BODY CONDITION OF BREEDING VERMILION FLYCATCHERS (PYROCEPHALUS RUBINUS) VARIES BETWEEN AREAS WITH AND WITHOUT CATTLE RANCHING IN CENTRAL ARGENTINA

Abstract

The body condition of birds may be conditioned by intrinsic (e.g., sex, age, migratory and breeding status) and extrinsic factors, such as anthropic activities (e.g., livestock raising). We describe the biometry and body condition of Vermilion Flycatchers (VEFL) according to sex and age and evaluate which factors best predict their body condition during the breeding season in the Espinal of central Argentina. The study area included “Parque Luro” Provincial Reserve and two nearby private ranches with livestock. We captured and banded VEFL using mist nets between October to February, from 2015 to 2019. We calculated the scaled mass indexes, which relates body mass to biometric measures (culmen, tarsus, and tail length, and wing chord) to choose the best indicator of body condition. As explanatory variables, we used the breeding condition of females in one model, breeding condition of males in another model, and in a final model we used date, year and site, and included all individuals. We banded 93 VEFL that did not vary according to age-dependent body size or reproductive condition. Nevertheless, females weighed more, had higher fat levels and shorter wings than males. The body condition was only explained by breeding site, being smaller in one ranch than the other ranch and the reserve. We highlight the importance of reserves and the need for further research to understand the ecological constraints that South American birds face, to promote their conservation.