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- Creator:
- Mullin, Stephen M.
- Description:
- The Western Snowy Plover (Charadrius alexandrinus nivosus) is a federally listed threatened species as well as a state listed “species of special concern” in California. Accurate survival estimates are required to determine the best conservation strategies for threatened and endangered species. The population located in Humboldt County, CA was studied for five breeding seasons (2001-2005) and apparent survival for adult and juvenile plovers was estimated using program MARK. In addition, the population structure over this time period was described to determine the importance of immigration. The growth rate of the population was also estimated using the Pradel model and site specific birth and death rates to quantify the importance of immigration. Apparent survival for adult males (φ = 0.64) was greater than that for adult females (φ =0.57) while apparent survival for adults was greater than that for juveniles (φ = 0.30). The estimated annual growth rate using Pradel models demonstrated a stable population (λ = 0.99); however, this included both local recruitment and immigration as sources of new individuals. When calculated algebraically, based on estimates of local recruitment and survival, the growth rate demonstrated a declining population (λ = 0.71), clearly indicating the importance of immigration to the persistence of the population. Source/sink dynamics probably occur in the spatially disjunct populations of Snowy Plovers along the Pacific coast due to differences in habitat quality. However, the Humboldt County population should not be defined as a sink population across all breeding sites. At a smaller scale, sites along gravel bars of the Eel River were closely approaching the recruitment requirements to be classified as source areas whereas beach breeding sites were sink areas. Continued management activities, especially those that were designed to increase productivity (e.g. exclosures) are recommended. Because productivity is a major problem for plovers in this area and due to the success observed in Oregon, population control of predators should be considered. Increased management, such as curtailing the access of off-road vehicles along the more productive gravel bar areas during the breeding season is also recommended.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Sperry, David M.
- Description:
- I examined the effect of forest buffer width and nest site characteristics on the nest survival of forest birds on Prince of Wales Island, Alaska. During 2002 and 2003, a total of 164 nests of three closed cup (Chestnut-backed Chickadee (Parus rufescens), Red-breasted Sapsucker (Sphyrapicus ruber) and Winter Wren (Troglodytes troglodytes)) and four open cup (Pacific-slope Flycatcher (Empidonax difficilis), Hermit Thrush (Cartharus guttatus), Swainson’s Thrush (Cartharus ustulatus) and Varied Thrush (Ixoreus naevius)) species were monitored within forested buffers along the coastline. I modeled daily survival rate (DSR) of closed (DSR = 0.989) and open (DSR = 0.982) cup nesting species independently using variables at two spatial scales. For closed cup nests the model best describing variation in DSR included height of nest and species. Nests located higher from the ground had better nest success. Variation in DSR of open cup nests was best explained by species. Pacific-slope Flycatcher nests had the highest success (87%) whereas Varied Thrush nests had the lowest (21%). DSR of Hermit Thrush nests, the only species for which I had adequate data to analyze separately, was related to distance to the coastline. Species with low DSR had similar nest site characteristics including diameter of nesting substrate and average percentage concealment of nest. However, these nest site characteristics alone do not determine DSR of the species evaluated in my study. Width of coastal forested buffers appears to have a negligible effect on DSR, however, some species exhibited low DSR within the buffers and further examination of these species is recommended.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Wagner, Marlene A.
