| dc.description.abstract | Billions of animals seasonally migrate long distances which allows them to exploit resources or favorable environmental conditions across time and space. In addition, long-distance migratory movements may allow animals to temporarily avoid certain hazards such as parasites or diseases associated with a particular habitat. This concept has been termed “migratory escape”, and it has been applied to taxa ranging from zebras to butterflies. In this study we test whether “migratory escape” applies to human-induced contamination by comparing heavy metal exposure in migratory and non-migratory birds captured at one of the most highly toxic areas in the United States, the Tar Creek Superfund Site (TCSS) in northeastern Oklahoma. Concentrations of lead, cadmium, and zinc (Pb, Cd, Zn) were measured in both the blood and feathers of adult passerines from TCSS and from a non-contaminated reference site. We also sampled nestlings of two migratory swallow species, Northern Rough-winged Swallow (Stelgidopteryx serripennis) and Bank Swallow (Riperia riperia) to enable comparisons between migrants that have never left TCSS and adult swallows (i.e. birds that have migrated at least once). We initially found limited evidence of “migratory escape” from a data set wherein swallows dominated our sample of migrant species. More specifically, both resident and migrant birds from TCSS exhibited higher levels of Pb in blood, and Pb, Cd, and Zn in feathers than birds sampled from a non-contaminated reference site. Also, Pb in feathers and Cd in blood of adult swallows were significantly lower than in nestling swallows. We found strong evidence of “migratory escape” when swallows were excluded from the migrant sample. Non-swallow migrants had significantly lower levels of Pb, Cd, and Zn in feathers than resident species at TCSS. The swallows we sampled nested directly in the contaminated mine tailings, which may explain why the evidence of “migratory escape” was not as strong when swallows were part of the analysis. Our results generally align with the idea that migrants benefit from migration by escaping long-term exposure to toxic heavy metals. “Migratory escape” studies have previously focused on disease and parasites; this is the first study to apply this concept to human-induced contamination. | en_US |
