Researchers have puzzled together hundreds of songbird fossils excavated from what’s now a Peruvian desert dotted by just a couple species of birds. According to their findings published in The Auk: Ornithological Advances, some 15,000 years ago, these tar seeps were grassy, forested areas home to dire wolves, saber-toothed cats, and at least 21 species of songbirds. 

Nowadays, more than half of the bird species on the planet are passerines, a group that includes songbirds, and they’re especially diverse in the Neotropics, which includes Central and South America. Yet, they have a scanty presence in the fossil record. To see how the birds were affected by the last ice age, Jessica Oswald and David Steadman from the Florida Museum of Natural History identified 625 fossilized bones excavated from the now arid Talara Tar Seeps in northwestern Peru (pictured below). The fossils are between 15,000 and 18,000 years old, and the identifiable birds include antbirds, crescentchests, flycatchers, swallows, mockingbirds, finches, sparrows, and blackbirds. 

Of the 21 passerine species identified, only two of them seem to live at the site today: the long-tailed mockingbird, Mimus longicaudatus, and the cinereous finch, Piezorina cinerea. The other 19 species are either extinct or require wetter conditions, although some of them still likely stop by during El Niño events. Furthermore, nearly half of all the individual fossils and eight of the 21 species were blackbirds, including three extinct species: one previously described, two new to science. These birds tend to form communal roosts near water. 

This songbird community at Talara suggests that the site supported savanna, grasslands and forests during the last glacial interval – all of which are absent there today. Climate fluctuations and the collapse of large mammal communities (which blackbirds form commensal relationships with) had a massive influence on the composition and geographic ranges of passerine birds. 
    
“Species respond idiosyncratically to historical change, which means that instead of entire communities shifting their distributions in response to climate change, some species became extinct or extirpated in certain areas, some moved to track shifting resources, and others adapted,” Oswald said in a statement. “I think understanding how some species responded to historical change can help predict how a species will respond to modern change."

^{15,000 years ago, the arid landscape seen here at Peru's Talara Tar Seeps was grassland and forest. J. Oswald}