ECOLOGY AND BEHAVIOR OF ALDER FLYCATCHERS (Empidonax alnorum) ON THEIR WINTERING GROUNDS IN ARGENTINA

ARETA, JUAN IGNACIO; MANGINI, GABRIELA; GANDOY, FACUNDO; GORLERI, FABRICIO; GOMEZ, DANIELA; DEPINO, EMILIANO; JORDAN, EMILIO ARIEL

WILSON JOURNAL OF ORNITHOLOGY

WILSON ORNITHOLOGICAL SOC

Año: 2016 vol. 128 p. 830 - 845

1559-4491

TheAlder (Empidonax alnorum) and Willow(E. trailli) flycatchers are crypticspecies, and their distribution outside the breeding season is poorly known,owing mostly to identification difficulties. Our new records suggestthat largenumbers of Alder Flycatchers overwinter in rivers crossing the Chaco region andin the foothill forests of the Yungas of Argentina, significantly increasing theirsouthern wintering range. Records in northern Argentina span 3 November to 23March. The key habitat for overwintering Alder Flycatchers in Argentina waspalo bobo (Tessaria integrifolia)standsalong the Río Bermejo and tributaries, either in association with sparse shrubsof chilca (Baccharis salicifolia) ormore rarely with canebrake (Gyneriumsagittatum). Other habitats used were old shrubby ´madrejones´ with Tessaria scrub and sacha café (Sesbania virgata), very dense Baccharis salicifolia scrub next toflowing creeks in foothill Yungas and dry Chaco, and riparian forests dominatedby palo flojo (Albizia inundata) and timbó(Enterolobium contortisiliquum). Seasonalflooding of these habitats did not affect the presence of Alder Flycatchers.Small territories of c. 20 x 20 or 25 x 25 mwere defended in Tessaria stands.Alder Flycathers fedmostly on insects in flight (aerial hawking), but also on green Lepidopteralarvae (upward sally-strikes), and on insects on leaves, and ripe fruits oftala (Celtis cf. ehrenbergiana) in forest understory (clinging). Vocalizationsgivenby overwintering birds (Fee-bee-oo, Zwee-oo, Wee-oo, Churr, Pit, Double-peakand kitter)were similar to those used whilebreeding.Alder Flycatchers collectedin Argentina had significantly longer wings and wider bills than specimens fromthe sympatric Euler´s Flycatchers (Lathrotriccuseuleri) from Argentina with which it has been confused in museum specimens.