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Wilcoxen T.E.,University of Memphis | Boughton R.K.,Avian Ecology Laboratory | Schoech S.J.,University of Memphis
Behavioral Ecology and Sociobiology | Year: 2010

In species that undergo actuarial senescence, the value of current reproduction is predicted to increase relative to the value of future reproduction with age, as the probability of survival to another reproductive event is reduced. Therefore, life history theory predicts that aging animals should increase their investment in reproduction. However, an increase in reproductive investment may carry significant costs to the breeding individuals. We recorded provisioning rates of Florida scrub-jay male breeders, followed by their immediate capture to assess body condition and collect blood for an in vitro test of immunocompetence and an assay of baseline corticosterone for a measure of stress. Older males provisioned offspring and brooding mates at the highest rates. There was no evidence of any physiological deficits in males with high provisioning rates, independent of age. It appears that birds that survive to old age are high quality birds that maintain good physiological condition, which complements the value of experience and permits maximal investment in offspring. © 2010 Springer-Verlag.

Wilcoxen T.E.,University of Memphis | Wilcoxen T.E.,Millikin University | Bridge E.S.,University of Oklahoma | Boughton R.K.,Avian Ecology Laboratory | And 3 more authors.
Ibis | Year: 2011

Hatching failure within clutches of eggs occurs to varying degrees in many avian species. We investigated predictors of hatching failure in a population of Florida Scrub-Jays, for which hatching success has been monitored for 15 years. We assessed whether hatching failure was related to parental traits (e.g. age, experience as a pair or body condition), lay date, social structure (e.g. number of helpers), environmental conditions, or some combination of these. We used linear mixed models and Akaike's information criterion to determine the models that best explain observed patterns of hatching failure. The best model showed that increased hatching failure was associated with below-average rainfall during the breeding season, and was more common for newly established breeding pairs than for pairs that had previously produced one or more clutches together. Other contributing models suggested that hatching failure was greatest for the youngest and oldest female breeders. Some aspects of our findings are consistent with conclusions drawn from other species. However, as a whole, our analyses suggest that hatching failure in the Florida Scrub-Jay is influenced by a complex set of environmental and parental factors. © 2010 The Authors. Journal compilation © 2010 British Ornithologists' Union.

McClure C.J.W.,Auburn University | McClure C.J.W.,Boise State University | Rolek B.W.,Avian Ecology Laboratory | Hill G.E.,Auburn University
Condor | Year: 2012

Information regarding microhabitat, here defined as small-scale vegetation structure, is often useful in predicting use of habitat by birds. Quantifying microhabitat, however, is expensive and labor intensive compared to assessment of habitat at a larger scale, possibly from remotely sensed imagery. To assess the importance of microhabitat information in constructing predictive models of habitat occupancy, we compared occupancy models built on the basis of macro- and microhabitat together and separately. We based our models on counts of wintering migratory bird species and vegetation surveys within Tuskegee National Forest, Alabama, completed during winter 2009. Models built from macrohabitat data only outperformed models built from microhabitat data only for five of the six species analyzed. however, the best model for every focal species included both macro- and microhabitat covariates. Pine forests-excluding plantation-were the only land-cover classification important to our focal species, and measures of density of vegetation were important in predicting occupancy. Our results suggest that migrants wintering at our study site select habitat at multiple scales-specializing in certain types of cover and then preferring specific structural aspects of vegetation within them. We conclude that microhabitat information is important for inference into use of habitat by wintering migratory birds. © The Cooper Ornithological Society 2012.

Tringali A.,University of Central Florida | Bowman R.,Avian Ecology Laboratory
Animal Behaviour | Year: 2012

Although sexual selection is undeniably important in the evolution and maintenance of ornamental traits, it remains an unsuitable explanation for juvenile ornamentation. Male-male competition has been important in the evolution of UV-blue plumage ornamentation in birds, suggesting that this type of plumage may signal status more generally. In the present study, we compared dominance status of juvenile Florida scrub-jays before and after experimental plumage manipulation and found that plumage reflectance signalled status. Male-male competition is important in maintaining UV-blue plumage ornamentation in adults of other species. However, our evidence shows that sexually dimorphic ornamentation can also mediate competition over food resources in juvenile Florida scrub-jays. Understanding status signalling among juveniles may yield insights into differences in fitness, especially in species with cohesive social systems where early interactions are likely to influence future competitions over resources or mates. © 2012 The Association for the Study of Animal Behaviour.

Rensel M.A.,University of Memphis | Boughton R.K.,Avian Ecology Laboratory | Schoech S.J.,University of Memphis
General and Comparative Endocrinology | Year: 2010

Nestlings of altricial species undergo a period of substantial growth and development in the nest after hatching. The hypothalamic-pituitary-adrenal axis regulates the release of stress hormones such as corticosterone, which in adults is critical in allowing an animal to respond to a stressor. However, activation of this axis in young birds may be detrimental to growth and possibly survival. The developmental hypothesis predicts that altricial nestlings should display a dampened corticosterone response to stress as a means of protection against the potentially harmful effects of elevated corticosterone. We examined this hypothesis in Florida scrub-jays, a cooperatively breeding species with altricial young. Blood samples were collected from nestlings, nutritionally independent young, and yearlings for measurement of corticosterone levels. Baseline corticosterone levels did not differ between age-classes; however, stress-induced corticosterone levels were highest in yearlings, intermediate in independent young, and lowest in nestlings. The nestling stress response was also of a shorter duration than the response in independent young and yearlings. This variation in stress responsiveness across ages may be an adaptive mechanism to protect the developing bird from the negative effects of corticosterone on growth and cognitive development. © 2009 Elsevier Inc. All rights reserved.

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