VTechWorks Repository :: Browsing by Author "Fraser, James D."

Browsing by Author "Fraser, James D."

Now showing 1 - 20 of 91

Application of Bayesian robust design model to assess the impacts of a hurricane on shorebird demography
Gibson, Daniel; Riecke, Thomas V.; Keyes, Tim; Depkin, Chris; Fraser, James D.; Catlin, Daniel H. (Ecological Society of America, 2018-08)
The increasing use of Bayesian inference in population demography requires rapid advancements in modeling frameworks to approach the rigor and flexibility of the current suite of maximum-likelihood models. We developed an unbiased, Jolly-Seber robust design (JSRD) model that is both accessible and generalizable in a Bayesian hierarchical multistate framework. We integrated band and age-classification data to estimate site entry, temporary emigration, and apparent survival rates, as well as estimate age-class specific abundances. The complete model parameterization is provided in the Appendix S1, as well as tools for simulating capture histories and an assessment of model fit. We applied this model to determine whether these demographic processes in non-breeding population of American oystercatchers (Haematopus palliatus) were affected by a major hurricane event (Hurricane Matthew) in coastal Georgia. The JSRD model was demonstrably unbiased at relatively small sample sizes, and the majority of parameters were identifiable in the fully saturated model parameterization. In the model application, we found that Hurricane Matthew temporarily altered local population abundances of American oystercatchers through increased movements of individuals into and out of the observable population, but mortality rates were largely unaffected. Together, our results suggest that American oystercatchers were largely able to avoid the immediate demographic consequences (i.e., reduced survival) of Hurricane Matthew. Integrating age and band ratios from survey data allowed for more descriptive and potentially less biased estimates of age-specific abundance, relative to estimates generated solely from either mark-resight or survey data.
Arthropod assemblages on longleaf pines: a possible link between the red-cockaded woodpecker and groundcover vegetation
Taylor, Thomas Brandon (Virginia Tech, 2003-02-26)
Little is known about arthropod communities inhabiting longleaf pines in the southeastern United States. This information is of particular importance because arthropods serve as the food base for the federally endangered red-cockaded woodpecker (RCW). In a recent study, this arthropod community has been suggested to be the mechanism by which RCW reproductive success is linked to the groundcover composition of the forest (which is a reflection of the forest's fire history). This is possible because it has been shown that much of the arthropod community found on longleaf pines originates from the forest floor. If the arthropod community is the link between the ground cover and the RCWs' reproductive success then higher amounts of arthropods should be found in areas with groundcover that is indicative of frequent burning. I conducted a one year study at three sites containing RCWs to determine whether the ground cover of the forest influences the abundance and mass of the arthropod communities on longleaf pines. I focused on impacts of groundcover on arthropods by controlling for tree species, tree age, soil type, hardwood midstory density, and overstory basal area. My results show that arthropod biomass was positively and significantly correlated to the percent coverage of herbaceous and graminoid vegetation and was negatively and significantly correlated to the percent coverage of woody vegetation. Arthropod biomass and abundance was also observed to vary seasonally with a peak occurring during spring and summer. Additionally, prescribed fire was not found to have a negative short-term impact on arthropod biomass.
Assessing the Effects of Sea-Level Rise on Piping Plover (Charadrius Melodus) Nesting Habitat, and the Ecology of a Key Mammalian Shorebird Predator, on Assateague Island
Gieder, Katherina Dominique (Virginia Tech, 2015-09-02)
The piping plover (Charadrius melodus) is a federally-listed shorebird that nests on barrier islands along the U.S. Atlantic Coast and is highly vulnerable to habitat change and predation. We have addressed these two threats by 1) developing and implementing a linked model system that predicts future change to piping plover habitat resulting from sea-level rise and beach management efforts by joining dynamic models of sea-level rise, shoreline change, island geomorphology and piping plover nest habitat suitability, and 2) quantifying occupancy and movement of the red fox (Vulpes vulpes), a key shorebird predator at Assateague Island, Maryland and Virginia. We constructed and tested a model that links changes in geomorphological characteristics to piping plover nesting habitat suitability. We then linked this model to larger scale shoreline change resulting from sea level rise and storms. Using this linked model to forecast future sea-level rise and beach management efforts, we found that modest sea-level rise rates (3 mm and 4.1 mm/yr; similar to current rates) may increase suitable piping plover nesting habitat area in 50-100 years and some beach management strategies (beach nourishment and artificial dune modifications) also influence habitat availability. Our development and implementation of this tool to predict change in piping plover habitat suitability provides a vital starting point for predicting how plover nesting habitat will change in a context of planned human modifications intended to address climate change-related threats. Our findings regarding red fox occupancy and movement complement the use of this model for planning future management actions by providing vital information on the effects of certain predator management activities and habitat use of a key mammalian predator, the red fox, for shorebirds along the U.S. Atlantic Coast. Overall, we found that 1) red fox occupancy was strongly tied to eastern cottontail (Sylvilagus floridanus) trap success, increasing sharply with increased eastern cottontail trap success, 2) red fox occupancy did not change in response to an intensive eradication program, and 3) red foxes in our study area generally moved little between camera stations spaced 300 m from each other, but may move large distances (> 6km) at times, likely to occupy new territory available after lethal control efforts. Our findings have important ramifications for the sustainability of long-term predator removal programs and our understanding of future habitat change on the red fox. For example how vegetation changes affect eastern cottontails, how resulting fluctuations in eastern cottontails affect red fox occupancy, and how consequential changes in red fox occupancy affect plover breeding productivity. Our predictive model combined with these predator findings will allow wildlife managers to better plan and implement effective management actions for piping plovers in response to the multiple stressors of SLR-induced habitat change and predation.
