Ravens are solitarily-breeding birds, which defend year-round domains against other ravens, and whose 4 to 5 young disperse by fall. Yet, very noisy groups of usually 20 to 40 ravens sometimes aggregate at food bonanzas such as animal carcasses. Although it sometimes takes months for a large group to arrive, other baits are visited by more than 30 ravens the day after they are discovered. Ravens are quite rare and forage solitarily. The carcasses are hidden and the birds noisy. Do they help each other find food? If so, they probably are not helping family members, the conventional explanation. Over the last four winters, Dr. Heinrich has found that specific calls that ravens give at baits are powerful attractants of other ravens, that these calls act only at close range, and that the aggregating birds are primarily juvenile ravens that come at dawn directly from a communal roost where they convene at night. He now wishes to discover how information is transferred at the roost and what the consequences are for those birds that provide the information. Experiments will be carried out with communally-roosting ravens in a large outdoor enclosure built into the forest at Dr. Heinrich's study site in Maine. Dr. Heinrich will try to learn how sharing with others benefits the raven doing the sharing. Active recruitment to share food with strangers has not previously been demonstrated for any wild animal. Furthermore, the mechanism of recruitment from a communal roost has never been experimentally examined. This innovative research will contribute to our understanding of the conditions under which cooperation is an adaptive behavioral strategy.
