Increased Reproductive Success with Age in the California Gull: Due to Increased Effort or Improvement of Skill?

Abstract

Pugesek (1981) recently claimed to demonstrate an increase in reproductive effort with age in the California gull Larus californicus. On the contrary, neither theory nor his own data support Pugesek's claim. Older parents invest no more time in (1) foraging for the young and (2) guarding the nest than do younger parents, but the former are (a) more effective at providing food for the young and (b) more efficient at alternating and coordinating guarding and feeding duties. The increase in territorial defense with age is likely due to older parents having more mature young to defend. Development of parental skills as a result of experience best explains the observed increase in reproductive success with age.