Migration strategies of wintering populations of red knots Calidris canutus rufa in South America: the role of parasite pressure

Authors: Verónica L. D´AMICO, Marcelo N. BERTELLOTTI, Allan J. BAKER, Wallace R. TELLINO JUNIOR and Patricia M. GONZÁLEZ

E-mail: damico@cenpat.edu.ar

Published: Volume 55(2), December 2008. Pages 193-202.

Language: English

Keywords: red knots, wintering sites, ectoparasites and blood parasite



Aims: To test whether different migratory strategies in red knots (Calidris canutus rufa) are a response to spatial variation in parasite pressure at different marine wintering sites as predicted by the´parasite' hypothesis of Piersma (1997).

Location: Río Grande and Tierra del Fuego, Argentina; Maranhão, Brazil; Delaware Bay, USA.

Methods: The abundance of ectoparasites and blood parasites and the frequency of parasitized birds were estimated at the three sites. Ectoparasites were scored visually and parasites in blood were searched for with molecular assays and observations of smears on slides. Birds caught in mixed flocks refueling in Delaware Bay were assigned to either northern (Maranhão or possibly Florida) or southern wintering sites (Tierra del Fuego) using stable isotopes in feathers.

Results: All ectoparasites found were feather lice were Mallophaga, Phthiraptera. The 4.4 % of birds in Tierra del Fuego and the 100 % in Maranhão had ectoparasites. In Delaware Bay the proportion of parasitized birds from northern and southern sites was not significantly different. No blood parasites (Plasmodium spp., Haemoproteus spp. and Leucocytozoon spp.) were found in the samples.

Conclusions: Only 4.4 % of birds wintering in Tierra del Fuego had ectoparasites whereas all birds wintering in Maranhão were parasitized, often heavily. During migration through Delaware Bay in May, the proportion of parasitized birds from northern (50 %) and southern (40.1 %) sites was not significantly different, indicating that many southern birds had been infected during a short stopover on the northwards migration or by direct contact in Delaware Bay. The parasite hypothesis predicts that red knots should evolve migrations to low-parasite marine wintering sites to reduce the fitness consequences of high ectoparasite load in tropical Maranhão, but there is likely to be a tradeoff with increased mortality for long-distance migration to cold-temperate Tierra del Fuego. All blood parasite assays were negative for Plasmodium spp., Haemoproteus spp. and Leucocytozoon spp, consistent with the low incidence of blood parasite vectors in marine shores. Observations in each wintering site support a role for parasite pressure in the evolution of migration strategies in red knots. However, it will be very important to extend studies to birds captured at Delaware Bay since results could suggest that southern populations would have detrimental effects of longer migratory distances and ectoparasites load, whereas northern populations only would suffer the negative effects of the parasite load. The results open the way for similar tests of the parasite hypothesis on other pathogens and endoparasites.

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