BROOD SIZE AND OFFSPRING AGE AFFECT RISK-TAKING AND AGGRESSION IN NEST-GUARDING COMMON GOBIES

The importance of brood size, offspring age, and male size for parenta l care behaviour was studied in the common goby, Pomatoschistus microp s. In field observations, the aggression of nest guarding males was me asured as attacks towards a finger when disturbing the nest. Attacking males had larger and more developed clutches compared to non-attackin g males, but did not differ in body size. In another set of observatio ns nest guarding males were exposed to a predator (eelpout, Zoarces vi viparus) and subsequently chased away from their nests. Time away from the nest decreased significantly with egg developmental stage, i.e. w ith the time the male had spent guarding a particular brood. However, no correlations with male body length or numbers of eggs in the nest w ere found. We conclude that male common gobies evaluate future reprodu ctive success by using brood age and brood size as cues for making dec isions about risk-taking and aggressive behaviour during parental care .