Population growth can be sensitive to changes in survival rates for many avian species. Understanding sources of mortality, and how to mitigate negative effects on survival, can give managers insight ...into factors contributing to population change. Harvest trends of eastern wild turkeys (Meleagris gallopavo silvestris) in northeastern South Dakota suggest a decline in abundance. We investigated factors influencing survival of wild turkeys to identify potential factors contributing to the decline. We monitored 122 female wild turkeys using VHF radio transmitters from February 2017 to April 2019. Annual survival was 0.52 (95% CI = 0.33–0.64) for juvenile and 0.49 (95% CI = 0.23–0.63) for adult females, respectively. Daily survival probability was significantly lower during the spring (log‐odds ratio LOR = −0.9; 95% CI = −1.5–−0.2) and while a juvenile female was incubating (LOR = −0.67; 95% CI = −1.23–−0.09) but not while an adult female was incubating (LOR = −0.35; 95% CI = −0.92–0.24). Mammalian predation was the leading cause of mortality, and female wild turkeys were most vulnerable to predation during the spring while engaging in nesting and rearing of young broods. Wild turkeys were at risk for additional sources of mortality while incubating nests that were not contributors to mortality during other periods of the year, as deaths caused by haying equipment—the second greatest cause of mortality—only occurred while a female was incubating. Reducing female mortality due to haying, by delaying cutting, installing flushing bars on haying equipment, or increasing availability of suitable nesting cover types to reduce the probability of nesting in hayfields, could improve female survival. Annual survival during our study was about 16–29% lower than survival estimates from northeastern South Dakota during the 1990s, suggesting that reduced female survival could be contributing to the apparent decline in wild turkey abundance.
We investigated factors influencing survival of female eastern wild turkeys to identify potential drivers of an apparent decline in abundance. Daily survival probability was significantly lower during the spring and while a juvenile female was incubating but not while an adult female was incubating. Mammalian predation and haying equipment were the leading causes of mortality. Mitigating negative impacts of haying or increasing availability of suitable nesting cover types to reduce the probability of nesting in hayfields could improve female survival.
Conservation of bat species is one of the most daunting wildlife conservation challenges in North America, requiring detailed knowledge about their ecology to guide conservation efforts. Outside of ...the hibernating season, bats in temperate forest environments spend their diurnal time in day-roosts. In addition to simple shelter, summer roost availability is as critical as maternity sites and maintaining social group contact. To date, a major focus of bat conservation has concentrated on conserving individual roost sites, with comparatively less focus on the role that broader habitat conditions contribute towards roost-site selection. We evaluated roost-site selection by a northern population of federally-endangered Indiana bats (Myotis sodalis) at Fort Drum Military Installation in New York, USA at three different spatial scales: landscape, forest stand, and individual tree level. During 2007-2011, we radiotracked 33 Indiana bats (10 males, 23 females) and located 348 roosting events in 116 unique roost trees. At the landscape scale, bat roost-site selection was positively associated with northern mixed forest, increased slope, and greater distance from human development. At the stand scale, we observed subtle differences in roost site selection based on sex and season, but roost selection was generally positively associated with larger stands with a higher basal area, larger tree diameter, and a greater sugar maple (Acer saccharum) component. We observed no distinct trends of roosts being near high-quality foraging areas of water and forest edges. At the tree scale, roosts were typically in American elm (Ulmus americana) or sugar maple of large diameter (>30 cm) of moderate decay with loose bark. Collectively, our results highlight the importance of considering day roost needs simultaneously across multiple spatial scales. Size and decay class of individual roosts are key ecological attributes for the Indiana bat, however, larger-scale stand structural components that are products of past and current land use interacting with environmental aspects such as landform also are important factors influencing roost-tree selection patterns.
