Spring migration patterns of red knots in the Southeast United States disentangled using automated telemetry.

Red Knots use the Southeast United States as a stopover during north and southbound migration and during the winter. We examined northbound red knot migration routes and timing using an automated telemetry network. Our primary goal was to evaluate the relative use of an Atlantic migratory route through Delaware Bay versus an inland route through the Great Lakes en route to Arctic breeding grounds and to identify areas of apparent stopovers. Secondarily, we explored the association of red knot routes and ground speeds with prevailing atmospheric conditions. Most Red Knots migrating north from the Southeast United States skipped or likely skipped Delaware Bay (73%) while 27% of the knots stopped in Delaware Bay for at least 1 day. A few knots used an Atlantic Coast strategy that did not include Delaware Bay, relying instead on the areas around Chesapeake Bay or New York Bay for stopovers. Nearly 80% of migratory trajectories were associated with tailwinds at departure. Most knots tracked in our study traveled north through the eastern Great Lake Basin, without stopping, thus making the Southeast United States the last terminal stopover for some knots before reaching boreal or Arctic stopover sites.

Estimating detection for salt-marsh songbirds during winter using the double-pass rope-drag technique.

Bird species that are restricted to tidal marshes during one or all of their life stages are under increasing pressure from sea-level rise. To date, most of the research focused on this group has been conducted during the breeding season despite the fact that more than half of the annual cycle is spent on wintering grounds and the high likelihood that the winter period is the most critical time for adult survival. We used a double-pass rope-drag technique to estimate the winter abundance of sharp-tailed sparrows (Ammospiza nelson and A. caudacutus collectively), seaside sparrows (A. maritimus) and marsh wrens (Cistothorus palustris) within tidal marshes of Virginia along 102 60X250 m transects between January and March, 2014. We used the first pass to remove birds from the transect and the second pass was used to estimate detection probabilities. The technique was highly effective producing detection rates of 98% for sharp-tailed sparrows, 95% for seaside sparrows, and 91% for marsh wrens. We conducted three rounds of surveys and found that species-specific detection rates were comparable when we restricted our analyses to two survey rounds. Availability and abundance estimates deviated to a greater degree than detection rates when restricting data to that collected during only two rounds but confidence intervals overlapped for all three taxa, regardless of which two survey periods were used for the comparison. However, results were less precise when we restricted our analyses to two of three rounds with confidence intervals averaging 13%, 45%, and 14% larger for detection, availability, and abundance respectively. The double-pass rope-drag technique provides an effective, unbiased sampling technique to estimate winter songbird abundance in saltmarsh habitat provided that at least two rounds are used and increasing the number of survey rounds will result in more precise estimates.

The annual cycle for whimbrel populations using the Western Atlantic Flyway.

Many long-distance migratory birds use habitats that are scattered across continents and confront hazards throughout the annual cycle that may be population-limiting. Identifying where and when populations spend their time is fundamental to effective management. We tracked 34 adult whimbrels (Numenius phaeopus) from two breeding populations (Mackenzie Delta and Hudson Bay) with satellite transmitters to document the structure of their annual cycles. The two populations differed in their use of migratory pathways and their seasonal schedules. Mackenzie Delta whimbrels made long (22,800 km) loop migrations with different autumn and spring routes. Hudson Bay whimbrels made shorter (17,500 km) and more direct migrations along the same route during autumn and spring. The two populations overlap on the winter grounds and within one spring staging area. Mackenzie Delta whimbrels left the breeding ground, arrived on winter grounds, left winter grounds and arrived on spring staging areas earlier compared to whimbrels from Hudson Bay. For both populations, migration speed was significantly higher during spring compared to autumn migration. Faster migration was achieved by having fewer and shorter stopovers en route. We identified five migratory staging areas including four that were used during autumn and two that were used during spring. Whimbrels tracked for multiple years had high (98%) fidelity to staging areas. We documented dozens of locations where birds stopped for short periods along nearly all migration routes. The consistent use of very few staging areas suggests that these areas are integral to the annual cycle of both populations and have high conservation value.

Whimbrel populations differ in trans-atlantic pathways and cyclone encounters.

Each year hundreds of millions of birds cross the Atlantic Ocean during the peak of tropical cyclone activity. The extent and consequences of migrant-storm interactions remain unknown. We tracked whimbrels from two populations (Mackenzie Delta; Hudson Bay) to examine overlap between migration routes and storm activity and both the frequency and consequence of storm encounters. Here we show that Mackenzie Delta and Hudson Bay whimbrels follow different routes across the ocean and experience dramatically different rates of storm encounters. Mackenzie Delta whimbrels departed North America from Atlantic Canada, made long ([Formula: see text] = 5440 ± 120.3 km) nonstop flights far out to sea that took several days ([Formula: see text] = 6.1 ± 0.18) to complete and encountered storms during 3 of 22 crossings. Hudson Bay whimbrels departed North America from the south Atlantic Coast, made shorter ([Formula: see text] = 3643 ± 196.2 km) nonstop flights across the Caribbean Basin that took less time ([Formula: see text] = 4.5 ± 0.29) to complete and encountered storms during 13 of 18 crossings. More than half of Hudson Bay storm encounters resulted in groundings on Caribbean islands. Grounded birds required longer ([Formula: see text] = 30.4 ± 5.32 days) to complete trans-Atlantic crossings and three were lost including 2 to hunters and 1 to a predator. One of the Mackenzie Delta whimbrels was lost at sea while crossing the Intertropical Convergence Zone. Whimbrels use two contrasting strategies to cross the Atlantic including (1) a long nonstop flight around the core of storm activity with a low likelihood of encountering storms but no safety net and (2) a shorter flight through the heart of Hurricane Alley with a high likelihood of encountering storms and a safety network of islands to use in the event of an encounter. Demographic consequences of storm encounters will likely play a role in the ongoing evolution of trans-Atlantic migration pathways as global temperatures continue to rise.

Mercury levels of Nelson's and saltmarsh sparrows at wintering grounds in Virginia, USA.

Nelson's and saltmarsh sparrows (Ammodramus nelsoni and A. caudacutus) have recently been recognized as separate species, and because of their limited distributions and the susceptibility of their wetland habitats to climate change, these two new species are of conservation concern. Both species are known to bioaccumulate mercury at breeding sites in New England, USA where their ranges overlap, with the saltmarsh sparrow reported to have twice the concentration of blood total mercury. In this study we sampled both species on their shared wintering grounds, and documented that mercury exposure is lower than that reported for the breeding range, with saltmarsh sparrow blood mercury 2.6 times higher than in Nelson's sparrow. Feather mercury, which is incorporated on the breeding grounds, confirmed that saltmarsh sparrows had incorporated 2.3 times more mercury than Nelson's sparrows during the previous breeding season. A comparison of stable isotopes of nitrogen and carbon suggests that the higher exposure of saltmarsh sparrows may be not due to feeding at a higher trophic level, as previously hypothesized, but rather could be related to a difference in the carbon source at the base of each species' food chain. This study, along with recently published data from both species on additional breeding and wintering grounds, provides a more complete picture of relative mercury exposure. Saltmarsh sparrows are exposed to mercury levels that warrant concern, with the highest exposure being during the breeding season. Areas set aside for the long-term conservation of this species should be carefully assessed for mercury bioaccumulation.