Figure 2 - uploaded by Richard Johnston González
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Map showing the migration route of a Whimbrel fitted with a satellite tag on the Eastern Shore of Virginia on 20 May 2008 (updated tracking map, Watts et al. 2008) (Courtesy of the Center for Conservation Biology at the College of William and Mary and Virginia Commonwealth University).
Citations
... northern South America (Wilke & Johnston-González 2010). Between 6800-8000 birds, comprising 8-10% of the continental population (Andres et al. 2012), are estimated to winter in Sanquianga (Johnston-González and Eusse-González 2009). ...
Roosts are important sites for shorebirds in non‐breeding areas at night and during high tides. How the spatial configuration of food and risk of predation and disturbance influence roost site use in tropical locations remains poorly known. We analysed the locations of nocturnal roosts of Whimbrel Numenius phaeopus in mangroves of Sanquianga National Park, Colombia, with respect to variation in spatial variables related to food resources and risk of predation and disturbance. We contrasted characteristics of all 13 known nocturnal roost locations with those of all other mangrove islands (n = 209) within the limits of the park. We estimated the distance from roosts and other mangrove islands to foraging sites, and sources of predators and human disturbance. Larger areas of feeding habitat surrounded nocturnal roosts than other mangrove islands, and the average distance to individual feeding patches was shorter. Roosts were also more isolated than other islands, but proximity to sources of human disturbance did not differ. We conclude that Whimbrel roost site use in Sanquianga was best explained by a combination of access to feeding territories and isolation from potential sources of mainland predators, but not by avoidance of human disturbance. Beyond identifying factors influencing roost site selection, the large aggregations of individuals in single locations may suggest that presence of conspecifics itself also plays a role in the formation of Whimbrel roosts. We highlight the interaction of food and risk landscapes with intraspecific attraction on the roost site selection by Whimbrels and the importance of mangroves as roosting sites in tropical regions.
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... The second population of Whimbrels breeds in Canada in the northern Yukon and Northwest Territories and west and south of Hudson Bay, and migrates through the Atlantic and Central Americas Flyways. This population over-winters primarily on the northern coast of South America (Skeel & Mallory 1996, Wilke & Johnston-González 2010, Johnson et al. 2016; see http://www. wildlifetracking.org/index.shtml?project_id=369). ...
... Habitat loss and degradation, largely from coastal development, are considered a major threat to Whimbrels at the global (Pearce-Higgins et al. 2017) and hemispheric scales (Wilke & Johnston-González 2010). If Whimbrels exhibit high site fidelity throughout the nonbreeding season, then loss of habitat at specific sites could reduce Whimbrel survival indirectly by causing changes in food resources needed for successful migration and reproduction (e.g. ...
... They are longdistance migratory shorebirds whose numbers have declined sharply at major stopover sites during the past two decades (Watts and Truitt 2011) and that are potentially under significant pressure from sport and subsistence hunting along portions of their migration route (Andres 2011, Watts et al. 2015. Both the U.S. and Canadian Shorebird Conservation Plans have deemed Whimbrels to be a species of high conservation concern (Donaldson et al. 2000, Brown et al. 2001) and the Whimbrel Conservation Plan considers studies of migration and connectivity a research priority (Wilke and Johnston-Gonz alez 2009). Understanding where individual Whimbrels spend time throughout the annual cycle is thus a crucial step toward effective conservation (Webster et al. 2002, Sheehy et al. 2011. ...
... Three subspecies breed in the Palearctic between Iceland and eastern Siberia, and the Nearctic subspecies N. p. hudsonicus breeds in disjunct eastern and western populations (Skeel and Mallory 1996). An alternative taxonomic classification (Engelmoer and Roselaar 1998) (Taverner 1942, Skeel andMallory 1996), and thus that the two breeding populations remained largely segregated during the non-breeding season (Wilke and Johnston-Gonz alez 2009). However, Whimbrels tracked from a coastal stopover site in Virginia with satellite transmitters were found to breed near Alaska's Coleville River (Watts et al. 2008). ...
... The movement phenology we documented was consistent with the expected timing of migration based on field surveys because it coincided with the timing of peaks reported in regional censuses (Wilke and Johnston-Gonz alez 2009). Our study, however, is the first to provide turnover rates at migratory stopovers for Whimbrels (Wilke and Johnston-Gonz alez 2009). It is thus notable that all tracked individuals in our study spent their entire stopover in a single area, for as long as 42 days, rather than gradually moving in the direction of their ultimate migratory endpoint. ...
The conservation of migratory birds requires internationally coordinated efforts that, in
turn, demand an understanding of population dynamics and connectivity throughout a species’ range.