The proliferation of energy rights‐of‐way (pipelines and powerlines; ROWs) in the central Appalachian region has prompted wildlife management agencies to consider ways to use these features to manage ...and conserve at‐risk songbird species. However, little empirical evidence exists regarding best management strategies to enhance habitat surrounding ROWs for the songbird community during stopover or breeding periods. We used a before–after–control–impact design to study cut‐back border (linear tree cuttings along abrupt forest edges) harvest width (15, 30, and 45 m wide into the forest), and harvest intensity (14 and 4.5 m2/ha basal area retention) prescriptions along ROWs and assessed their effects on mature forest and young forest songbird species and avian guilds (forest gap habitat, forest interior habitat, young forest habitat, and species of regional conservation priority) up to 2 years after treatment throughout West Virginia. Species richness during the spring stopover period initially decreased at the 1‐year post‐treatment period but returned to pre‐treatment levels by 2 years post‐treatment. Breeding season responses to cut‐back border treatments varied across harvest width, harvest intensity, and time, but all responses of focal species abundance and guild richness were neutral or positive. Cut‐back border harvest intensity had a stronger influence (i.e., more positive responses) than harvest width on breeding focal species abundances and guild richness. For harvest intensity, the more intense, 4.5 m2/ha retention treatment had a stronger influence (i.e., more positive responses) than the less intense, 14 m2/ha retention treatment. For harvest width, the narrowest treatment (15‐m wide) had the strongest influence (i.e., more positive responses) of all width treatments, followed by the widest (45‐m wide treatment) with the least influence from the 30‐m wide treatment. Abundances and richness increased from pre‐treatment to 2 years post‐treatment across all species and guilds that exhibited a response. These results suggest that cut‐back borders increase breeding season habitat suitability along ROWs for the mature forest and young forest songbird community as well as for species of regional conservation priority in the short‐term. These findings can aid the development of management guidelines for the forest songbird community along abrupt forest edges of man‐made habitat features in forest‐dominated landscapes.
Wetlands enrolled in the Agricultural Conservation Easement Program (ACEP) are established as a means of restoring wetland ecosystems and wildlife habitat on private, agricultural land. In West ...Virginia, USA, ACEP wetlands have never been evaluated to determine how they function as wildlife habitat in comparison to other available wetland habitat in the state. We measured the wintering occupancy of Passerellidae species and apparent avian species richness on ACEP wetlands and a set of reference wetlands located on public land in West Virginia to evaluate if ACEP wetlands are being used similarly by avian species to other available wetland habitat in the state. Apparent avian species richness and the occupancy probability of four Passerellidae species-song sparrows (Melospiza melodia), dark-eyed juncos (Junco hyemalis), swamp sparrows (Melospiza georgiana), and white-throated sparrows (Zonotrichia albicollis)-did not differ between ACEP and reference sites. In addition to other vegetative and habitat associations for each species, dark-eyed junco occupancy was negatively correlated with wetland size while swamp sparrow occupancy and apparent avian species richness were positively associated with wetland size. These results indicate that ACEP wetlands are providing winter avian habitat as well as another source of wetland habitat in the state. Maintaining and expanding ACEP wetlands in West Virginia would continue to provide wetland systems in areas that are otherwise lacking these habitats.
Developed areas are thought to have low species diversity, low animal abundance, few native predators, and thus low resilience and ecological function. Working with citizen scientist volunteers to ...survey mammals at 1427 sites across two development gradients (wild-rural-exurban-suburban-urban) and four plot types (large forests, small forest fragments, open areas and residential yards) in the eastern US, we show that developed areas actually had significantly higher or statistically similar mammalian occupancy, relative abundance, richness and diversity compared to wild areas. However, although some animals can thrive in suburbia, conservation of wild areas and preservation of green space within cities are needed to protect sensitive species and to give all species the chance to adapt and persist in the Anthropocene.
Occupancy estimation and the closure assumption Rota, Christopher T; Fletcher Jr, Robert J; Dorazio, Robert M ...
