The loudest begger is not always the hungriest, just bigger. Carrie Straight 05.03.01 Many baby birds (nestlings) make calls called food begging in the when the parent comes near. The nestlings probably use these noises to tell the parents that they are hungry. Some Canadian scientists wondered if the length, rate, and loudness of the calls was related to the things that nestlings need. Maybe the type of call can tell the parents how hungry or how cold a nestling is. The scientists tried to answer their questions by taking some tree swallow (Tachycineta bicolor nestlings into a laboratory. Tree swallows are small birds that live in North America during the breeding season (April-August). They build their nests in cavities (a hole in a tree) or bird houses. When the scientists brought the nestlings into the lab, they placed them into fake nests in a nestbox. They replaced one of the sides of the box with plexiglass, so they could see into the box and watch what the nestlings did. They also put a microphone in the box to record the sounds that the nestlings made. Then, they fed the nestlings at different rates. They compared how often, how long, and how loud were the calls of big and little nestlings. Both large and small nestlings called faster and longer when they were hungry, but larger nestlings called louder than small nestlings when they were hungry. These differences might be detectable by the parents, but scientists haven’t tested this prediction yet. If they are detectable by parents, then parents could adjust their amount of feeding depending on how hungry the nestlings are. Leonard, Marty L. and Andrew G. Horn. 2001. Acoustic signalling of hunger and thermal state by nestling tree swallows. Animal Behaviour 61: 87-93. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.