- Description:
- Conservation of a keystone species requires knowledge of habitat use across the species’ range. The factors that influence habitat selection by Red-breasted Sapsucker (Sphyrapicus ruber) in the temperate rainforests of southeast Alaska are poorly understood. I examined habitat selection of this keystone species during the breeding season in 2008 and 2009. I quantified the structural characteristics of sapwell trees and compared them to trees without sapwells, and I located nests to describe nest trees and compare characteristics of used and available nest trees and nest sites using model selection techniques. Sapsuckers selected trees for building sapwells that were intermediate in size, had high bark furrow depth, and had a greater incidence of conks and dwarf mistletoe. Nesting Sapsuckers did not show bias for cavity orientation and nest trees were predicted primarily by size and the presence of fungal infection at intermediate stages of decay. Nest sites contained a lower volume of trees, higher DBH, increased incidence of fungal infection, and older decay classes of coarse woody debris than available sites. These findings suggest that during the breeding season, Red-breasted Sapsuckers select habitats with attributes characteristic of the full range of old-growth forest succession, and they therefore may need substantial forest structural diversity for their feeding and nesting activities. The results from this study provide information that can be used to identify habitat for breeding and foraging Red-breasted Sapsuckers. Due to their status as a keystone species, maintaining adequate breeding habitat in southeast Alaska is important not only to the local population of Red-breasted Sapsuckers, but for other species as well.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Elkinton, Elizabeth
- Description:
- Black brant (Branta bernicla nigricans) breed in the Arctic and sub-Arctic in spring, a time when food resources are limited. They rely largely on energy stores, acquired at staging sites, for migration and to support egg laying and incubation. In California, Humboldt Bay is the most important staging site for black brant due to abundant eelgrass (Zostera marina). Previously, it was thought that the birds’ access to eelgrass was limited to periods of low-tide when plants were within reach. I tested this assumption by quantifying foraging behavior and intake rates throughout the tidal cycle. I also examined factors contributing to the occurrence of detached floating eelgrass leaves that became available to the birds at higher tides. During winter and spring periods (January - April 2011) black brant at Humboldt Bay foraged directly on eelgrass beds during low tides and continued feeding on drifting leaves during higher tides. They switched from bed-feeding to drift-feeding at a tide height of approximately 0.9 m. Forty-eight percent of flock members typically fed when eelgrass beds were reachable during low tides and 24% of birds fed on drifting eelgrass during higher tides. The proportion of birds bed-feeding was not influence by tide height or month, whereas the proportion of drift-feeding individuals decreased significantly with increasing tide heights in January and February but increased with increasing tide heights in March and April. The amount of drifting eelgrass increased significantly with higher maximum wind speeds, greater tidal range during the previous 24 hrs, and a greater number of brant present on the bay. Intake rates were significantly higher when the birds fed directly on eelgrass beds (0.21 g min-1) than on drifting eelgrass (0.16 g min-1). Mean intake rate achieved during bed-feeding was highest in January and February combined (0.23 g min-1) and lowest in April (0.16 g min-1). Intake rates achieved on drifting eelgrass decreased as tide height increased beyond 0.9 m. Paired adults had the lowest intake rates during drift-feeding (0.15 g min-1) and unpaired adults had the highest intake rates (0.18 g min-1). This study will inform management of spring staging sites and future projections of the carrying capacity of Humboldt Bay for staging brant.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Zalewski, Jennifer Terry
- Description:
- Baseline levels of stress hormones are necessary for maintaining physical homeostasis in mammals. Excessive amounts of stress, however, can cause serious pathologies. Chronic effects of stress include increased susceptibility to infectious diseases due to suppressed functioning of the immune system, diminished growth rates, protein loss, neuron cell death and inhibited reproduction. A myriad of external factors including unhealthy, human-induced environmental conditions as well as naturally occurring fluctuations in resources, habitat attributes, health and sociality have the potential to cause deleterious changes in stress response in mammals. I validated a non-invasive enzyme immunoassay (EIA) for use in river otters (Lontra canadensis) and used these techniques to evaluate stress hormone concentrations extracted from feces of northern river otters in coastal northern California. I assessed how stress was correlated with anthropogenic and socioecological factors. Fecal samples were collected from river otter latrines at seven coastal river otter activity centers. I evaluated the relative importance of several ecological variables including location (as a surrogate for river otter activity center contamination level), water turbidity, water temperature variation, diet, parasite presence and scat grouping size (as an index of conspecific interactions or group size) as predictors of cortisol stress hormone concentrations of the river otters using AICc and multiple regression. The best fit model included location, turbidity, diet and parasite presence which explained 23% of the variation in stress response observed in this coastal river otter population. When the variables were assigned to one of two a priori models, anthropogenically influenced environmental conditions (location and turbidity) or socioecological variables (diet and parasite presence) and compared using multiple regression, the socioecological variables contributed more than twice as much to variations in stress levels than the anthropogenic variables. These results suggest that a complex combination of human induced and naturally occurring pressures are associated with physiological stress levels in this population of river otters. Indirect measures of river otter population health gained utilizing these techniques can be useful to help establish the ecological status of aquatic ecosystems that may affect many other wildlife species, as well as nearby human communities.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Campos, Brent R.