An Assessment of the Biological and Socioeconomic Feasibility of Elk Restoration in Virginia
McClafferty, Julie A. (Virginia Tech, 2000-02-09)
The biological and socioeconomic feasibility of restoring elk (Cervus elaphus) to Virginia was assessed. Biological feasibility was determined by evaluating habitat suitability for elk while considering potential impacts of elk on existing fauna and flora in Virginia. Suitability was assessed by creating a habitat suitability index (HSI) model that measured the availability and accessibility of open foraging areas and forested cover areas, the availability of permanent water sources, and the degree of fragmentation by roads. Eight areas were identified as potential elk habitat: 1 in Southwest Virginia, 4 in the Shenandoah Mountains (Shenandoah, Highland, Big Meadows, Peaks of Otter), and 3 in the Southern Piedmont (Danville, Brookneal, Rehobeth). The highest potentials for supporting an elk herd were found in the Highland and Big Meadows study areas, medium biological feasibilities were found in the Southwest, Shenandoah, and Brookneal study areas, and low biological feasibilities were found in the Peaks of Otter, Danville, and Rehobeth study areas. A restored elk herd could negatively affect indigenous fauna and flora by changing the structure and diversity of existing forested ecosystems, but impacts can be minimized by maintaining elk populations at or below cultural carrying capacity. The introduction of diseases during restoration and possible transmission of those diseases from elk to humans, livestock, and other wildlife also are concerns, but these issues can be addressed by following a risk minimization protocol. Socioeconomic feasibility was assessed with a statewide mail survey of Virginia residents, 4 regional stakeholder workshops, an analysis of economic costs and benefits associated with elk restoration, and an assessment of the risks of elk-human conflicts in each of the 8 study areas. Overall, most (61%) respondents agreed that elk restoration would be good for Virginia. However, the low response rate (30%) and low confidence among respondents (49%) in their knowledge about elk indicated that most residents do not have the interest and/or necessary information to form a definitive opinion. Residents believe that the greatest benefits of restoration would be the value-based and indirect ecological benefits, such as returning an extirpated species to its native range, whereas the greatest perceived costs were the economic impacts to property, crop depredation, and public safety hazards. In contrast, local stakeholder representatives identified economic returns from increased tourism due to the presence of elk and the creation of new recreational opportunities as the most anticipated benefits; important concerns were the potential for property damage by elk, the potential impacts on local ecosystems, and the costs of implementing and administering an elk restoration program and subsequent elk management. Proposed resolutions for these issues varied by region. Representatives from the Southwest and northern Shenandoah Mountain (Shenandoah and Big Meadows study site) Regions preferred not to restore elk, whereas those from the southern Shenandoah Mountain (Highland and Peaks of Otter study site) and the Southern Piedmont Regions preferred to start out small with a carefully controlled and monitored "experimental" population. Economic benefits of elk restoration, as determined through analysis of data from other eastern states currently managing elk populations, are associated with tourism and the revenues brought to the community during elk hunting seasons, whereas economic costs are associated with crop damage, elk-vehicle collisions, and the administrative costs of managing an elk herd. Although the initial costs of transporting, releasing, and monitoring a founder population likely will exceed immediate benefits, once an elk population is established, benefits likely will exceed costs. However, an equitable distribution of costs and benefits must be devised so that the individuals who bear the costs are afforded a comparable or greater set of benefits. Risk of landowner elk-conflicts was examined by comparing human population densities and growth rates, percent private versus public land, and agricultural trends across the 8 study areas. Highest risk for elk-human conflicts was identified in the Southern Piedmont Region and in the Shenandoah study site, risk was moderate in the Southwest, Big Meadows, and Peaks of Otter study sites, and risk in the Highland study site was low. Overall, the Highland study site had the highest feasibility for elk restoration of all study areas examined; the Big Meadows and Southwest study sites both demonstrated moderate feasibility. Restoration in these areas is possible so long as management objectives remain flexible, plans are made in advance to address potential concerns, and the public is involved in the decision-making processes both before and after elk are released.
Bald eagle distribution, abundance, roost use and response to human activity on the northern Chesapeake Bay, Maryland
Buehler, David A. (Virginia Tech, 1990-01-11)
I studied bald eagle (Haliaeetus leucocephalus) distribution, abundance, roost use and response to human activity on the northern Chesapeake Bay from 1984-89. The eagle population consisted of Chesapeake breeding eagles, Chesapeake nonbreeding eagles, northern-origin eagles and southern-origin eagles; changes in overall eagle distribution and abundance reflected the net changes in these 4 groups. Breeding territories on the northern Chesapeake increased from 12 to 28 from 1984 to 1988. Breeding eagles were resident all year, always ~7 km from the nest. Chesapeake nonbreeding eagles moved throughout most of the bay, but rarely left it (~5% of the radio-tagged eagles were off the bay during any month). Northern eagles migrated into the bay in late fall (x = 21 December! n = 7! range = 61 days) and departed in early spring (x = 27 March, n = 14, range = 43 days). Southern eagles arrived on the northern bay throughout April-August (x = 6 June, n = 11, range = 94 days) and departed from June - October (x = 3 September, n = 22, range = 119 days). Northern Chesapeake eagle abundance peaked twice annually; in winter (261 eagles, December 1987), driven by the presence of northern eagles, and in summer (604 eagles, August 1988), driven by the presence of southern birds. Of 1,117 radio-tagged eagle locations, only 55 (4.90/0) occurred in human-developed habitat, which composed 27.7% of 1,442 km2 of potential eagle habitat on the northern Chesapeake Bay (P < 0.001). During 36 aerial shoreline surveys, eagles were observed on only 111 of 700 (15.9%) 250-m shoreline segments that had development within 100 m, whereas eagles were observed on 312 of 859 (36.30/0) segments when development was absent (P < 0.001). On average, eagles were observed on 1.0 segment/survey that had coincident pedestrian use within 500 m, compared to 3.6 segments/survey expected if eagles and pedestrians were distributed along the shoreline independently (n = 34 surveys, P < 0.001).
