Urbanization introduces a set of novel stressors for animals in these modified habitats. Developing young, in particular, can be at risk due to increased predation, exposure, and high food intake requirements. Song sparrows (Melospiza melodia) are a model wild songbird system that persist in both urban and rural habitats, and have young that develop very quickly. I investigated how urbanization changes the arthropod community, how that in turn affects nestling diet, and ultimately if there were any differences in nestling amino acid profiles or body condition between habitat types. Prior work found that urban habitats also have far higher rates of brood parasitism, which can additionally restrict food intake for urban nestlings. However, this prior work has also found that urban song sparrow adults avoid consequences for living in urban habitats, so I wanted to see if nestlings were also able to avoid the consequences of urban living. In chapter one, I found our urban arthropod communities had lower average arthropod abundance, biomass, and diversity when compared to rural arthropod communities. Song sparrow nestling diets differed somewhat in composition of arthropod prey items by habitat, but urban and rural nestlings had the same average biomass of stomach contents. In chapter two, I investigated whether different habitat types or brood parasitism altered body size and amino acid concentration of song sparrow nestlings. Only gamma-aminobutyric acid differed, being significantly lower in urban, parasitized nestlings. No groups differed in metrics of body condition. In chapter three, I performed a meta-analysis to investigate how brood-parasitic brown-headed cowbirds (Molothrus ater) affect host clutch size and nest success. Host clutch sizes were lower when parasitized, but surprisingly non-parasitized nests were more likely to fail. Despite lower arthropod food availability and high levels of brood parasitism, urban song sparrow nestlings are not compromised, supporting the conclusion that urbanization does not necessarily have negative consequences for individuals of this species. / Doctor of Philosophy / Urbanization introduces a set of new challenges for animals. Young animals, in particular, can be at risk due to increased predation, exposure, and lack of food. Song sparrows (Melospiza melodia) are a model wild songbird system that persist in both urban and rural habitats, and have young that develop very quickly and rely on parents providing a diet of arthropods, including spiders and insects. I investigated how urbanization changes the arthropod community, how that in turn affects nestling diet, and ultimately if there were any differences in nutrition or body condition. Urban habitats also have higher rates of cowbirds laying their eggs in the nests of other species, which can make it even harder for urban song sparrow nestlings to get enough food. However, this prior work has also found that urban song sparrow adults avoid consequences for living in urban habitats, so I wanted to see if nestlings were also able to avoid the consequences of urban living. In chapter one I found our urban arthropod communities had lower average number and mass of arthropods, when compared to rural arthropod communities. Song sparrow nestling diets differed somewhat in composition of arthropod prey items by habitat, but urban and rural nestlings had the same average biomass of stomach contents. In chapter two, I investigated whether different habitat types or having cowbird 'siblings' resulted in different nutrition and body size of song sparrow nestlings. Out of nearly 30 measures of nutrition only one differed, being significantly lower in urban nestlings with siblings. No groups differed in body size. For chapter three I analyzed the literature to investigate how brown-headed cowbirds (Molothrus ater) affect the number of eggs host birds lay and host nest success. Host clutch sizes were lower when cowbirds were present, but surprisingly, it was nests without cowbirds that were more likely to fail. Despite lower arthropod food availability and high levels of cowbird presence, urban song sparrow nestlings avoided negative consequences, supporting the conclusion that urbanization does not necessarily harm individuals of this species.

Over the last 40 years North American grassland bird populations have declined more than any other bird guild. This trend is especially evident in Vermont, where species experiencing precipitous declines include the Savannah Sparrow (Passerculus sandwichensis) and Bobolink (Dolichonyx oryzivorus). These declines are linked to habitat loss due to reforestation and suburbanization as well as the intensification of grassland management. Modern grassland management includes earlier first-haying dates (late-May) and shorter intervals between haying events (35 days). These management practices have severe repercussions for songbird populations because 1) early-haying results in complete nest failure (99% Savannah Sparrow and 100% Bobolink nests), 2) the interval between the first and second haying is too short for birds to renest, and 3) intensively managed fields comprise a significant portion of the total available habitat (as much as 40%). In 2002-2006, I examined how hayfield and pasture management affected grassland songbird ecological and evolutionary behavior in the agricultural landscape of the Champlain Valley, Vermont and New York. I studied songbirds in four grassland management types: early-hayed fields harvested in late-May or early-June and again in mid-July; middle-hayed fields harvested in late-June or early-July; late-hayed fields harvested after 1 August; rotationally-grazed pastures, a matrix of small paddocks where cows are moved after the grass in a paddock is eaten to a low point. I addressed the following objectives: 1. Determined the annual productivity, survival, and recruitment of Bobolinks and Savannah Sparrows in the four treatment types. 2. Identified the effects of early-haying on the social and genetic mating systems of Savannah Sparrows. 3. Conducted a population viability analysis for Bobolinks and Savannah Sparrows nesting in the Champlain Valley, assessing sensitivities of life-history parameters and identifying effective management alternatives. This study provides information on how agricultural management affects the ecology, evolution, and viability of grassland birds. It will help inform landowners, managers, and law-makers about management practices and habitat requirements needed to sustain populations.