- Description:
- Ecosystem services provided by mobile organisms are influenced by the availability of the habitats those organisms select. On Jamaica’s coffee farms, birds serve as agents of biological control of the coffee berry borer (Hypothenemus hampei), coffee’s most devastating pest worldwide. The black-throated blue warbler (Setophaga caerulescens) is likely the foremost avian predator of coffee berry borer in Jamaica. Using radio telemetry I investigated habitat selection, habitat use, and home range size of black-throated blue warblers on two coffee farms with different vegetative complexity in western Jamaica. I developed individual-optimized and population-optimized models of habitat selection using four variables describing coffee habitat. Despite considerable variation in habitat selection among individual birds, population-based models demonstrated that birds selected home ranges in areas of high canopy cover and coffee crop cover, and at intermediate distances from uncultivated habitat on both farms. Within home ranges, birds exhibited weak selection for increasing canopy cover. Home range size was correlated with the proportion of the locations in coffee habitat and the availability of canopy cover and noncultivated habitat within the home range. However, the direction of several of these relationships differed between farms. Birds at the farm with higher vegetation complexity spent, on average, 63% more time in coffee habitat and 60% more time in the coffee crop layer where birds are most likely to encounter the coffee berry borer. I conclude that substantial differences in physiognomy between farms translated into the pattern of differential use of the coffee farm habitat relative to peripheral habitats. These results suggest that managing for the habitat attributes selected by warblers in this study can have measurable impacts on bird use of coffee farms in Jamaica with potential implications for bird-provisioned ecosystem services.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Kalinowski, Ryan S.
- Description:
- The great gray owl (Strix nebulosa) has been a state endangered species in California since 1980 because of low population size. Annual productivity of the great gray owl in California is thought to be largely dependent on vole (Microtus spp.) and pocket gopher (Thomomys spp., hereafter gopher) abundance, yet the factors influencing these prey populations have not been thoroughly investigated. The abundance of voles and gophers has been influenced by vegetation and cattle grazing in other regions, and many meadows are grazed within the breeding range of the great gray owl in the Sierra Nevada Mountains of California. Therefore I evaluated the influence of vegetation and cattle grazing on great gray owl foraging habitat by quantifying vole abundance, gopher abundance, and vegetative conditions in grazed and ungrazed meadows during owl nestling and fledgling stages. I surveyed 17 grazed and 15 ungrazed meadow sites in 2010, and 19 grazed and 19 ungrazed meadow sites in 2011. I found that vole presence was positively associated with plant sward height and corn lily (Veratrum californicum) dominance; vole abundance was weakly negatively associated with cattle grazing. Gopher abundance was negatively associated with site wetness, and positively associated with stem density, the frequency of forb presence, cattle grazing, and the dominance of corn lily. When managing meadows for great gray owl conservation, cattle grazing and vegetation should be monitored to accommodate the habitat relationships of both voles and gophers. Management of owl prey may be most efficient by prioritizing wet meadow sites for voles since gophers were not likely to be abundant in wet sites, and vole abundance has been correlated with moist soils in other studies. Therefore particularly in areas with moist soils, I recommend maintaining plant sward height commensurate with the habitat relationships of voles found in this study.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Nelson, Zachary J.
- Description:
- I examined evidence that conspecific attraction influenced the spatial distributions of Western Snowy Plovers (Charadrius alexandrinus nivosus) breeding in coastal northern California over 6 years. Most (85%) yearlings and immigrants first nested in the study area at occupied sites. This produced a significant positive correlation between the abundance of experienced plovers and recruitment of naive plovers at 16 breeding sites. At the site with the most breeding plovers, nests were clustered within suitable habitat. Spatial variation in habitat features (i.e., beach width, debris, vegetation cover), and indices of predators and human activity explained less of this aggregated pattern than variation in nest density in previous years. Plovers often (males: 86%, females: 67%) nested in the same areas in consecutive years. Moreover, at the time they initiated clutches, most plovers nested closer to conspecifics than expected by chance. These results suggest that the likelihood of success of management actions (i.e., habitat restoration) to recover the population of this threatened species may hinge on social stimulation to encourage plovers to (re)colonize historical breeding sites. And, if plovers cue on conspecifics to assess the quality of breeding sites, then the use of predator exclosures to increase nest success could mislead naïve individuals into settling in sub-optimal habitat.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Sholty, Kathleen E.
