Sexy sparrows: Professor Hill uncovers the shocking truthby Mona Prufer
They look so cute and innocent, the way they blend into the environment with their muted brown and grey tones, the way they feed their babies and protect their young, the way they sing like, well, like cheery songbirds.
You just don’t expect them to be promiscuous.
Yet, the Saltmarsh Sparrows, especially the females, are perhaps the most sexually indiscriminate birds in the world.
As new research by Coastal Carolina University biologist Chris Hill and colleagues Chris Elphick of the University of Connecticut and Carina Gjerdrum of Environment Canada shows, the sparrows exhibit “scramble-competition polygyny,” a condition that is most unusual in the bird world.
The sparrows mate and nest along the coast from Virginia to Maine.
In an article in The Auk, the journal of the American Ornithologists’ Union, Hill and his co-authors describe the little birds as exhibiting “extreme levels of multiple mating.”
Fifty-seven of the 60 broods tested had at least two chicks with different fathers. Ninety-seven percent of females were mating with more than one male.
“Frequently, every single egg in a nest would have a different father,” says Hill, who conducted molecular analyses of paternity in his laboratory at CCU.
Hill’s collaboration with Elphick and Gjerdrum came about through a meeting at a conference in 2002. “I had wanted to study the mating system of saltmarsh sparrows, but they do not breed in South Carolina,” says Hill. “Chris and Carina, who were studying the nesting ecology of saltmarsh sparrows in Connecticut, agreed to gather blood samples from chicks in the nest and from adults on the breeding grounds, and then sent the blood to me to determine paternity.”
Before Hill’s study, the species had been known to lack the pair bonds common to most songbirds (instead, the female sparrows nest and feed the young without any assistance from males), but exactly who mated with whom was not clear.
“There have even been reports of forced copulation, which is very odd among songbirds, almost anatomically impossible,” says Hill.
He was assisted by Scott Tomko and Katie Copenhaver, recent CCU graduates, and Whitney Bryan, a student from the South Carolina Governor’s School for Science and Math.
The sparrows are thought to be even more promiscuous than the previously known extremes of multiple mating, the Greater Vasa Parrot of Madagascar and the Superb Fairy-Wren of Australia.
Hill, who is currently studying the nesting ecology of Least Terns in South Carolina with CCU graduate student Alex Kohorst, remains interested in Saltmarsh Sparrows. “They spend their entire life in salt marshes, which makes them vulnerable to habitat loss as sea levels rise,” notes Hill. “This is a species whose future is in question. They need watching.”