Ecologists and conservation biologists are interested in explaining why animal abundance and reproductive success vary among habitats. Initial motivation for this research arose from concerns for Northern Pintail (Anas acuta) populations in North America. Unlike many prairie-nesting dabbling duck populations, pintails failed to increase during periods of excellent wetland conditions, and remained below conservation goals. Low pintail populations have been linked to degraded landscape conditions on the Canadian prairies. Current habitat management for pintails aims to protect and create larger areas of perennial cover either by encouraging better management of grazing lands, by converting cropland to grassland, or by promoting adoption of fall-seeded crops like winter wheat. The central premise is that larger areas of natural grassland cover will attract breeding pintails to nest earlier in the season in low-predation-risk habitat. I studied pintail nesting ecology near the Milk River Ridge, Alberta, 2004-2006, in terms of a life-cycle perspective, from spring arrival and settling on breeding areas, to assess age and quality of nesting females, to determine timing and investment in reproduction, and finally to measure nesting success. A gradient in presumed high (grassland) to low (agriculture) habitat quality provided a landscape template for testing habitat selection models. Pintail breeding pair densities were 1.5-3 times higher in grassland than agricultural landscapes in all three years, regardless of regional population size, with pairs occupying grassland landscapes at higher densities immediately upon arrival in early spring. Northern Shoveler (A. clypeata), gadwall (A. strepera) and blue-wing teal (A. discors) had similar settlement patterns as pintails, but mallard (A. platyrhynchos) pair density was higher in agricultural areas. Relatively more, older female pintails were captured at nests in grassland landscapes whereas yearling females were encountered more often in agricultural areas, a pattern that was not detected in female shovelers. This response suggests that older female pintails may be better able to recognize and settle in higher quality grassland habitats. Body mass of pintail females did not vary among years, decreased seasonally, and was positively related to body size index and incubation stage. Furthermore, pintail body mass did not differ between grassland (650 ± 24 g), ecotone (678 ± 27 g) and agriculture (672 ± 33 g). In female shovelers, body mass varied among years (555 ± 29 g in 2004, 481 ± 18 g in 2005, 508 ± 21 g in 2006), and increased with nesting date. Shoveler body mass did not differ between grassland (519 ± 32 g), ecotone (519 ± 44 g), or agriculture (507 ± 35 g). Nest initiation dates did not vary by landscape for pintail, shoveler or mallard, but all species nested earlier in 2006 versus 2004. In pintail, shoveler and mallard, clutch size was negatively related to nest initiation date. Pintail and shoveler clutch sizes were generally larger in a wet year with abundant wetlands (2006) when compared with a dry year (2004), but no landscape differences were detected. Mallard clutch size did not vary by year or landscape. Female reproductive timing and investment (in terms of clutch size) were unrelated to upland habitat characteristics, counter to a hypothesis that predicts larger pintail clutch sizes in agricultural landscapes. However, pintail and shoveler invested in larger clutches in 2006, a wet year with abundant wetlands, possibly due to greater abundance of aquatic foods. Finally, nest survival rates of duck species, except mallard, tended to be higher in grassland landscapes and lower in agricultural landscapes. Pintail nest survival was consistently higher in grassland than in agricultural landscapes and was highest in 2006 when wetland conditions were excellent. Shoveler and blue-winged teal nest survival rates did not vary strongly with landscape, but were also higher in 2006, whereas mallard and gadwall nest survival estimates did not vary with landscape or year. Overall, pintails settled at higher densities in grassland landscapes where breeding success was higher (indexed by nesting success). This suggests that pintails respond appropriately to cues that enable them to recognize suitable habitat, at least in regions where large contiguous areas of grassland habitat remain. Furthermore, assuming that findings for pintails reflect those of other grassland bird species, large remnant areas of intact natural grassland seem particularly in need of protection or restoration, and management regimes that maintain their habitat integrity. By integrating applied and theoretical aspects of pintail reproductive ecology, I attempted to provide deeper insights into the processes that could shape behavioral decisions by breeding pintails and other duck species. Older pintails may occupy wetlands in higher quality grassland habitat early in spring, forcing subordinate or later-arriving individuals into poorer quality habitat (i.e., where nesting success is lower); however, mechanisms involved in this putative process are unknown. Overall, results suggest that grassland restoration or enhancement (e.g., managing grazing intensity) could improve reproductive success of pintails and possibly other grassland bird species.