Bald eagle habitat use on B. Everett Jordan Lake and Falls Lake, North Carolina
Chester, Dennis Nathan (Virginia Tech, 1988-06-30)
I examined the roosting and perching habitat preferences of a nonbreeding population of bald eagles in North Carolina during 1986 and 1987. I characterized roosting habitat at 2 scales; those of forest stands and individual roost trees. Eagles chose roost areas that were less dense, had less canopy cover, were closer to forest edges, and had larger trees than random forest areas (P < 0.05). Within roost areas eagles choose trees that were larger (height and dbh) than random trees. Additionally. eagles roosting at the Morgan Creek roost preferred dead hardwoods close to the forest edge and eagles at the Mason Point roost preferred trees farther from a frequently used dirt road within the roost. Suitable perch trees were the most important attribute of perching habitat. Eagles preferred loblolly pines and trees with leafless crowns (P < 0.05), which relates to their accessible crown structures. Perch trees were larger (height and dbh, P < 0.05) than adjacent trees along the shore. Eagles utilized the bottom of tree crowns during summer but used treetops during fall and winter. I found no evidence that eagles selected perches in relation to forest stand characteristics within 20 m of perch trees, forest cover types in 1 ha blocks surrounding perches, or habitat disturbances. Management recommendations include techniques to enhance bald eagle habitat on the study area. Primary emphasis should be toward managing for roosting habitat because of its apparent scarcity. Perch trees are plentiful but long-term management is desirable. Future nesting seems likely and management techniques for potential nesting habitat are suggested.
Blood characteristics as predictors of reproductive success in quail species exposed to DDT
Sullivan, Joseph P. (Virginia Tech, 1991)
Present sampling techniques are not capable of assessing both contamination with an organochlorine chemical and reproductive success without the need for removing individuals from that population. Experiments were performed to evaluate vitellogenin, vitamin A, and vitamin E as biomarkers of contamination with DDT, an organochlorine pesticide, and reproductive success in Japanese quail (Coturnix coturnix japonica) or northern bobwhites (Colinus virginianus). The utility of vitellogenin as a biomarker in northern bobwhites was investigated. Female northern bobwhites were dosed with 0, 1, 10, or 100 μg DDT/g body weight via corn oil intubation. The females were induced to lay eggs by providing the proper daylength, and number of eggs laid was monitored. No differences were found for number of eggs laid, egg morphology, or plasma concentration of vitellogenin among dose groups. Dietary supplementation and corn oil intubation were evaluated as alternative dosing techniques because handling involved with intubation may have caused decreased egg production in all treatment groups in the first experiment. Nonlaying female bobwhites were dosed with 0 μg DDT, 25 μg DDT/g food, or 25 μg/g body weight (intubation). Bobwhites receiving DDT via intubation accumulated more DDT in brains and livers than did bobwhites receiving DDT via their diet. The two techniques were found not to be equivalent. Vitamins A and E were investigated as biomarkers of DDT contamination and reproductive success in Japanese quail. Female Japanese quail were given 0, 1, 10, or 25 μg dietary DDT. Significant differences were found among dose groups for reproductive success (number of eggs showing embryonic development), and for plasma concentrations of vitamin A. Concentrations of vitamin E were not measurable. Correlation and regression analyses failed to show a relationship between reproduction and vitamin A concentrations. Vitamins A and E also were investigated as biomarkers in northern bobwhites. Female bobwhites were given 0, 1, 10, or 25 ppm dietary DDT. No significant differences were found among dose groups for reproductive success or for concentrations of either vitamin A or vitamin E. Correlation and regression analyses again failed to show any relationship between reproduction and plasma concentrations of vitamins A or E. During each experiment, concentrations of DDT and its metabolites were measured. DDE/DDT ratios in livers, a means of estimating liver enzyme induction, were calculated. The DDE/DDT ratios in livers of Japanese quail and northern bobwhites were found to be markedly different. More work needs to be done to better evaluate the relationship between differences in enzyme induction and reproductive success among different species.
Building a Predictive Model of Delmarva Fox Squirrel (Sciurus niger cinereus) Occurrence Using Infrared Photomonitors
Morris, Charisa Maria (Virginia Tech, 2006-09-11)
Habitat modeling can assist in managing potentially widespread but poorly known biological resources such as the federally endangered Delmarva fox squirrel (DFS; Sciurus niger cinereus). The ability to predict or identify suitable habitat is a necessary component of this species' recovery. Habitat identification is also an important consideration when evaluating impacts of land development on this species distribution, which is limited to the Delmarva Peninsula. The goal of this study was to build a predictive model of DFS occurrence that can be used towards the effective management of this species. I developed 5 a'priori global models to predict DFS occurrence based on literature review, past models, and professional experience. I used infrared photomonitors to document habitat use of Delmarva fox squirrels at 27 of 86 sites in the southern Maryland portion of the Delmarva Peninsula. All data were collected on the U.S. Fish and Wildlife Service Chesapeake Marshlands National Wildlife Refuge in Dorchester County, Maryland. Preliminary analyses of 27 DFS present (P) and 59 DFS absent (A) sites suggested that DFS use in my study area was significantly (Wilcoxon Mann-Whitney, P < 0.10) correlated with tree stems > 50 cm dbh/ha (Pmean = 16 + 3.8, Amean = 8+ 2.2), tree stems > 40 cm dbh/ha (Pmean = 49 + 8.1, Amean = 33 + 5.5), understory height (Pmean = 11 m + 0.8, Amean = 9 m + 0.5), overstory canopy height (Pmean = 31 m + 0.6, Amean = 28 m + 0.6), percent overstory cover (Pmean = 82 + 3.9, Amean = 73 + 3.1), shrub stems/ha (Pmean = 8068 + 3218, Amean = 11,119 + 2189), and distance from agricultural fields (Pmean = 964 m + 10, Amean = 1308 m + 103). Chi-square analysis indicated a correlation with shrub evenness (observed on 7% of DFS present sites and 21% of DFS absent sites). Using logistic regression and the Information Theoretic approach, I developed 7 model sets (5 a priori and 2 post hoc) to predict the probability of Delmarva fox squirrel habitat use as a function of micro- and macro-habitat characteristics. Of over 200 total model arrays tested, the model that fit the statistical, biological, and pragmatic criteria postulated was a post hoc integrated model: DFS use = percent overstory cover + shrub evenness + overstory canopy height. This model was determined to be the best of its subset (wi = 0.54), had a high percent concordance (>75%), a significant likelihood ratio (P = 0.0015), and the lowest AICc value (98.3) observed. Employing this predictive model of Delmarva fox squirrel occurrence can benefit recovery and consultation processes by facilitating systematic rangewide survey efforts and simplifying site screenings.
