In the same year Konrad Lorenz, Niko Tinbergen and Carl Von Frisch jointly won the Nobel Prize in medicine for their pioneering work in animal behavior, the Israeli behaviorist, Amotz Zahavi, hypothesized that some birds aggregate in roosts to share information on locations of profitable food sources. Lorenz shared the Nobel prize, in part, for his work on imprinting: a phenomenon where hatchling birds immediately accept as parents the first object they see upon hatching (often Lorenz himself). In comparison, Zahavi’s ideas about the function of bird roosts, if correct, meant that some birds have much greater mental abilities.
It appears that ravens (relatives of crows and blue jays and our mascot at Carleton) support Zahavi’s ideas and also tells a tale about co-operation in the animal world.On mid-winter days as dusk descends, one often can find aggregations of 10-50 juvenile ravens in pine trees. The birds call, display, and resettle on perches to spend the night.
Do these roosts function as centers for exchanging information about food locations? To ravens, the most profitable food source is a carcass of a moose or deer. Such bonanzas of food tend to be widely separated and birds that share their food locations could benefit given similar acts of kindness from other ravens.
Through a series of experimental trials using naive ravens, two biologists from University of Vermont (Bernd Heinrich and John Marzluff) showed that ravens that are attracted to a roost will be led the next day to a food source. Ravens that are too distant to hear the cacophony of calls from a roost site, do not attend the roost, and also go hungry the next day. And even if these wayward ravens happen upon a carcass, they do not feed, rather they fly off in search of other roosting birds (with which they presumably share the spoils).
But why should food sharing be the rule among ravens in winter? Selfless behavior tends not to evolve in animal populations, and that such acts of altruism are only apparent. As Heinrich and Marzluff put it: “selfishness often lies behind seemingly selfless behavior.”
One possibility is that ravens at roosts are close kin, and that by sharing food resources, kin help beget kin (or at least help kin survive the winter). Such helping behavior among close relatives does occur in birds. However, DNA fingerprinting by Heinrich, Marzluff and their collaborators shows that individuals at carcasses are distantly related.Another possibility is that food sharing in ravens is a true case of reciprocal altruism (in anthropomorphic terms: if I show you my food locations, then you show me yours). Such cases of reciprocal altruism are rare in nature and require that social structure is stable. Again in anthropocentric terms why show a stranger a food source is the stranger leaves the next day (and is not heard from for the rest of the winter)? In fact, social structure in ravens is extremely dynamic in the winter. Thus, reciprocal altruism, like helping kin, does not explain food sharing.
So what does explain food sharing in our mascots? To answer this question Heinrich and Marzluff spent thousands of hours observing ravens in the wild. From these observations, they noted that vicious fights can occur at a carcass, but that such fights are rare when many ravens are present. Heinrich and Marzluff marked ravens and soon discovered that there were residents and wanderers. Residents were adults that defended territories. Wanderers were juvenile ravens.
When a (few) wanderer(s) attempt to feed at a carcass within a resident’s territory, they are viciously attacked and driven off. It is not until at least nine juveniles attend the carcass that the adults’ aggressive tendencies are thwarted and all ravens feed. Thus, juvenile ravens act in their own selfish interests and join “parties” to suppress aggression from adults. The juveniles are not suppressing self-interest as theory predicts, and yet they are serving a common good.
Professor & student