Post‐breeding migration and connectivity of red knots in the Western Atlantic

Abstract

Red knots (Calidris canutus rufa) have 3 distinct nonbreeding regions: 1 in the southeastern United States and Caribbean, another on the northeast coast of Brazil in the Maranhão region, and a third along the Patagonian coasts of Chile and Argentina. Effective conservation and recovery of this threatened long-distance migrant will require knowledge of population structure, migration ecology, and abundance and distribution throughout the annual cycle. We conducted a stopover population and biogeographic assessment of knots at the Altamaha River Delta, Georgia, an important stopover area in the southeastern United States. We estimated stopover population size and stopover duration during post-breeding migration in 2011 at the Altamaha study area using mark-resight data, and we inferred nonbreeding regions for this stopover population using stable isotope ratios of carbon and nitrogen in feathers, and observations (sightings and captures) during boreal winter from across the hemisphere. With an integrated Bayesian analysis of all these data, we also estimated the number of birds in the southeastern United States and northern Brazil during boreal winter. For mark-resight analyses in Georgia, we made observations of marked individuals during 14 weeks from early August to early November 2011 and detected 814 individually marked birds. We used the Jolly-Seber mark-recapture model and estimated the southbound passage population at approximately 23,400 red knots. In ongoing studies elsewhere, isotope samples were collected from 175 (21%) of the 814 birds detected in our study, and !1 sighting or capture record during boreal winter was located in data repositories for 659 birds (81%). Isotopic signatures and boreal winter records indicate that the majority (82-96%) of the birds that stopped at the Altamaha Delta spend the boreal winter in the northern part of the nonbreeding range (southeast USA, Caribbean, and northern Brazil). Knots migrating to the southeastern United States, Caribbean, or Brazil remained on the Altamaha Delta for 42 days, whereas birds migrating to Tierra del Fuego remained only 21 days. Combining our estimate of the Altamaha stopover population size (23,400 birds) and the estimated proportion in the northern nonbreeding region (82-96%), we derived a minimum estimate of the number of knots in the southeastern United States, Caribbean, and northern South America during the boreal winter: approximately 20,800 knots, of which approximately 10,400 knots occupy the southeastern United States and 5,400 occupy Brazil. Our results provide additional evidence that coastal Georgia is an important migration area for red knots, and provide information about population structure and migratory connectivity that will be valuable for conservation planning. Ó 2017 The Wildlife Society.

Migratory connectivity and local site fidelity in red knots on the southern Pacific coast of South America

“…Both of them show declining population trends (Andres et al, ): C. c. rufa is currently listed as ‘Threatened’ under the Endangered Species Act in the USA and as ‘Endangered’ in Canada (International Union for Conservation of Nature, ), whereas C. c. roselaari is listed as of ‘Greatest concern’ in the USA (U.S. Shorebird Conservation Plan Partnership, ) and as ‘Endangered’ in Mexico (Secretaría de Medio Ambiente y Recursos Naturales, ). Population estimates and trends (Andres et al, ), distribution range (Baker et al, ), migratory connectivity (Atkinson et al, ; Lyons, Winn, Keyes, & Kalasz, ; Newstead et al, ), and factors driving population declines (Baker et al, ; Escudero, Navedo, Piersma, De Goeij, & Edelaar, ) seem to be well understood for C. c. rufa (Niles et al, ).…”

“…as 'Endangered' in Mexico (Secretaría de Medio Ambiente y Recursos Naturales, 2010). Population estimates and trends (Andres et al, 2012), distribution range (Baker et al, 1996), migratory connectivity (Atkinson et al, 2005;Lyons, Winn, Keyes, & Kalasz, 2018;Newstead et al, 2013), and factors driving population declines (Baker et al, 2004;Escudero, Navedo, Piersma, De Goeij, & Edelaar, 2012) seem to be well understood for C. c. rufa (Niles et al, 2008).…”

Migratory routes and wintering locations of declining inland North American Common Terns

“…Migratory connectivity is considered strong (positive) when populations remain together between seasons and weak (negative) when there is little or no cooccurrence between seasons . Knowledge of connectivity is especially important for migratory species in decline (Fraser et al 2012, Lyons et al 2018. Thus, tracking individuals during their full annual cycle is crucial to identifying important locations used by these inland birds during the nonbreeding season, identifying potential risks, and developing strategies to target nonbreeding-season actions.…”

Objective prior distributions for Jolly‐Seber models of zero‐augmented data

“…Although population dynamics motivated the initial development of JS models, these models have also been used in studies focused primarily on estimating the total number of individuals in the population that were ever alive during all sampling periods (ie, in studies where estimating changes in the population is of less interest). For example, abundance is expected to change while sampling a migratory species at a stopover location or at a destination; however, capturerecapture surveys of these species can be used to estimate the total number of individuals that visited the location during the entire period of sampling (Carroll et al, 2013;Lyons et al, 2016Lyons et al, , 2017Weithman et al, 2018). Similarly, abundance is expected to change during prolonged sampling of a species that exhibits asynchronous breeding behavior.…”