Why do avian responses to change in Arctic green-up vary?

Global climate change has altered the timing of seasonal events (i.e., phenology) for a diverse range of biota. Within and among species, however, the degree to which alterations in phenology match climate variability differ substantially. To better understand factors driving these differences, we evaluated variation in timing of nesting of eight Arctic-breeding shorebird species at 18 sites over a 23-year period. We used the Normalized Difference Vegetation Index as a proxy to determine the start of spring (SOS) growing season and quantified relationships between SOS and nest initiation dates as a measure of phenological responsiveness. Among species, we tested four life history traits (migration distance, seasonal timing of breeding, female body mass, expected female reproductive effort) as species-level predictors of responsiveness. For one species (Semipalmated Sandpiper), we also evaluated whether responsiveness varied across sites. Although no species in our study completely tracked annual variation in SOS, phenological responses were strongest for Western Sandpipers, Pectoral Sandpipers, and Red Phalaropes. Migration distance was the strongest additional predictor of responsiveness, with longer-distance migrant species generally tracking variation in SOS more closely than species that migrate shorter distances. Semipalmated Sandpipers are a widely distributed species, but adjustments in timing of nesting relative to variability in SOS did not vary across sites, suggesting that different breeding populations of this species were equally responsive to climate cues despite differing migration strategies. Our results unexpectedly show that long-distance migrants are more sensitive to local environmental conditions, which may help them to adapt to ongoing changes in climate.

Drought at a coastal wetland affects refuelling and migration strategies of shorebirds.

Droughts can affect invertebrate communities in wetlands, which can have bottom-up effects on the condition and survival of top predators. Shorebirds, key predators at coastal wetlands, have experienced widespread population declines and could be negatively affected by droughts. We explored, in detail, the effects of drought on multiple aspects of shorebird stopover and migration ecology by contrasting a year with average wet/dry conditions (2016) with a year with moderate drought (2017) at a major subarctic stopover site on southbound migration. We also examined the effects of drought on shorebird body mass during stopover across 14 years (historical: 1974-1982 and present-day: 2014-2018). For the detailed comparison of two years, in the year with moderate drought we documented lower invertebrate abundance at some sites, higher prey family richness in shorebird faecal samples, lower shorebird refuelling rates, shorter stopover durations for juveniles, and, for most species, a higher probability of making a subsequent stopover in North America after departing the subarctic, compared to the year with average wet/dry conditions. In the 14-year dataset, shorebird body mass tended to be lower in drier years. We show that even short-term, moderate drought conditions can negatively affect shorebird refuelling performance at coastal wetlands, which may carry-over to affect subsequent stopover decisions. Given shorebird population declines and predicted changes in the severity and duration of droughts with climate change, researchers should prioritize a better understanding of how droughts affect shorebird refuelling performance and survival.

Breeding populations of Marbled Godwits and Willets have high annual survival and strong site fidelity to managed wetlands.

The Prairie Pothole Region of central Canada supports a diverse community of breeding waterbirds, but many species have declining populations and the demographic mechanisms driving the declines remain unknown. We conducted a 7-year field study during 1995-2001 to investigate the demographic performance of Marbled Godwits (Limosa fedoa) and Willets (Tringa semipalmata) breeding in managed wetlands near Brooks, Alberta. Mark-recapture analyses based on Cormack-Jolly-Seber models revealed that the annual rates of apparent survival for Marbled Godwits ( ϕ ^  = 0.953 ± 0.012SE) and Willets ( ϕ ^  = 0.861 ± 0.015SE) are among the highest rates of survivorship reported for any breeding or nonbreeding population of large-bodied shorebirds. Our estimates of life expectancy for males were comparable to longevity records in godwits (17.3 years ±5.8SE vs. 25-29+ years) and willets (7.7 ± 1.5SE vs. 10+ years). The two species both showed strong breeding site fidelity but differed in rates of mate fidelity. Pairs that reunited and males that switched mates usually nested <300 m from their previous nests, whereas females that switched mates usually moved longer distances >1.1-1.5 km. Returning pairs usually reunited in godwits (85%) but not in willets (28%), possibly because of species differences in adult survival or patterns of migration. Baseline estimates of annual survival for banded-only birds will be useful for evaluating the potential effects of new tracking tags or the environmental changes that have occurred during the past 20 years. Conservation strategies for large-bodied shorebirds should be focused on reduction of exposure to anthropogenic mortality because low rates of natural mortality suggest that losses to collisions at breeding sites or harvest at nonbreeding areas are likely to cause additive mortality.

Multi-year monitoring of Piping Plovers (Charadriusmelodus) and other shorebirds in The Bahamas.

