Study explores the possible benefits of rare behavior
Date: May 2, 2019
Source: Cornell University
Acorn Woodpeckers live in close-knit family groups and have one of the most complex breeding systems of any bird in the world. In about 20 percent of family groups, up to 3 related females may lay eggs in the same nest. They raise the chicks cooperatively with one or more related males. This behavior is known as joint nesting or "cooperative polyandry." Only five other species of birds worldwide are known to do this. The reasons that may be driving the behavior are outlined in a study recently published in The American Naturalist.
Lead authors Sahas Barve at Old Dominion University (Cornell Ph.D. '17), and Cornell Lab of Ornithology scientist Walt Koenig, used demographic data collected during 35 years (1982-2016) at the Hastings Natural History Reservation in central coastal California. They analyzed the costs and benefits of joint nesting, hoping to explain why some woodpecker females exhibit this rare behavior.
They found that joint nesting was more common in years when Acorn Woodpecker population density was high, all the breeding territories were occupied, and opportunities for a female to nest on her own were very unlikely.