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The Western Atlantic population of Red Knot (Calidris canutus rufa) has undergone dramatic declines in recent decades and conservation biologists have sought to improve knowledge about the species' ecology in an effort to understand these declines. One major information gap has been the lack of a detailed understanding of range and habitat use during the breeding season, when the species is distributed sparsely across the Canadian Arctic. Airborne radiotelemetry surveys of Red Knots tagged in Delaware Bay, New Jersey, were conducted across the south and central Canadian Arctic, from Victoria Island in the west to Baffin Island in the east. Intensive field surveys were conducted on Southampton Island, Nunavut, over successive summer field seasons to locate nesting Red Knots and record characteristics of their nesting habitat. Maximum entropy modeling (Maxent) and geographic information system (GIS) data on environmental characteristics were used to predict Red Knot habitat suitability at 2 spatial scales: nesting site location suitability at the local scale across Southampton Island, and breeding habitat suitability (i.e. both nesting and foraging habitat) at a broader, regional scale across the south and central Canadian Arctic. Comparison of the local and regional scale models with independent validation data (i.e. occurrence data not used in the model calibration), showed both models to be useful predictors of habitat suitability. At both spatial scales, Red Knots were found to prefer sparsely vegetated tundra on sedimentary, primarily limestone, bedrock at elevations below 150 m. Our results suggest that it is highly unlikely that the availability of breeding habitat limits the population size of the subspecies. Regional scale mapping provides the basis for more precise geographic targeting of future survey efforts that will aid in the conservation and management of this threatened species. [ABSTRACT FROM AUTHOR]

Mating strategy and social behavior influence gene flow and hence affect levels of genetic differentiation and potentially speciation. Previous genetic analyses of closely related plovers Charadrius spp. found strikingly different population genetic structure in Madagascar: Kittlitz's plovers are spatially homogenous whereas white-fronted plovers have well segregated and geographically distinct populations. Here, we test the hypotheses that Kittlitz's plovers are spatially interconnected and have extensive social interactions that facilitate gene flow, whereas white-fronted plovers are spatially discrete and have limited social interactions. By experimentally removing mates from breeding pairs and observing the movements of mate-searching plovers in both species, we compare the spatial behavior of Kittlitz's and white-fronted plovers within a breeding season. The behavior of experimental birds was largely consistent with expectations: Kittlitz's plovers travelled further, sought new mates in larger areas, and interacted with more individuals than white-fronted plovers, however there was no difference in breeding dispersal. These results suggest that mating strategies, through spatial behavior and social interactions, are predictors of gene flow and thus genetic differentiation and speciation. Our study highlights the importance of using social behavior to understand gene flow. However, further work is needed to investigate the relative importance of social structure, as well as intra- and inter-season dispersal, in influencing the genetic structures of populations. [ABSTRACT FROM AUTHOR]

Sexual selection may act as a promotor of speciation since divergent mate choice and competition for mates can rapidly lead to reproductive isolation. Alternatively, sexual selection may also retard speciation since polygamous individuals can access additional mates by increased breeding dispersal. High breeding dispersal should hence increase gene flow and reduce diversification in polygamous species. Here, we test how polygamy predicts diversification in shorebirds using genetic differentiation and subspecies richness as proxies for population divergence. Examining microsatellite data from 79 populations in 10 plover species (Genus: Charadrius) we found that polygamous species display significantly less genetic structure and weaker isolation-by-distance effects than monogamous species. Consistent with this result, a comparative analysis including 136 shorebird species showed significantly fewer subspecies for polygamous than for monogamous species. By contrast, migratory behavior neither predicted genetic differentiation nor subspecies richness. Taken together, our results suggest that dispersal associated with polygamy may facilitate gene flow and limit population divergence. Therefore, intense sexual selection, as occurs in polygamous species, may act as a brake rather than an engine of speciation in shorebirds. We discuss alternative explanations for these results and call for further studies to understand the relationships between sexual selection, dispersal, and diversification. [ABSTRACT FROM AUTHOR]

