The bounded-hybrid superiority hypothesis (BHSH) predicts stable hybrid zones are characterized by hybrids having the highest fitness within the zone. The dynamic-equilibrium hypothesis (DEH) predicts hybrids to have the lowest fitness and mating should be strongly assortative in the hybrid zone. I used phenotypic-based hybrid indices (HI) to assess mating patterns, reproductive success, and survival of hybridizing northern flickers (Colaptes auratus) within the hybrid zone at Riske Creek, British Columbia. Contrary to the BHSH, flickers showed significant assortative pairing (P = 0.038) which may result via passive mate choice if yellow and red flickers migrate from allopatric winter ranges. North American band recoveries show red-shafted and yellow-shafted flickers winter on different sides of the Rocky Mountains while red-orange hybrids from Riske Creek winter in the range of red-shafted flickers. Arrival dates of phenotypes did not support the idea that mating patterns are caused passively via different arrival schedules. However, assortative mating patterns did correlate with regional weather patterns along flicker migration routes as well as the North Atlantic Oscillation (NAO) a continental weather pattern that has been shown to influence various aspects of the annual cycle in other birds. If variable weather patterns result in different mating patterns by affecting migration, the geographic location of the northern portion of the zone may be variable due to the migratory behaviour of individuals.<p>There were no differences among yellow, orange and red flickers to win more agonistic contests or have earlier nest initiation dates, larger clutch sizes, greater hatching success, or produce more fledglings. No colour group had a higher likelihood of having a successful compared to a depredated nesting attempt. Aggression was similar between red (N = 21) and yellow flickers (N = 20) during taxidermy model presentations of pure red-shafted and yellow-shafted flickers. Using Akaikes information criterion (AIC) in Program MARK, I determined survival was best modeled as either constant between males and females or varying annually according to weather. Models incorporating HI had less support but suggested that survival is best modeled as a linear relationship where red-shafted flickers have the highest survival. Survival modeled in quadratic relationships found hybrid flickers to have the highest apparent survival estimates in support of the BHSH. Overall there was no support for reduced hybrid fitness, but survival appears to be influenced more by annual variation rather than strictly by an individuals HI. Overall, I failed to find reduced hybrid fitness in support of the DEH but also failed to find increased hybrid fitness as predicted by the BHSH. Annual changes in selection pressure could prevent introgression of hybrid genes throughout the zone if selection favours red-shafted genes in some years and yellow-shafted genes in other years.

The bounded-hybrid superiority hypothesis (BHSH) predicts stable hybrid zones are characterized by hybrids having the highest fitness within the zone. The dynamic-equilibrium hypothesis (DEH) predicts hybrids to have the lowest fitness and mating should be strongly assortative in the hybrid zone. I used phenotypic-based hybrid indices (HI) to assess mating patterns, reproductive success, and survival of hybridizing northern flickers (Colaptes auratus) within the hybrid zone at Riske Creek, British Columbia. Contrary to the BHSH, flickers showed significant assortative pairing (P = 0.038) which may result via passive mate choice if yellow and red flickers migrate from allopatric winter ranges. North American band recoveries show red-shafted and yellow-shafted flickers winter on different sides of the Rocky Mountains while red-orange hybrids from Riske Creek winter in the range of red-shafted flickers. Arrival dates of phenotypes did not support the idea that mating patterns are caused passively via different arrival schedules. However, assortative mating patterns did correlate with regional weather patterns along flicker migration routes as well as the North Atlantic Oscillation (NAO) a continental weather pattern that has been shown to influence various aspects of the annual cycle in other birds. If variable weather patterns result in different mating patterns by affecting migration, the geographic location of the northern portion of the zone may be variable due to the migratory behaviour of individuals.<p>There were no differences among yellow, orange and red flickers to win more agonistic contests or have earlier nest initiation dates, larger clutch sizes, greater hatching success, or produce more fledglings. No colour group had a higher likelihood of having a successful compared to a depredated nesting attempt. Aggression was similar between red (N = 21) and yellow flickers (N = 20) during taxidermy model presentations of pure red-shafted and yellow-shafted flickers. Using Akaikes information criterion (AIC) in Program MARK, I determined survival was best modeled as either constant between males and females or varying annually according to weather. Models incorporating HI had less support but suggested that survival is best modeled as a linear relationship where red-shafted flickers have the highest survival. Survival modeled in quadratic relationships found hybrid flickers to have the highest apparent survival estimates in support of the BHSH. Overall there was no support for reduced hybrid fitness, but survival appears to be influenced more by annual variation rather than strictly by an individuals HI. Overall, I failed to find reduced hybrid fitness in support of the DEH but also failed to find increased hybrid fitness as predicted by the BHSH. Annual changes in selection pressure could prevent introgression of hybrid genes throughout the zone if selection favours red-shafted genes in some years and yellow-shafted genes in other years.