Individual organisms often use cues from their natural environments to determine many behavioral and life-history "decisions." These "decisions" are usually adaptive, i.e. a response to selection, because the environmental cues on which they are based reliably correlate with increased fitness over time. When the selected behavioral response to a natural cue no longer provides a fitness benefit, then selection for a new response may occur but individuals maintaining the previously selected response may suffer reduced survival and reproduction. Especially in human-modified landscapes individuals making a maladaptive behavioral or life-history choice based on those formerly reliable environmental cues may be faced with an "evolutionary trap". In urban, or suburban, environments many factors have been altered in ways that could lead to evolutionary traps. Inappropriate behavioral responses by many individuals could lead to reduced demographic performance of urban populations relative to their wildland counterparts and to the decline of entire urban populations. In birds, maladaptive patterns of nest provisioning or vigilance may occur (a) when human-provided adult foods are easier to feed young because they are more abundant and predictable than foods appropriate for nestlings, or (b) when birds' perception of predation risk, which can be influenced by human disturbance, is greater than the real risk. By provisioning or attending their nests more or less than what is appropriate given the environmental level of resources and risks, the behavior of suburban parents may be contributing to high levels of nest failure during the nesting stage. To determine whether maladaptive parental care influences nest survival during the nestling stage, I conducted an experiment using Florida Scrub-Jays (Aphelocoma coerluscens). Suburban scrub-jays have lower nest survival during the nestling stage but higher survival during the incubation stage relative to wildland jays. Both predators and food abundance vary greatly between suburban and wildland scrub. The suburbs have a greater abundance of predators that may prey on both adult scrub-jays and their nests and more foods appropriate for adults but less nestling-appropriate food. This variation in risks and resources should affect the parental care behavior of suburban scrub-jays, which in turn may affect patterns of nest survival. In pre-treatment observations, I found that suburban females spent more time brooding than wildland birds but suburban males did not provision any more than wildland males. Experimentally increasing the perception of adult predation risk reduced parental care in both suburban and wildland females. Increasing the availability of nestling food reduced parental care in suburban females but had no effect in wildland females. Increasing food availability, but not predation risk, decreased call rates but increased call frequency in nestling scrub-jays from both habitats. However, neither parental care nor food availability had much influence on nest survival during the nestling stage. Instead, side nest concealment and the presence of helpers were the most important variables in nest survival analyses prompting other explanations besides maladaptive parental behavior or lack of nestling food resources for the habitat-specific difference in nest survival during the nestling stage.

Grassland birds are the most rapidly declining bird guild in North America, due in large part to extensive loss and fragmentation of grassland habitat resulting from the spread of agriculture and other human-dominated landscapes. Over the past several decades, grassland birds have increasingly become a guild of high conservation and management interest as their populations continue to decline and suitable grassland habitat becomes continually scarcer. Although studies investigating grassland bird responses to management actions and habitat structure are common, few studies are concerned with clarifying the mechanisms through which habitat structure may affect grassland birds. Filling this knowledge gap is critical for increasing our understanding of grassland bird ecology and improving the effectiveness of management and restoration actions for grassland birds. To address this knowledge gap, I took a uniquely holistic approach to traditional grassland bird-habitat studies by concurrently gathering data on multiple wildlife taxa that may interact with birds to examine how these different taxa respond to habitat characteristics across multiple spatial scales, and how those responses may in turn impact grassland birds. Research was conducted on 10 grassland sites at Burning Star State Wildlife Management Area in northeast Jackson County, Illinois, during the bird breeding season (May-July) from 2018 to 2021. My first five objectives were to determine the grassland habitat characteristics that were most highly associated with the following taxa: arthropods, an important food source for adult and nestling grassland birds; small mammals, which are occasional nest predators and an alternate prey source for more prolific nest predators; snakes; raccoons; and grassland birds. My final objective was to estimate the extent to which grassland bird habitat associations were mediated through nest predator abundance, alternate