FUNCTIONS OF MUDBALLING BEHAVIOR IN THE EUROPEAN FIDDLER-CRAB UCA TANGERI

European fiddler crabs place mudballs around their burrow openings. Bo th males and females placed mudballs, but there were major differences between the sexes in mudballing behaviour, suggesting that the female 's mudballs were a by-product of digging out the burrow whereas the ma le's may have additional functions. When the male's mudballs were remo ved experimentally, the number and intensity of male-male agonistic in teractions increased significantly; Experimentally visually isolated m ales spent longer making mudballs and less time waving. In a binary ch oice test, females were more likely to approach dummy males with mudba lls, spent longer near these males and were more likely to enter their burrows than dummy males without mudballs. The same pattern was appar ent for males with 30 rather than 20 mudballs. These results are consi stent with a dual function for mudballs in U. tangeri: to reduce the n umber and intensity of aggressive interactions between neighbouring ma les and to attract females. (C) 1998 The Association for the Study of Animal Behaviour.