Smith, K. W., W. S. Keeton, T. M. Donovan, and B. Mitchell. 2008. Stand-level forest structure in avian habitat: scale dependencies in predicting occurrences in a heterogeneous forest. Forest Science 54:36-46.
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February 2008
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We explored the role of stand-level forest structure and spatial extent of forest sampling in models of avian occurrence in northern hardwood-conifer forests for two species: black-throated blue warbler (Dendroica caerulescens) and ovenbird (Seiurus aurocapillus). We estimated site occupancy from point counts at 20 sites and characterized the forest structure at these sites at three spatial extents (0.2, 3.0, and 12.0 ha). Weight of evidence was greatest for habitat models using forest stand structure at the 12.0-ha extent and diminished only slightly at the 3.0-ha extent, a scale that was slightly larger than the average territory size of both species. Habitat models characterized at the 0.2-ha extent had low support, yet are the closest in design to those used in many of the habitat studies we reviewed. These results suggest that the role of stand-level vegetation may have been underestimated in the past, which will be of interest to land managers who use habitat models to assess the suitability of habitat for species of concern.
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Rinehart, K., T. Donovan, B. Mitchell, R. Long. 2009. Factors influencing occupancy patterns of Eastern Newts across Vermont. Journal of Herpetology 43(3):521-531.
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September 2009
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Of the threats facing amphibian populations today, habitat transformation due to land-use is among the most pressing. Although conservation of pond-breeding salamanders clearly requires protection of breeding ponds and their surrounding habitat, little is known about the effects of land use and other factors on the occurrence of salamanders in the dispersal/terrestrial phase of their life cycle. To determine these effects, we surveyed populations of Eastern Newts (Notophthalmus viridescens) at 551 stations across Vermont, and modeled salamander distribution as a function of environmental variables hypothesized to influence site occupancy. We developed a set of 12 models based on seven a priori hypotheses of site occupancy. We hypothesized that occupancy was influenced by 1) amounts of available habitat types, 2) arrangement of these habitat types, 3) geographic position, 4) housing density, 5) road density, 6) short term changes in habitat distribution, or 7) habitat structure at the stand-level. We used a single-season occupancy model to rank and compare the 12 models. 232 Eastern Newts were detected at 82 of 551 stations. Of the 12 models, amount of habitat within 0.5 km of the survey station best represented the field data. Strong effects were indicated for developed land (-), open water (+), and forest (+) cover. Given a survey station with average forest and open water characteristics, stations with > 5% developed land classes within a 0.5 km buffer had a very low probability of occupancy. Further research is needed to determine the direct role of development on occupancy patterns.
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Mitchell, B. R., and T. M. Donovan. Mob mentality: the effect of a mobbing tape on detections during point count surveys. Open Ornithology Journal 1:8-19.
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July 2008
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The probability of detecting an individual or species is an important parameter in studies using mark-recapture and occupancy models to estimate population sizes and occurrence. Because low detection probabilities result in biased estimators and decreased precision, biologists seek methods that maximize detection probability. We evaluated whether we could increase detections of bird species by playing a tape of Black-capped Chickadee (Poecile atricapillus) mobbing calls during point counts. We conducted trios of 10-minute counts (two pre-playback and a playback) at 684 stations throughout Vermont, in forested, agricultural/grassland, and developed habitats. For each of 73 species detected during the surveys, we used occupancy modeling and information-theoretic model selection and averaging methods to evaluate whether detection probabilities varied due to playback or habitat type. Models containing a playback effect accounted for over 90% of the Akaike weights for 41 species. With 15 of these species, habitat effects also accounted for over 90% of the Akaike weights. The playback increased estimated detection probability in all habitats for 14 species, decreased estimated detection probability for 20 species, and had an estimated effect that varied by habitat for 7 species (many species with habitat effects simply had differing magnitudes of the effect dependent on habitat). Smaller resident species were detected more often during tape playbacks, but responses were highly variable for most species and the responses did not appear to follow a taxonomic pattern. We encourage researchers to evaluate their list of target species carefully before deciding to use mobbing playbacks to enhance response rates; in many situations mobbing tapes will not enhance detections and may complicate the interpretation of model parameters.
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Long, R. A., T. M. Donovan, P. MacKay, W. J. Zielinski, and J. S. Buzas. 2007. Effectiveness of scat detection dogs for detecting forest carnivores. Journal of Wildlife Management 71:2007-2017.