The two main goals of my thesis were to further our understanding of how parental effort is related to life-history trade-offs and to see how parental investment is reflected in various potential measures of nestling quality. I looked at how fitness is maximized by examining (1) the trade-off between current and future reproduction, and (2) the trade-off between quantity and quality of offspring. To see how parents responded to energetic demands and whether each sex reacted in a similar way, I experimentally manipulated brood sizes and quantified provisioning rates. Both male and female parents with enlarged broods increased their feeding rates, but provisioning on a per nestling basis declined, so that parents fledged lighter nestlings with shorter wings. Although the incidence of mortality did not differ between control and enlarged broods, nestlings from enlarged broods were lighter than those from control broods with the same brood size, suggesting that clutch size may be individually optimized. I also looked at how nestlings responded to different levels of nutritional stress in the manipulated broods by quantifying size and body condition, plumage colouration, and the physiological measures of T-cell mediated immune responses, and corticosterone levels in nestling feathers as a long-term integrated measure of stress physiology. The size of melanin ornaments on feathers and the saturation and brightness of carotenoid colouration was associated with nestling mass in such a way that suggested that plumage characteristics reflect nestling quality. The immune function of nestlings was negatively related to brood size and nestlings in better body condition could mount greater immune responses to foreign antigens suggesting that immune responses are energetically costly. Corticosterone levels in the feathers were not related to nestling body condition and were unaffected by the experimental brood manipulation. The ii mass of male nestlings, which are the larger sex, was more compromised by brood size than female mass was. I also found sex-specific relationships between plumage characteristics and measures of physiological performance. These findings help to explain optimal clutch size and the classic trade-off between quality and quantity of offspring. They also offer new insights into the reliability of putative measures of quality in nestlings and relationships between physiological and morphological traits.

Cavity-nesting communities are structured by the creation of and competition for cavities as nest-sites. Viewing these communities as interconnected webs can help identify species interactions that influence community structure. This study examines cavity-nesting bird community interactions within the fire-maintained longleaf pine (Pinus palustris) ecosystem at Eglin Air Force Base, Florida. In chapter 1, I provide a background review of the ecology of my study system. In chapter 2, I use nest webs to depict the flow of cavity-creation and use at Eglin. I identified 2 webs into which most species could be placed. One web contained 6 species associated with pines. The second web contained 5 species associated with hardwoods. Red-cockaded woodpeckers (Picoides borealis) and northern flickers (Colaptes auratus) created most cavities used by other species within this community. In chapter 3, I describe snag densities and nest-site selection of the cavity-nesting bird community at Eglin. Large, mature pine snags were abundant, exceeding other reported densities for southern pine forests. Pine snags were heavily-used, despite the abundance of available red-cockaded woodpecker cavities in living pine. Hardwood snags accounted for 10% of nests found, and were used by 12 of 14 species. Diameters of nest-trees and available snags were below the range of optimal nest-snag diameters reported in other studies, indicating the need for site-specific snag management guidelines. In chapter 4, I combine a study of basic ecological principles with endangered species management to examine interactions within the cavity-nesting bird community at Eglin. I used a nest web to identify a potential indirect interaction between the red-cockaded woodpecker and large secondary cavity-nesters, mediated by the northern flicker. I used structural equation modeling to test a path model of this interaction. By experimentally manipulating cavity availability, I blocked links described in the model, confirming cavity creation and enlargement as mechanisms that influence this indirect relationship. I demonstrated that a red-cockaded woodpecker cavity-management technique could disrupt this indirect relationship by affecting northern flicker behavior, and provided an empirical example of how, in interactive ecological communities, single-species management can have indirect effects on non-target species. / Ph. D.