Contrasting long-term population trends of beach-nesting shorebirds under shared environmental pressures
Kwon, Eunbi; Robinson, Samantha G.; Weithman, Chelsea E.; Catlin, Daniel H.; Karpanty, Sarah M.; Altman, Jon; Simons, Theodore R.; Fraser, James D. (Elsevier, 2021-08-01)
Identifying the drivers of long-term population change is a key goal of ecological studies. It is complicated by extrinsic and intrinsic factors that may covary with time and/or operate on a time lag. For migratory shorebirds that breed on the barrier islands of eastern North America, populations may be limited by the anthropogenic, climatic, biological environments they encounter throughout the annual cycle. Using three-decades (1989–2017) of breeding monitoring data collected by the National Park Service at two national seashores in North Carolina (Hatteras and Lookout), we examined the potential drivers of nesting piping plover (Charadrius melodus) and American oystercatcher (Haematopus palliates) populations. Hatteras had five times more annual visitors than Lookout, and our modelling revealed a strong negative relationship between the population size of breeding plovers and human activity and a positive relationship with protection efforts aimed at reducing disturbance. Breeding and wintering climatic conditions, population productivity, and nesting habitat availability showed only weak effects. Thus, a decade-long decline in plover numbers at both seashores starting in the mid-90s reversed as the parks' visitor counts decreased and stricter protections from potential disturbance were implemented. However, the two sympatric populations of oystercatchers showed the opposite population trends from each other at the neighboring seashores, increasing only on Lookout after a hurricane improved habitat and subsequently the reproductive output. Our study suggests a strong relationship between the anthropogenic environment and the population trend of a threatened species and, simultaneously, the important role of stochastic events in shaping populations of long-lived shorebird species.
Day-roosting Social Ecology of the Northern Long-eared Bat (Myotis septentrionalis) and the Endangered Indiana Bat (Myotis sodalis)
Silvis, Alexander (Virginia Tech, 2014-12-08)
Day-roost use by northern long-eared bat (Myotis septentrionalis) maternity colonies on the Fort Knox military reservation, Kentucky, USA, resulted in formation of non-random networks of roosts that exhibited a trend toward centralization. Centralization of day-roost networks was reflected in the social structure of colonies, which were characterized by dense associations among individuals within colonies. Social structure varied among colonies and appeared to be related to reproductive condition; colonies exhibited greater cohesiveness during parturition and lactation. Northern long-eared bat maternity colonies appeared to be exclusive, occupying distinct roosting areas with one or several areas receiving intense use. Day-roost removal simulations suggested a linear relationship between colony fragmentation and roost loss, and that loss of >20% of roosts is required to initiate colony fragmentation. Experimental hierarchical removal of day-roosts yielded results consistent with simulations, as removal of the single most-central (primary) roost had no impact on colony fragmentation, whereas removal of 24% of less-central (secondary) roosts resulted in partial network fragmentation. Patterns of colony day-roost and space use were similar pre- and post-removal treatments. Day-roost removal did not alter the number of roosts used by individual bats, but distances moved between roosts were greater in the secondary roost-removal treatment group. Day-roost characteristics largely were consistent pre-post treatment for both treatment groups. Historical data from an Indiana bat (Myotis sodalis) maternity colony revealed that this species also exhibits a non-random social assorting dynamic. Non-random social assortment resulted in a closely connected centralized network of day-roosts. Individuals within the Indiana bat maternity colony exhibited close social connections with colony members, but subgroups likely existed within the colony. Indiana bat day-roosting ecology appears flexible, as patterns of roost and space use differed substantially between years. Development of specific, but tactical, management approaches for individual colonies of both northern long-eared and Indiana bats may be possible. Such approaches would allow land managers to manage for both northern long-eared bat habitat and other objectives. However, the nature of targeted management approaches employed likely will depend on the unique forest context and dynamic within which individual colonies reside.
