A dynamic game model for the decision to join an aggregation

A dynamic game model is presented for the decision-making of female saiga a ntelopes (Saiga tatarica) gathering in temporary aggregations to give birth . Spatial aggregation is assumed to be a predator-swamping mechanism that i nvolves a cost of an increased risk of calf death from disease. A female's decision to join an aggregation or to calve solitarily depends on her partu rition date relative to other individuals and on the number of other female s in the birth area. The results are robust to changes in other parameter v alues. The Evolutionarily Stable Strategy is to join an aggregation and sta y for the full period of neonatal vulnerability if calving early in the bir th period, to join the aggregation but to leave it early if calving later i n the birth period, and to calve solitarily if calving at the end of the bi rth period. The possible effects of human disturbance on female behaviour a re investigated, and testable hypotheses are presented about the behaviour of females in the birth period. The game-theoretic approach to the decision to join an aggregation developed here is broadly applicable to many proble ms in the ecology of grouping behaviour. (C) 2001 Elsevier Science B.V. All rights reserved.