Do Neotropical austral migrants use stopover sites en route to their breeding areas? Evidence from the Monte desert, Argentina

M. CECILIA SAGARIO; VICTOR R. CUETO; JAVIER LOPEZ DE CASENAVE

Campos do Jordao, Brasil

Simposio; XXV International Ornithological Congress; 2010

Stopover sites are essential for a successful journey during the migration of birds. However, there is no evidence of use of stopover sites by South American migrant landbirds. We compared site fidelity, breeding activity and fat accumulation of one resident (Greater Wagtail-Tyrant) and two migratory bird species (White-crested Elaenia and Southern Scrub-Flycatcher) to evaluate whether these migrants use mesquite woodlands in the Monte desert as stopover sites during spring migration. We mist-netted birds in mesquite woodlands at Ñacuñán Biosphere Reserve, Argentina, during five breeding seasons (2004-2008). Birds were banded with numbered and colored bands. After net sampling, color-banded birds were searched for at least 10 days or until no new banded individuals were observed after searching for at least 10 person-hours. We captured 103 Greater Wagtail-Tyrants, 75 White-crested Elaenias and 43 Southern Scrub-Flycatchers. We recaptured or re-sighted more than 40 % of Greater Wagtail-Tyrants and 7 % of Southern Scrub-Flycatchers, the latter of which exhibited breeding site fidelity. In contrast, we never recaptured or re-sighted White-crested Elaenias. The three species had a similar percentage of individuals with a cloacal protuberance (Greater Wagtail-Tyrant 12 %, Southern Scrub-Flycatcher 18 %, and White-crested Elaenia 13 %), but individuals with an incubation patch were recorded only among Greater Wagtail-Tyrants and Southern Scrub-Flycatchers (88 % and 53 %, respectively). White-crested Elaenias had low (48 %), medium (29 %) and high (23 %) fat accumulation. In contrast, Greater Wagtail-Tyrants and Southern Scrub-Flycatchers were mainly characterized by low fat accumulation (93 % and 91 %, respectively). Our results suggest that Southern Scrub-Flycatcher uses Monte desert woodlands for breeding. In contrast, White-crested Elaenia appears to use these woodlands as stopover sites “en route” to its breeding areas in the southern Patagonian forests.