Interaction of climate change with effects of conspecific and heterospecific density on reproduction

We studied the relationship between temperature and the coexistence of great titParus majorand blue titCyanistes caeruleus, breeding in 75 study plots across Europe and North Africa. We expected an advance in laying date and a reduction in clutch size during warmer springs as a general response to climate warming and a delay in laying date and a reduction in clutch size during warmer winters due to density-dependent effects. As expected, as spring temperature increases laying date advances and as winter temperature increases clutch size is reduced in both species. Density of great tit affected the relationship between winter temperature and laying date in great and blue tit. Specifically, as density of great tit increased and temperature in winter increased both species started to reproduce later. Density of blue tit affected the relationship between spring temperature and blue and great tit laying date. Thus, both species start to reproduce earlier with increasing spring temperature as density of blue tit increases, which was not an expected outcome, since we expected that increasing spring temperature should advance laying date, while increasing density should delay it cancelling each other out. Climate warming and its interaction with density affects clutch size of great tits but not of blue tits. As predicted, great tit clutch size is reduced more with density of blue tits as temperature in winter increases. The relationship between spring temperature and density on clutch size of great tits depends on whether the increase is in density of great tit or blue tit. Therefore, an increase in temperature negatively affected the coexistence of blue and great tits differently in both species. Thus, blue tit clutch size was unaffected by the interaction effect of density with temperature, while great tit clutch size was affected in multiple ways by these interactions terms.Peer reviewe

Behavioural syndromes and trappability in free-living collared flycatchers, **Ficedula albicollis**

Abstract: The concept of behavioural syndromes hypothesizes that consistent behaviours across various situations mediate important life history trade-offs, and predicts correlations among behavioural traits. We studied the consistency of behavioural responses across three ecological situations (exploration of an environment altered with a novel object, aggression towards conspecifics, risk taking) in male collared flycatchers. We developed behavioural tests that could be applied in the birds natural habitat, thus not requiring the capture of animals. Across individuals, we found positive covariation between exploration, aggression and risk taking, but the magnitude of these relationships varied. Variation in behaviour was also related to capture probability. Exploratory and risk-taking individuals were more likely to enter a trap than individuals with averse characteristics. Moreover, with the trapped birds, there was an association between the time needed for successful capture and exploration, and we found stronger correlations between behaviours in comparison with effects calculated from the whole sample of individuals. These patterns were independent of territory quality, male age, condition and breeding experience. Consequently, behavioural responses to different ecosocial challenges are determined by individual-specific characteristics that are manifested in correlative behaviours. Hence, behavioural types may be potential subjects for reproductive and life history adaptations. Our results have important implications for field studies of animals, because they suggest that capturing protocols may not randomly sample the observed populatio

Age-dependent expression of song in the collared flycatcher, **Ficedula albicollis**

Theory suggests that male ornaments should be reliable signals of age, with more elaborated ornaments reflecting superior quality in terms of experience and/or viability. Bird song is immensely involved in sexual selection, thus not-surprisingly, it usually shows age-dependent variation. Although the collared flycatcher Ficedula albicollis has been intensively studied for its sexual traits, and female preference for male age is expected to be strong, there is no quantitative information on age-dependent expression of song in this species. Here, we fill this gap and, based on phenotypic correlations, we report the relationship between age and several song features. Repertoire size was consistently smaller in yearlings than in older males, but it also tended to increase after the second year of breeding. In a meta-analysis of effect sizes using data from the literature, we found that the strength of the relationship between age and repertoire size in the collared flycatcher is similar to patterns observed in other passerines. Song rate was inversely related to age, as yearlings sang at higher rates than older males. Generally, effect sizes for the relationship between age and other song traits were of medium level on average, and had broad confidence intervals. Song traits covaried with survival in a direction suggesting that differences in song between age categories are unlikely to result from phenotype dependent survival. Our results generally support the hypothesis that song holds the potential to function as a reliable indicator of male age in the collared flycatcher. However, it seems that not all song traits are unambiguously more expressed in older males than in yearlings