RESIDENCY AND SIZE AFFECT FIGHT DURATION AND OUTCOME IN THE FIDDLER-CRAB UCA ANNULIPES

We performed a field experiment to investigate the effect of carapace width, major cheliped length and burrow ownership on the fighting succ ess of male fiddler crabs (Uca annulipes). We removed males from their burrows and released them back into the colony (n = 82). Released mal es tended to initiate encounters with burrow owners slightly smaller t han themselves. Several general predictions of Sequential Assessment G ame models of contest behaviour were supported: (1) residents won more encounters; (2) intruders were more likely to ruin when larger than r esidents. When body size (carapace width) was controlled for, intruder s with relatively large claws for their body size were more likely to win contests; (3) the duration of encounters was related to the size d ifference between males; (4) encounters won by the larger male were of shorter duration than those won by the smaller male; (5) encounters w on by the resident tended to be of shorter duration than those won by intruders (P = 0.07); (6) on average, encounter duration was longer wh en the intruder was larger than the resident. However, the encounters we documented began with seemingly costly behaviour such as pushing an d the inter-locking of daws and did not unambiguously escalate from in itial low cost behaviours. Sequential assessment of relative fighting ability may therefore not have been occurring. Prior visual assessment of opponents' fighting ability, followed by 'all-out fights' during p hysical encounters may also provide a plausible explanation for our re sults. (C) 1996 The Linnean Society of London