Demography of a declining Dunlin (Calidris alpina arcticola): influences on adult survival and mate fidelity of an Arctic-breeding migratory shorebird
Hermanns, Lindsay F. (Virginia Tech, 2024-03-15)
Understanding what restricts vital rates is crucial in conservation efforts. For migratory birds, vital rates can be impacted by conditions experienced throughout the year. Migratory shorebird populations are rapidly declining, including populations of Dunlin (Calidris alpina arcticola), an Arctic-breeding shorebird. Prior adult survival estimates (0.41– 0.60) appeared insufficient to maintain a stationary population, however, it was unclear if estimates were reflective of bias or a real survival signal. Additionally, C. a. arcticola mate fidelity has yet to be determined, and because demographic rates can be linked to breeding ecology, understanding factors affecting both adult survival and mate fidelity might illuminate specific constraints on demographic rates for this species. I used a Barker (1997) model to estimate true survival (unbiased relative to fidelity) rates of adult C. a. arcticola using 19 years (2003 – 2021) of mark-recapture data and environmental data, collected from a breeding area, Utqiaġvik, Alaska, U.S.A. Breeding site data were supplemented with resighting observations and habitat data from non-breeding sites in eastern Asia (Japan, China, Taiwan). I examined breeding site environmental (temperature, snow melt date, precipitation) and ecological (predator abundance and predator-prey cycles, food resources, shorebird nesting density) in conjunction non-breeding site habitat (area of intertidal extent) effects on survival estimates. True survival averaged 0.62 (95% C.I. 0.50 – 0.72), and marginally declined six percent throughout the study period. Survival was positively related to intertidal extent on non-breeding grounds and heavy precipitation events on the breeding grounds; with precipitation influence on survival likely being driven by outliers in the data. I propose intertidal habitat (which declined 22% across 19 years) is likely a core driver of low survival rates. These results enforce that low adult survival rates are suppressing C. a. arcticola populations, as while other demographic rates (reproductive output, breeding propensity) are comparable with North American Arctic-breeding C. alpina subspecies, both adult survival rates and estimated population growth remain relatively lower. I emphasize that conservation efforts should be focused at areas currently losing intertidal habitat within the East Asian-Australasian Flyway to mitigate future C. a. arcticola declines. Using C. a. arcticola breeding site data, I tested four hypotheses to understand divorce in C. a. arcticola: the better option hypothesis, in which divorce improves reproductive success by obtaining a higher quality mate; the habitat mediated hypothesis, when divorce might occur if an opportunity exists to nest at a higher quality site than the prior breeding season; musical chairs, in which divorce is related to site-specific settlement choices upon arrival to the breeding grounds; and bet-hedging, in which divorce is more likely when mates arrive to the breeding grounds asynchronously, and an individual will pair with a new mate to avoid the cost of waiting for a previous mate to return to it. I used a logistic regression model to investigate effects on C. a. arcticola divorce with environmental and ecological factors that might influence divorce. Of the females nesting in consecutive years, 20% of those females divorced; and in the cases of males nesting in consecutive years, 55% of those males divorced. Both sexes were more likely to divorce when there was greater availability of experienced mates on the breeding grounds, significantly in males (β = 0.81, 95% CI = -0.65 – 2.28), compared to females (β = 1.27, 95% CI = 0.28 − 2.25). The results indicate males divorce behavior supports the better-option hypothesis, in which males divorced to "upgrade" to a mate with more breeding experience than their prior mate. However, male divorce behaviors also supported the bet-hedging hypothesis, as evidenced by similar nest initiation dates between divorced and reuniting males, which indicated males may divorce to avoid reproductive costs associated with waiting for a later-returning mate. Female divorce behavior was linked to either the habitat-mediated hypothesis, in which individuals attempt to acquire better habitat than their prior breeding site, or the better-option hypothesis, both evidenced by divorced females improving their reproductive success from the prior year. Divorced females exhibited higher egg success rates compared to divorced males, indicating females are likely the sex breaking the pair. Together, the results present novel information concerning C. a. arcticola. The first chapter presents direct connections between intertidal habitat loss and lower adult survival, and enforce calls for restoration of Asian intertidal areas along flyways to aid the conservation of migratory shorebirds. The second chapter provides the first estimates of C. a. arcticola mate fidelity and insight towards better understanding migratory shorebird breeding ecology.
Demography, Nest Site Selection, and Physiological and Behavioral Responses to Overflights and other Human Activities, of Wilson's Plover (Charadrius wilsonia) at Cape Lookout National Seashore, North Carolina
DeRose-Wilson, Audrey Laura (Virginia Tech, 2012-09-12)
There is little information on demographic trends of, or threats to the Wilson's Plover (Charadrius wilsonia), despite concerns that habitat degradation may be causing the species to decline. I studied Wilson's Plover demography, nest site selection, and physiological and behavioral responses to overflights at Cape Lookout National Seashore, North Carolina, where the National Park Service and U.S. Marine Corps recently lowered the altitude for overflights at tactical speeds. I monitored the responses of incubating Wilson's Plovers to overflights and other human activities and compared heart rate, incubation rate, and vigilance behaviors during time periods with and without these stimuli. I compared habitat use vs. availability at the island-scale, and nest placement relative to geomorphic features and vegetative cover, both on a local and island-wide scale. Wilson's Plovers increased vigilance during military rotary-wing and civilian fixed-wing overflights, but not during military fixed-wing overflights. Plovers were vigilant more and incubated less when researchers were present. Wilson's Plovers selected for interdune areas, flats and isolated dunelets on flats, and against beach and dunes. At the local scale, nests were more likely to be near dense vegetation than random points. Mayfield nest survival was 25%, and predation caused most of the nest failure. Daily nest survival was negatively correlated with nest age and initiation date. Nests with cameras and heart rate monitors had lower survival, and nests with predator exclosures had higher survival. The mean number of chicks fledged per pair was 0.78.
