Understanding the influence of harvest regulations on wildlife populations is crucial for successful population management and species conservation. This is true of greater sage-grouse (Centrocercus ...urophasianus), a species of great conservation concern in western North America that is a candidate for protection under the United States Endangered Species Act and is hunted in nine states within the United States. Recent recommendations have proposed shifting hunting seasons to later in the year, with a goal of reducing harvest of adult female and juvenile sage-grouse. Foundational principles of harvest theory, however, suggest that such changes to harvest timing could have unintentional and adverse effects on greater sage-grouse populations. I used published estimates of seasonal survival to reconstruct weekly mortality curves for adult female and juvenile greater sage-grouse in Nevada, USA. Under a hypothesis of compensatory mortality, I then calculated the maximum harvest occurring during any 1-week interval that could be compensated by non-harvest mortality that occurs after the hunting season. This value universally declines as harvest is held later in the season. Under a hypothesis of additive mortality, I calculated the realized reductions in both survival and subsequent reproductive success that would be expected for a given level of harvest. Both of these values increase if harvest is conducted later in the season, resulting in a larger additive effect than if harvest had occurred earlier. If reduced mortality of specific age or sex classes is desired, I suggest managers employ reduced bag limits, shortened season lengths, or permit systems to meet this objective. Holding hunting seasons later in the year than is presently custom (i.e., beginning sometime during Sep) should be avoided unless specific information exists to predict the change in harvest rate that would occur following changes to harvest timing.
Iconic sagebrush ecosystems of the American West are threatened by larger and more frequent wildfires that can kill sagebrush and facilitate invasion by annual grasses, creating a cycle that alters ...sagebrush ecosystem recovery post disturbance. Thwarting this accelerated grass–fire cycle is at the forefront of current national conservation efforts, yet its impacts on wildlife populations inhabiting these ecosystems have not been quantified rigorously. Within a Bayesian framework, we modeled 30 y of wildfire and climatic effects on population rates of change of a sagebrush-obligate species, the greater sage-grouse, across the Great Basin of western North America. Importantly, our modeling also accounted for variation in sagebrush recovery time post fire as determined by underlying soil properties that influence ecosystem resilience to disturbance and resistance to invasion. Our results demonstrate that the cumulative loss of sagebrush to direct and indirect effects of wildfire has contributed strongly to declining sage-grouse populations over the past 30 y at large spatial scales. Moreover, long-lasting effects from wildfire nullified pulses of sage-grouse population growth that typically follow years of higher precipitation. If wildfire trends continue unabated, model projections indicate sage-grouse populations will be reduced to 43% of their current numbers over the next three decades. Our results provide a timely example of how altered fire regimes are disrupting recovery of sagebrush ecosystems and leading to substantial declines of a widespread indicator species. Accordingly, we present scenario-based stochastic projections to inform conservation actions that may help offset the adverse effects of wildfire on sage-grouse and other wildlife populations.
American eel (Anguilla rostrata) often pass hydropower dams during adult spawning migrations. We conducted a 4-year acoustic telemetry study that characterized passage risks through two dams (West ...Enfield and Milford) in the Penobscot River, Maine, USA. We released tagged fish (n = 355) at two sites, estimated survival and delay under variable river conditions, and compared performance among dammed and free-flowing river sections. Survival rates (standardized per river kilometre, rkm) were lower at West Enfield (Φ
rkm
= 0.984 ± 0.006 SE) and Milford (Φ
rkm
= 0.966 ± 0.007 SE) compared with undammed River sections (Φ
rkm
= 0.998 ± 0.0003 SE). Cumulative mortality was 8.7% (4.4 km) and 14.2% (5.5 km) through dammed sections and 8.7% throughout the rest of the river (58.1 km). Fish that already passed an upstream dam incurred higher downstream mortality compared with individuals without passage experience. Additionally, fish endured long delays at dams, and >10% of fish were delayed >24 h. Low flows exacerbated the risk of mortality and delay. These results offer evidence for direct, latent, and sublethal consequences of dam passage for migrating eels.
Millions of dams impair watershed connectivity across the globe and have severely affected migratory fish populations. Fishways offer upstream passage opportunities, but artificial selection may be ...imposed by these structures. Using juvenile American eel Anguilla rostrata as a model species, we consider whether individual differences in behaviour (i.e. personality) and fish size can predict passage success.
We evaluated the expression of bold and exploratory behaviours using open field and emergence assays in the laboratory. Then we assessed the propensity for individuals to volitionally climb through an experimental fishway to understand if personality and fish size could predict climbing success.