prey abundance, and food availability. In Chapter 2, I examined associations between grassland arthropod communities and habitat characteristics representing three spatial scales: local (within-patch vegetation structure and composition), patch (size, shape, edge composition), and landscape (landcover composition within a 400 m buffer). In addition to their relevance for grassland birds, arthropods play important functional roles in grasslands and are useful indicators of grassland health. I collected arthropod samples using pan traps in grassland patches at Burning Star, and used generalized linear mixed models to relate variation in arthropod biomass and diversity to habitat predictor variables. I found that arthropod biomass increased with vegetation height at the local scale and proportion of forest/shrub edge at the patch scale, while arthropod diversity responded only to local-scale variables, including a negative association with vegetation height and woody vegetation cover, and a positive association with forb cover. I conclude that local vegetation structure and composition are the main drivers shaping arthropod communities at Burning Star, and that limiting woody encroachment and increasing forb cover and variation in vegetation height within grassland patches may encourage arthropod abundance and diversity in tallgrass prairies. In Chapter 3, I estimated associations between small mammal abundance and habitat variables, again representing three spatial scales. I surveyed small mammal communities using a grid of 100 Sherman traps set out for three nights at each study site. I identified all captured individuals to genus, individually marked them with ear tags, and estimated abundance using a combination of Huggins P and C models in Program Mark and generalized linear mixed models in Program R. I found that small mammal abundance was positively related to vegetation density and negatively related to plant diversity, though variation in plant diversity affected Microtus voles more strongly than Peromyscus mice. At the landscape scale, small mammal abundance was positively associated with the amount of water surrounding a patch, and negatively associated with the amount of grassland surrounding a patch. Variation in small mammal community composition (proportions of Microtus vs Peromyscus) was mostly governed by differences in habitat structure at the landscape scale, rather than differences in vegetation structure at the local scale. I suggest that managers interested in influencing small mammal abundance in grasslands encourage dense vegetation growth by limiting disturbance if increased small mammal abundance is desired, or reduce vegetation density by increasing disturbance frequency to reduce small mammal abundance. Additionally, increasing plant diversity by sowing a high diversity of seeds may be an effective way to control Microtus vole populations. In Chapter 4, I estimated the habitat associations of snakes at Burning Star, focusing on the relative abundance of snakes among different grassland sites, as well as snake diversity and species-specific occupancy. Although snakes are prolific nest predators of grassland birds, they are also integral components of grassland systems, and there may be instances where managers and decision-makers wish to increase, rather than decrease, their abundance in grasslands. I found that snake community metrics were strongly and positively related to an increase in woody plant cover at the local (within-patch) scale. Snake relative abundance was also positively related to an increase in grass cover and a decrease in forb cover, though my occupancy results suggest that this was primarily driven by an increase in black kingsnakes (Lampropeltis nigra). At the patch scale, snake relative abundance and diversity were both positively related to the proportion of patch edge composed of roads. Habitat structure at the landscape scale had the smallest impact on snakes in this study, though the proportion of trees in the landscape was positively related to snake diversity. I suggested that managers and conservationists interested in manipulating snake abundance in grasslands focus on within-patch vegetation structure and composition. Decreasing woody cover in grasslands, or increasing the ratio of forbs to grasses, may reduce the presence of snakes, while maintaining a woody component could encourage both snake abundance and diversity. In Chapter 5, I estimated the habitat characteristics that were most strongly associated with raccoon abundance estimates in grassland patches at Burning Star. Raccoons have become increasingly important avian nest predators in midwestern grasslands due to rampant habitat fragmentation. I estimated raccoon abundance using an occurrence index from a series of baited trail cameras located in grassland sites. I found no convincing evidence of raccoon abundance being influenced by local scale habitat structure, beyond a weak association with vegetation height. At the patch scale, raccoon abundance was positively related to the proportion of patch edge composed of roads. At the landscape scale, raccoon abundance was negatively related to grassland, and positively related to water, within 400 meters of a grassland patch. I recommended that managers concerned with