I studied nest characteristics, breeding dispersal, and nest defence behaviour of Northern Flickers (<i>Colaptes auratus</i>, hereafter flickers) in central interior British Columbia with respect to nest predation. My research focused on three questions: (1) Are there nest characteristics associated with the risk of nest predation and nest loss to European Starlings (<i>Sturnus vulgaris</i>)? (2) Does nest predation influence breeding dispersal? (3) Do parental attributes influence nest defence behaviour? <p> An examination of flicker nest-site characteristics at five spatial scales revealed that nests were safer from mammalian predators (N=81) when they were higher, concealed by vegetation, farther from continuous coniferous forest blocks, and contained fewer conifers within the nesting clump. Proximity to conifers increased predation risk, but nests safe from competitors (N=18) were closer to coniferous forest blocks and contained a higher percentage of conifers in the nesting clump. Flickers face a trade-off between being safe from predators and safe from competitors. <p> Nesting success did not influence between-year breeding dispersal by 159 male or 76 female flickers. Because nests and forest clumps were not predictably safe from predators, benefits of dispersing likely outweigh costs. Other factors such as mate-switching, nest ectoparasites, and a fluctuating food source may play larger roles in dispersal than nest predation. Within years, 73% of pairs switched nest sites after their first attempt failed due to predation (N=37); however, there was no reproductive advantage for these pairs compared to pairs that remained at their original nest. Stressful encounters with predators involving nest defence may trigger dispersal, although it seems to offer no greater nest success. Of 24 flicker pairs presented with a control model before egg-laying, 3 pairs abandoned their nest, whereas 4 out of 24 pairs presented with a squirrel model abandoned their nest. This suggests that a one-time encounter with a nest predator is not a sufficient deterrent against continued nesting. Rather, costs of finding and excavating or renovating a new cavity may cause individuals to tolerate some risk in nesting at a location with an active predator. <p> In experimental trials (N=94), intensity of nest defence behaviour against a model predator was not related to the sex, age, body size, and body condition of the defending adult(s). The sexes may have behaved similarly because they are similar in size and have similar survival patterns. Costs and benefits of nest defence for flickers of different ages may also be equal because flickers are relatively short-lived and their survival rate is not linked with age. Brood size of the defending adult was also unrelated to the intensity of nest defence. If flickers have adjusted their clutch size in relation to the number of young for which they can optimally provide care, then no effects of brood size on nest defence behaviour should be recorded, as was the case here.</p>

I studied nest characteristics, breeding dispersal, and nest defence behaviour of Northern Flickers (<i>Colaptes auratus</i>, hereafter flickers) in central interior British Columbia with respect to nest predation. My research focused on three questions: (1) Are there nest characteristics associated with the risk of nest predation and nest loss to European Starlings (<i>Sturnus vulgaris</i>)? (2) Does nest predation influence breeding dispersal? (3) Do parental attributes influence nest defence behaviour? <p> An examination of flicker nest-site characteristics at five spatial scales revealed that nests were safer from mammalian predators (N=81) when they were higher, concealed by vegetation, farther from continuous coniferous forest blocks, and contained fewer conifers within the nesting clump. Proximity to conifers increased predation risk, but nests safe from competitors (N=18) were closer to coniferous forest blocks and contained a higher percentage of conifers in the nesting clump. Flickers face a trade-off between being safe from predators and safe from competitors. <p> Nesting success did not influence between-year breeding dispersal by 159 male or 76 female flickers. Because nests and forest clumps were not predictably safe from predators, benefits of dispersing likely outweigh costs. Other factors such as mate-switching, nest ectoparasites, and a fluctuating food source may play larger roles in dispersal than nest predation. Within years, 73% of pairs switched nest sites after their first attempt failed due to predation (N=37); however, there was no reproductive advantage for these pairs compared to pairs that remained at their original nest. Stressful encounters with predators involving nest defence may trigger dispersal, although it seems to offer no greater nest success. Of 24 flicker pairs presented with a control model before egg-laying, 3 pairs abandoned their nest, whereas 4 out of 24 pairs presented with a squirrel model abandoned their nest. This suggests that a one-time encounter with a nest predator is not a sufficient deterrent against continued nesting. Rather, costs of finding and excavating or renovating a new cavity may cause individuals to tolerate some risk in nesting at a location with an active predator. <p> In experimental trials (N=94), intensity of nest defence behaviour against a model predator was not related to the sex, age, body size, and body condition of the defending adult(s). The sexes may have behaved similarly because they are similar in size and have similar survival patterns. Costs and benefits of nest defence for flickers of different ages may also be equal because flickers are relatively short-lived and their survival rate is not linked with age. Brood size of the defending adult was also unrelated to the intensity of nest defence. If flickers have adjusted their clutch size in relation to the number of young for which they can optimally provide care, then no effects of brood size on nest defence behaviour should be recorded, as was the case here.</p>