We demonstrate personality in juvenile eels, and swimming speed in the open field was negatively associated with climbing propensity. Slower swimmers were up to 60% more likely to use the passage device suggesting that more exploratory eels incurred greater passage success. For successful climbers, climbing time was negatively associated with fish length.
Synthesis and applications. Our results suggest fish may segregate at barriers based on personality and size. Preventing a subset of individuals from accessing upstream habitat is likely to have negative consequences for fish populations and aquatic ecosystems. Selection may be alleviated by increasing passage opportunities, maximizing fishway attraction and avoiding inefficient passage solutions.
Our results suggest fish may segregate at barriers based on personality and size. Preventing a subset of individuals from accessing upstream habitat is likely to have negative consequences for fish populations and aquatic ecosystems. Selection may be alleviated by increasing passage opportunities, maximizing fishway attraction and avoiding inefficient passage solutions.
Weather is a source of environmental variation that can affect population vital rates. However, the influence of weather on individual fitness is spatially heterogeneous and can be driven by other ...environmental factors, such as habitat composition. Therefore, individuals can experience reduced fitness (e.g., decreased reproductive success) during poor environmental conditions through poor decisions regarding habitat selection. This requires, however, that habitat selection is adaptive and that the organism can correctly interpret the environmental cues to modify habitat use. Greater Sage-Grouse (Centrocercus urophasianus) are an obligate of the sagebrush ecosystems of western North America, relying on sagebrush for food and cover. Greater Sage-Grouse chicks, however, require foods with high nutrient content (i.e., forbs and insects), the abundance of which is both temporally and spatially dynamic and related primarily to water availability. Our goal was to assess whether nest site selection and movements of broods by females reduced the negative effect of drought on offspring survival. As predicted, chick survival was negatively influenced by drought severity. We found that sage-grouse females generally preferred to nest and raise their young in locations where their chicks would experience higher survival. We also found that use of habitats positively associated with chick survival were also positively associated with drought severity, which suggests that females reduced drought impacts on their dependent young by selecting more favorable environments during drought years. Although our findings suggest that female nest site selection and brood movement rates can reduce the negative effects of drought on early offspring survival, the influence of severe drought conditions was not completely mitigated by female behavior, and that drought conditions should be considered a threat to Greater Sage-Grouse population persistence.
Adaptive habitat-selection theory predicts that individuals should use habitats that maximize lifetime fitness. However, trade-offs between life-history stages, environmental variability, and ...predator–prey dynamics can interact with individual preferences, which may result in individuals selecting suboptimal habitats. Understanding the distinction between adaptive and maladaptive animal use of habitat is central to effective species conservation, because use of maladaptive habitat is counter to conservation objectives. Our objectives were to assess whether habitat characteristics selected by Greater Sage-Grouse (Centrocercus urophasianus) were correlated with increased production of fledged young. We monitored 411 nests and 120 broods from 234 females between 2004 and 2012 in central Nevada, USA. We determined which habitat characteristics were selected as nesting habitat and assessed whether these characteristics influenced nest success and early offspring survival. The relationships between characteristics selected at nest sites and metrics of reproductive success were variable, in that certain characteristics (e.g., forb cover, amount of pinyon–juniper woodlands) were correlated with higher nest survival and chick survival, but other characteristics (e.g., amount of sagebrush, residual grass height) did not improve reproductive success. Despite variability among predictor variables, we found a positive effect of selection of fine-scale habitat characteristics on nest (βNS-Local = 0.14, 85% confidence interval CI: 0.04–0.23) and chick survival (βCS-Local = 0.39, 85% CI: 0.27–0.50); however, we did not find that selection of broad-scale habitat characteristics predicted reproductive success (βNS-Landscape = −0.04, 85% CI: −0.15 to 0.06; βCS-Landscape = 0.06, 85% CI: −0.06 to 0.18). Additionally, nest-site selection was more predictive of chick survival than of nest survival, which suggests that females' selection of nesting habitat was based primarily on its qualities as brood-rearing habitat. Together, these findings suggest that nest-site selection may be influenced by more than increased reproductive success, or that there is a landscape-level pattern to local-scale habitat characteristics.
Diadromous fish populations have incurred precipitous declines across the globe. Among many stressors, these species are threatened by anthropogenic barriers that impede movement, alter riverine ...habitat, and augment predator communities. In this study, we used acoustic transmitters ( n = 220) with predation and temperature sensors to characterize Atlantic salmon ( Salmo salar) smolt predation risk in the Penobscot River, Maine, USA. Across two seasons, we documented 79 predation events through a 170 km migratory pathway, which included three hydropower projects and a large estuary. We detected tagged smolts that were predated by fish ( n = 42), marine mammals ( n = 28), and birds ( n = 9). Using a multistate mark-recapture framework, we estimated that 46% of smolts were predated during downstream migration, which accounted for at least 55% of all mortality. Relative predation risk was greatest through impoundments and the lower estuary, where on average, predation rates were 4.8-fold and 9.0-fold greater than free-flowing reaches, respectively. These results suggest that predation pressure on Atlantic salmon smolts is exacerbated by hydropower projects and that predation in the lower estuary may be greater than expected.
