Intra-tropical migration and wintering areas of Fork-tailed Flycatchers (Tyrannus savana) breeding in São Paulo, Brazil

Breeding latitude predicts timing but not rate of spring migration in a widespread migratory bird in South America

“…A potentially fruitful future line of research would be to evaluate the seasonal carryover effects that Fork‐tailed Flycatchers may have to deal with when transitioning from winter to the breeding season. Fork‐tailed Flycatchers are known to track rainfall during winter (MacPherson et al, ), arriving at the wintering grounds in northern South America at the beginning of the wet season, which peaks in July and August (Poveda, Waylen, & Pulwarty, ) and where Fork‐tailed Flycatchers undergo an annual flight feather molt (Jahn, Giraldo, et al, ; Jahn, Seavy, et al, ). Winter represents a critical period during which they must properly time flight feather molt prior to spring migration, since Fork‐tailed Flycatchers generally avoid molting and migrating simultaneously (Jahn et al, ).…”

“…Winter represents a critical period during which they must properly time flight feather molt prior to spring migration, since Fork‐tailed Flycatchers generally avoid molting and migrating simultaneously (Jahn et al, ). Given that northern South America is susceptible to notably lower rainfall levels in some years (i.e., during the “El Niño” phase of the El Niño/La Niña climatic cycle, Poveda et al, ), understanding the relationship between interannual variation in food resource availability, which is key to completing feather molt (Jahn, Giraldo, et al, ; Jahn, Seavy, et al, ), and the timing of events in the flycatcher's annual cycle, will provide novel insights into the constraints molding the annual cycle and population dynamics of this and other species migrating within South America.…”

“…Upon capture, flycatchers were banded with an individually numbered metal band and up to three Darvic color bands. Flycatchers were aged and sexed using the shape of the notch of primaries 8–10 and/or the presence of a brood patch or cloacal protuberance (Jahn, Giraldo, et al, ; Jahn, Seavy, et al, ; Pyle, ). Wing chord, tarsus length, and tail length were collected following methods in Ralph, Guepel, Pyle, Martin, and DeSante (), and body mass was measured to the nearest 0.1 g using a portable digital scale (Ohaus LS 200).…”

“…To do so, we deployed light‐level geolocators on migratory Fork‐tailed Flycatchers ( Tyrannus s. savana ) in South America. This subspecies breeds from central Brazil to central Argentina (Mobley, ), with Brazilian populations breeding at tropical latitudes and overwintering in northern South America (Jahn, Giraldo, et al, ; Jahn, Seavy, et al, ); they are thus intratropical migrants. Populations that breed at south‐temperate latitudes in Argentina also overwinter in northern South America (Jahn et al, ) and are thus Neotropical austral migrants (Cueto & Jahn, ).…”

“…Populations that breed at south‐temperate latitudes in Argentina also overwinter in northern South America (Jahn et al, ) and are thus Neotropical austral migrants (Cueto & Jahn, ). Fall migration patterns (Jahn, Giraldo, et al, ; Jahn, Seavy, et al, ; Jahn et al, ), tracking of environmental conditions (MacPherson et al, ), and, for one site in Brazil, timing of arrival of males versus females (Bejarano & Jahn, ) have been studied in Fork‐tailed Flycatchers, but little is known about spring migration strategies.…”