Whimbrels (Numenius phaeopus) are a widespread long-distance migratory shorebird with two disparate North
American breeding populations. Monitoring efforts suggest that at least one of these populations is declining,
but the level of migratory connectivity linking the two populations to specific non-breeding sites or
identifiable conservation threats remains unclear. We deployed light-level geolocators in 2012 to track the
migration of Whimbrels breeding near Churchill, Manitoba, Canada. In 2013, we recovered 11 of these
geolocators, yielding complete migration tracks for nine individuals. During southbound migration, six of the
nine Whimbrels stopped at two staging sites on the mid-Atlantic seaboard of the United States for an average
of 22 days, whereas three individuals made nonstop flights of ~8000 km from Churchill to South America.
All individuals subsequently spent the entire non-breeding season along the northern coasts of Brazil and
Suriname. On their way north, all birds stopped at the same two staging sites used during southbound
migration. Individuals staged at these sites for an average of 34 days, significantly longer than during
southbound migration, and all departed within a 5-day period to undertake nonstop flights ranging from
2600 to 3100 km to the breeding grounds. These extended spring stopovers suggest that female Whimbrels
likely employ a mixed breeding strategy, drawing on both endogenous and exogenous reserves to produce their
eggs. Our results also demonstrate that this breeding population exhibits a high degree of connectivity among
breeding, staging, and wintering sites. As with other long-distance migratory shorebirds, conservation efforts
for this population of Whimbrels must therefore focus on a small, but widely spaced, suite of sites that
support a large proportion of the population.
... Current population estimates include 26,000 and 40,000 individuals for the western and Hudson Bay populations, respectively (Morrison et al. 2006). However, confidence in these estimates remains low (Morrison et al. , 2006 due to the paucity of population-level work and the difficulty of studying the species during most of the annual cycle (Wilke and Johnston-González 2009). Recent ground counts of birds during winter along the Pacific Coast have been used to increase estimates for the western breeding population by 27% (Andres et al. 2009). ...
Whimbrels (Numenius phaeopus) were monitored during spring migration across a network of ten aerial transects within the barrier island-lagoon system along the lower Delmarva Peninsula, Virginia, USA. Transects were surveyed weekly from the last week of April through the first week of June (1994–1996, 2008–2009). Whimbrel numbers increased to a peak during the first and second weeks of May then decreased sharply during the third and fourth weeks of May in all years. Between the 1990's and 2000's, peak numbers declined by 50%, corresponding to a 4.2% annual rate of decline. A similar decline was detected in accumulated, season-wide numbers. Though similar in pattern, migration phenology was significantly different between the decades. The phenology difference resulted from a greater reduction in numbers during the first half of the study period compared to the last. Habitats used by Whimbrels (N = 31,314) included mudflats (95%) and salt marshes (5%). Habitat-specific densities (birds/km2) were 443 ± 26.6 and 9 ± 1.6 (mean ± SE) for mudflat and marsh patches, respectively, during the 1990's and 222 ± 11.1 and 8 ± 4.6 during the 2000's. These results support suggestions that Whimbrels are declining on the Hudson Bay breeding grounds and perhaps at major Atlantic Coast wintering sites.
Survival estimates are critical components of avian ecology. In well‐intentioned efforts to maximize the utility of one's research, survival estimates often derive from data that were not originally collected for survival assessments, and such post hoc analyses may include unintentional biases. We estimated the survival of Whimbrels captured and marked at two breeding sites in Alaska using divergent data streams that in isolation were subject to methodological biases. Although both capture sites were chosen to study the migration ecology of Alaska‐breeding Whimbrels, maximizing the conservation value of the data we collected was obviously desirable. We used multi‐year telemetry information to infer survival from one site (Colville River) and mark‐resight techniques to estimate survival from a second site (Kanuti River). At the Colville River, we could not feasibly include a control group of birds to assess potential survival effects of externally mounted transmitters, while at Kanuti River we were unable to accurately account for potential emigration events because we used resightings alone. We integrated these datasets in a Bayesian hierarchical framework, an approach that permitted insights across sites that moderated methodological biases within sites. Using telemetry enabled us to detect permanent emigration events from breeding sites in two of ten birds; results that informed estimates for birds without tracking devices. These datasets yielded point estimates of true survival of Whimbrels from Colville River equipped with solar‐powered satellite transmitters that were higher (0.83) than true survival estimates of Whimbrels from Kanuti River marked with leg flags alone (0.74) or equipped with surgically implanted satellite transmitters (0.50), but the 95% credible intervals on these estimates overlapped across groups. For species like Whimbrels that are difficult and costly to study, combining information from disparate data streams allowed us to derive novel demographic estimates, an approach with clear application to other similar studies.