minimizing the presence of raccoons in grasslands should limit roads along grassland perimeters, maximize the proportion of grassland in the landscape surrounding a grassland patch, and avoid planning a grassland restoration in close proximity to open water if possible. In Chapter 6, I estimated the habitat characteristics that were most strongly associated with daily nest survival, nest density, and abundance of Dickcissels (Spiza americana), Field Sparrows (Spizella pusilla), and Common Yellowthroats (Geothlypis trichas), but also considered responses of all grassland bird species combined. I considered habitat characteristics representing four spatial scales: nest site, within-patch, patch, and landscape, though the nest site scale was only considered for nest survival analyses. I found that Dickcissels, an obligate grassland species, exhibited the strongest response to fire, as nest density drastically improved after previously undisturbed grasslands were burned. Dickcissel abundance was positively related to agriculture at the landscape scale and negatively related to woody cover. Field sparrows demonstrated a preference for woody cover and proximity to forests and shrublands, and Common Yellowthroats were positively associated with forb cover. Both Field Sparrow and Common Yellowthroat nest survival increased with greater distance from an edge, though no edge effect was detected for Dickcissel nest survival. All bird species benefitted from increased plant diversity and greater patch size. All species also responded negatively to vegetation height or litter depth, suggesting that fire, which reduces vegetation biomass and litter, may indirectly benefit the facultative grassland birds of Burning Star in addition to Dickcissels. In Chapter 7, I used structural equation models and data gathered in the previous five chapters to estimate whether the effects of habitat structure on breeding Field Sparrows is mediated through changes in predator (snake and raccoon) abundance, alternate prey availability, or arthropod biomass. I used Field Sparrows as the focal species for this chapter because they were the most common grassland bird in my dataset. I found no evidence of nest survival or nest density of Field Sparrows being directly influenced by nest predator abundance, alternate prey, or arthropod biomass, although habitat characteristics associated with increased nest survival were also associated with greater arthropod biomass and reduced predator abundance. I suggested that habitat structure at Burning Star may primarily impact breeding Field Sparrows through direct means, such as influencing nest concealment or foraging efficiency. These results also suggest that nest success and nest density are decoupled in this study area, so Field Sparrows may be preferentially selecting nest sites with structural characteristics that do not increase nest survival. Ultimately, my findings from this study indicate that while predator avoidance and food provisioning likely play an important role in determining nest survival for grassland birds, predator abundance and arthropod biomass may not necessarily predict predation risk and foraging efficiency to the extent that is often assumed.

The abundance of Rio Grande wild turkeys (Meleagris gallopavo intermedia) in the southeastern Edwards Plateau of Texas has declined since the late 1970s. Because knowledge of reproductive rates is important to understanding the dynamics of a population, radio-tagged hens were monitored during the 2005–2007 reproductive seasons to evaluate and compare reproductive parameters from areas with both declining and stable population trends. During January–March of 2005–2007, turkey hens were captured and radiotagged on 4 study areas; 2 within a region of stable turkey populations, and 2 within a region of declining populations. Monitoring occurred from January–July each season to determine nest- site locations. Nesting attempts, nest fate, clutch size, initiation date, and nest age were recorded. Nests were monitored ≥3 times weekly in order to estimate production parameters and daily nest survival. Poults were captured by hand and fitted with a 1.2 glue-on transmitter and monitored daily to estimate daily survival. Estimates show production was greater in stable regions than declining regions of the Edwards Plateau. Eighty-four percent of hens attempted to nest in the stable region and 67% attempted in the declining region. Eighteen of 102 nests were successful (≥1 egg hatched), in the stable region and 7 of 60 nests were successful in the declining region. Nest-survival analysis showed an influence of temporal variation within years, yet no differences in nest survival were detected between stable and declining regions. Poult survival also showed no difference between regions. The 2 overall objectives of this study were to determine if nesting parameters and nest survival were limiting factors in Rio Grande wild turkey abundance in the Edwards Plateau. Regional differences in production suggest the cause of the decline in the southeastern portion of the Edwards Plateau could be associated with lower reproductive output and consequently, success. Regional differences in nest survival were not detected, thus not likely to cause differences in turkey abundance between regions.

