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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.

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...

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.

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.

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.

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 ...

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.

Elevated levels of Escherichia coli(E. coli) in bathing waters at North Beach, a popular recreational site in Racine, Wisconsin, have been a persistent problem often resulting in the issuance of poor water quality advisories. Moreover, waterfowl (mostly Larus delawarensis and L. argentatus) in nearshore and offshore areas are common and may serve as non-point sources for bacterial contamination of recreational waters. Current beach management practice involves daily mechanical grooming of the nearshore sand for aesthetics and removal of hazardous debris. However, this practice has not been evaluated in terms of its effects on E. coli loading to beach sand and potential introduction to contiguous swimming water. In this study, we tested E. coli responses to three treatments: mechanical groomer, daily and twice weekly hand raking, and a control (no raking/grooming). A randomized block design consisted of replicated treatments and one control (10 each), for a total of 40 blocks sampled daily for 10 ...

The Ring-billed Gull (Larus delawarensis) experienced a significant contraction of its range from the Great Lakes eastward during the nineteenth century, but it staged a remarkable recovery in the late twentieth century that continues to the present. A rapid increase in population size in Maine, indexed by Christmas Bird Counts and field sighting data, occurred from the early 1970s through the 1990s. The timing of population growth in Maine closely paralleled the growth and spread of breeding populations along the St. Lawrence River in Quebec, and eastward into the Maritimes. At this time, Ring-billed Gulls also began to appear in greater numbers during summer on interior lakes in Maine. Breeding colonies are now known on two inland lakes.

Simple Summary We evaluated the long-term effect of an intensive integrated program based on falconry to deter gulls, mostly ring-billed gulls (Larus delawarensis), from a landfill. Gulls were counted at different periods each day, and the annual sum of the maximum count at any observation period each day declined from over 1.1 million to only 20,300 during the 20 years of the study. This could not be explained by a decline in the local breeding population that remained relatively large throughout this period as determined in a concomitant study. The effectiveness of the falconry program was also confirmed by tracking individual birds fitted with GPS data loggers. The tagged gulls stopped less often and spent less time at the landfill with falconry than at another one where a selective culling program was conducted. We conclude that the use of an integrated program using falconry, which we consider more socially acceptable than culling, can be effective in deterring gulls from landfills. Abstract Gulls are commonly attracted to landfills, and managers are often required to implement cost-effective and socially accepted deterrence programs. Our objective was to evaluate the effectiveness of an intensive program that integrated the use of trained birds of prey, pyrotechnics, and playback of gull distress calls at a landfill located close to a large ring-billed gull (Larus delawarensis) colony near Montreal, Quebec, Canada. We used long-term survey data on bird use of the landfill, conducted behavioral observations of gulls during one season and tracked birds fitted with GPS data loggers. We also carried out observations at another landfill located farther from the colony, where less refuse was brought and where a limited culling program was conducted. The integrated program based on falconry resulted in a 98% decrease in the annual total number of gulls counted each day between 1995 and 2014. A separate study indicated that the local breeding population of ring-billed gulls increased and then declined during this period but remained relatively large. In 2010, there was an average (±SE) of 59 ± 15 gulls/day using the site with falconry and only 0.4% ± 0.2% of these birds were feeding. At the other site, there was an average of 347 ± 55 gulls/day and 13% ± 3% were feeding. Twenty-two gulls tracked from the colony made 41 trips towards the landfills: twenty-five percent of the trips that passed by the site with falconry resulted in a stopover that lasted 22 ± 7 min compared to 85% at the other landfill lasting 63 ± 15 min. We concluded that the integrated program using falconry, which we consider more socially acceptable than selective culling, was effective in reducing the number of gulls at the landfill.

Environmental and behavioral factors have long been assumed to affect variation in avian field metabolic rate (FMR). However, due to the difficulties in measuring continuous behavior of birds over prolonged periods of time, complete time-activity budgets have rarely been examined in relation to FMR. Our objective was to determine the effect of activity (measured by detailed time-activity budgets) and a series of extrinsic and intrinsic factors on FMR of the omnivorous ring-billed gull (Larus delawarensis). The experiment was conducted during the incubation period when both members of the pair alternate between attending the nest-site and leaving the colony to forage in aquatic and anthropogenic environments (city, agricultural). FMR was determined using the doubly labeled water method. Time-activity budgets were extrapolated from spatio-temporal data (2-5 days) obtained from bird-borne GPS data loggers. Gulls had low FMRs compared to those predicted by allometric equations based on recorded FMRs from several seabird species. Gulls proportioned their time mainly to nest-site attendance (71% of total tracking time), which reduced FMR/g body mass, and was the best variable explaining energy expenditure. The next best variable was the duration of foraging trips, which increased FMR/g; FMR/g was also elevated by the proportion of time spent foraging or flying (17% and 8% of tracking time respectively). Most environmental variables measured did not impact FMR/g, however, the percent of time birds were subjected to temperatures below their lower critical temperature increased FMR. Time-activity budgets varied between the sexes, and with temperature and capture date suggesting that these variables indirectly affected FMR/g. The gulls foraged preferentially in anthropogenic-related habitats, which may have contributed to their low FMR/g due to the high availability of protein- and lipid-rich foods. This study demonstrates that activities were the best predictors of FMR/g in ring-billed gulls, thus providing strong support for this long-standing theory in bioenergetics.

