct measurement of volume are available (e.g., Loftin & Bowman 1978, Van Noordwijk et al. 1981), we felt that certain design features made them cumbersome and impractical for field use. Accordingly, we undertook to produce a volumetric device of sufficient accuracy and precision that was easy to use in the field, Here, we present a description of the device and the results of field trials designed to contrast egg volume determination using the device, with that from calculation using length and breadth measurements.

Many species are adapted for fasting during parts of their life cycle. For species undergoing extreme fasts, lipid stores are mobilized and accumulated contaminants can be released to exert toxicological effects. However, it is unknown if short-term fasting events may have a similar effect. The objective of this study was to determine if short successive fasts are related to contaminant levels in liver and plasma of birds. In ring-billed gulls (Larus delawarensis), both members of the pair alternate between incubating the nest for several hours (during which they fast) and foraging, making them a useful model for examining this question. Birds were equipped with miniature data loggers recording time and GPS position for two days to determine the proportion and duration of time birds spent in these two activities. Liver and plasma samples were collected, and halogenated flame retardants (HFRs) (PBDEs and dechlorane plus) and organochlorines (OCs) (PCBs, DDTs, and chlordane-related compounds) were determined. Most birds (79%) exhibited plasma lipid content below 1%, indicating a likely fasted state, and plasma lipid percent declined with the number of hours spent at the nest site. The more time birds spent at their nest site, the higher were their plasma and liver concentrations of HFRs. However, body condition indices were unrelated to either the amount of time birds fasted at the nest site or contaminant levels, suggesting that lipid mobilization might not have been severe enough to affect overall body condition of birds and to explain the relationship between fasting and HFR concentrations. A similar relationship between fasting and OC levels was not observed, suggesting that different factors are affecting short-term temporal variations in concentrations of these two classes of contaminants. This study demonstrates that short fasts can be related to increased internal contaminant exposure in birds and that this may be a confounding factor in research and monitoring involving tissue concentrations of HFRs in wild birds. © 2015 Elsevier Inc.

Carotenoid pigments produce the red, orange, and yellow plumage of many birds. Carotenoid- containing feathers are typically rich in color and displayed by all adult members of the species. In many gulls and terns, however, an unusual light pink coloring (or flush) to the normally white plumage can be found in highly variable proportions within and across populations. The carotenoid basis of plumage flush was determined in an Elegant Tern (Sterna elegans; Hudon and Brush 1990), but it is not clear if all larids use this same mechanism for pink plumage coloration. We examined the carotenoid content of pink feathers in Franklin's (Larus pipixcan) and Ring-billed (Larus delawarensis) gulls and found that a single carotenoid—astaxanthin—was present. Astaxanthin was primarily responsible for the flush in Elegant Terns as well, but was accompanied by other carotenoids (e.g., canthaxanthin and zeaxanthin), as is typical of most astaxanthin-containing bird feathers. In both gull and tern species, carotenoids were contained within feathers and did not occur on the plumage surface in preen oil, as some have previously speculated. We hypothesize that some gulls turn pink because they acquire unusually high amounts of astaxanthin in their diets at the time of feather growth. It is tempting to link the increase in sightings of pink Ring- billed Gulls since the late 1990s with the introduction of pure, synthetic astaxanthin to the diets of hatchery-raised salmon. SINOPSIS. Astaxantina, responsible del plumaje Rosado en Larus pixpican y Larus

Nest predators commonly limit productivity of Least Tern (Sterna antillarum) breeding colonies in both natural and artificial habitats. In 2003 and 2004 we used remote still cameras aimed at model nests and remote video cameras aimed at occupied Least Tern nests to identify predators of Least Terns breeding at Gibson Lake, an artificial breeding area in southwestern Indiana, USA. At the primary breeding site, a narrow gravel dike that bisects Gibson Lake (center dike), Ring-billed Gulls (Larus delawarensis) were responsible for 100% and 75% of known predation events on model nests in 2003 and 2004, respectively. Throughout the 2004 breeding season, the proportion of model nests disturbed by Ring-billed Gulls on the center dike was strongly correlated with their numbers roosting on the center dike. We recorded predation by Ring-billed Gulls on six Least Tern chicks and two eggs in 2004 with remote video cameras. Our evaluation of the predator community at Gibson Lake strongly implicated Ring-bille...

During 1999-2002, we studied the abundance of fish-eating birds, primarily Ring-billed Gulls (Larus delawarensis) and California Gulls (L. californicus), and estimated their consumption of fish at Horn Rapids Dam and the Chandler Irrigation Canal return pipe on the Yakima River in eastern Washington. Earlier observations of gulls at these structures suggested a high level of predation of juvenile salmonids. The relationship between river flow, gull use at the sites and fish taken was also examined. Numbers of gulls (instantaneous counts of foraging and non-foraging individuals) at the structures varied daily between their arrival in late March-early April and departure in late June. Daily averages across the four years were 9.8 (SE ± 1.5) and 19.1 (SE ± 2.5) gulls at Horn Rapids and Chandler, respectively. Gull numbers at Horn Rapids peaked dramatically during the last two weeks in May, reaching maxima of 37 (SE ± 2.2) to 133 (SE ± 4.2) gulls/day. This increase appeared to be associated with the ...

From observations made on Manawagonish Island, NB in 2002 and 2004, we provide first documentation of the Ring-billed Gull (Larus delawarensis Ord) nesting in the Bay of Fundy. These observations counter suggestions that this species is no longer expanding its breeding range in the Maritimes. We also place this event in a broader context in which other coastal marine bird species have been recorded expanding or reclaiming breeding ranges in the region in recent decades.

Pulegone is a chemical derived from plants of the mint family ( Mentha spp.) that irritates the trigeminal nerve of mammals when inhaled and causes gastric distress when consumed. We examined whether free-ranging mammalian predators would stop depredating untreated eggs in gulls’ nests that smelled of pulegone. Prior to the nesting period, we distributed pulegone-injected eggs around a gull colony so that local mammalian predators could learn that opening such eggs was painful. We then selected 165 ring-billed gull ( Larus delawarensis ) and 165 California gull ( Larus californicus ) nests in the colony and randomly assigned them to one of the three treatments: (1) nests treated by placing two drops of pulegone (each 1 ml) on the ground on opposite sides of the nest, (2) nests treated by spraying 2 ml of pulegone around the nest's periphery, or (3) nests left untreated as a control. For both gull species, there were no differences among treatments in proportion of nests that were depredated. In a second experiment, which was also preceded by an exposure period when pulegone-injected eggs were distributed, 400 ring-billed and 150 California gull nests located in three colonies were selected to receive one of the two treatments. Half were treated by placing 2 ml of pulegone in a cup and burying it beneath the nest and half were left untreated as a control. Although 30–40% of the control and treated nests were depredated, differences between treated and control nests were not detected. Application of pulegone to nests did not decrease viability of those eggs that escaped depredation. Nevertheless, these results failed to support the hypothesis that egg survival of colonial birds could be increased by training free-ranging predators not to open untreated eggs in pulegone-scented nests.