How seasonality in the southern hemisphere affects migration of austral migrant Tyrannus savana

CUETO, V.R.; TUERO, D.; MAMANI, A.M.; MACPHERSON, M.; JAHN, A.E,; J. CEREGHETTI; SARASOLA, J.H.; PIZO, MARCO AURELIO; BEJARANO, VANESA; HILL, E.

Puerto Iguazú

Simposio; Ornithological Congress of the Americas, XVII Reunion Argentina de Ornitología, XXIV Congresso Brasileiro de Ornitologia & XCV Annual Meeting of the Association of Field Ornithology; 2017

We lack athorough understanding of the degree to which the seasonal changes in locationsof animals are driven by the timing and sequence of resource availabilityacross the annual cycle, a necessary component for their conservation in achanging global climate. However, recent advancements in animal trackingtechnology offer an unprecedented ability to explore how individual animalstrack seasonal changes. This has been an especially fast-growing question inthe study of bird migrations with evidence supporting a major role ofseasonality in temperature, rainfall and primary productivity in drivingseasonal movements of individuals. To test which environmental factors(temperature, rainfall and/or primary productivity) affect seasonaldistributions of austral migrants, we used Maxent models of presence-only datagathered from 56 Tyrannus savana individuals fit with light-level geolocatorsat five breeding locations in Bolivia, Brazil, and Argentina. We found that T.savana tracked predominantly with temperature and NDVI (a measure of primaryproductivity) during the breeding months in southern South America, but trackedwith temperature and rainfall during both spring and fall migrations, andprimarily with rainfall while overwintering in northern South America. Thissupports the general idea that seasonality is important to annual routines inmigratory birds, even within South America where seasonality is driven largelyby wet-dry cycles. Since wet-dry seasons vary inter-annually, migration in theaustral system may be more flexible in timing than in boreal systems whereseasonal movements are strongly linked to temperature.