The drinking and sieving of Khaki Campbell ducklings have been used as suitable behaviour patterns with which to study the social interactions in flock-living birds. Duckling from four-bird flocks were deprived of water for 3 hr, either in isolation or in groups of four. When the flocks were allowed access to water it was found that the isolated ducklings drank less than the non-isolated ducklings. Whilst both deprived and non-deprived birds engaged in sieving activity during the test, the sieving movements of the non-deprived birds were of longer duration than those of the deprived birds. Pre-test isolation of flock members was also shown to increase the duration of sieving movements. Re-introducing the isolated ducklings to each for the last 5 min of deprivation failed to eliminate the difference in either the drinking or the sieving behaviour between the isolated and non-isolated birds. The difference in drinking, but not sieving, could be eliminated by reuniting the birds for the last 30 min of deprivation. The disruption of flock 'cohesion' may lead to the failure of the mechanism of social facilitation despite a similar motivational condition in all flock members.
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