Several species of small, cavity-nesting owls occur in the Sierra Nevada, including in areas impacted by human activities. The owls typically use standing dead trees (snags) for nest sites. Although descriptive studies exist regarding habitats associations around nest and roost sites, few studies have examined habitat associations at larger spatial scales or relative to certain snag characteristics (e.g., density, decay class). To improve our understanding of the habitat associations of these owls, I compared habitat characteristics at 2 spatial scales around areas of owl detection and non-detection. I also examined distances between conspecifics and heterospecifics to determine if clustering of conspecifics or avoidance of predators occurred. I conducted owl broadcast surveys and snag sampling during the spring and summer of 2006 and 2007 in the Lake Tahoe Basin of central Sierra Nevada. I measured additional habitat variables (e.g., vegetation cover, distance to roadways) from pre-existing geographical information system layers. I used stepwise logistic regression to ascertain which variables were influential in predicting owl occurrence. The northern saw-whet owl (Aegolius acadicus) was the only species detected in sufficient numbers for statistical analysis, with a detection probability of 0.25. I detected saw-whets in a wide range of conditions and it appeared that few factors influenced their distribution in the basin. Areas dominated by white fir, however, were correlated with the absence of saw-whets at both the macrohabitat and microhabitat scales. White fir-dominated areas tend to occur on the west side of the basin and it is possible white fir was acting as a proxy for other factors not measured in this study, such as microclimate conditions or prey availability. I was also more likely to find a saw-whet within 1000 m of another saw-whet than within 1000 m of a non-use point, indicating clustering of conspecifics in the basin. While it appears saw-whet needs are being met in the basin, restoration projects are ongoing to decrease both the number of snags and relative abundance of white fir. Continued monitoring of the species is essential to understand potential effects of restoration activities. Suggestions are provided for appropriate timing and effort of future surveys.

Several species of small, cavity-nesting owls occur in the Sierra Nevada, including in areas impacted by human activities. The owls typically use standing dead trees (snags) for nest sites. Although descriptive studies exist regarding habitats associations around nest and roost sites, few studies have examined habitat associations at larger spatial scales or relative to certain snag characteristics (e.g., density, decay class). To improve our understanding of the habitat associations of these owls, I compared habitat characteristics at 2 spatial scales around areas of owl detection and non-detection. I also examined distances between conspecifics and heterospecifics to determine if clustering of conspecifics or avoidance of predators occurred. I conducted owl broadcast surveys and snag sampling during the spring and summer of 2006 and 2007 in the Lake Tahoe Basin of central Sierra Nevada. I measured additional habitat variables (e.g., vegetation cover, distance to roadways) from pre-existing geographical information system layers. I used stepwise logistic regression to ascertain which variables were influential in predicting owl occurrence. The northern saw-whet owl (Aegolius acadicus) was the only species detected in sufficient numbers for statistical analysis, with a detection probability of 0.25. I detected saw-whets in a wide range of conditions and it appeared that few factors influenced their distribution in the basin. Areas dominated by white fir, however, were correlated with the absence of saw-whets at both the macrohabitat and microhabitat scales. White fir-dominated areas tend to occur on the west side of the basin and it is possible white fir was acting as a proxy for other factors not measured in this study, such as microclimate conditions or prey availability. I was also more likely to find a saw-whet within 1000 m of another saw-whet than within 1000 m of a non-use point, indicating clustering of conspecifics in the basin. While it appears saw-whet needs are being met in the basin, restoration projects are ongoing to decrease both the number of snags and relative abundance of white fir. Continued monitoring of the species is essential to understand potential effects of restoration activities. Suggestions are provided for appropriate timing and effort of future surveys.

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.