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Fort Collins, CO, United States

Schorr R.A.,Colorado State University | Ellison L.E.,U.S. Geological Survey | Lukacs P.M.,17 West Prospect Road
Acta Chiropterologica | Year: 2014

Concern for migratory tree-roosting bats in North America has grown because of possible population declines from wind energy development. This concern has driven interest in estimating population-level changes. Mark-recapture methodology is one possible analytical framework for assessing bat population changes, but sample size requirements to produce reliable estimates have not been estimated. To illustrate the sample sizes necessary for a mark-recapture-based monitoring program we conducted power analyses using a statistical model that allows reencounters of live and dead marked individuals. We ran 1,000 simulations for each of five broad sample size categories in a Burnham joint model, and then compared the proportion of simulations in which 95% confidence intervals overlapped between and among years for a 4-year study. Additionally, we conducted sensitivity analyses of sample size to various capture probabilities and recovery probabilities. More than 50,000 individuals per year would need to be captured and released to accurately determine 10% and 15% declines in annual survival. To detect more dramatic declines of 33% or 50% survival over four years, then sample sizes of 25,000 or 10,000 per year, respectively, would be sufficient. Sensitivity analyses reveal that increasing recovery of dead marked individuals may be more valuable than increasing capture probability of marked individuals. Because of the extraordinary effort that would be required, we advise caution should such a mark-recapture effort be initiated because of the difficulty in attaining reliable estimates. We make recommendations for what techniques show the most promise for mark-recapture studies of bats because some techniques violate the assumptions of mark-recapture methodology when used to mark bats. © Museum and Institute of Zoology PAS.

Clements W.H.,Colorado State University | Vieira N.K.M.,17 West Prospect Road | Church S.E.,U.S. Geological Survey
Journal of Applied Ecology | Year: 2010

Evaluating the effectiveness of stream restoration is often challenging because of the lack of pre-treatment data, narrow focus on physicochemical measures and insufficient post-restoration monitoring. Even when these fundamental elements are present, quantifying restoration success is difficult because of the challenges associated with distinguishing treatment effects from seasonal variation, episodic events and long-term climatic changes.2. We report results of one of the most comprehensive and continuous records of physical, chemical and biological data available to assess restoration success for a stream ecosystem in North America. Over a 17 year period we measured seasonal and annual changes in metal concentrations, physicochemical characteristics, macroinvertebrate communities, and brown trout Salmo trutta populations in the Arkansas River, a metal-contaminated stream in Colorado, USA.3. Although we observed significant improvements in water quality after treatment, the effectiveness of restoration varied temporally, spatially and among biological response variables. The fastest recovery was observed at stations where restoration eliminated point sources of metal contamination. Recovery of macroinvertebrates was significantly delayed at some stations because of residual sediment contamination and because extreme seasonal and episodic variation in metal concentrations prevented recolonization by sensitive species. Synthesis and applications. Because recovery trajectories after the removal of a stressor are often complex or nonlinear, long-term studies are necessary to assess restoration success within the context of episodic events and changes in regional climate. The observed variation in recovery among chemical and biological endpoints highlights the importance of developing objective criteria to assess restoration success. Although the rapid response of macroinvertebrates to reduced metal concentrations is encouraging, we have previously demonstrated that benthic communities from the Arkansas River remained susceptible to other novel anthropogenic stressors. We suggest that the resistance or resilience of benthic macroinvertebrate communities to novel stressors may be effective indicators of restoration success that can account for the non-additive (e.g. synergistic) nature of compound perturbations. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.

Sanders T.A.,17 West Prospect Road | Sanders T.A.,U.S. Fish and Wildlife Service | Dooley J.L.,17 West Prospect Road
Journal of Wildlife Management | Year: 2014

