Social and environmental factors modulate the learning of pine-cone stripping techniques by black rats, Rattus rattus

Black rats inhabit Jerusalem pine forests in Israel, where they nest in the trees and feed on the seeds extracted from the pine-cones. The rats obtain the seeds by systematically stripping the cone's scales in a spiral pattern, using a sequence of stereotyped behaviour patterns termed the spiral technique. This stripping behaviour is culturally transmitted from mothers to their pups. Adults do not learn this task culturally, and only a few adults require it spontaneously even under favourable conditions. Experiment 1 tested whether the age of separation from the mother, sex of the pups, litter size and age at first exposure to cones affected the pups' stripping ability. Only the age of separation from the mother affected the proportion of pups that learned to strip cones; litter size, sex or age when pups were exposed to cones had no affect. Under laboratory conditions pups obtained pine seeds by using a second technique, termed shaving, which required a greater energy expenditure than the spiral technique. Experiment 2 tested whether the age at which pups were first exposed to cones influenced the type of stripping technique which they would acquire. Most pups (76%) exposed to pine-cones since birth used the shaving technique, and most pups (68%) exposed to pine-cones from age either 20 or 30 days developed the spiral technique. A third experiment examined whether developing pups can learn to strip cones when exposed only to mature brown cones, which are woodier and tougher than the green cones. None of the pups that were exposed only to brown cones learned to strip cones, even following exposure to cones for 80 days. (C) 1996 The Association for the Study of Animal Behaviour.