The Journal of applied ecology,
December 2009, Letnik:
46, Številka:
6
Journal Article
Recenzirano
Odprti dostop
1. Recent advances in occupancy estimation that adjust for imperfect detection have provided substantial improvements over traditional approaches and are receiving considerable use in applied ...ecology. To estimate and adjust for detectability, occupancy modelling requires multiple surveys at a site and requires the assumption of 'closure' between surveys, i.e. no changes in occupancy between surveys. Violations of this assumption could bias parameter estimates; however, little work has assessed model sensitivity to violations of this assumption or how commonly such violations occur in nature. 2. We apply a modelling procedure that can test for closure to two avian point-count data sets in Montana and New Hampshire, USA, that exemplify time-scales at which closure is often assumed. These data sets illustrate different sampling designs that allow testing for closure but are currently rarely employed in field investigations. Using a simulation study, we then evaluate the sensitivity of parameter estimates to changes in site occupancy and evaluate a power analysis developed for sampling designs that is aimed at limiting the likelihood of closure. 3. Application of our approach to point-count data indicates that habitats may frequently be open to changes in site occupancy at time-scales typical of many occupancy investigations, with 71% and 100% of species investigated in Montana and New Hampshire respectively, showing violation of closure across time periods of 3 weeks and 8 days respectively. 4. Simulations suggest that models assuming closure are sensitive to changes in occupancy. Power analyses further suggest that the modelling procedure we apply can effectively test for closure. 5. Synthesis and applications. Our demonstration that sites may be open to changes in site occupancy over time-scales typical of many occupancy investigations, combined with the sensitivity of models to violations of the closure assumption, highlights the importance of properly addressing the closure assumption in both sampling designs and analysis. Furthermore, inappropriately applying closed models could have negative consequences when monitoring rare or declining species for conservation and management decisions, because violations of closure typically lead to overestimates of the probability of occurrence.
Understanding survival probabilities is critical for the sustainable harvest of wildlife and fisheries populations. Age‐ and stage class‐specific survival probabilities are needed to inform a suite ...of population models used to estimate abundance and track population trends. However, current techniques for estimating survival probabilities using age‐at‐harvest methods require restrictive assumptions or incorporate potentially unknown parameters within the model.
Using a Bayesian approach, we developed a flexible age‐at‐harvest model that incorporates either age‐ or stage‐structured populations, while accounting for uncertainty in age structure, population growth rates and relative selectivity. Survival probabilities can vary by age or stage class, as well as by environmental covariates, and both population growth rates and selectivity for each age or stage class can be specified as fixed and known or these parameters can be specified as informative priors, allowing for the incorporation of expert opinion. We evaluated our model with simulations and empirical data from harvested bobcats Lynx rufus and American paddlefish Polyodon spathula.
Models fit to simulated age‐at‐harvest data yielded unbiased estimates of survival probability when population growth rates and selectivity were centered on the data‐generating parameter. We obtained unbiased estimates of survival probability even with biased prior estimates of selectivity and random departures from the assumed stage distribution, although the latter increased uncertainty in those estimates. We found biased estimates of survival probability when the prior distribution for population growth rate was not centered on the data‐generating value. When fit to empirical harvest data, our proposed age‐at‐harvest model produced estimates of survival probability congruent to those reported in the literature within similar geographic regions.
We demonstrate the utility of a novel age‐at‐harvest model that estimates survival probability and realistically account for uncertainty in model parameters, transcending the restrictive assumptions and auxiliary data requirements of other methods. Furthermore, we advise collecting information about population trends and age structure alongside age‐at‐harvest data to help reduce bias. Although our model cannot replace more rigorous methods, we believe our model will be transformative for wildlife and fisheries practitioners who collect age‐at‐harvest data to estimate age‐ or stage‐specific survival probabilities to help inform management decisions.
