 By LEE BOWMAN Scripps Howard News Service September 06, 2006
It's well-known that adult birds feed their young directly while they're in the nest, and some youngsters even come back to the nest for brief visits around feeding time once they're able to fly on their own. A team led by Andrew Radford of the University of Cambridge in England documented that certain species go a step further, using special calls to summon their adolescents to spots that offer the best foraging. Studying young birds outside the nest is normally tough because they tend to take flight whenever an observer gets close. But by gradually getting the birds used to their presence, Amanda Ridley and other researchers from the University of Cape Town, South Africa, and members of Radford's team, were able to closely monitor the behavior of a group of African pied babblers, medium-sized birds that subsist mainly on insects in the Kalahari Desert. Over time, the researchers were able to get within a few feet of the birds, allowing them to photograph and audio record behavior - and even training them to hop on scales from time to time to check their weight. Babblers tend to nest and forage in groups of about a dozen adults and a lesser number of juveniles, with non-parents assisting with care of the young to some degree, such as sitting on eggs and defending nests. Working with an experimental flock for several years, Ridley and colleagues had noted that young pied babblers seemed to take a while getting the knack of finding bugs and other prey on their own. Parents were also heard repeatedly making a sort of purring noise around fledglings at feeding time, giving the kids a peck if they ignored the sound, but a treat if they responded promptly. In the new study, published Tuesday in the journal Current Biology, the researchers found that parents and other adult helpers would call inexperienced fledglings to an area that contained easily shared food. Ninety percent of the time, another group member would join within about half a minute, usually one of the juveniles. But if an adult answered the purring "here's dinner" call, the adult sounding the call usually chased it away. A foraging babbler wouldn't give the call when it had caught something difficult to share, say a small scorpion, but readily spoke up if it came upon something like a termite nest or anthill, where there were many individual prey items. Immature birds responding most often to what the researchers termed "recruitment" calls increased their success at finding food, gained more weight and enjoyed other advantages because they had to spend less time searching for food on their own. "This form of extended offspring care may well be widespread, as the young of many bird species continue to associate closely with their parents even after they are no longer fed directly," said Radford, whose work is funded, in part, by Britain's Biotechnology and Biological Sciences Research Council.
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