Background: The Bahamas provides a wide range of crucial coastal habitats to many declining resident and migratory birds. Amongst these species is the Piping Plover (Charadriusmelodus), whose breeding populations are all listed as federally threatened or endangered in the United States and Canada. This species winters in the southern U.S. and the Caribbean, including The Bahamas, spending most of the year on the wintering grounds. Nonetheless, prior to the census data presented here, reports of Piping Plovers from The Bahamas were few and incidental. Therefore, repeated surveys are essential to increase understanding of the distribution, abundance and movement patterns of Piping Plovers and other shorebirds in the Bahamian territory. This dataset provides information on the abundance and distribution of the Piping Plover across multiple islands and much of the suitable habitat that exists in The Bahamas. It also provides some information on the variability of Piping Plover count data and presence of other shorebird species. Furthermore, these data may serve as baseline information on Piping Plover abundance and shorebird site occupancy by which to assess key candidate sites for protection and also future impacts of climate change, such as sea level rise and hurricanes. New information: The National Audubon Society (NAS), Environment and Climate Change Canada (ECCC) and the United States Geological Survey (USGS) conducted a multi-year shorebird census in The Bahamas. Surveys initiated by ECCC and many other collaborators were also part of a multi-year survival study. Censuses were conducted across 16 different islands between the years 2006 and 2020. These surveys were performed with the cooperation of the Bahamas National Trust (BNT), volunteer biologists and scientists from the United States and Canada. Biologists working with NAS, ECCC and USGS used satellite imagery, historical records and local knowledge from Bahamian residents to identify sites with suitable habitat for Piping Plovers. Experienced researchers visited each site during winter (November-February), identified and counted Piping Plovers and, when possible, other bird species in each of the sampled locations. In total, the resulting database holds 2,684 observations of 62 bird species, of which 77% belong to 24 shorebird species. Approximately 30% of all presence records belong to the Piping Plover. It is important to emphasise that the counts reported in this dataset represent minimum estimates of local shorebird assemblages. Since abundance and distribution of birds vary with changing conditions, representative estimates are best achieved via repeated surveys that reflect a range of conditions including timing (day, year, month), weather (wind direction and speed, precipitation), tide state etc.

Consistent declines in wing lengths of Calidridine sandpipers suggest a rapid morphometric response to environmental change.

A recent study demonstrated that semipalmated sandpiper (Calidris pusilla) wing lengths have shortened from the 1980s to the present-day. We examined alternative and untested hypotheses for this change at an important stopover site, James Bay, Ontario, Canada. We evaluated morphometric patterns in wing length and bill length by age and sex, when possible, and assessed if wing shape has also changed during this time-period. We investigated patterns of morphological change in two additional Calidridine sandpipers, white-rumped sandpipers (Calidris fuscicollis) and least sandpipers (Calidris minutilla), to determine if shorter wing lengths are a widespread pattern in small sandpipers. We also examined allometric changes in wing and bill lengths to clarify if wing length declines were consistent with historical scaling relationships and indicative of a change in body size instead of only wing length change. We found that including sex and wing shape in analyses revealed important patterns in morphometric change for semipalmated sandpipers. Wing lengths declined for both sexes, but the magnitude of decline was smaller and not significant for males. Additionally, semipalmated sandpiper wings have become more convex, a shape that increases maneuverability in flight. Wing lengths, but not bill lengths, declined for most species and age classes, a pattern that was inconsistent with historical allometric scaling relationships. For juvenile semipalmated sandpipers, however, both bill and wing lengths declined according to historical scaling relationships, which could be a consequence of nutritional stress during development or a shift in the proportion of birds from smaller-sized, western breeding populations. Except for juvenile semipalmated sandpipers, we did not find evidence for an increase in the proportion of birds from different breeding populations at the stopover site. Given the wide, hemispheric distribution of these sandpipers throughout their annual cycles, our results, paired with those from a previous study, provide evidence for wide-spread reduction in wing lengths of Calidridine sandpipers since the 1980s. The shorter wing lengths and more convex wing shapes found in this study support the hypothesis that selection has favored more maneuverable wing morphology in small sandpipers.

Long-distance migratory shorebirds travel faster towards their breeding grounds, but fly faster post-breeding.

Long-distance migrants are assumed to be more time-limited during the pre-breeding season compared to the post-breeding season. Although breeding-related time constraints may be absent post-breeding, additional factors such as predation risk could lead to time constraints that were previously underestimated. By using an automated radio telemetry system, we compared pre- and post-breeding movements of long-distance migrant shorebirds on a continent-wide scale. From 2014 to 2016, we deployed radio transmitters on 1,937 individuals of 4 shorebird species at 13 sites distributed across North America. Following theoretical predictions, all species migrated faster during the pre-breeding season, compared to the post-breeding season. These differences in migration speed between seasons were attributable primarily to longer stopover durations in the post-breeding season. In contrast, and counter to our expectations, all species had higher airspeeds during the post-breeding season, even after accounting for seasonal differences in wind. Arriving at the breeding grounds in good body condition is beneficial for survival and reproductive success and this energetic constraint might explain why airspeeds are not maximised in the pre-breeding season. We show that the higher airspeeds in the post-breeding season precede a wave of avian predators, which could suggest that migrant shorebirds show predation-minimizing behaviour during the post-breeding season. Our results reaffirm the important role of time constraints during northward migration and suggest that both energy and predation-risk constrain migratory behaviour during the post-breeding season.

Long-term continental changes in wing length, but not bill length, of a long-distance migratory shorebird.

We compiled a >50-year record of morphometrics for semipalmated sandpipers (Calidris pusilla), a shorebird species with a Nearctic breeding distribution and intercontinental migration to South America. Our data included >57,000 individuals captured 1972-2015 at five breeding locations and three major stopover sites, plus 139 museum specimens collected in earlier decades. Wing length increased by ca. 1.5 mm (>1%) prior to 1980, followed by a decrease of 3.85 mm (nearly 4%) over the subsequent 35 years. This can account for previously reported changes in metrics at a migratory stopover site from 1985 to 2006. Wing length decreased at a rate of 1,098 darwins, or 0.176 haldanes, within the ranges of other field studies of phenotypic change. Bill length, in contrast, showed no consistent change over the full period of our study. Decreased body size as a universal response of animal populations to climate warming, and several other potential mechanisms, are unable to account for the increasing and decreasing wing length pattern observed. We propose that the post-WWII near-extirpation of falcon populations and their post-1973 recovery driven by the widespread use and subsequent limitation on DDT in North America selected initially for greater flight efficiency and latterly for greater agility. This predation danger hypothesis accounts for many features of the morphometric data and deserves further investigation in this and other species.