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 substrates. This was likely due to mud being common near freshwater inflow sites and in lower salinity bays, areas waterfowl concentrate in because of the lower osmoregulatory demands compared to more pelagic areas of the Great Salt Lake. Knowing the relationship between waterbird densities and substrate will help managers estimate avian populations on hypersaline lakes.

*Present address: Department of Genetics, University of Leicester, Adrian Building, University Road, LE1 7RH, UK Correspondence to: C. A. Bishop, Canadian Wildlife Service, Environment Canada, 5421 Robertson Road, Delta BC, Canada, V4K 3N2 Bull. Environ. Contam. Toxicol. (2001) 66:563–569 © 2001 Springer-Verlag New York Inc. DOI: 10.1007/s00128-001-0045-7 B ul le ti n of Environmental Contamination and Toxicology

We examined predictions derived from three hypotheses (hurry-up, peak-load reduction, and brood reduction) regarding the adaptive significance of hatching asynchrony. The study was conducted, in 1991 and 1992, in a colony of Ring-billed Gulls (Larus delawarensis) on l'ile de la Couvee, Montreal, Quebec, Canada. The hypotheses were examined by comparing the mass and size of 18- to 20-day-old chicks from broods that hatched asynchronously (unmanipulated) and synchronously (manipulated). We also compared feeding rates and fledging success between asynchronous and synchronous broods. Also, in 1992, a sample of asynchronous and synchronous broods was experimentally food stressed by providing them with an additional chick when the oldest resident chick was 4 or 5 days old. Consistent with the hurry-up hypothesis, hatch spreads were significantly shorter in 1991 when the mean clutch initiation date was significantly earlier compared with 1992. Also consistent with the hypothesis, hatch spreads increased significantly through the breeding season. In agreement with the peak-load-reduction hypothesis, feeding rates were significantly lower in asynchronous broods compared with synchronous broods. Contrary to the hypothesis, however, the feeding rate was similar for food-stressed asynchronous and food-stressed synchronous broods. As predicted by the brood-reduction hypothesis, survivorship was higher for first-hatched chicks in asynchronous broods compared with chicks in synchronous broods. Total brood loss as a result of starvation tended to occur less often in asynchronous broods compared with synchronous broods. Likewise, fledging success was higher in asynchronous broods compared with synchronous broods. However, contrary to the brood-reduction hypothesis, survival rate of first- hatched chicks, total brood loss, and fledging success were similar in food-stressed asynchronous and synchronous broods. The above results indicate that several benefits accure to Ring-billed Gulls from hatching asynchrony. 523 Resume : Nous avons procede a l'examen des predictions reliees a trois hypotheses, l'hypothese de la reduction du temps minimum requis pour rendre au moins un jeune a l'envol, l'hypothese de l'echelonnement de la demande

Recent models suggest that begging vocalizations are honest signals communicating a chick's nutritional needs to its parents. We investigated the effects on begging of short-term food deprivation ('hunger') and long-term reduction in body condition under controlled laboratory conditions in ring-billed gulls, Larus delawarensis. We tested two condition groups (high: fed to satiation; low: fed 75% wet mass of high-condition diet) at three levels of short-term food deprivation (1, 4 and 12 h). Begging call rate, intensity and peck rate were significantly greater in the low-condition chicks. Begging in both high- and low-condition groups increased with short-term deprivation, tending to asymptotic levels by 12 h of deprivation. Overall level of begging was graded according to both short- and long-term need for food, with steep slopes at the beginning of the begging curves providing a strong basis for parental discrimination of signalling level. The system appears to agree with the design requirements of a homeostatic control system, and with predictions of current game-theoretic models of honest signalling. Possible effects of sibling competition and parent-offspring conflict are discussed. These issues require further study under natural conditions in this species. Copyright 1998 The Association for the Study of Animal Behaviour.

