Habitat influence on life history and behavioural traits of cavity nesting birds

Resumen

Identifying general patterns of habitat selection, behavioural adaptations and life-history traits are central issues in evolutionary ecology. Many organisms have been studied to address these issues, but one of the groups with greater influence on current perspectives is birds. This thesis overall aim is to increase knowledge from an evolutionary perspective of the differences associated to habitat characteristics of life-history strategies and behavioural syndromes in cavity-nesting birds such as the Blue tit (Cyanistes caeruleus) and the Great tit (Parus major). By means of descriptive studies and field and captivity experiments this PhD thesis aim to explain the mechanisms underlying nest-site selection, diet composition, personality types and individual foraging strategies in contrasting habitat types. The use of nestboxes to study bird breeding biology, as well their use as a management tool, is widespread. Different nestbox placements could be differentially chosen by birds; however the influence of determinant factors (e.g., nestbox density) in occupation rates or breeding parameters has not been sufficiently covered. We used the Blue tit as a model species to investigate the influence of nestbox position and breeding pair density on occupation rate and breeding success, controlling for habitat structure. Blue tits preferentially selected nestboxes located high on the tree and with fewest neighbours. Laying date was earlier in higher nestboxes and in those with fewer neighbours and at a greater distance from the nearest neighbour. Also, fledgling number was positively related to shrub cover and medium tree height, fledging mass was higher when distance to the nearest neighbor was greater and fledging tarsus was positively related to oak-species abundance. Our results suggest that disentangling the important factors for nestbox placement and distribution is important to adapt to species-specific requirements in each given habitat. Nestlings diet composition and feeding rates seem to depend on parental effort, habitat type and their interactions. We compare the nestling diet of Blue tits in two Mediterranean forests (pinewood and oakwood) and its implications in breeding success through recordings within nestboxes when chicks were 11-days-old. We found that although caterpillars (Order Lepidoptera) constituted the largest proportion of nestling diet in both habitats, chicks in pinewood were fed more noctuid and tortricid larvae, showing a more homogeneous diet composition than those in oakwood. In contrast, spiders were more frequently fed to oakwood chicks. We demonstrated that these diet differences affect the number of chicks fledged and their body condition. Habitat-specific selection pressures have been widely recognized but whether selection favours different personality types in different habitats has rarely been evaluated. We aimed to test whether personality-related differences in annual reproductive success differed between two populations of Blue tits occupying different Mediterranean habitats (oakwood and pinewood). We measured exploration and parental provisioning behaviours, and used a path analytical approach to ask how the interplay between these two behavioural traits affected reproductive success in each of these two habitats. We found that blue tits breeding in the pinewood were slow-exploring compared to blue tits breeding in the oakwood, suggesting the occurrence of personality-related differences in settlement, or phenotypic plasticity in response to habitat differences. Faster explorers were favoured in the pinewood, while there was no selection acting on exploration behaviour in the oak habitat. Our findings emphasize the importance of integrating habitat selection, plasticity, and personality in the study of behavioural evolution. The tendency to innovate and the reactive-proactive personality axis have been linked to foraging behaviour but their role in driving intake rate and food selectivity remains unclear. We conducted standardized assays on wild-captured Great tits from different habitats to characterize individual variation in exploratory and innovative problem-solving performance, both of which are repeatable and have been linked to foraging behaviour. During trials, birds of known exploration behaviour were provided with three different types of food in order to detect any diet preference, and daily energy intake was measured. There was no link between exploration behaviour and the amount of calories ingested; however, bolder great tits consumed a higher proportion of sunflower seeds, while slower individuals preferred peanuts. Problem solving performance showed a significant positive correlation with energy intake for those birds that solve twice. Related to habitat type, birds from the coniferous patches ate more peanuts thought mealworms eaten were marginally higher in those from the deciduous plots. Our results evidence the relationship between exploration behaviour and foraging performance in captivity and contribute to the idea that birds may follow alternative foraging strategies, but obtaining the same energy intake.