Communally breeding skuas: breeding success of pairs, trios and groups of Catharacta lonnbergi on the Chatham Islands, New Zealand

One-third of territories on South East Island are occupied by trios or groups of communally breeding skuas. Comparisons were made of the reproductive performance of pairs, trios and groups over three (and ten) seasons to assess whether any 'advantage'–in terms of offspring production–could be demonstrated for communal breeding. Egg size was not significantly different between pairs and trios, or between years. There were no significant differences between the chicks of pairs, trios or groups in growth characteristics and chick condition appeared similarly good. Overall breeding success was generally lower for trios than for pairs. Although chick production per territory was not significantly different between pairs and trios, it was substantially lower on a per-adult basis. The breeding success of this population is generally high compared to others studied, however, there is no evidence to suggest that skua communal breeding has advantages in terms of offspring production.