- Description:
- Borrelia burgdorferi (Lyme disease) and Anaplasma phagocytophilum (granulocytic anaplasmosis) are two tick-borne pathogens in the western United States. The ecology of both pathogens varies among areas in northwestern California due to multiple rodent hosts, diverse landscapes, and multiple genotypes within B. burgdorferi sensu lato and A. phagocytophilum sensu lato. I documented prevalence of both pathogens in Del Norte, Humboldt, and Mendocino counties and identified associations among hosts and strain types. Rodents were live-trapped between October 2005 and October 2013. Ear-punch biopsies and whole blood samples were collected to determine the presence of B. burgdorferi sensu lato and A. phagocytophilum sensu lato via polymerase chain reaction (PCR), and positive samples were sequenced to determine genotypes. The program SaTScan was used to evaluate spatial clustering of genotypes. Overall prevalence of B. burgdorferi sensu lato and A. phagocytophilum sensu lato between 2005-2013 was 33.8% and 18.9%, respectively. The top models predicting genotypes of B. burgdorferi were ranked via a corrected Akaike’s Information Criterion (AICc) value and included the variables “Host,” “Habitat,” and the interaction term “Host*Season,” and the top model predicting genotypes of A. phagocytophilum included the single variable “Host.” Dusky-footed woodrats (Neotoma fuscipes) had a higher prevalence of B. bissettii than B. burgdorferi sensu stricto and both N. fuscipes and sciurids had a higher prevalence of the DU1 strain than A. phagocytophilum sensu stricto. SaTScan detected clusters for both DU1 and B. bissettii at Del Norte study area (P<0.001 and P=0.01, respectively). Another cluster was found for DU1 at North Humboldt study area (P=0.001). A greater proportion of captured individuals found within each cluster were N. fuscipes. The results suggest a relationship between strain type and rodent host. Because B. burgdorferi sensu stricto and A. phagocytophilum sensu stricto are more likely to be infective to humans, these results may help identify risks for transmission among humans living and recreating in northwestern California.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife
- Creator:
- Brown, Gregory G.
- Description:
- Previous research suggests that Varied thrushes (Ixoreus naevius) in redwood forests (Sequoia sempervirens) are sensitive to forest edges and are unlikely to breed in small forest fragments. Food abundance is likely to vary at the forest edge, and has been linked to habitat use and edge avoidance in some other forest-interior passerines, particularly other ground foraging insectivores. To determine the degree to which Varied thrushes avoid forest edges, and how this might be influenced by food abundance, I monitored third-order habitat selection of individual birds using radio telemetry, and sampled relative abundance of ground-dwelling invertebrates with pitfall traps across edge gradients in redwood forests of north coastal California. In addition, I measured vegetation structure and other habitat variables that may vary near forest edges and influence Varied thrush habitat use either directly or through effects on invertebrate distribution. I predicted that Varied thrush habitat use would be associated with invertebrate abundance, with both decreasing in proximity to forest edges, and increasing in proximity to streams. Of the 10 Varied thrushes monitored, only two used locations significantly farther from the edge than expected, and overall there was no clear pattern of edge avoidance or preference for streams in the birds studied. Invertebrate abundance was greater near forest edges, contrary to predictions, and was not affected by distance to streams or any of the habitat variables measured. Previous research indicating edge avoidance by Varied thrushes did not distinguish between second-order and third-order habitat selection. Since neither third-order edge avoidance nor edge effects on food abundance were apparent in this study, future research should focus on other potential edge effects at larger scales. The lack of evidence for edge effects also suggests that other mechanisms, such as conspecific attraction, may account for the absence of Varied thrushes from small redwood forest fragments.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Wildlife