MADISON, WISCONSIN--Steal a loaf of bread to feed the kids, and neighbors might wonder how your children will turn out. But it's different for endangered seabirds called roseate terns, according to research presented here on 7 August at the annual meeting of the Ecological Society of America. Terns that steal food for their kids raise the strongest young of all, suggesting that crime can pay if you're a bird.
Biologists have debated for years exactly what qualities make birds successful parents. To find out, behavioral ecologist David Shealer, now of Loras College in Dubuque, Iowa, in 1995 began observing roseate terns feeding on 4.5-acre Falkner Island in Long Island Sound. One pair consistently fed its chicks half-eaten fish. One day, Shealer noticed the same mother bird grabbing fish in mid-flight from the mouths of other roseate terns and from slightly larger common terns. Shealer wondered if the larceny made a difference for her chicks.
After 4 years, Shealer and Jeffrey Spendelow of the U.S. Geological Survey's Patuxent Wildlife Research Center in Laurel, Maryland, found more repeat-offender thieves. Of the 150 breeding pairs of terns on the island, 10 included at least one parent that, year after year, stole most of the food for the pair's young. Some birds swooped down on other flying birds like a fighter pilot; others pounced on birds feeding on the ground. But however they stole, the thieving birds fledged 50% more chicks over 10 years than birds that made an honest living fishing, the researchers discovered when they pored over their own data and previous observations.
Thievery made the biggest difference to chicks born later in the season; they grew faster and bigger than chicks of birds that flew the straight and narrow. Preliminary experiments also suggest that chicks born to thieving birds are more likely to survive the winter journey to the south Atlantic to return another year.
The results challenge dogma among behavioral ecologists that "if you're being lazy and stealing, you must not be a very good feeder," says ecologist Paul Brunkow of Southern Illinois University, Edwardsville.