Detection and prediction of biodiversity patterns as a rapid assessment tool in the tropical forest of East Usambara, Eastern Arc Mountains, Tanzania
Sengupta, Nina (Virginia Tech, 2003-11-20)
As a strategy to conserve tropical rainforests of the East Usambara block of the Eastern Arc Mountains, Tanzania, I developed a set of models that can identify above-average tree species richness areas within the humid forests. I developed the model based on geo-referenced field data and satellite image-based variables from the Amani Nature Reserve, the largest forest sector in the East Usambara. I then verified the model by applying it to the Nilo Forest Reserve. The field data, part of the Tanzanian National Biodiversity Database, were collected by Frontier-Tanzania between 1999 and 2001, through the East Usambara Conservation Area Management Program, Government of Tanzania. The field data used are rapidly collectible by people with varied backgrounds and education. I gathered spectral reflectance values from pixels in the Landsat Enhanced Thematic Mapper (Landsat ETM) image covering the study area that corresponded to the ground sample points. The spectral information from different bands formed the satellite image-based variables in the dataset. The best satellite image logistic regression and discriminant analysis models were based on a single band, raw Landsat ETM mid-infrared band 7 (RB7). In the Amani forest, the RB7-based model resulted in 65.3% overall accuracy in identifying above average tree species locations. When the logistic and discriminant models were applied to Nilo forest sector, the overall accuracy was 62.3%. Of the rapidly collectible field variables, only tree density (number of trees) was selected in the logistic regression and the discriminant analysis models. Logistic and discriminant models using both RB7 and number of trees recorded 76.3% overall accuracy in Amani, and when applied to Nilo, 76.8% accuracy. It is possible to apply and adapt the current set of models to identify above-average tree species richness areas in East Usambara and other forest blocks of the Eastern Arc Mountains. Potentially, managers and researchers can periodically use the model to rapidly assess, monitor, update, and map the tree species rich areas within the forest. The same or similar models could be applied to check their applicability in other humid tropical forest areas.
Direct and indirect effects of nesting density on survival and breeding propensity of an endangered shorebird
Catlin, Daniel H.; Gibson, Daniel; Hunt, Kelsi L.; Friedrich, Meryl J.; Weithman, Chelsea E.; Karpanty, Sarah M.; Fraser, James D. (ESA, 2019-04-08)
Density-dependent regulation is a fundamental part of ecological theory and a significant driver of animal demography often through complex feedback loops. We investigated the relationship between flood- and demographically induced fluctuations in density and the breeding propensity and survival of a pioneer species, the piping plover (plover, Charadrius melodus).We captured and marked adult and hatchling plovers on the Gavins Point Reach of the Missouri River in South Dakota and Nebraska, USA, from 2005 to 2014. In 2010 and 2011, historically high water levels and flooding inundated much of the plover’s sandbar nesting habitat on theMissouri River.We developed a Bayesian formulation of a multievent model, or a multistate survival model with state uncertainty to estimate breeding propensity simultaneously with survival. Although plovers are conspicuous, their breeding status can be difficult to establish with certainty, which necessitated the use of uncertain states.With this model, we investigated the effect of sex, habitat availability, river flow, and density (birds/ha nesting habitat) on survival of hatch year and breeding and non-breeding adult plovers. In addition, we estimated the transition rates for these age classes between breeding and nonbreeding states. Non-breeding adults (ɸAHY, n = 0.58 ± 0.06) had lower survival rates than breeding adults (ɸAHY, b = 0.80 ± 0.04), and both breeding survival and breeding propensity decreased with increasing nesting density. Not only did survival and breeding propensity decrease directly at higher nest densities, but survival also was indirectly impacted by increasing the proportion of non-breeding birds with relatively low survival. Thus, plovers were regulated through a complex set of feedback loops, acting as densities increased. Our findings underscore the intricacy of density-dependent regulation and suggest that detailed demographic studies are needed to fully understand these effects.
Disturbance and Environmental Effects on Staging Roseate Tern Parent-Offspring Interactions and Hatch Year Survival at Cape Cod National Seashore
Davis, Kayla L. (Virginia Tech, 2017-01-31)
The study that I detail in the following thesis is a component of a three-part collaborative project to provide the U. S. National Park Service and Cape Cod National Seashore (CCNS) with data needed to inform management decisions for protection of the endangered northwest Atlantic Roseate Tern (ROST) during fall pre-migratory staging. This study was designed to address objectives related to hatch-year (HY) ROST behavior and survival in response to human and non-human activities and environmental variables at CCNS. Behavioral data showed that disturbance, specifically human and non-human activities, were related to increased HY ROST locomotion (flying and walking). We also found that environmental variables, including day of season and time of day were related to increased locomotion. Flock-level HY ROST begging behavior was decreased in the presence of human disturbance, but we did not see the same effect at the individual level. We found no evidence that the observed behavioral effect of disturbance resulted in decreased residency, recruitment, or staging duration of HY ROST at CCNS. Our work demonstrates that disturbance events around staging flocks have behavioral consequences, but it is unknown whether HY ROST behavioral responses to disturbances are great enough to impact survival after departure from CCNS. A conservative and proactive management strategy to minimize the potential for negative carryover effects on survival should limit ROST exposure to disturbance, particularly human activities, by exclosing staging sites between mid-July–mid-September to encompass the period of time when the highest number of ROST use CCNS.
