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 parental care behaviour was studied in the common goby, Pomatoschistus microps. In field observations, the aggression of nest guarding males was measured as attacks towards a finger when disturbing the nest. Attacking males had larger and more developed clutches compared to non-attacking males, but did not differ in body size. In another set of observations nest guarding males were exposed to a predator (eelpout, Zoarces viviparus) and subsequently chased away from their nests. Time away from the nest decreased significantly with egg developmental stage, i.e. with the time the male had spent guarding a particular brood. However, no correlations with male body length or numbers of eggs in the nest were found. We conclude that male common gobies evaluate future reproductive success by using brood age and brood size as cues for making decisions about risk-taking and aggressive behaviour during parental care.