DOMINANCE AND THE DYNAMICS OF PHENOTYPE-LIMITED DISTRIBUTION IN COMMON CRANES

We studied the behavior of 13 radiotagged cranes dispersing from a com munal roost over days when they changed their main daily foraging area between consecutive days during two winter seasons. Individuals went to a new foraging zone when on the previous day their morning food int ake had fallen below their mean morning food intake measured over the whole winter. Food intake on the day before a change in foraging area was positively correlated with dominance rank. Dominant cranes changed to new zones with higher numbers of birds and food density, while sub ordinate cranes went to new zones with lower numbers of birds. As a re sult, all birds increased their food intake over that of the previous day., Dominant cranes remained more faithful to their most preferred f oraging zone, where they spent 69% of the mornings, while subordinate birds were more mobile, switching among zones frequently. Dominant bir ds left the roost later than subordinate birds on the days they change d to a new zone, which could be used to track the main departing flows . The results suggest that the dynamics that led to a truncated phenot ype-limited distribution were determined by social dominance and food abundance, with dominant cranes shifting to a new zone to maintain the ir high intake levels and subordinates changing more frequently whenev er their daily intake did not reach the minimum metabolic requirements .