Conspecific Attraction and the Conservation of Territorial Songbirds MICHAEL P. WARD * ‡ AND SCOTT SCHLOSSBERG† * Department of Animal Biology, University of Illinois, Urbana-Champaign, 201 Shelford Vivarium, 606 E. Healey Street, Champaign, IL 61820, U.S.A., email mpward@uiuc.edu †Program in Ecology and Evolutionary Biology, University of Illinois, Urbana-Champaign, 201 Shelford Vivarium, 606 E. Healey Street, Champaign, IL 61820, U.S.A., email schlssbr@uiuc.edu Abstract: Conspecific attraction, the tendency for individuals of a species to settle near one another, is well described in colonial species, especially birds. Although this behavior may occur in territorial birds, evidence has been lacking. If territorial birds do exhibit this behavior, it would have major conservation implications. Birds could potentially be attracted to specific sites with artificial stimuli, making conservation of those species more efficient. In 2001 and 2002, we tested whether conspecific attraction occurs in an endangered, territorial songbird, the Black-capped Vireo (Vireo atricapilla) by playing vireo vocalizations in unoccupied habitats at Fort Hood, Texas. We were successful in attracting 73 birds to five experimental sites in 2001 and 75 birds to seven experimental sites in 2002. No birds settled on comparable control sites. Many birds attracted to the vocalizations paired and bred. At most research sites the primary threat to the species, the brood-parasitic Brown-headed Cowbird (Molothrus ater), was controlled, allowing vireos to achieve high nesting success relative to a nearby, unmanipulated population. Second-year birds were more responsive to conspecific vocalizations than older birds, as they were more common on experimental sites than in the established population. In 2002 birds recolonized experimental sites from 2001 where vocalizations were not played in 2002, indicating that 1 year of playbacks may be sufficient to establish a population. Our results provide the first experimental evidence that territorial songbirds use the presence of conspecifics when deciding where to settle and suggest that conspecific attraction may provide a valuable conservation tool. Key Words: Black-capped Vireo, conspecific attraction, endangered species, habitat selection Atracci´ on Conespec´ ıfica y la Conservaci´ on de Aves Canoras Territoriales Resumen: La atracci´ on conespec´ ıfica, tendencia de los individuos de una especie a establecerse cerca de otro de la misma especie, est´ a bien descrita en especies coloniales, especialmente aves. Aunque este comportamiento puede ocurrir en aves territoriales, se carece de evidencia. Si aves territoriales muestran este comportamiento, tendr´ ıa implicaciones mayores en la conservaci´ on. Las aves potencialmente ser´ ıan atra´ ıdas a sitios espec´ ıficos mediante est´ ımulos artificiales, haciendo m´ as eficiente la conservaci´ on de esas especies. En 2001 y 2002, probamos si ocurre la atracci´ on conespec´ ıfica en una especie de ave canora territorial, en peligro, Vireo atricapilla, con la reproducci´ on de vocalizaciones de vireo en h´ abitats desocupados en Fort Hood, Texas. Tuvimos ´ exito al atraer a 73 aves a cinco sitios experimentales en 2001 y 75 aves a siete sitios experimentales en 2002. No se establecieron aves en sitios controles comparables. Muchas de las aves atra´ ıdas a las vocalizaciones formaron pareja y se reprodujeron. En la mayor´ ıa de los sitios, la principal amenaza para la especie, el par´ asito Molothrus ater, fue controlada, lo que permiti´ o un elevado ´ exito de anidaci´ on a los vireos en comparaci´ on con una poblaci´ on no manipulada cercana. Las aves de dos a˜ nos tuvieron mayor respuesta a las vocalizaciones conespec´ ıficas que las aves m´ as viejas, porque fueron m´ as comunes en los sitios experimentales que en la poblaci´ on establecida. En 2002 aves recolonizaron sitios experimentales de 2001 en los que no se reprodujeron ‡Order of authorship determined by coin flip. Paper submitted November 13, 2002; revised manuscript accepted June 4, 2003. 519 Conservation Biology, Pages 519–525 Volume 18, No. 2, April 2004