Female Songbirds: Quiet for Good Reason

Female birds are capable of song in 71% of songbird species, So how come we don't hear them as often as we hear the males? New research indicates that sometimes female songbirds have good reasons to stay quiet. 

Sonia Kleindorfer, a behavioral ecologist at Flinders University in Adelaide, Australia, studied the singing patterns of female and male Superb Fairywrens (Malarus cyaneus), a small Australian songbird species. Like the females of many species, female Superb Fairywrens often sing for territorial defense, sometimes even when they're on their nests. They use a melody known as a "chatter song." The male uses it too, but he is not as often near the nest when he sings.  This is a key difference, since singing alerts predators such as rodents, cats, and foxes. Kleindorfer investigated whether male singing or female singing poses a greater risk.

During the nesting seasons of 2013 and 2014, Kleindorfer and her colleagues monitored male and female singing on and near 72 wild Superb Fairywren nests, as well as the eggs and chicks in the nests. The scientists counted a nest as “attacked” if eggs or chicks vanished in under 25 days. In other words, if eggs disappeared unhatched or chicks disappeared before they were capable of fledging, researchers assumed they'd been eaten. 

Kleindorfer's team leaned that both males and females sang the chatter song more often when they were just beginning to nest. They sang it less often when they had eggs and chicks in the nest, and with one major gender difference: The males sang away from the nest and the females near or inside it. In fact, some females never sang at all, and some sang only in response to their noisy mates. To put it differently, the females sang less when doing so would endanger their nests. Proof? The scientists baited artificial nests with quail eggs and broadcast female chatter songs infrequently (six calls per hour) and frequently (20 calls per hour). Predators ate the eggs at 40% of the "frequent" nests, but at only 20% of the "infrequent" nests: the quieter nests were safer for the kids. 

Jordan Price, a behavioral ecologist at St. Mary’s College of Maryland, posits that danger to the nest could be the reason that female songbirds of other species sing far less than their partners—or not at all—when they're the primary on-nest parents. It's even possible that, generally, male songbirds sing not to attract mates but simply because there's no reason for them not to. The females, on the other hand, have to be more wary.