Local populations that fluctuate synchronously are at a greater risk of extinction than those that do not. The closer the geographic proximity of populations, the more prone they are to synchronizing. Shorebird species select habitat broadly, and many breed across regions with diverse nesting habitat types. Under these conditions, nearby populations may experience conditions sufficiently different to prevent population synchrony, despite dispersal. In the U.S. Northern Great Plains, the Piping Plover ( Charadrius melodus), federally listed as Threatened, is a migratory shorebird species that nests on the shorelines of rivers, reservoirs, and alkaline lakes. We assessed the degree to which local plover breeding population abundances were correlated (population synchrony), changed over time (population stability), and were influenced by environmental factors such as available habitat, precipitation, and within-season reservoir level rise. We found that the abundances of breeding populations nesting in riverine and reservoir habitats were the most synchronous, while populations nesting in alkaline lake habitats exhibited the greatest stability. Changes in local breeding population abundances were not explained by a single factor across habitat types. However, the abundances of local populations nesting in alkaline lake and river shoreline habitats were positively correlated with changes in nesting habitat availability. Our results suggest that dispersal among populations nesting in either river or reservoir and alkaline lake shoreline habitat may have an overall stabilizing effect on the persistence of the Great Plains Piping Plover metapopulation. [ABSTRACT FROM AUTHOR]

Wetland stopover use by migratory shorebirds Is concurrently Influenced by habitat characteristics within a stopover site and characteristics related to the broader context surrounding the stopover site. To conserve wetland habitats essential for shorebird migration through the Interior of North America, we need to understand how these dual scales Influence stopover use. We surveyed >14,000 wetlands within 10 broad-scale landscapes In north-central Oklahoma from 2007 through 2009 to determine how characteristics within (Intra) and surrounding (context) wetlands Influence the density and species richness of migrating shorebirds at stopover sites. We used zero-inflated modeling and an Information theoretic framework to separately examine and then compare the relative Importance of Intra-habitat variables and habitat context variables In explaining use of stopovers. We observed 38,288 migratory shorebirds of 29 species. Shorebirds were least likely to occur In Isolated, small, steep-sided wetland habitats. Among Intra-patch variables, shorebird density and richness were best explained by wetland habitat area, slope, and the cover and height of vegetation within a wetland. Shorebird density and richness were more than 2 times higher In large wetland habitats (l.e. >3.3 ha), and both decreased with Increased vegetation and slope. The density of wetlands within 1.5 km of a stopover site had the greatest Impact on shorebird density and richness among patch context variables. As habitat density Increased from 0.07 to 1, shorebird abundance and richness Increased by >200%. Shorebirds were positively related to grazing pressure but negatively related to forest/shrubland, urban/suburban development, and grassland land cover contexts. When compared to models with Intra-habitat variables, models containing habitat context variables better explained migratory shorebird density and richness. We conclude that characteristics related to the broader context surrounding a wetland stopover sites strongly Influence stopover use by migratory shorebirds. Conservation and management of shorebirds migrating through the continental Interior should aim to provide large expanses of sparsely vegetated and shallow habitats within stopover sites and focus on open landscapes that contain high densities of stopover habitats. [ABSTRACT FROM AUTHOR]

The use of stable isotopes in animal ecology depends on accurate descriptions of isotope dynamics within individuals. The prevailing assumption that laboratory-derived isotopic parameters apply to free-living animals is largely untested. We used stable carbon isotopes (δ13C) in whole blood from migratory Dunlin ( Calidris alpina arcticola) to estimate an in situ turnover rate and individual diet-switch dates. Our in situ results indicated that turnover rates were higher in free-living birds, in comparison to the results of an experimental study on captive Dunlin and estimates derived from a theoretical allometric model. Diet-switch dates from all 3 methods were then used to estimate arrival dates to the Arctic; arrival dates calculated with the in situ turnover rate were later than those with the other turnover-rate estimates, substantially so in some cases. These later arrival dates matched dates when local snow conditions would have allowed Dunlin to settle, and agreed with anticipated arrival dates of Dunlin tracked with light-level geolocators. Our study presents a novel method for accurately estimating arrival dates for individuals of migratory species in which return dates are difficult to document. This may be particularly appropriate for species in which extrinsic tracking devices cannot easily be employed because of cost, body size, or behavioral constraints, and in habitats that do not allow individuals to be detected easily upon first arrival. Thus, this isotopic method offers an exciting alternative approach to better understand how species may be altering their arrival dates in response to changing climatic conditions. [ABSTRACT FROM AUTHOR]

