Yellow warbler Galapagos data

Animals across diverse lineages use referential calls to warn of and respond to specific threats, though the ability to understand these calls may be dependent on experience with the threat being referenced. Yellow warblers (<em>Setophaga petechia</em>) produce referential ‘seet’ calls towards brood parasitic brown-headed cowbirds (<em>Molothrus ater</em>), which threaten the warblers’ reproductive success. Seet calls are produced frequently in populations sympatric with cowbirds, but rarely in allopatric populations, even when those populations are genetically similar, begging the question of the role of personal experience in anti-parasitic responsiveness in aggression and propensity to seet call towards brood parasites. Here we tested for seet call responses from a yellow warbler population on the Galapagos Islands (subspecies <em>aureola</em>), which has been geographically isolated from the mainland and brood parasites for ~300,000 years. We presented playbacks of brown-headed cowbird calls (allopatric brood parasite), seet calls (North American yellow warbler’s referential anti-parasitic call), chip calls (yellow warbler’s general alarm call), sympatric predator calls, and harmless allopatric and sympatric control songs to breeding yellow warblers, and compared behavioral and vocal responses between treatments. We found that in response to playbacks signaling brood parasitic risk (seet and cowbird calls), Galapagos yellow warblers showed aggression comparable to controls, and much lower compared to chip or predator playbacks. Galapagos yellow warblers never produced any seet calls in response to the playbacks. Our results suggest that in geographic isolation from cowbirds, Galapagos yellow warblers do not produce or respond to referential alarm calls indicating mainland brood parasitic nest threats.