The purpose of this research was to determine how predator control influences nest survival and changes in life history strategies of birds. All studies were conducted at two sites: one site had very little mammal control, while the other site is a 'mainland island' in which all introduced mammals were trapped or poisoned. Nest survival rates of introduced and native species were compared between the two sites by locating and monitoring nests of nine species. I found that mammalian predator control increased nest survival rates of both introduced and native species, but the incrase of nest survival was more pronounced in native species. The influence of predator control on the plasticity of life history strategies in introduced and native New Zealand birds was also examined. Some life history strategies (e.g. time spent incubating, frequency of visits to the nest) changed significantly in the area with predator control, while other life history traits (e.g. clutch size) did not vary between areas. I found that both introduced and native New Zealand birds changed a variety of life history traits and that the changes were likely a plastic response to the recent change in predator numbers. As it has been suggested that birds may become less responsive to mammals when predators are controlled, I tested the response of birds to a model of a feral cat. Birds in the predator control area were significantly less likely to recognise the cat model as a potential threat. This suggests the recognition of predators can be rapidly lost from a population. My research confirms that mammal control can increase nest success of native species, but reductions in predator numbers can also change a variety of life history traits and behaviours. As the removal of mammalian predators also appears to make birds less responsive to potential predators, it is important for continued mammalian control once management has begun. Otherwise, any reintroduction of predatory mammals into controlled sites would likely place such bird populations at greater risk as they would have behaviours suited to an environment with lowered nest predation risk.

Population surveys indicate a declining trend in abundance for the scoter genus at the continental level. Little is known about changes in life history traits responsible for the recent population decline of white-winged scoters (<i>Melanitta fusca deglandi</i>, hereafter scoters). Therefore, I studied nesting and duckling ecology of scoters at Redberry Lake, Saskatchewan, Canada during summers 2000-2001 when I found 198 nests. To examine nest-site selection, I compared habitat features between successful nests, failed nests, and random sites. Discriminant function analysis differentiated habitat features, measured at hatch, between successful nests, failed nests, and random sites; lateral (r = 0.65) and overhead (r = 0.35) concealment were microhabitat variables most correlated with canonical discriminant functions. I also modeled daily survival rate (DSR) of nests as a function of year, linear and quadratic trends with nest age, nest initiation date, and seven microhabitat variables. Nest survival from a time constant model (i.e., Mayfield nest success estimate) was 0.35 (95% CL: 0.27, 0.43). Estimates of nest success were lower than those measured at Redberry Lake in the 1970s and 1980s. In addition to nest survival increasing throughout the laying period and stabilizing during incubation, nest survival showed positive relationships with nest concealment and distance to water, and a negative relationship with distance to edge. Considering these factors, a model-averaged estimate of nest survival was 0.24 (95% CL: 0.09, 0.42). I conclude that scoters selected nesting habitat adaptively because (1) successful sites were more concealed than failed sites, (2) nest sites (i.e., successful and failed) had higher concealment than random sites, and (3) nest sites were on islands where success is greater than mainland. I then estimated duckling and brood survival with Cormack-Jolly-Seber models, implemented in Program Mark, from observations of 94 and 664 individually marked adult hens and ducklings, respectively. I tested hypotheses about duckling survival and (1) hatch date, (2) initial brood size at hatch, (3) duckling size and body condition at hatch, (4) offspring sex, (5) maternal female size and body condition at hatch, and (6) weather conditions within one week of hatching. Most mortality occurred during the first six days of duckling age. Variation in both duckling and brood survival were best modeled with effects of hatch date and initial brood size, while effects of female condition, female size, duckling size, and duckling condition were inconsistent. Survival probability clearly decreased with advancing hatch date and increased with larger initial brood sizes. Effects of weather and offspring sex in 2001, the only year such information was collected, suggested survival was negatively related to poor weather, but sex of ducklings, beyond size-related differences (i.e., sexual-size dimorphism), was unimportant. Estimates of survival to 28 days of age (30-day period), whether for ducklings (0.016, 0.021) or broods (0.084, 0.138) in 2000 or 2001, respectively, are the lowest of published studies and first for scoter broods in North America. I suspect intense gull predation shortly after hatch had the largest influence on duckling survival. Further research is needed to ascertain if low nesting success and duckling survival as well as other life cycle components are limiting scoter populations locally and throughout the rest of their breeding range.