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August 2007
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We assessed the detection and accuracy rates of detection dogs trained to locate scats from free-ranging black bears (Ursus americanus), fishers (Martes pennanti), and bobcats (Lynx rufus). During the summers of 2003–2004, 5 detection teams located 1,565 scats (747 putative black bear, 665 putative fisher, and 153 putative bobcat) at 168 survey sites throughout Vermont, USA. Of 347 scats genetically analyzed for species identification, 179 (51.6%) yielded a positive identification, 131 (37.8%) failed to yield DNA information, and 37 (10.7%) yielded DNA but provided no species confirmation. For 70 survey sites where confirmation of a putative target species' scat was not possible, we assessed the probability that ≥1 of the scats collected at the site was deposited by the target species (probability of correct identification; PID). Based on species confirmations or PID values, we detected bears at 57.1% (96) of sites, fishers at 61.3% (103) of sites, and bobcats at 12.5% (21) of sites. We estimated that the mean probability of detecting the target species (when present) during a single visit to a site was 0.86 for black bears, 0.95 for fishers, and 0.40 for bobcats. The probability of detecting black bears was largely unaffected by site- or visit-specific covariates, but the probability of detecting fishers varied by detection team. We found little or no effect of topographic ruggedness, vegetation density, or local weather (e.g., temp, humidity) on detection probability for fishers or black bears (data were insufficient for bobcat analyses). Detection dogs were highly effective at locating scats from forest carnivores and provided an efficient and accurate method for collecting detection–nondetection data on multiple species.
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Long, R. A., T. M. Donovan, P. MacKay, W. J. Zielinski, and J. S. Buzas. 2007. Comparing scat detection dogs, cameras, and hair snares for surveying carnivores. Journal of Wildlife Management 71:2018-2025.
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August 2007
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Carnivores typically require large areas of habitat, exist at low natural densities, and exhibit elusive behavior—characteristics that render them difficult to study. Noninvasive survey methods increasingly provide means to collect extensive data on carnivore occupancy, distribution, and abundance. During the summers of 2003–2004, we compared the abilities of scat detection dogs, remote cameras, and hair snares to detect black bears (Ursus americanus), fishers (Martes pennanti), and bobcats (Lynx rufus) at 168 sites throughout Vermont. All 3 methods detected black bears; neither fishers nor bobcats were detected by hair snares. Scat detection dogs yielded the highest raw detection rate and probability of detection (given presence) for each of the target species, as well as the greatest number of unique detections (i.e., occasions when only one method detected the target species). We estimated that the mean probability of detecting the target species during a single visit to a site with a detection dog was 0.87 for black bears, 0.84 for fishers, and 0.27 for bobcats. Although the cost of surveying with detection dogs was higher than that of remote cameras or hair snares, the efficiency of this method rendered it the most cost-effective survey method.
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Long, R. A., T. M. Donovan, P. MacKay, J. S. Buzas, and W. J. Zielinski. Predicting carnivore occurrence using data collected with multiple, noninvasive methods.Landscape Ecology 26:327-340.
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October 2010
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Terrestrial carnivores typically require large areas of habitat and exist at low densities. As “top level” consumers, carnivores affect the biological structure and composition of ecosystems. We employed multiple, noninvasive survey methods—scat detection dogs, remote cameras, and hair snares—to collect detection-nondetection data for American black bears (Ursus americanus), fishers (Martes pennanti), and bobcats (Lynx rufus) throughout Vermont. We analyzed these data using an occupancy modeling approach that explicitly incorporated detectability as well as habitat and landscape variables. Model results were then used to predict occurrence for each species across the study area. Receiver operating characteristic (ROC) analyses of our models for species with high detectability suggest that the results of such surveys and modeling efforts may be useful for those striving to conserve or manage species at the regional or landscape scale. The noninvasive methods used for this project enabled us to collect important detection-nondetection information from low density, secretive, and wide-ranging species, without the need to capture or interact with the study subjects directly.
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Brown, M. L., T. M. Donovan, W. S. Schwenk, and D. M. Theobald. 2013. Predicting impacts of future human population growth and development on occupancy rates of forest-dependent birds . Biological Conservation. Available online 31 October 2013, ISSN 0006-3207, http://dx.doi.org/10.1016/j.biocon.2013.07.039
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October 2013
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Forest loss and fragmentation are among the largest threats to forest-dwelling wildlife species today, and projected increases in human population growth are expected to increase these threats in the next century. We combined spatially-explicit growth models with wildlife distribution models to predict the effects of human development on 5 forest-dependent bird species in Vermont, New Hampshire, and Massachusetts, USA. We used single-species occupancy models to derive the probability of occupancy for each species across the study area in the years 2000 and 2050. Over half a million new housing units were predicted to be added to the landscape. The maximum change in housing density was nearly 30 houses per hectare; however, 30% of the towns in the study area were projected to add less than 1 housing unit per hectare. In the face of predicted human growth, the overall occupancy of each species decreased by as much as 38% (ranging from 19% to 38% declines in the worst-case scenario) in the year 2050. These declines were greater outside of protected areas than within protected lands. Ninety-seven percent of towns experienced some decline in species occupancy within their borders, highlighting the value of spatially-explicit models. The mean decrease in occupancy probability within towns ranged from 3% for hairy woodpecker to 8% for ovenbird and hermit thrush. Reductions in occupancy probability occurred on the perimeters of cities and towns where exurban development is predicted to increase in the study area. This spatial approach to wildlife planning provides data to evaluate trade-offs between development scenarios and forest-dependent wildlife species.
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