Monitoring population response to conservation actions, such as habitat management, is critical to evaluate conservation outcomes. Greater Sage-Grouse (Centrocercus urophasianus) has been the ...recipient of substantial recent conservation efforts in North America. Sage-Grouse are often surveyed using counts of males displaying on breeding leks, and these lek counts offer a practical method for monitoring Sage-Grouse population trends. Although substantial work has assessed the utility of lek count data for large-scale population monitoring, there has been comparably little effort focused on the use of lek counts to evaluate local-scale management. We used Greater Sage-Grouse lek count data from Oregon, USA, combined with simulation, to evaluate the sample sizes (number of leks, years of monitoring) required to detect a positive outcome of habitat management on population growth. We further assessed assumptions associated with male detection, and compared analyses that both did (N-mixture models) and did not (Poisson regression) account for detection probability. We found that when treatments produced a 5% increase in annual population growth, and leks were monitored for at least 10 years, lek counts produced unbiased and detectable estimates of treatment effects with as few as seven treatment and seven control leks. Using an unbalanced design with a greater number of control leks (n = 16) permitted inference from even fewer treatment leks (n = 4), however, we found no scenarios where use of more control leks permitted detection of smaller treatment effects or allowed shorter duration studies. We found that N-mixture models and Poisson regression of the maximum of three repeated counts produced equivalent results when detection probability was constant, but at the small sample sizes we evaluated, confounding between detection probability and habitat management compromised the accuracy of all analysis methods. Our results show that lek counts hold promise for efficient monitoring of local-scale conservation, but further work is needed to understand the mechanisms that affect male detection during lek surveys.
Plant phenological processes produce temporal variation in the height and cover of vegetation. Key aspects of animal life cycles, such as reproduction, often coincide with the growing season and ...therefore may inherently covary with plant growth. When evaluating the influence of vegetation variables on demographic rates, the decision about when to measure vegetation relative to the timing of demographic events is important to avoid confounding between the demographic rate of interest and vegetation covariates. Such confounding could bias estimated effect sizes or produce results that are entirely spurious. We investigated how the timing of vegetation sampling affected the modeled relationship between vegetation structure and nest survival of greater sage‐grouse (Centrocercus urophasianus), using both simulated and observational data. We used the height of live grasses surrounding nests as an explanatory covariate, and analyzed its effect on daily nest survival. We compared results between models that included grass height measured at the time of nest fate (hatch or failure) with models where grass height was measured on a standardized date – that of predicted hatch date. Parameters linking grass height to nest survival based on measurements at nest fate produced more competitive models, but slope coefficients of grass height effects were biased high relative to truth in simulated scenarios. In contrast, measurements taken at predicted hatch date accurately predicted the influence of grass height on nest survival. Observational data produced similar results. Our results demonstrate the importance of properly considering confounding between demographic traits and plant phenology. Not doing so can produce results that are plausible, but ultimately inaccurate.
The decision about when to measure vegetation relative to the timing of demographic events is important to avoid sampling covariance between the demographic rate of interest and vegetation covariates. Such covariance could bias estimated effect sizes or produce spurious results. Our simulations indicate that models of covariate effects based on improperly measured covariates will be favored as predictive based on established model selection procedures even in situations where no effect of the covariate exists in nature.
Conventional life-history theory predicts that energy-demanding events such as reproduction and migration must be temporally segregated to avoid resource limitation. Here, we provide, to our ...knowledge, the first direct evidence of 'itinerant breeding' in a migratory bird, an incredibly rare breeding strategy (less than 0.1% of extant bird species) that involves the temporal overlap of migratory and reproductive periods of the annual cycle. Based on GPS-tracking of over 200 female American woodcock, most female woodcock (greater than 80%) nested more than once (some up to six times) with short re-nest intervals, and females moved northwards on average 800 km between first and second nests, and then smaller distances (
200+ km) between subsequent nesting attempts. Reliance on ephemeral habitat for breeding, ground-nesting and key aspects of life history that reduce both the costs of reproduction and migration probably explain the prevalence of this rare phenotype in woodcock and why itinerant breeding so rarely occurs in other bird species.
PDF
