Role of parasite pressure in the migratory strategies of red knots (Calidris canutus rufa) wintering populations in South America.

D'AMICO VERÓNICA LAURA; MARCELO N. BERTELLOTTI; ALLAN J. BAKER; PATRICIA M. GONZÁLEZ

Mazatlán, Sinaloa

Simposio; III Western Hemisphere Shorebird Group Meeting; 2009

We test whether migratory strategies in Red knots (Calidris canutus rufa) are a response to spatial variation in parasite pressure at different sites: Río Grande (RG), Tierra del Fuego, Maranhão (MA), Brazil and Delaware Bay (DB), USA along the same migratory cycle. A ?parasite? hypothesis predicts that birds should evolve migrations to low-parasite marine wintering sites to reduce the fitness consequences of high parasite load in tropical MA, but there is likely to be a tradeoff with increased mortality for long-distance migration to cold-temperate RG. Ectoparasites were scored visually and blood parasites were searched for with molecular assays and observations of smears. Birds refueling in DB were assigned to either northern (MA) or southern wintering sites (RG) using stable isotopes in feathers. All ectoparasites found were feather lice were Mallophaga. 4.4 % of birds in RG had ectoparasites whereas all birds in MA were parasitized. In DB the proportion of parasitized birds from northern and southern 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 DB. Blood parasite assays were negative consistent with the low incidence of vectors in marine shores. Observations in each wintering site support the ?parasite hypothesis? in Red knots. However, studies in birds at DB have to be extended since results could suggest that southern populations would have detrimental effects of longer migration and ectoparasites, whereas northern populations only would suffer the negative effects of the ectoparasites.