Population surveys indicate a declining trend in abundance for the scoter genus at the continental level. Little is known about changes in life history traits responsible for the recent population decline of white-winged scoters (<i>Melanitta fusca deglandi</i>, hereafter scoters). Therefore, I studied nesting and duckling ecology of scoters at Redberry Lake, Saskatchewan, Canada during summers 2000-2001 when I found 198 nests. To examine nest-site selection, I compared habitat features between successful nests, failed nests, and random sites. Discriminant function analysis differentiated habitat features, measured at hatch, between successful nests, failed nests, and random sites; lateral (r = 0.65) and overhead (r = 0.35) concealment were microhabitat variables most correlated with canonical discriminant functions. I also modeled daily survival rate (DSR) of nests as a function of year, linear and quadratic trends with nest age, nest initiation date, and seven microhabitat variables. Nest survival from a time constant model (i.e., Mayfield nest success estimate) was 0.35 (95% CL: 0.27, 0.43). Estimates of nest success were lower than those measured at Redberry Lake in the 1970s and 1980s. In addition to nest survival increasing throughout the laying period and stabilizing during incubation, nest survival showed positive relationships with nest concealment and distance to water, and a negative relationship with distance to edge. Considering these factors, a model-averaged estimate of nest survival was 0.24 (95% CL: 0.09, 0.42). I conclude that scoters selected nesting habitat adaptively because (1) successful sites were more concealed than failed sites, (2) nest sites (i.e., successful and failed) had higher concealment than random sites, and (3) nest sites were on islands where success is greater than mainland. I then estimated duckling and brood survival with Cormack-Jolly-Seber models, implemented in Program Mark, from observations of 94 and 664 individually marked adult hens and ducklings, respectively. I tested hypotheses about duckling survival and (1) hatch date, (2) initial brood size at hatch, (3) duckling size and body condition at hatch, (4) offspring sex, (5) maternal female size and body condition at hatch, and (6) weather conditions within one week of hatching. Most mortality occurred during the first six days of duckling age. Variation in both duckling and brood survival were best modeled with effects of hatch date and initial brood size, while effects of female condition, female size, duckling size, and duckling condition were inconsistent. Survival probability clearly decreased with advancing hatch date and increased with larger initial brood sizes. Effects of weather and offspring sex in 2001, the only year such information was collected, suggested survival was negatively related to poor weather, but sex of ducklings, beyond size-related differences (i.e., sexual-size dimorphism), was unimportant. Estimates of survival to 28 days of age (30-day period), whether for ducklings (0.016, 0.021) or broods (0.084, 0.138) in 2000 or 2001, respectively, are the lowest of published studies and first for scoter broods in North America. I suspect intense gull predation shortly after hatch had the largest influence on duckling survival. Further research is needed to ascertain if low nesting success and duckling survival as well as other life cycle components are limiting scoter populations locally and throughout the rest of their breeding range.

Many factors affect the productivity of songbirds. Which vegetation types the birds inhabit, nest-site characteristics, and adult behavior at the nest may affect predation and parasitism frequencies, fecundity, and nest survival and fledgling survival. All of these metrics determine reproductive success of individuals and may influence population persistence, especially for threatened and endangered species. My research investigated factors that affected these metrics for endangered black-capped vireos (Vireo atricapilla). Shrubland is considered high quality vireo habitat, with woodland vegetation types considered marginal. I located and monitored nests, conducted nest behavior observations, recorded behavior and predation at nests using video cameras, and resighted fledglings in shrubland, oak-juniper woodland, and deciduous woodland during the 2008–2010 breeding seasons. I monitored 302 black-capped vireo nests in 259 territories and resighted 350 fledglings with unique color combinations. Apparent nest success, nest survival, success of first nest attempts, parasitism and predation frequency, and fecundity did not differ statistically among vegetation types. Parasitism frequency was nearly twice as high in shrubland (22 percent) than in either woodland (12 percent in each) and varied by year. Nest-site characteristics differed among vegetation types, but nest survival was affected only by nest height and year; nests placed higher from the ground and nest attempts in 2008 and 2009 had lower survival. Fledgling survival was not affected by vegetation type or proximity of the nest to oak-juniper woodland. Nest behavior was not affected by vegetation characteristics, though nest attentiveness during incubation increased as average cover from 0 to 2 m increased. Females spent 80 percent more time on nests during incubation and 250 percent more time on nests during the nestling stage than males, but visitation was similar for each sex. Overall, the probability of nest success improved as male participation increased. My results emphasize the importance of male participation in determining the outcome of nests for species exhibiting bi-parental care. Furthermore, woodland habitats previously considered marginal may be good quality habitat in areas with large populations of black-capped vireos. Recognizing woodlands as non-typical, yet still suitable, habitat will allow managers to incorporate these vegetation types into management plans and recommendations for landowner conservation incentive programs.