Egg oiling is a form of management in which bird eggs are coated with mineral or corn oil, preventing gas exchange through the shell and killing embryos. Unlike other nest disturbance techniques, egg oiling reportedly precludes colony abandonment and, thus, can be advantageous when managers wish to limit dispersal within the breeding season to other locations while stabilizing the population or reducing productivity. However, unintended, indirect effects of egg oiling are not well-characterized. We evaluated the influence of egg oiling on ring-billed gulls (Larus delawarensis) within the Lake Champlain basin, Vermont, during the nesting season to determine whether egg oiling affected colony presence of adults. We radiomarked 58 ring-billed gulls captured on Young Island during 2008 to 2009 and treated all ring-billed gull nests in the colony with egg oiling except for 50% of the nests of radio-marked gulls (control group). Using a radio receiver with automated data logger, we documented the presence of ring-billed gulls at the colony throughout the breeding season. We examined effects of treatment (nests oiled or control), sex, reproductive period (pre- and post-hatch), year, and interactive effects on colony presence (i.e., the proportion of nights ring-billed gulls spent at Young Island). Although we found no effect of treatment, sex, or interactive effects on colony presence, colony presence was 87% greater in the pre-hatch period, presumably due to behavioral mechanisms related to incubation or foraging. Overall colony presence was 118% greater in 2009 than in 2008, potentially a consequence of increased colony disturbance in 2008. We suggest that egg oiling does not influence colony presence of ring-billed gulls within the breeding season

Hamilton Harbour, at the west end of Lake Ontario, supports breeding colonies of six piscivorous waterbirds: double-crested cormorant (Phalacrocorax auritus), black-crowned night-heron (Nycticorax nycticorax), herring gull (Larus argentatus), ring-billed gull ( Larus delawarensis), common tern (Sterna hirundo), and Caspian tern (Sterna caspia). Most breeding pairs of all species nest on privately owned mainland locations that are subject to multiple industrial and development activities. The construction of three artificial islands in the eastern basin of Hamilton Harbour in the winter of 1995-1996 presents an opportunity to simultaneously reduce current land-use conflict and maintain the existing avian biodiversity. Accordingly, we used ecological information to determine suitable substrates and vegetation to satisfy nesting habitat preferences and to facilitate the occupation of the islands by nesting waterbirds. Our recommendations for habitat design and management emphasize techniques to prevent displacement of both tern species by ring-billed gulls and of night-herons by cormorants. We propose long-term management procedures based on aspects of the biology and known ecological interactions among the various species. Resume : Le havre de Hamilton, situe a l'extremite ouest du lac Ontario, heberge des colonies reproductrices de six oiseaux aquatiques piscivores : le cormoran a aigrettes ( Phalacrocorax auritus), le bihoreau gris (Nycticorax nycticorax), le goeland argente (Larus argentatus), le goeland a bec cercle (Larus delawarensis), la sterne pierregarin ( Sterna hirundo) et la sterne caspienne (Sterna caspia). Chez toutes ces especes, la plupart des couples de reproducteurs nichent sur la terre ferme, sur des terrains prives soumis a de multiples activites industrielles ou travaux d'amenagement. La construction de trois iles

ABsTAcT.-When animals that provide parental care to offspring are faced with actual or potential failure during a breeding bout, the option to continue breeding is countered by the option to cut losses and forego reproduction until the next breeding season. In 1990, we recorded laying date and laying order of eggs in 51 Ring-billed Gull (Larus delawarensis) clutches prior to their total loss by flooding. Pairs remained on territory and produced new clutches following a refractory period of 11.6 ? SD of 1.9 days. Post-loss clutches were initiated synchronously (n = 51 clutches in four days; 89% of all clutches marked in the 7 x 7 m study plot) but mostly contained significantly fewer and lighter eggs than first clutches. We contrast incubation, hatching and chick survival patterns of these storm-delayed pairs in 1990 with patterns of early-, peak- and late-nesting pairs at the same colony in 1992. The incubation and within-clutch hatching patterns of post-loss clutches 1990 were most similar to those of late nesting pairs in 1992, yet these storm-delayed pairs realized a fledging success similar to that of early-and peak-nesting pairs in 1992. We discuss larid reproductive strategies in the context of conditions that favor successful renesting. Received 22 August 1994, accepted 27 January 1995.

Bone metabolism is a tightly regulated process that controls bone remodeling and repair in addition to maintaining circulating calcium and phosphate levels. It has been shown that certain organohalogen contaminants may adversely impact bone tissue metabolism and structure in wildlife species. However, exceedingly few studies have addressed the bone-related effects of organohalogen exposure in birds. The objective of the present study was to investigate the associations between markers of bone metabolism and structural integrity, and concentrations of established and current-use halogenated flame retardants (FRs) in ring-billed gulls (Larus delawarensis) nesting in a known FR hotspot area in the St. Lawrence River (Montreal, Canada). Bone metabolism was assessed using plasma calcium and inorganic phosphate levels, and alkaline phophatase activity, while bone (tarsus; trabecular and cortical sections) structure quality was examined using the percentage of bone tissue comprised in the total bone volume (Bv/Tv) and bone mineral density (BMD). Bv/Tv and BMD of the tarsus tended (not significant) to be positively associated with circulating calcium levels in male ring-billed gulls. Moreover, concentrations of FRs in male bird liver (brominated diphenyl ether (BDE)-154, -183, -201, and -209) and plasma (BDE-209) were negatively correlated with trabecular and cortical BMD of the tarsus. These correlative associations may suggest light demineralization of bone tissue associated with FR exposure in male ring-billed gulls. Present findings provide some evidence that bone (tarsus) metabolism and mineral composition may be impacted in high FR-exposed (mainly to PBDEs) ring-billed gulls breeding in the highly urbanized Montreal region.

