Unravelling the migration and moult strategies of a long‐distance migrant using stable isotopes: Red Knot Calidris canutus movements in the Americas

Abstract

For long‐distance migrants, such as many of the shorebirds, understanding the demographic implications of behavioural strategies adopted by individuals is key to understanding how environmental change will affect populations. Stable isotopes have been used in the terrestrial environment to infer migratory strategies of birds but rarely in marine or estuarine systems. Here, we show that the stable isotope ratios of carbon and nitrogen in flight feathers can be used to identify at least three discrete wintering areas of the Red Knot Calidris canutus on the eastern seaboard of the Americas, ranging from southeastern USA to Patagonia and Tierra del Fuego. In spring, birds migrate northwards via Delaware Bay, in the northeastern USA, the last stopping point before arrival in Arctic breeding areas, where they fatten up on eggs of spawning Horseshoe Crabs Limulus polyphemus. The isotope ratios of feather samples taken from birds caught in the Bay during May 2003 were compared with feathers obtained from known wintering areas in Florida (USA), Bahia Lomas (Chile) and Rio Grande (Argentina). In May 2003, 30% of birds passing through the Bay had Florida‐type ‘signatures’, 58% were Bahia Lomas‐type, 6% were Rio Grande‐type and 7% were unclassified. Some of the southern wintering birds had started moulting flight feathers in northern areas, suspended this, and then finished their moult in the wintering areas, whereas others flew straight to the wintering areas before commencing moult. This study shows that stable isotopes can be used to infer migratory strategies of coastal‐feeding shorebirds and provides the basis for identifying the moult strategy and wintering areas of birds passing through Delaware Bay. Coupled with banding and marking birds as individuals, stable isotopes provide a powerful tool for estimating population‐specific demographic parameters and, in this case, further our understanding of the migration systems of the declining Nearctic populations of Red Knot.

Travelling on a budget: predictions and ecological evidence for bottlenecks in the annual cycle of long-distance migrants

“…Evidence from long-term ringing programmes indicates that distinct flyways exist and correspond to separate breeding areas in the Arctic (Piersma & Davidson 1992). During the course of migration, some subspecies share certain staging areas; for example, C. c. rufa and C. c. roselaari in Delaware Bay and the southeastern USA (Atkinson et al 2005), and C. c. islandica and C. c. canutus in the Wadden Sea in Europe (Nebel et al 2000). However, the subspecies can usually be distinguished using the timing of passage and their primary moult status.…”

Geographic variation in the trophic ecology of an avian rocky shore predator, the African black oystercatcher, along the southern African coastline

“…obs.). Moreover, other shorebirds (Klaassen et al 2001, Atkinson et al 2005) and oystercatcher species (Dare & Mercer 1974, Hulscher 1977 are known to moult during the wintering/nonbreeding season. Therefore, we assume that the isotopic composition of adult body feathers reflects their diet during the nonbreeding season (Jaeger et al 2009 (Tieszen et al 1983, Vanderklift & Ponsard 2003, Cherel et al 2005.…”

“…This baseline signal is then transmitted along the food chain in a predictable manner and is ultimately reflected in organisms at higher trophic levels (Cherel & Hobson 2007). This effect has been widely used to investigate spatial and temporal aspects of the feeding ecology of oceanic predators (Burton & Koch 1999, Quillfeldt et al 2005, Cherel & Hobson 2007, but rarely used in largescale studies involving higher trophic level organisms of intertidal ecosystems (but see Atkinson et al 2005). δ 13 C has been particularly exploited at the lower trophic levels to distinguish between the 2 main potential sources of carbon in intertidal habitats: nearshore benthic and offshore pelagic primary production (Fry & Sherr 1984, France 1995, Post 2002.…”

Shorebird hunting in Barbados: Using stable isotopes to link the harvest at a migratory stopover site with sources of production

“…Local deuterium is incorporated into food webs, allowing the creation of continent-wide, tissue-dependent ''isoscapes'' that can be used to assign individuals to approximate regions of origin (Wunder et al 2005, Hobson et al 2014. The application of stable isotopes to determining the origins of migratory animals can target the segment of the population exposed to harvest and has been used effectively to describe the origins of many migratory species, including shorebirds (Atkinson et al 2005, Catry et al 2012, Franks et al 2012). However, their application has been limited to only a few species and populations, and most studies have not used probabilistic models to determine likely areas of origin.…”