Incubation is energetically demanding, but it is debated whether these demands constrain incubation-scheduling (i.e., the length, constancy, and timing of incubation bouts) in cases where both parents incubate. Using 2 methods, we experimentally reduced the energetic demands of incubation in the semipalmated sandpiper, a biparental shorebird breeding in the harsh conditions of the high Arctic. First, we decreased the demands of incubation for 1 parent only by exchanging 1 of the 4 eggs for an artificial egg that heated up when the focal bird incubated. Second, we reanalyzed the data from the only published experimental study that has explicitly tested energetic constraints on incubation-scheduling in a biparentally incubating species (Cresswell et al. 2003). In this experiment, the energetic demands of incubation were decreased for both parents by insulating the nest cup. We expected that the treated birds, in both experiments, would change the length of their incubation bouts, if biparental incubation-scheduling is energetically constrained. However, we found no evidence that heating or insulation of the nest affected the length of incubation bouts: the combined effect of both experiments was an increase in bout length of 3.6 min (95% CI: -33 to 40), which is equivalent to a 0.5% increase in the length of the average incubation bout. These results demonstrate that the observed biparental incubation-scheduling in semipalmated sandpipers is not primarily driven by energetic constraints and therefore by the state of the incubating bird, implying that we still do not understand the factors driving biparental incubation-scheduling. [ABSTRACT FROM AUTHOR]

For species with precocial young, survival from hatching to fledging is a key factor influencing recruitment. Furthermore, growth rates of precocial chicks are an indicator of forage quality and habitat suitability of brood-rearing areas. We examined how growth and fledging rates of Piping Plover (Charadrius melodus) chicks were influenced by landscape features, such as hatchling density (hatchlings per hectare of remotely sensed habitat [H ha-1]), island vs. mainland, and wind fetch (exposure to waves) at 2-km segments (n = 15) of Lake Sakakawea, North Dakota, during 2007-2008. Hatchling growth was comparable with published estimates for other habitats. Models for fledging rate (fledged young per segment) assuming density dependence had more support (i = 96%) than those assuming density independence (wi = 4%). Density-dependent processes appeared to influence fledging rate only at densities >5 H ha1, which occurred in 19% of the segments we sampled. When areas with densities >5 FI ha-1 were excluded, density-dependence and density-independence models were equally supported (wi = 52% and 48%, respectively). Fledging rate declined as the wind fetch of a segment increased. Fledging rate on mainland shorelines was 4.3 times greater than that on islands. Previous work has indicated that plovers prefer islands for nesting, but our results suggest that this preference is not optimal and could lead to an ecological trap for chicks. While other researchers have found nesting-habitat requirements to be gravelly areas on exposed beaches without fine-grain substrates, our results suggest that chicks fledge at lower rates in these habitats. Thus, breeding plovers likely require complexes of these nesting habitats along with protected areas with fine, nutrient-rich substrate for foraging by hatchlings. [ABSTRACT FROM AUTHOR]

Stopover locations represent critical hábitat in the life cycle of migratory birds and the alteration of this hábitat can profoundly influence a population. American Golden-Plovers {Pluvialis dominica) migrate though the Midwestern United States each spring, where most natural hábitat has been converted to row crop agriculture. We investigated the stopover ecology of the golden-plover in the agricultural matrix of east-central Illinois and west-central Indiana between 2008 and 2012. We found that golden-plovers remained in the region for ~45 days and individuals spent on average 24 days in the area before departing to the northwest. During a period of peak migration, golden-plovers preferred fields with standing water and, to a lesser extent, soybean fields. Over the 45-day stopover duration, golden-plovers moved extensively (shown by a dynamic occupancy model and area used estimation), with some evidence for tilled fields becoming unoccupied at greater rates than untilled fields. The tendency to use fields with standing water and the movement of individuals from tilled fields suggests that food accessibility, rather than food abundance, is likely a critical factor associated with the prolonged stay, movement, and field type selection of golden-plovers. Food accessibility is important to the golden-plover because they undergo molt into breeding plumage in the region and must refuel for the next leg of their migration. The Midwest is a key stopover location for American Golden-Plovers and promoting foraging conditions by manipulating the drainage of agricultural fields, via the temporary blockage of drain tiles, should be a management focus. [ABSTRACT FROM AUTHOR]

Although much of the Arctic Coastal Plain has remained undeveloped, oil and gas industries, new and expanding villages, as well as tourism are likely to increase in the near future. One potential effect of increased human development is increased anthropogenic waste and the need to dispose of this waste in landfills. We investigated potential indirect effects of the North Slope Borough landfill on breeding shorebirds by examining changes in environmental conditions (predator densities and timing of snow melt) and measures of shorebird reproduction (nest-initiation dates, nest density, nest survival, and return rates) in relation to construction and deposition of waste in the landfill. This study included one year of pre-construction data (2004), three years when landfill roads and fences were being constructed (2005-2007), and five years when waste was being deposited (2008-2012). We monitored 364 shorebird nests within a 36-ha plot (approximately half of which was inside the landfill and half outside). Construction of a fence around the landfill reduced snow levels inside the landfill, leading to earlier snow melt and likely to shorebirds initiating nests earlier. Densities of avian predators increased following waste deposition, but nest densities, nest survival, and return rates were generally greater inside the landfill than outside in all years after landfill construction. Our results indicate that fences placed around landfills and procedures to reduce attraction of predators to landfills can minimize indirect negative effects of landfill construction and operation and even favor species breeding in the area. [ABSTRACT FROM AUTHOR]

