Ecology and behavior of Alder Flycatchers (Empidonax alnorum) on their wintering grounds in Argentina

ARETA JI; MANGINI G; GANDOY F; GORLERI F; GÓMEZ D; DEPINO E; JORDAN EA

WILSON JOURNAL OF ORNITHOLOGY

WILSON ORNITHOLOGICAL SOC

Año: 2016 p. 830 - 845

1559-4491

<!-- /* Font Definitions */@font-face{font-family:"Cambria Math";panose-1:2 4 5 3 5 4 6 3 2 4;mso-font-charset:0;mso-generic-font-family:auto;mso-font-pitch:variable;mso-font-signature:-536870145 1107305727 0 0 415 0;}@font-face{font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;mso-font-charset:0;mso-generic-font-family:auto;mso-font-pitch:variable;mso-font-signature:-520092929 1073786111 9 0 415 0;} /* Style Definitions */p.MsoNormal, li.MsoNormal, div.MsoNormal{mso-style-unhide:no;mso-style-qformat:yes;mso-style-parent:"";margin-top:0in;margin-right:0in;margin-bottom:10.0pt;margin-left:0in;line-height:115%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:Calibri;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;}.MsoChpDefault{mso-style-type:export-only;mso-default-props:yes;font-size:11.0pt;mso-ansi-font-size:11.0pt;mso-bidi-font-size:11.0pt;font-family:Calibri;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;}.MsoPapDefault{mso-style-type:export-only;margin-bottom:10.0pt;line-height:115%;}@page WordSection1{size:8.5in 11.0in;margin:1.0in 1.25in 1.0in 1.25in;mso-header-margin:.5in;mso-footer-margin:.5in;mso-paper-source:0;}div.WordSection1{page:WordSection1;}-->The Alder (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 suggest that 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) stands along the Río Bermejo andtributaries, either in association with sparse shrubs of chilca (Baccharis salicifolia) or more rarelywith canebrake (Gynerium sagittatum).Other habitats used were old shrubby ´madrejones´ with Tessaria scrub and sacha café (Sesbaniavirgata), very dense Baccharissalicifolia scrub next to flowing creeks in foothill Yungas and dry Chaco,and riparian forests dominated by palo flojo (Albizia inundata) and timbó (Enterolobiumcontortisiliquum). Seasonal flooding of these habitats did not affect thepresence of Alder Flycatchers. Small territories of c. 20 x 20 or 25 x 25 m weredefended in Tessaria stands. AlderFlycathers fed mostly on insects in flight (aerial hawking), but also on greenLepidoptera larvae (upward sally-strikes), and on insects on leaves, and ripefruits of tala (Celtis cf. ehrenbergiana) in forest understory (clinging).Vocalizations given by overwintering birds (Fee-bee-oo, Zwee-oo, Wee-oo, Churr,Pit, Double-peak and kitter) were similar to those used while breeding. AlderFlycatchers collected in Argentina had significantly longer wings and widerbills than specimens from the sympatric Euler´s Flycatchers (Lathrotriccus euleri) from Argentinawith which it has been confused in museum specimens.