Tracking habitat use of a long-distance migratory bird, the american redstart Setophaga ruticilla, using stable-carbon isotopes in cellular blood

The successful use of stable isotopes to track migratory animals between different seasons of the annual cycle depends, in part, on the turnover rate of isotopes in sample tissue. We examined whether stable‐carbon isotopes in the blood of a long‐distance migratory bird, the American redstart Setophaga ruticilla, sampled upon arrival to the temperate breeding grounds could be used to track the quality of habitat used the previous season on the tropical wintering grounds. Stable‐carbon isotopes in red‐blood cells sampled upon arrival (δ¹³C_RBC) were significantly less negative relative to: 1) plasma sampled upon arrival from the same individuals, 2) red‐blood cells of redstarts recaptured more than a month later on the breeding grounds, and 3) nestling feathers grown at the same breeding location. δ¹³C_RBC was also significantly different between sexes, consistent with findings from the wintering grounds where sex‐biased habitat use is known to occur. Although individuals likely integrate some isotopic signatures during migration, we provide evidence that cellular blood can be used to track the relative habitat use of migratory birds during the wintering period. Non‐destructive methods of sampling stable‐isotopes, such as this, are particularly useful because it provides a technique for tracking the patterns of habitat use and/or geographic location of migratory animals. Such approaches allow researchers to understand how events throughout the annual cycle interact to influence population dynamics.