Nonlethal disturbance can impose fitness costs, particularly during sensitive life history stages such as reproduction. Prey animals are thus expected to assess the costs and benefits of expressing antipredator behavior in different circumstances and to respond optimally according to the perceived risk of predation. One prediction of this hypothesis is that the response to nonlethal disturbance should be elevated when the risk of predation is high, although few studies have tested this prediction with respect to the distribution of actual predators in nature. We used landscape-level variation in the distribution of large mammalian predators (feral cats) to investigate antipredator behavior in a small breeding shorebird, the Two-banded Plover Charadrius falklandicus. We used 8 sites in the Falkland Islands and Argentina and measured the flushing distances of incubating Two-banded Plovers in response to a controlled human approach to the nest. We found that flushing distances were increased at sites where mammalian predators were present and decreased where exposure to humans was high. These effects were additive, and we interpret them as the effects of generalization and habituation, respectively. [ABSTRACT FROM PUBLISHER]

The article discusses a study which investigates the mate retention, dispersal, renesting, and apparent survival of the Semipalmated Plover in Akimiski Island, Nanavut, Canada. It reveals that encounters and return rates of adult male plovers were higher compared to those of female plovers, but their apparent survival were the same and renesting was common. It notes that weather differences affect the breeding season duration and seem to have impacts on the intense of social monogamy.

The article presents a study which examines the factors that prompted Red knots birds to stop over in Iceland and northern Norway during its migration. It notes the use of the species' stable carbon isotypes in whole blood, blood cells and plasma ratios to generate evidences for its stopover activities. The result indicates that the levels of the bird's blood cells and plasma played a significant role which prompted it to stop over in the area.

The article presents a study on the probability of detection of nests and its significance to survey design. The researchers used a double sampling method to predict closely complete counts of birds in the intensively surveyed plots by calculating the probability of detecting active shorebird nests. Results show that the probability varies considerably by species and it suggests that the method is likely to be met for bird's nests that survive over several visits.

The article offers information on the use of plasma metabolites to predict weekly body-mass change in red knots. It states that plasma metabolite concentrations have been used to predict body-mass changes over intervals in small passerines and shorebirds. It also provides information concerning triglyceride concentrations associated with body-mass change. The residual triglyceride correlates with short-term body mass change. It is believed that weekly body mass-change was best anticipated with a model that consists all metabolites and body mass.

Western sandpiper (Calidris mauri) chicks are precocial and leave the nest shortly after hatch to forage independently. Chicks require thermoregulatory assistance from parents (brooding) for 5–7 days posthatch, and parents facilitate chick survival for 2–3 weeks posthatch by leading and defending chicks. Parental vocal signals are likely involved in protecting chicks from predators, preventing them from wandering away and becoming lost and leading them to good foraging locations. Using observational and experimental methods in the field, we describe and demonstrate the form and function of parent–chick communication in the western sandpiper. We document 4 distinct calls produced by parents that are apparently directed toward their chicks (brood, gather, alarm, and freeze calls). Through experimental playback of parental and non–parental vocalizations to chicks in a small arena, we demonstrated the following: 1) chicks respond to the alarm call by vocalizing relatively less often and moving away from the signal source, 2) chicks respond to the gather call by vocalizing relatively more often and moving toward the signal source, and 3) chicks respond to the freeze call by vocalizing relatively less often and crouching motionless on the substrate for extended periods of time. Chicks exhibited consistent directional movement and space use to parental and non–parental signals. Although fewer vocalizations were given in response to non–parental signals, which may indicate a weaker response to unfamiliar individuals, the relative number of chick calls given to each type of call signal was consistent between parental and non–parental signals. We also discovered 2 distinct chick vocalizations (chick-contact and chick-alarm calls) during arena playback experiments. Results indicate that sandpiper parents are able to elicit antipredatory chick behaviors and direct chick movement and vocalizations through vocal signals. Future study of parent–offspring communication should determine whether shorebird chicks exhibit parental recognition though vocalizations and the role of chick vocalizations in parental behavior. [ABSTRACT FROM PUBLISHER]

