The Causes and Consequences of Complex Behavioral Trait Variation in a Resident Montane Bird
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Authors
Sonnenberg, Benjamin
Issue Date
2024
Type
Dissertation
Language
Keywords
Avian Cognition , Behavioral Ecology , Complex Behavior , Nest Building
Alternative Title
Abstract
The causes and consequences of complex trait variation are of broad interest in the field of behavioral ecology. In the wild, animals experience wide ranging environmental conditions, and understanding the impact of this heterogeneity in shaping behavioral traits, such as cognition, is critical to understanding their evolution. Though it is thought that environmental conditions contribute to large inter- and intra-species variation in cognitive abilities, the mechanisms generating this variation remain poorly understood. Past laboratory-based work has shown that energetically expensive cognitive traits are impacted by developmental perturbations such as non-optimal developmental conditions (e.g. poor parental care, low-quality nest environment, etc.), but whether these same patterns are exhibited in natural populations is relatively unstudied. This dissertation provides novel insights into the mechanisms shaping complex behavioral trait variation in wild systems focusing on two behavioral traits, spatial cognitive abilities and nest building, in free-living mountain chickadees ( Poecile gambeli ). Chapter 1 describes the role of directional natural selection acting on spatial cognitive ability using a cohort comparison approach in a wild population. This study showed that spatial cognitive ability does not change within individuals across years, that adult birds on average performed better than first-year birds, and that members of a first-year cohort that performed worse on a spatial cognitive task were less likely to survive than those with better performance. This is some of the first evidence of natural selection acting on a cognitive trait in the wild. Chapter 2 investigates causes and consequences of variation in nest size in chickadees at different montane elevations with different climatic conditions. This study showed a large degree of temperature variation across all nestling developmental periods and between elevations, but this variation was unrelated to nest size or reproductive output in chickadees. This result contrasts results from studies in other populations of cavity-nesting birds that appear to construct nests corresponding to local environmental conditions. However, I found that female chickadees build highly repeatable sized nests across years. High repeatability in behavioral traits implies a heritable component, suggesting that female nest size is controlled by an innate mechanism. Chapter 3 considers variation in nestling immune response, ectoparasite load, and nest composition to determine how these developmental conditions shape behavioral trait variation. Ectoparasites are known to have fitness consequences for their hosts, but there is mixed evidence of how widespread and impactful these effects are on the traits of developing avian nestlings. I found that there was no relationship between greater ectoparasite infestation in the nest and offspring mass or immune response, seeming to indicate that this aspect of nestlings' developmental environment may not drive future behavioral trait variation. However, I did find that nest composition�"including overall size (i.e., mass), amount of plant materials, and amount of animal materials (i.e., animal hair)�"was highly repeatable within individual females, strengthening the evidence that individual variation in nest building behavior is heritable. Identifying potential post-fledging consequences related to parasite load remains understudied. Chapter 4 builds upon the work of my earlier chapters by investigating the underlying mechanisms that result in observed chickadee nest repeatability. I found evidence that apparent non-functional trait variation may be related to variation that is under selection through potential shared physiological mechanisms. In this study, I found that food-caching propensity and nest building propensity are not only highly repeatable behaviors within individual female chickadees but also highly correlated. This suggests that food caching, a trait under selection that has a strong underlying drive, may be directly affecting an unrelated behavioral trait, nest building, through a shared mechanism, resulting in a potential behavioral syndrome. Lastly, chapter 5 presents data testing whether there is a relationship between the physiological burden during offspring development and spatial cognitive abilities, which could explain some of the existing variation in cognitive abilities in wild food-caching mountain chickadees. I used ptilochronology (feather growth rates reflecting nutritional intake) and amount of corticosterone (a hormone associated with broad metabolic processes including stress responses) in feathers (Cortf) of juvenile chickadees to estimate the variation in developmental condition. I found that developmental variation had a limited effect on spatial cognitive abilities, suggesting potential compensatory mechanisms that buffer these specialized cognitive abilities critical for survival in food-caching chickadees from harmful ontological perturbations.