Drivers of a habitat shift by critically endangered Siberian cranes: Evidence from long-term data
Hou, Jinjin; Liu, Yifei; Fraser, James D.; Li, Lei; Zhao, Bin; Lan, Zhichun; Jin, Jiefeng; Liu, Guanhua; Dai, Nianhua; Wang, Wenjuan (2020-09)
Many waterbird populations have become increasingly dependent on agricultural habitats for feeding. While habitat destruction has been proposed as a key reason forcing waterbirds to move from natural habitats to agricultural habitats, few have used long-term data to test this hypothesis. The Siberian crane (Leucogeranus leucogeranus) is an IUCN Critically Endangered species. About 98% of its global population winters at Poyang Lake, China. Recently, many cranes shifted from feeding in natural wetlands to agricultural habitats. Here, we integrate bird surveys,Vallisneriatuber (the traditional food of cranes in natural wetlands) surveys, water level data, and remotely sensed images from 1999 to 2016 to explore the drivers of this habitat shift. Changes in Siberian crane numbers in natural wetlands and agricultural fields indicated that the habitat shift occurred in the winters of 2015-2016. Analyses using generalized linear mixed models suggested that crane numbers in natural wetlands were positively related to tuber density and the interaction between dry season (October-March) water level and tuber density. The changes in tuber density and dry season water level in 2015-2016 indicated that tuber disappearance may have been the primary driver of the habitat shift, with a smaller effect of high water level. Submerged plants at Poyang Lake have degraded seriously in the past two decades. The plant degradation at Shahu Lake, a sublake of Poyang Lake, may have been caused by high spring water, high winter temperature, and low summer temperature. However, the drivers of tuber disappearance at Poyang Lake may not be restricted to these variables. Because Poyang Lake is an important refuge for many waterbirds in the Yangtze River floodplain, it is urgent to take effective measures to restore its submerged plants and ecosystem health. Agricultural fields can be important refuges for Siberian cranes, mitigating the negative impacts of wetland deterioration.
Ecology and conservation of Formosan clouded leopard, its prey, and other sympatric carnivores in southern Taiwan
Chiang, Po-Jen (Virginia Tech, 2007-11-14)
During 2000-2004 I studied the population status of the Formosan clouded leopard (Neofelis nebulosa brachyurus) and the ecology of its prey and other sympatric carnivores in the largest remaining lowland primary forest in southern Taiwan. My research team and I set up 232 hair snare stations and 377 camera trap sites at altitudes of 150-3,092m in the study area. No clouded leopards were photographed in total 13,354 camera trap days. Hair snares did not trap clouded leopard hairs, either. Assessment of the prey base and available habitat indicated that prey depletion and habitat loss, plus historical pelt trade, were likely the major causes of extinction of clouded leopards in Taiwan. Using zero-inflated count models to analyze distribution and occurrence patterns of Formosan macaques (Macaca cyclopis) and 4 ungulates, we found habitat segregation among these 5 herbivore species. Formosan macaques, Reeve's muntjacs (Muntiacus reevesi micrurus), and Formosan serows (Nemorhaedus swinhoei) likely were the most important prey species of Formosan clouded leopards given their body size and high occurrence rates in lower altitudes. In contrast, sambar deer (Cervus unicolor swinhoii) tended to occur more frequently as altitude increased. Formosan macaques exhibited seasonal differences in occurrence rates and were absent at altitudes > 2,500m in winter. Only Formosan serows showed preference for cliffs and rugged terrain, while the other 4 species, except wild boars (Sus scrofa taivanus), avoided these areas. Habitat segregation in forest understory and structure were more pronounced among the 4 ungulates. Forest structure rarely affected occurrence rates of Formosan macaques on the ground. Niche relationships of the other sympatric carnivores were studied through habitat, diet, and temporal dimensions. Resource partitioning by carnivores was observed. Altitude was the strongest factor explaining the composition of the carnivore community in the local study-area scale and in the landscape scale across Taiwan. Carnivores could be divided into 2 groups: low-mid altitude consisting of Formosan ferret badgers (Melogale moschata subaurantiaca), gem-faced palm civets (Paguma larvata taivana), lesser oriental civets (Viverricula indica taivana), crab-eating mongooses (Herpestes urva formosanus), leopard cats (Prionailurus bengalensis chinensis), and feral cats (Felis catus), and the mid-high altitude group consisting of yellow-throated martens (Martes flavigula chrysospila), Siberian weasels (Mustela sibirica taivana), and Asiatic black bears (Ursus thibetanus formosanus). Carnivore richness was higher at mid altitudes where these 2 groups overlapped (i.e. mid-domain effect). The low-mid altitude carnivores were more nocturnal and tolerant of human activity and forest alteration except crab-eating mongooses, which were diurnal and avoided human encroachment. Similar to crab-eating mongooses, the mid-high altitude carnivores also avoided human encroachment and were diurnal except for Siberian weasels, which were more nocturnal. Diet summary based on their major food items for all sympatric carnivores revealed 3 groups of foragers which foraged on: invertebrates, small mammals, and plant fruits. Felidae, yellow-throated martens, and Siberian weasels preyed on small mammals. Asiatic black bears and gem-faced palm civets ate mostly plant fruits. The other 3 carnivores were mainly invertebrate foragers. These 9 carnivores partitioned resource uses in the 3 niche dimensions except for some overlap in resource use by leopard cats and feral cats. Prey base for Formosan clouded leopards and the carnivore richness in Taiwan were found to be lower in areas with higher levels of human activity. On the other hand, Formosan macaques and ungulates could become over-abundant without human hunting and top carnivore predation. Mesopredator release may occur because of vanishing top carnivores, causing reduction of the lower trophic level prey species. It is important to assess the cascading impacts of the loss of the Formosan clouded leopards and Eurasian otters (Lutra lutra chinensis) and the declining Asiatic black bears and to consider reintroduction of Formosan clouded leopards, as well as active management of the other larger mammals. These results provided baseline information for reintroduction of clouded leopards and management of their prey and generated new hypotheses regarding the ecology of these large mammals for future investigation.