Many organisms use both vegetation structure and social cues in selecting habitats. Many species of songbirds use the presence of breeding conspecifics as a social cue and sign of habitat quality, and can be induced to settle in unoccupied habitats by artificially broadcasting breeding song, a process referred to as “conspecific attraction”. In our study, we tested response to conspecific attraction a low-density population of the threatened Golden-winged Warbler (Vermivora chrysoptera) in Highland County, VA. Response to broadcast song was observed, with a modest increase in mean male abundance at survey points within 250 meters of treatments, and mean abundance decreasing outside of this range throughout the study area. Recruitment to conspecific playback was lower in our study than observed in previous research on high-density systems. Our results suggest more research is needed of the effectiveness of conspecific attraction in low density species and that its use should be tailored to the spatial and demographic conditions of the managed population.

The Australian zebra finch (Taeniopygia guttata) serves as an excellent model organism for studying the mechanisms that influence brain sexual differentiation. The brain and behavior of the zebra finch are sexually dimorphic. The regions of the brain that control the learning and production of song (song control nuclei) are significantly larger in the male brain than in the female brain and only males sing courtship songs, thus the majority of past research has focused on the development of these sex differences. In the majority of mammals, brain sexual differentiation occurs because hormones secreted from the gonads act to initiate male or female brain development. In zebra finches, estradiol is sufficient to masculinize the male brain, however manipulations of developmental hormone exposure fail to fully reverse the sex differences in song nuclei size. Furthermore, genetic females induced to develop functional testicular tissue do not develop a completely masculinized song system and castration has no effect on development of the song system in males. The source of the increased estrogenic signal in male zebra finch brain has yet to be identified, but data suggest that other neuronal factors play a role in development of the song control nuclei. Coregulators, such as coactivators and corepressors, are proteins and RNA activators that work by enhancing or depressing transcriptional activity of the nuclear steroid receptor with which they associate. Coregulators also modulate the development of sex-specific brain morphology and behavior in rodents and birds and may help to explain the difficulties observed in altering song nuclei development via castration and gonadal hormone replacement. As an estrogen receptor-α coactivator, ribosomal protein L7 (RPL7) is able to make the brain more sensitive to estradiol by enhancing the effects of steroid receptor action. Therefore, this dissertation addressed the following questions regarding RPL7: (1) is RPL7 expression sexually dimorphic in the song nuclei of the zebra finch brain?; (2) is RPL7 protein expression regulated by steroid hormones?; and (3) does decreasing RPL7 protein expression with antisense oligonucleotides alter neuronal survival in vivo and song nuclei size and neuron number in vitro? Collectively, these studies will provide valuable information about the role of steroid receptor coactivators in development of the zebra finch song system and on the role of coactivators on sexual differentiation of the brain.

