The importance of male age on the breeding success of small tree finches (#708)
Because of the high costs related to reproduction, females seek reliable indicators of male quality when choosing their mate. Plumage characteristics can be such an indicator in birds, giving information about health, nutritional stage and in several species also the age. Age can also be seen as indirect indicator for male experience. In Darwinâs small tree finches (Camarhynchus parvulus ), male head colouration becomes progressively darker with age and can be reliably tell the age of a male individual. A previous study by Kleindorfer (2007) showed that females of this species prefer older males and have a higher breeding success when paired with older males. To find out why older males are better, we compared several parameters of the breeding biology between younger and older males over the course of three breeding seasons. Analysis showed no significant differences between the two age groups in terms of clutch size and brood size. However, in 2012 but not in 2014, older males had a significantly higher number of fledglings. A possible explanation lies in the different weather conditions of the two years: 2012 was characterised by periods of intense rain and a high percentage of nests were abandoned; 2014 was a very dry year and nest abandonment was rare. Older males tended to abandon nests more frequently than younger males, suggesting that they were better in assessing when environmental conditions do not favour successful rearing of the current brood. An alternative explanation is that older males are better at compensating for increased environmental stress (e.g. food shortage). Furthermore, males seem to perfect different abilities (e.g. foraging, evaluation of breeding conditions) successively pointing towards the possibility that males learn different competences at different points during their life cycle.