Ecology and distribution of the Florida bog frog and flatwoods salamander on Eglin Air Force Base
Bishop, David Christopher (Virginia Tech, 2005-06-09)
I studied the ecology and distribution of the Florida bog frog (Rana okaloosae) and flatwoods salamander (Ambystoma cingulatum) on Eglin Air Force Base in northwest Florida. I report data on the breeding ecology, population dynamics, home ranges, microhabitat, and distribution of the endemic bog frog and make comparisons to its closest relative, the bronze frog (Rana clamitans clamitans). Bog and bronze frogs occur in the same habitats and are suspected to hybridize. I investigated the potential for auditory and visual mate recognition errors between R. okaloosae and R. clamitans. I also described the vocal repertoire of the bog frog and observed the response of resident males to the playback of unfamiliar conspecific and heterospecific (R. clamitans) calls. The advertisement calls of bog frogs vary among individuals, and individual voice recognition is possible. I exposed tadpoles of bog frogs, bronze frogs, and leopard frogs (R. sphenocephala) to chemical cues from 2 predators, the banded water snake (Colubridae: Nerodia fasciata) and the red fin pickerel (Esocidae: Esox americanus) to evaluate whether swimming behavior or habitat selection differed among tadpole species. The time spent swimming differed among tadpole species and predator treatments, differences which potentially could affect growth rates, survivorship rates, and distribution patterns. Lastly, I discuss the relationship between fire and the federallyâ threatened flatwoods salamander (Ambystoma cingulatum). I compared 13 breeding wetlands with different fire histories in addition to burned and unburned halves of a partiallyâ burned wetland. In general, areas that burned more recently had more open canopies, higher dissolved oxygen concentrations, higher water temperatures, more understory vegetation, and were shallower than unburned areas. Rangewide surveys indicate that prescribed fires typically are applied in winter and early spring in areas inhabited by flatwoods salamanders. Based on what is known about the natural history of the species, the historical burning regime of the longleaf ecosystem, and the effects of fires on ephemeral wetlands, I suggest that land mangers diversify their fireâ management strategy to increase the likelihood of burning the breeding wetlands of flatwoods salamanders.
Ecology Of Non-Breeding And Breeding Crested Caracaras (Caracara cheriway) In Florida
Dwyer, James F. (Virginia Tech, 2010-05-06)
Like many species, Florida's population of Northern Crested Caracaras (Caracara cheriway, hereafter "caracara") is likely declining due to loss of breeding habitat. Consequently, management-oriented restrictions on landscape modification are applied where breeding occurs, but management rarely is extended beyond breeding areas. Focusing management on breeding areas can be effective if all caracaras occupy breeding areas, all breeding areas are detected, and no intermittent breeding occurs. Management may not operate as intended if any of these criteria are unmet. To explore this possibility, I investigated the movement, habitat, survival, and social biology of non-breeding caracaras. I also investigated long-term occupancy of breeding habitat, and factors contributing to detection of breeding. Non-breeding caracaras occupy areas much larger than individual breeding territories, particularly during breeding seasons. Pastures occupied by cattle were the most used habitat, but non-breeding caracaras also occupied habitats atypical of breeding areas. Specifically, citrus groves were occupied extensively, and row crops were used particularly during breeding seasons. Non-breeding caracaras also shared communal roosts, sometimes with hundreds of conspecifics, and roosts were occupied year-round. Survival of non-breeding caracaras was lowest during breeding seasons. Adult non-breeding caracaras persisted in groups for multiple years without establishing breeding territories. This implies that breeding habitat is limited and saturated. Given the proportion of adults in groups, adults also were the first to find carrion more often than expected. Apparently, young caracaras benefit from grouping by following adults. I found caracaras at all sampled breeding areas where nests were originally documented during the 1990s, and found nests at 83% of territories where nests likely existed. I also found that observer experience, visit start time, and weather affected the probability that a nest would be detected. Thus, not all caracaras occupy breeding areas, and not all breeding attempts are likely to be detected. Long-term occupancy of breeding areas should render annual verification of nesting unnecessary as a trigger for maintaining management actions. Rather management should persist even without confirmation of annual breeding. Caracara management also may be optimized through supporting the non-breeding population by maintaining a matrix of cattle pasture and citrus groves, particularly around roosts.
Effects of climate change and anthropogenic modification on a disturbance-dependent species in a large riverine system
Zeigler, Sara L.; Catlin, Daniel H.; Brown, Mary Bomberger; Fraser, James D.; Dinan, Lauren R.; Hunt, Kelsi L.; Jorgensen, Joel G.; Karpanty, Sarah M. (Ecological Society of America, 2017-01)
Humans have altered nearly every natural disturbance regime on the planet through climate and land-use change, and in many instances, these processes may have interacting effects. For example, projected shifts in temperature and precipitation will likely influence disturbance regimes already affected by anthropogenic fire suppression or river impoundments. Understanding how disturbance-dependent species respond to complex and interacting environmental changes is important for conservation efforts. Using field-based demographic and movement rates, we conducted a metapopulation viability analysis for piping plovers (Charadrius melodus), a threatened disturbance-dependent species, along the Missouri and Platte rivers in the Great Plains of North America. Our aim was to better understand current and projected future metapopulation dynamics given that natural disturbances (flooding or high-flow events) have been greatly reduced by river impoundments and that climate change could further alter the disturbance regime. Although metapopulation abundance has been substantially reduced under the current suppressed disturbance regime (high-flow return interval similar to 20 yr), it could grow if the frequency of high-flow events increases as predicted under likely climate change scenarios. We found that a four-year return interval would maximize metapopulation abundance, and all subpopulations in the metapopulation would act as sources at a return interval of 15 yr or less. Regardless of disturbance frequency, the presence of even a small, stable source subpopulation buffered the metapopulation and sustained a low metapopulation extinction risk. Therefore, climate change could have positive effects in ecosystems where disturbances have been anthropogenically suppressed when climatic shifts move disturbance regimes toward more historical patterns. Furthermore, stable source populations, even if unintentionally maintained through anthropogenic activities, may be critical for the persistence of metapopulations of early-successional species under both suppressed disturbance regimes and disturbance regimes where climate change has further altered disturbance frequency or scope.

Browsing by Author "Fraser, James D."

Results Per Page

Sort Options