In an attempt to manage values other than timber production, forestry companies have sought a new paradigm to manage forest resources. Based on the hypothesis that wildlife in the boreal forest has adapted to habitat structures created by natural disturbances, some forest harvests have been modified to approximate patterns left after natural disturbance. Attempts at approximating natural disturbance have included retention of patches of live trees within cutblock boundaries, cutting to natural stand boundaries and application of harvest plans with spatio-temporally aggregated cutblocks (single-pass harvests). Single-pass harvesting is a recent attempt to better approximate natural disturbance in the boreal and has not been evaluated for its potential to sustain wildlife. I therefore contrasted residual patch pattern and composition, as well as landscape-scale avian abundance and composition in 1) single-pass; 2) multi-pass; and 3) salvage logged post-fire harvests, and contrasted these with unsalvaged post-fire sites. Post-fire sites were used to define the Natural Range of Variation (NRV). Seventy-two plots (12 post-fire, 15 post-salvage harvest, 16 single-pass harvest, and 29 multi-pass harvest) were surveyed for avian community composition and abundance one to five years post disturbance. <p>I contrasted the composition of remaining live forest stands at the landscape-scale and in residual patches by pairwise comparison of pre- and post-disturbance composition. At the landscape-scale, non-metric mutlidimensional scaling suggested post-disturbance landscape composition of post-fire and salvage-logged plots was similar to pre-disturbance landscape composition, with a tendency toward greater survival of hardwoods and lower survival of jack pine (Pinus banksiana) or black spruce (Picea mariana). However, harvesting of hardwoods and mixedwood stand types in single and multi-pass harvests led to landscapes with more bog and swamp habitats. <p>Comparison of residual patch composition with pre-disturbance composition was made using blocked multi-response permutation procedures. Post-fire plots (i.e. NRV) had residual patches that were representative of pre-disturbance composition, but with slightly more hardwoods and less black spruce/jack pine than expected by chance. All harvested treatments had similar biases among residuals to those left by fire, except that multi-pass harvests tended to leave less mixedwood habitat than expected. Multi-pass harvests also had less area in residual patches, and patches were smaller, more isolated and less complex in shape. Single-pass harvests had residual patches that were more representative of the size, shape, complexity, and change in composition seen post-fire. Multi-pass harvests only had 14% of the residual patch area in patches at least 5 ha in size, whereas this proportion was higher in fire (83%), salvage-logged areas (42%), and single-pass harvests (57%). Old-growth associated species might only persist in patches 5 ha or larger, and so multi-pass harvesting may have negative consequences for these forest birds.<p>Redundancy analysis indicated that bird communities differed from the NRV in all harvest treatments. However, single-pass harvests provided a slightly better fit to NRV than did multi-pass harvesting. Community similarity was influenced by non-linear responses to area harvested, residual retention, residual composition and pre-disturbance forest composition. An optimization routine was used to select harvest characteristics that would maximize community similarity to NRV. Optimization suggested that community similarity to NRV can be maximized by using single-pass harvests over multi-pass harvests, harvesting 66-88% of of a planning unit, and retaining 5-19% of the harvest area as live residual patches.<p>My results suggest that single-pass harvesting may be ecologically more sustainable than multi-pass harvests. Future studies are required to determine whether both harvesting treatments converge with NRV through time. Greater overlap of salvage-logged avian communities with NRV suggests that experimentation with prescribed fire as a post-harvest treatment may be the best method to bring harvests ecologically closer to NRV, and highlights the need to conserve early post-fire habitats.

