SNEAKING BEHAVIOR AND NEST DEFENSE ARE AFFECTED BY PREDATION RISK IN THE COMMON GOBY

In the marine fish, Pomatoschistus microps, the common goby, males bui ld nests, attract females to the nest to spawn, and guard the eggs unt il hatching. Males, too small to compete successfully for nest sites a nd mates, act as sneakers, enter other males' nests during spawning, a nd presumably fertilize some of the eggs. Sneaking behaviour changed i n several aspects in the presence of predators (sea scorpions, Myoxoce phalus scorpius) compared with in their absence; the number of 'inspec tion' approaches to the nest decreased, as well as the number of attem pts to enter the nest. Number of intrusions also tended to decrease, b ut not significantly so. Nest owners frequently chased and attacked sn eakers. Number of attacks was correlated with the other male's behavio ur, both in the absence and in the presence of predators. Without pred ation risk, the number of nest approaches by the second male was of mo st importance for number of attacks, but in the presence of predators, the number of entering attempts was the factor that best explained th e nest owner's attack rate. Thus, both nest owners and sneakers modify their behaviour in order to decrease the risks of being eaten. (C) 19 95 The Association for the Study of Animal Behaviour