How bronzed cowbirds (Molothrus aeneus) find nests to parasitize is poorly known, especially whether they use host vocalizations as sources of information about nest location and status. We conducted 120 point-count surveys, followed by broadcasts of host songs, at Santa Ana National Wildlife Refuge in the Lower Rio Grande Valley of Texas in 2008 and 2009. Bronzed cowbirds responded to songs of potential host species by flying toward the source of the playback as single females or males or multiple females and males. Bronzed cowbirds responded in greater numbers to the songs of oriole species (Icterus) than to olive sparrow (Arremonops rufivirgatus), a lower-quality host species. Such responses by bronzed cowbirds could facilitate the location of host nests for nests of species difficult to find or to look into.
Mary J. Janecka and Timothy Brush "Differential response by bronzed cowbirds to songs of potential hosts in the lower Rio Grande Valley of Texas," The Southwestern Naturalist 59(4), 556-561, (1 December 2014). https://doi.org/10.1894/EKL-03.1
The Southwestern Naturalist