Breeding populations of Canada geese (Branta canadensis) were established throughout western Colorado during 1955-1988 using geese transplanted from other areas. Subsequently, there has been no assessment of demographics and winter distributions on these local populations. Managers need this information to effectively manage breeding populations of Canada geese to provide publics with recreational opportunities and to reduce human-goose conflicts in western Colorado, particularly for segments of internationally recognized populations with cooperative management plans. We conducted a band recovery study during 2000-2006 to assess demographics and winter distributions of Canada geese breeding in 7 subareas of western Colorado. Cooperators banded 19,189 geese during June and early July. We recaptured 5,185 of these geese 1-4 times during banding operations in subsequent years and most (97%) were recaptured in the subarea of banding the year after banding. We obtained 2,921 useable band recoveries through May 2007, and most (98%) recoveries were a result of either being shot or found dead during hunting season. Direct band recoveries (<1 year after banding) were recovered almost exclusively in Colorado (87%) and New Mexico (12%), and indirect band recoveries (≥1 year after banding) showed similar distribution (73% in Colorado and 16% in New Mexico). Geese in subareas of western Colorado had different recovery distributions, and contributed to 4 wintering concentrations of Canada geese in western and central Colorado and New Mexico. Annual survival probability for adult geese was 0.864±0.012. The survival probability for juvenile geese was 0.503±0.026, but we did find evidence that this estimate may be biased low. We used the band reporting probability of 0.525±0.071 to derive harvest rates from band recovery rates. Harvest rate was 0.128±0.018 for adult geese and 0.169±0.024 for juvenile geese. Survival probability was lesser and harvest rate greater for the 3 western subareas (Western Plateau) compared to the 4 eastern subareas (Rocky Mountains). Our results suggest that Canada geese that breed and molt in western Colorado have high survival probability and are largely non-migratory with some movement in winter from high to low elevation areas primarily in Colorado. To effectively manage the growing resident goose population in western Colorado, managers may need to increase harvest rates for these geese. © 2014 The Wildlife Society.

Dooley J.L.,Colorado State University | Sanders T.A.,17 West Prospect Road | Doherty Jr. P.F.,Colorado State University
Wildlife Biology | Year: 2010

Information on waterfowl survival during the overwintering season (i.e. autumn and winter), when hunting seasons occur, is important for making harvest management decisions. However, the relationship of overwintering survival to hunting season structure, weather and body condition are not well understood. We measured survival of 235 radio-marked adult female and male mallards Anas platyrhynchos along the South Platte River corridor in northeastern Colorado, USA, during the overwintering seasons of 2005/06 (pilot year), 2006/07 and 2007/08, and we determined the primary factors affecting survival. Hunting was the most important factor affecting survival. Of mortality, 67% were direct results of hunting, and survival was lower during hunting periods compared to non-hunting periods. Within hunting periods, survival was lowest during the first 2-3 weekends of the hunting periods. During the seasons 2006/07 and 2007/08, survival of radio-marked mallards was monitored during September-February. The estimated survival was 0.65 (95% CI = 0.50-0.78) for females and 0.54 (95% CI = 0.39-0.68) for males during 2006/07, and 0.55 (95% CI = 0.40-0.69) for females and 0.42 (95% CI = 0.28-0.58) for males during 2007/08. We did not observe a strong correlation between body condition index and survival (= 0.36, SE = 0.43). Accumulated snowfall and daily minimum temperature were unimportant variables for predicting survival. Of hunting recoveries, 89% occurred in our study area, and 15% and 18% of radio-marked mallards went missing during 2006/07 and 2007/08, respectively. Our results suggest that split hunting seasons are an effective management tool to increase hunter harvest and affect overwintering survival. Given a set bag limit and season length, managers may be able to increase hunter harvest by: 1) having hunting periods of at least three weeks in length, 2) including as many weekend days (i.e. Saturdays and Sundays) within hunting periods as possible and 3) interspersing hunting periods with non-hunting periods of at least 2-3 weeks. © 2010 Wildlife Biology, NKV.

Clements W.H.,Colorado State University | Vieira N.K.M.,17 West Prospect Road | Sonderegger D.L.,Colorado State University
Journal of the North American Benthological Society | Year: 2010

Ecological thresholds have been applied conventionally to characterize relationships between stressors and biological responses. We demonstrated how ecological thresholds can be used to assess recovery in a system where stressors have been removed. We applied a relatively new statistical approach, the significant zero crossings (SiZer) model, which approximates a response function and its derivatives and then shows how these functions vary across the range of an explanatory variable. We applied the model to a long-term macroinvertebrate data set collected from the Arkansas River, a Colorado stream undergoing restoration from historical mining pollution. SiZer analysis identified distinct threshold responses of benthic communities through time and related these shifts to improvements in water quality. With respect to restoration success, a recovery threshold was observed ∼10 y after clean up was initiated. Recovery trajectories in the Arkansas River were relatively complex, with multiple thresholds, and these responses were strongly influenced by temporal variation in heavy metal concentrations and stream discharge. A unique aspect of SiZer is that it easily handles multiple thresholds and displays significant change points along a predictor variable graphically. In addition, SiZer allows investigators to examine potential thresholds at different levels of resolution and provides a transparent representation of the threshold and how it responds to variability of the data. © 2010 The North American Benthological Society.

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