Wild animals often encounter adverse conditions, and in response, activate their hypothalamic–pituitary–adrenal (HPA) axis. To date, work examining the development of the stress response has focused on altricial species, with little work focusing on species with other developmental patterns. Additionally, the effects of acute stress on indices of innate and adaptive immunity have been little studied in birds, particularly during development. We examined the ontogeny of the stress response in the semi-precocial ring-billed gull (Larus delawarensis). At hatch, 10, and 20 days post-hatching, chicks underwent a standardized handling stress protocol, with blood samples taken within 3 min of, and 30 min after, initial disturbance. Levels of corticosterone (CORT), natural antibodies (NAb), complement activity, and immunoglobulins (IgY) were assessed in plasma samples. In contrast with altricial species, ring-billed gull chicks had detectible CORT levels at hatch, and were able to mount a stress response. At all ages, acute handling stress depressed NAb levels and complement-mediated lysis, but not IgY levels. IgY levels were higher in two chick broods than three chick broods, suggesting levels are determined in part by resource dependence. Our data provide insight into the development of the stress response and immune function in a colonial waterbird species, in which chicks are mobile shortly post hatch, and subject to aggression and possible injury from nearby adults.

During the summer of 1986, more than 400 California gulls (Larus californicus) and ring-billed gulls (Larvus delawarensis), primarily fledglings, died on an island in Lake Sakakawea near New Town, North Dakota (USA). Mortality was attributed largely to chlamydiosis. Necropsy findings in nine carcasses included splenomegaly (n = 9), hepatomegaly (n = 4), and pericarditis (n = 1). Livers from three California gulls and two ring-billed gulls, and spleens from the same five birds plus a third ring-billed gull were positive for Chlamydia psittaci by the direct immunofluorescence test. Chlamydia psittaci was isolated from separate pools of liver and spleen from one California gull and one ring-billed gull. This is believed to be the first record of epizootic chlamydiosis in gulls and the second report of epizootic chlamydial mortality in wild birds in North America.

Many birds bob their head as they walk or run on the ground. The functional significance of this behaviour is unclear, but there is strong evidence that it plays a significant role in enhancing visual perception. If head-bobbing is advantageous, however, then it is a puzzle that some birds do not head-bob. As a group, gulls (Laridae) are among the birds that reportedly do not head-bob,yet here we report head-bobbing among Ring-billed Gulls (Larus delawarensis), observed and filmed in Ontario, when walking relatively slowly while foraging on the ground. This suggests that head-bobbing plays a key role in the visual detection of food items in this species. We suggest that head-bobbing may be a relatively common behaviour in foraging Ring-billed Gulls and speculate that other gulls (and indeed other birds) previously thought not to head-bob may in fact do so under certain circumstances.

Although at variance with Darwinian theory, adoption of unrelated offspring has been reported in a variety of ground-nesting colonial seabirds. Pierotti & Murphy (1987, Anim. Behav. , 35, 435-444) suggest that an inter-generational conflict exists between disadvantaged chicks and unrelated adults, a conflict that often results in wandering chicks successfully soliciting investment from foster parents. Of 47 ring-billed gull, Larus delawarensis , chicks that departed their natal broods over four summers of field work, 34 remained in recipient broods for 3 or more days and received parental care (i.e. were successfully adopted), and 13 remained in recipient broods for less than 3 days (‘runners’). Chicks in broods that were subsequently subject to abandonment were fed at a significantly lower rate (on a per chick basis) than chicks in control broods (which neither adopted nor had a chick depart) or broods that subsequently adopted a chick. In most cases, adoptees were older than the oldest resident chick in the accepting brood, but runners were younger than resident chicks. Pairs whose oldest chick was less than 7 days were more likely to adopt foreign offspring than pairs with older chicks. Twenty-six (76%) of the 34 adopted chicks survived to at least 24 days (fledged). Pairs that adopted a chick realized a lower annual breeding success (chicks fledged/pair) than control pairs or pairs that had a chick depart their brood. Disadvantaged chicks that gain permanent acceptance into foreign broods ‘win’ the inter-generational conflict at the expense of the foster parents.