In environments such as arctic tundra, where bird densities are low and habitats are comparatively homogeneous, suitable nest sites likely are not limited. Under these conditions, reproductive success of birds may be determined by factors other than the habitat characteristics of nest sites. We studied the relative influence of nest habitat, food, nest distribution, and parental behavior on the reproductive success of tundra- breeding shorebirds at East Bay, Southampton Island, Nunavut, Canada. From 2000 to 2002, we monitored the nests of five species: Black-bellied Plover (Pluvialis squatarola), Semipalmated Plover (Charadrius semipalmatus), Ruddy Turnstone (Arenaria interpres), White-rumped Sandpiper (calidris fuscicollis), and Red Phalarope (Phalaropus fulicarius). For each species, habitat differed between nest sites and random sites. In contrast, habitat differed between successful and failed nest sites only for White-rumped Sandpipers. Shorebirds did not prefer to nest in habitats where food was most abundant. Although nest success varied among species in all years, artificial nest experiments suggested that interspecific variation in predation rate was not related to habitat type. Instead, the marked interspecific variation in nest success may have been related to incubation behavior. Species taking fewer incubation recesses had higher nest success, although these results should be viewed as preliminary. The factor with the greatest interannual influence on nest success was fluctuating predation pressure, apparently related to the abundance of predators and lemmings. [ABSTRACT FROM AUTHOR]

Information on how migratory populations are genetically structured during the overwintering season of the annual cycle can improve our understanding of the strength of migratory connectivity and help identify populations as units for management. Here, we use a genotype-by-sequencing approach to investigate whether population genetic structure exists among overwintering aggregations of the Pacific Dunlin subspecies (Calidris alpina pacifica) sampled at 2 spatial scales (within and among overwintering sites) in the eastern Pacific Flyway. Genome-wide analyses of 874 single nucleotide polymorphisms across 80 sampled individuals revealed no evidence for genetic differentiation among aggregations overwintering at 3 locations within the Fraser River Estuary (FRE) of British Columbia. Similarly, comparisons of aggregations in the FRE and those overwintering in southern sites in California and Mexico indicated no genetic segregation between northern and southern overwintering areas. These results suggest that Pacific Dunlin within the FRE, Sacramento Valley (California), and Guerrero Negro (Mexico) are genetically homogeneous, with no evident genetic structure between sampled sites or regions across the overwintering range. Despite no evidence for differentiation among aggregations, we identified a significant effect of geographical distance between sites on the distribution of individual genotypes in a redundancy analysis. A small proportion of the total genotypic variance (R 2 = 0.036, P = 0.011) was explained by the combined effect of latitude and longitude, suggesting weak genomic patterns of isolation-by-distance that are consistent with chain-like migratory connectivity between breeding and overwintering areas. Our study represents the first genome-scale investigation of population structure for a Dunlin subspecies and provides essential baseline estimates of genomic diversity and differentiation within the Pacific Dunlin. [ABSTRACT FROM AUTHOR]

Species listed under the U.S. Endangered Species Act are required to meet stated recovery goals for delisting. These goals often are developed early in the species' conservation history and may need to be updated or refined as new information becomes available. The Atlantic Coast Piping Plover (Charadrius melodus), which was listed more than 30 yr ago, has not met recovery goals through much of its range. Initial recovery goals included maintaining a reproductive output of 1.5 fledged chicks per pair for 5 yr. This goal was based on modelling that assumed equal survival rates for adults throughout the range, but recent studies suggest that demographic rates may vary with latitude. To investigate latitudinal variation, we developed demographic and population growth estimates for 2 breeding populations of Piping Plovers on the U.S. Atlantic Coast on Fire Island, New York (40.7°N), and on the Outer Banks of North Carolina (35.3°N) in 2013–2017. Breeding success (nest success and pre-fledge chick survival) varied annually but was lower in North Carolina than New York. Average adult true survival in New York (x̅ = 0.73, SE = 0.04) was similar to average survival in North Carolina (x̅ = 0.69, SE = 0.07). Annual post-fledging survival for both sites, however, was variable and often higher than had been previously reported for Atlantic Coast Piping Plovers (0.43–0.66 for New York; 0.31 and 1.0 for North Carolina). While the estimated reproductive output needed for a stationary population for both sites was similar (1.10 chicks per pair for New York, 95% CI: 0.83–1.41; 1.08 for North Carolina, 95% CI: 0.67–1.59), only the New York population achieved or exceeded these values during our study. Our findings suggest that understanding annual and latitudinal demographic variability would be helpful in refining recovery goals. [ABSTRACT FROM AUTHOR]