Breeding Biology of Two Neotropical Austral Migrants at the Center of Argentina: Vermilion and Fork-Tailed Flycatchers

REBOLLO, M.E.; CEREGHETTI, J.; SARASOLA, J.H.; JAHN, A.E.

Conferencia; VII NORTH AMERICAN ORNITHOLOGICAL CONFERENCE; 2020

American Ornithological Society

Reproduction is a central aspect of bird life history strategies because it allows persistence of populations time and space. We studied the breeding ecology of Vermilion Flycatcher (VEFL, Pyrocephalus rubinus) and Fork-tailed Flycatcher (FTFL, Tyrannus savana) in the Espinal biome of central Argentina from 2015-16 to 2018-19 by monitoring 112 and 123 breeding attempts, respectively. We compared breeding data between the Parque Luro Provincial Reserve, where livestock has been excluded for five decades, and two private cattle ranches Los lamos and Giuliani. The breeding season for both species lasted from early November to February. Clutch size, brood size, and number of fledglings were =3 for VEFL and =4 for FTFL. VEFL reduced clutch size with clutch start date by up to13.65% and had a later clutch start date at the reserve than at Giuliani Ranch, explaining 13.53% of the variation between sites. FTFL had a later clutch start date in the 2015-16 season than in the 2017-18 season, explaining 11.88% of their variation between years. The incubation and nestling period were 12-13 and 14-15 days for VEFL, and 13-15 and 13-15 days for FTFL. Breeding success were 12% and 24%, respectively. Only one VEFL nest was parasitized by Shiny Cowbird (Molothrus bonariensis), while 34.96% of FTFL nest attempts were parasitized. The breeding biology of both species is variable and similar to other areas of their distribution and we discuss possible drivers of these patterns in central Argentina.