In an attempt to manage values other than timber production, forestry companies have sought a new paradigm to manage forest resources. Based on the hypothesis that wildlife in the boreal forest has adapted to habitat structures created by natural disturbances, some forest harvests have been modified to approximate patterns left after natural disturbance. Attempts at approximating natural disturbance have included retention of patches of live trees within cutblock boundaries, cutting to natural stand boundaries and application of harvest plans with spatio-temporally aggregated cutblocks (single-pass harvests). Single-pass harvesting is a recent attempt to better approximate natural disturbance in the boreal and has not been evaluated for its potential to sustain wildlife. I therefore contrasted residual patch pattern and composition, as well as landscape-scale avian abundance and composition in 1) single-pass; 2) multi-pass; and 3) salvage logged post-fire harvests, and contrasted these with unsalvaged post-fire sites. Post-fire sites were used to define the Natural Range of Variation (NRV). Seventy-two plots (12 post-fire, 15 post-salvage harvest, 16 single-pass harvest, and 29 multi-pass harvest) were surveyed for avian community composition and abundance one to five years post disturbance. <p>I contrasted the composition of remaining live forest stands at the landscape-scale and in residual patches by pairwise comparison of pre- and post-disturbance composition. At the landscape-scale, non-metric mutlidimensional scaling suggested post-disturbance landscape composition of post-fire and salvage-logged plots was similar to pre-disturbance landscape composition, with a tendency toward greater survival of hardwoods and lower survival of jack pine (Pinus banksiana) or black spruce (Picea mariana). However, harvesting of hardwoods and mixedwood stand types in single and multi-pass harvests led to landscapes with more bog and swamp habitats. <p>Comparison of residual patch composition with pre-disturbance composition was made using blocked multi-response permutation procedures. Post-fire plots (i.e. NRV) had residual patches that were representative of pre-disturbance composition, but with slightly more hardwoods and less black spruce/jack pine than expected by chance. All harvested treatments had similar biases among residuals to those left by fire, except that multi-pass harvests tended to leave less mixedwood habitat than expected. Multi-pass harvests also had less area in residual patches, and patches were smaller, more isolated and less complex in shape. Single-pass harvests had residual patches that were more representative of the size, shape, complexity, and change in composition seen post-fire. Multi-pass harvests only had 14% of the residual patch area in patches at least 5 ha in size, whereas this proportion was higher in fire (83%), salvage-logged areas (42%), and single-pass harvests (57%). Old-growth associated species might only persist in patches 5 ha or larger, and so multi-pass harvesting may have negative consequences for these forest birds.<p>Redundancy analysis indicated that bird communities differed from the NRV in all harvest treatments. However, single-pass harvests provided a slightly better fit to NRV than did multi-pass harvesting. Community similarity was influenced by non-linear responses to area harvested, residual retention, residual composition and pre-disturbance forest composition. An optimization routine was used to select harvest characteristics that would maximize community similarity to NRV. Optimization suggested that community similarity to NRV can be maximized by using single-pass harvests over multi-pass harvests, harvesting 66-88% of of a planning unit, and retaining 5-19% of the harvest area as live residual patches.<p>My results suggest that single-pass harvesting may be ecologically more sustainable than multi-pass harvests. Future studies are required to determine whether both harvesting treatments converge with NRV through time. Greater overlap of salvage-logged avian communities with NRV suggests that experimentation with prescribed fire as a post-harvest treatment may be the best method to bring harvests ecologically closer to NRV, and highlights the need to conserve early post-fire habitats.

Rapid increases in plasma androgens are generally associated with short-term aggressive challenges in many breeding vertebrates. However, some animals such as song sparrows (Melospiza melodia) are aggressive year-round, even during the non-breeding season, when gonads are regressed and systemic testosterone (T) levels are non-detectable. In contrast, levels of the prohormone dehydroepiandrosterone (DHEA) are elevated year-round in the plasma and brain. The local conversion of brain DHEA to potent androgens may be critical in regulating non-breeding aggression. 3β-hydroxysteroid dehydrogenase/Δ4-Δ5 isomerase (3β-HSD) catalyzes DHEA conversion to androstenedione (AE) and the cofactor NAD⁺ assists in this transformation. In this thesis, I asked whether brain 3β-HSD activity is regulated by social encounters in seasonally breeding male songbirds. In Experiment 1, I looked at the long-term seasonal regulation of brain 3β-HSD activity. 3β-HSD activity was highest in the non-breeding season compared to the breeding season and molt. In Experiment 2, I hypothesized that brain 3β-HSD activity is rapidly regulated by short-term social encounters during the non-breeding season. A 30 min social challenge increased aggressive behavior. Without exogenous NAD⁺, there was ~355% increase in 3β-HSD activity in the caudal telencephalon and ~615% increase in the medial central telencephalon compared to controls (p<0.05). With exogenous NAD⁺, there was no effect of social challenge on 3β-HSD activity. These data suggest that endogenous cofactors play a critical role in the neuroendocrine response to social challenges. The increase in brain DHEA conversion to AE during social challenges may be a mechanism to rapidly increase local androgens in the non-breeding season, when there are many costs of systemic T.

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I examined the effects of nest site vegetation structure and cattle grazing on songbird nesting success in native mixed-grass prairie in Grasslands National Park of Canada and Mankota Community Pastures in southwestern Saskatchewan. This is the first study to compare songbird nesting success in season-long grazed and ungrazed native mixed-grass prairie. Sprague’s pipit, Baird’s sparrow, vesper sparrow, lark bunting, and chestnut-collared longspur all selected for denser vegetation at the nest than was generally available. Sprague’s pipit daily nest survival declined with increased vegetation density and litter depth at the nest site. Vegetative cover did not influence daily nest survival of the other species. Environmental conditions during the study may have resulted in an increased risk of predation for Sprague’s pipits nesting in greater cover. Grazing did not influence daily nest survival of any of the 5 species. Low-moderate intensity cattle grazing appears compatible with management for prairie songbirds in native mixed-grass prairie.