Researchers are realizing that animal communication is more complicated than previously thought, and that the information animals share in their vocalizations can be complex. For example, some animals produce calls that warn of specific dangers in the environment, such as a predator, and these calls can even contain information about the type of predator (e.g. flying vs ground predator). These calls are known as referential calls.

Yellow warblers are hosts to brood parasitic brown-headed cowbirds, which rely on other species to raise their offspring. Warblers use referential “seet” calls to warn female warblers specifically of the brood parasitic brown-headed cowbirds that may try to lay eggs in their nests. When exposed to experimental playbacks of seet calls one day, female warblers were more vigilant the next morning, researchers report in the current issue of the journal Biology Letters.

Brown-headed cowbirds show a bias in the sex ratio of their offspring depending on the time of the breeding season, researchers report in a new study. More female than male offspring hatch early in the breeding season in May, and more male hatchlings emerge in July.

Cowbirds are brood parasites: They lay their eggs in the nests of other birds and let those birds raise their young. Prothonotary warblers are a common host of cowbirds.

They say it takes a village to raise a child. But if you are a cowbird, left by your parents to be hatched and raised in the nest of unwitting foster parents, how do you know who your village is? If the signature behaviors of your bird identity are not instinctive, how do you know who to learn them from?