Behavioural traits modulate the use of heterospecific social information for nest site selection: experimental evidence from a wild bird population.

The use of social information for making decisions is common but can be constrained by behavioural traits via, for example, the ability to gather information. Such constrained information use has been described in foraging habitat selection; yet it remains unexplored in the breeding habitat selection context, despite potentially strong fitness consequences. We experimentally tested whether three behavioural traits (aggressiveness, boldness and neophobia) affected the use of heterospecific social information for nest site selection in wild collared flycatchers Ficedula albicollis. Flycatchers have previously been found to copy or reject an artificial apparent preference of tits (their main competitors) for a nest site feature: they preferred nest-boxes with the same or a different feature, depending on tit early reproductive investment. Here, we confirmed this result and showed that shy individuals and less aggressive old males (i.e. 2 years old or older) copied tit apparent preference, while more aggressive old males rejected the tit preference. Aggressiveness and boldness may allow males to access more information sources or affect males' interactions with dominant tits when selecting a nest site. Our study highlights the links between variation in behaviours and social information use for breeding habitat selection and calls for further work to explore underlying mechanisms.

Natal dispersers pay a lifetime cost to increased reproductive effort in a wild bird population.

Natal dispersal is assumed to be costly. Such costs can be difficult to detect, and fitness consequences of dispersal are therefore poorly known. Because of lower phenotypic quality and/or familiarity with the environment, natal dispersers may be less buffered against a sudden increase in reproductive effort. Consequently, reproductive costs associated with natal dispersal may mostly be detected in harsh breeding conditions. We tested this prediction by comparing lifetime reproductive success between natal dispersers and non-dispersers in a patchy population of collared flycatchers (Ficedula albicollis) when they reared either a non-manipulated brood or an experimentally increased or decreased brood. Natal dispersers achieved lower lifetime reproductive success than non-dispersers only under more stressful breeding conditions (i.e. when brood size was experimentally increased). This was mostly due to a lower number of recruits produced in the year of the increase. Our results suggest a cost associated with natal dispersal paid immediately after an increase in reproductive effort and not subsequently compensated for through increased survival or future offspring recruitment. Natal dispersers adjusted their breeding investment when reproductive effort is as predicted but seemed unable to efficiently face a sudden increase in effort, which could affect the influence of environmental predictability on dispersal evolution.