Bobcats (Lynx rufus) are the most broadly distributed native felid in North America and have substantial ecological and economic importance. Despite this importance, little is known about factors ...influencing population dynamics of this cryptic carnivore. Given recent apparent declines in abundance, we investigated population growth rate (λ) for a bobcat population in the Black Hills, South Dakota, USA, 2016–2022. We constructed and evaluated a females‐only matrix population model. Our estimate of asymptotic λ, derived from estimates of vital rates obtained over 6 years, was 0.85 (95% CI = 0.72, 1.02), which indicates that the vital rates in 2016–2022 were inadequate to sustain the population. Elasticity and sensitivity values were highest for changes in adult survival probability followed by, in order, changes in kitten and juvenile survival and adult reproductive contribution. Life‐stage simulation analysis also supported that adult survival was most important; however, the juvenile survival (91 day–1 year) component of a bobcat's first year of life was also important and a stronger influence on population growth than the kitten survival (first 90 days) component. For the combination of survival and reproductive rates we estimated positive population growth required either annual adult survival >0.85 or 275‐day juvenile survival >0.35, regardless of other vital rates. When assuming a baseline harvest rate of 23.5%, reducing the harvest rate to 9% led to a positive mean growth rate and a >0.50 probability of a growing population. Monitoring juvenile‐to‐adult harvest ratios can provide an indicator of age structure in the population, and we recommend restricting harvest when that ratio falls below 10%, particularly when managers lack research information on population growth.
Given recent apparent declines in abundance, we investigated population growth rate (λ) for a bobcat population in the Black Hills, South Dakota, USA, 2016–2022. Our estimate of asymptotic λ, derived from estimates of vital rates obtained over a 6‐year period, was 0.85 (95% CI = 0.72, 1.02), which indicates that the vital rates in 2016–2022 were inadequate to sustain the population. Monitoring juvenile‐to‐adult harvest ratios can provide an indicator of age structure in the population, and we recommend restricting harvest when that ratio falls below 10%, particularly when managers lack research information on population growth.
Multispecies occupancy models estimate dependence among multiple species of interest from patterns of co-occurrence, but problems associated with separation and boundary estimates can lead to ...unreasonably large estimates of parameters and associated standard errors when species are rarely observed at the same site or when data are sparse. In this paper, we overcome these issues by implementing a penalized likelihood, which introduces a small bias in parameter estimates in exchange for a potentially large reduction in variance. We compare parameter estimates obtained from both penalized and unpenalized multispecies occupancy models fit to simulated data that exhibit various degrees of separation and to a real-word data set of bird surveys with little apparent overlap between potentially interacting species. Our simulation results demonstrate that penalized multispecies occupancy models did not exhibit boundary estimates and produced lower bias, lower mean squared error, and improved inference relative to unpenalized models. When applied to real-world data, our penalized multispecies occupancy model constrained boundary estimates and allowed for meaningful inference related to the interactions of two species of conservation concern. To facilitate the use of our penalized multispecies occupancy model, the techniques demonstrated in this paper have been integrated into the unmarked package in R programing language.
1. Managed public wild areas have dual mandates to protect biodiversity and provide recreational opportunities for people. These goals could be at odds if recreation, ranging from hiking to legal ...hunting, disrupts wildlife enough to alter their space use or community structure. 2. We evaluated the effect of managed hunting and recreation on 12 terrestrial wildlife species by employing a large citizen science camera trapping survey at 1947 sites stratified across different levels of human activities in 32 protected forests in the eastern USA. 3. Habitat covariates, especially the amount of large continuous forest and local housing density, were more important than recreation for affecting the distribution of most species. The four most hunted species (white-tailed deer, raccoons, eastern grey and fox squirrels) were commonly detected throughout the region, but relatively less so at hunted sites. Recreation was most important for affecting the distribution of coyotes, which used hunted areas more compared with unhunted control areas, and did not avoid areas used by hikers. 4. Most species did not avoid human-made trails, and many predators positively selected them. Bears and bobcats were more likely to avoid people in hunted areas than unhunted preserves, suggesting that they perceive the risk of humans differently depending on local hunting regulations. However, this effect was not found for the most heavily hunted species, suggesting that human hunters are not broadly creating 'fear' effects to the wildlife community as would be expected for apex predators. 5. Synthesis and applications. Although we found that hiking and managed hunting have measureable effects on the distribution of some species, these were relatively minor in comparison with the importance of habitat covariates associated with land use and habitat fragmentation. These patterns of wildlife distribution suggest that the present practices for regulating recreation in the region are sustainable and in balance with the goal of protecting wildlife populations and may be facilitated by decades of animal habituation to humans. The citizen science monitoring approach we developed could offer a long-term monitoring protocol for protected areas, which would help managers to detect where and when the balance between recreation and wildlife has tipped.
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