The purpose of this research was to determine how predator control influences nest survival and changes in life history strategies of birds. All studies were conducted at two sites: one site had very little mammal control, while the other site is a 'mainland island' in which all introduced mammals were trapped or poisoned. Nest survival rates of introduced and native species were compared between the two sites by locating and monitoring nests of nine species. I found that mammalian predator control increased nest survival rates of both introduced and native species, but the incrase of nest survival was more pronounced in native species. The influence of predator control on the plasticity of life history strategies in introduced and native New Zealand birds was also examined. Some life history strategies (e.g. time spent incubating, frequency of visits to the nest) changed significantly in the area with predator control, while other life history traits (e.g. clutch size) did not vary between areas. I found that both introduced and native New Zealand birds changed a variety of life history traits and that the changes were likely a plastic response to the recent change in predator numbers. As it has been suggested that birds may become less responsive to mammals when predators are controlled, I tested the response of birds to a model of a feral cat. Birds in the predator control area were significantly less likely to recognise the cat model as a potential threat. This suggests the recognition of predators can be rapidly lost from a population. My research confirms that mammal control can increase nest success of native species, but reductions in predator numbers can also change a variety of life history traits and behaviours. As the removal of mammalian predators also appears to make birds less responsive to potential predators, it is important for continued mammalian control once management has begun. Otherwise, any reintroduction of predatory mammals into controlled sites would likely place such bird populations at greater risk as they would have behaviours suited to an environment with lowered nest predation risk.

Master of Science / Department of Biology / Brett K. Sandercock / Grassland birds are declining throughout their native range. The Flint Hills of eastern Kansas and Oklahoma contain large tracts of tallgrass prairie, but intensification of agricultural practices may be contributing to ongoing population declines. Common rangeland management practices include annual burning coupled with heavy grazing by cattle. This system, known as intensive early stocking and burning, promotes homogeneous utilization of forage by cattle but may not provide habitat for some grassland bird species. Patch-burn grazing is an alternative management system that aims to restore heterogeneity on rangelands by recreating the fire-grazing interaction that would have historically occurred throughout the Great Plains. From 2011-2013, we examined responses of grassland birds to traditional rangeland management and patch-burn grazing by conducting vegetation surveys, line transect surveys, and nest monitoring on privately-owned pastures in Chase County and Greenwood County, Kansas. Vegetative heterogeneity was higher on patch-burned pastures, with unburned patches having higher visual obstruction and less bare ground. Densities of grassland birds differed by species and among habitat strata. Unburned patches on patch-burned pastures were associated with increased densities of Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna) and Grasshopper Sparrows (Ammodramus savannarum). Henslow’s Sparrows (A. henslowii) were only detected on patch-burned pastures. Nest survival of grassland songbirds was similar among management systems but varied by year. Probability of nest parasitism by Brown-headed Cowbirds (Molothrus ater) varied among years and between treatments for Dickcissels and Grasshopper Sparrows, with overall lower rates on burned areas and during drought years. For Dickcissels and Grasshopper Sparrows, there was a significant reduction in host clutch size between parasitized versus unparasitized nests. Overall, nest survival of grassland songbirds in managed rangelands was low. Patch-burn grazing improved rangeland conditions and provided habitat for more species of birds, but did not increase nest survival. Drought conditions in 2012 and 2013 may have influenced the results of this study, as many landowners were unable to burn as planned. Further study is needed to determine underlying factors driving variation in nest success and parasitism rates for grassland birds, particularly on private lands which make up the vast majority of remnant tallgrass prairies.