Scott E. Stephens

Effects of habitat fragmentation on avian nesting success: a review of the evidence at multiple spatial scales

We reviewed published literature to examine the effect of habitat fragmentation on avian nesting success at three spatial scales (i.e., edge, patch, and landscape scales). We identified 86 relevant manuscripts that provided 117 individual tests of hypotheses regarding the effects of habitat fragmentation on nesting success. Most papers and reviews on this topic have been narrow in scope and have not examined multiple spatial scales. However, our results suggest that the scale at which fragmentation is measured (i.e., edge, patch and landscape) and the duration of the studydo influence the probabilitythat a studywill detect a fragmentation effect. Studies that measured fragmentation at landscape scales and studies conducted over several years were more likely to detect effects of fragmentation on nesting success. A recent review of research on nest predators and habitat fragmentation found a verysimilar scale-dependent pattern; predator effects were more prevalent when fragmentation occurs at landscape scales than patch or edge scales. Based on these findings, we recommend future research on the topic should be conducted at the landscape scale, over several years, and incorporate accompanying work on nest-predator ecology. Correspondingly, conservation actions that limit fragmentation at landscape scales should have positive impacts on nesting success rates and bird populations. # 2003 Elsevier Ltd. All rights reserved.

DUCK NEST SURVIVAL IN THE MISSOURI COTEAU OF NORTH DAKOTA: LANDSCAPE EFFECTS AT MULTIPLE SPATIAL SCALES

Nest survival is one of the most important parameters in the population dynamics of grassland-nesting ducks (Anas and Aythya spp.) that breed in the Prairie Pothole Region of North America. Grassland habitats used by these species are increasingly threatened by habitat loss and the coincident fragmentation, which may indirectly alter nest survival through effects on predators. Although predators are the dominant cause of nest loss, they are difficult to monitor directly. Thus, indirect analyses of habitat variables are required. Many studies have attempted to address the relationship between fragmentation and nest survival; however, few studies have examined the influence of fragmentation at multiple spatial scales. Understanding how landscape characteristics at multiple spatial scales explain variation in nest survival is important, because no single correct scale is likely to exist for a diversity of landscape metrics. We examined the relationships between habitat variables and duck nest survival (n ≈ 4...

Predicting Risk of Habitat Conversion in Native Temperate Grasslands

Native grasslands that support diverse populations of birds are being converted to cropland at an increasing rate in the Prairie Pothole Region of North America. Although limited funding is currently available to mitigate losses, accurate predictions of probability of conversion would increase the efficiency of conservation measures. We studied conversion of native grassland to cropland in the Missouri Coteau region of North and South Dakota (U.S.A.) during 1989-2003. We estimated the probability of conversion of native grassland to cropland with satellite imagery and logistic regression models that predicted risk of conversion and by comparing the overlap between areas of high biological value and areas most vulnerable to conversion. Annualized probability of conversion was 0.004, and 36,540 ha of native grassland were converted to cropland during the period of our study. Our predictive models fit the data and correctly predicted 70% of observed conversions of grassland. Probability of conversion varied spatially and was correlated with landscape features like amount of surrounding grassland, slope, and soil productivity. Tracts of high biological value were not always at high risk of conversion. We concluded the most biologically valuable areas that are most vulnerable to conversion should be prioritized for conservation. This approach can be applied broadly to other systems and offers great utility for implementing conservation in areas with spatially variable biological value and probability of conversion.

A General Bayesian Hierarchical Model for Estimating Survival of Nests and Young

ABSTRACT. Models for estimating survival probability of nests and young have changed dramatically since the development of the Mayfield method. Improvements in software and a steady increase in computing power have allowed more complexity and realism in these models, allowing researchers to provide better estimates of survival and to relate survival rates to relevant covariates. However, many current analysis methods utilize fixed-effects models with the implicit assumption that the covariates explain all of the variation in the data, other than random variation within a specified family of distributions. This is generally a strong assumption, and, in the presence of heterogeneity and lack of independence, these estimates have been shown to be negatively biased. Others have begun to explore random-effects models for these situations, but a readily applicable Bayesian approach has been lacking. We present a general Bayesian modeling framework appropriate for survival of both nests and young that simultaneously allows for the inclusion of individual covariates and random effects and provides a measure of goodness-of-fit. We used previously published data on survival of Common Goldeneye (Bucephala clangula) ducklings in interior Alaska and on nest survival in three species of prairie-nesting ducks that nested in the Missouri Coteau region of North Dakota to demonstrate this approach. The inclusion of a brood-level random effect in the Common Goldeneye example increased point estimates and credible interval [CI] coverage from 0.62 (95% CI: 0.49–0.73) and 0.66 (95% CI: 0.58–0.74) for 2002 and 2003, respectively, to 0.69 (95% CI: 0.42–0.88) and 0.74 (95% CI: 0.57–0.88) for 2002 and 2003, respectively.

Evaluation of a plasticine-filled leg band for day-old ducklings

We evaluated plasticine-filled leg bands via recapture and band recovery information from 7,172 day-old wood ducks (Aix sponsa) double-marked (plasticine band and a web tag) in Kentucky, Mississippi, and Missouri in 1993-98. These bands performed relatively well, with highest retention rates achieved in Missouri 1997-98 (98.6%) and Mississippi 1996-97 (97.3%). As part of an international project, we also conducted a study to test the null hypothesis of no difference in survival rates between 2 cohorts of ducklings marked with (1) plasticine-filled bands, and (2) web tags, Data from 2,745 double-marked, newly batched ducklings of 6 species and 117 subsequent recaptures or recoveries in the United States and Latvia were used in 4 different tests; none provided any evidence (P > 0.11) that ducklings marked with plasticine-filled leg bands exhibited greater mortality than those with web tags. We encourage extending use of this technique to other species of ducks, mergansers, and coots, because these leg bands have high retention rates, are easily detected by hunters. and permit additional inferences about posthatch movements, natal dispersal, neonate survival, and true recruitment The handing technique may be applicable in studies of most precocial bird species if a universal filling material is developed.

Time-lagged variation in pond density and primary productivity affects duck nest survival in the Prairie Pothole Region

The Prairie Pothole Region (PPR) is the primary breeding region for most species of North American dabbling ducks (Anas spp.). Conservation of these species is guided in part by knowledge of relationships between nest survival probability and habitat features. Positive relationships between duck nest survival and amount and configuration of herbaceous perennial vegetation have been observed in previous studies, but these 2- to 4-year studies might not have adequately characterized the temporal effect of wet-dry episodes on nest survival. Over an eight-year period, we studied nest survival of five species of ducks in the PPR relative to spatial and temporal variation in pond density, primary productivity, and hydrologic status of wetlands, soil, and vegetation on 52 study sites selected to span a gradient of spatial variation in proportion of herbaceous perennial vegetation and in number of wetland basins. We observed the fate of 12 754 nests. Consistent with past studies, 90% of nests that failed to hatch were destroyed by predators. Nest survival probability was positively related to current-year pond density and primary productivity, negatively related to pond density and primary productivity during the previous two years, and positively related to the number of wetland basins on the study site. Predicted relationships between nest survival and proportion or configuration of herbaceous perennial vegetation in the surrounding landscape were not supported. For mallard (Anas platyrhynchos), median estimated nest survival probability ranged from 0.02 (SE = 0.01) to 0.22 (SE = 0.02). Estimated nest survival was greatest on sites with numerous wetland basins that had transitioned from dry, unproductive conditions to wet, productive conditions in the previous 1-2 years. Our results were consistent with time-lagged responses of food webs to resource pulses in a broad array of ecosystems. Our study highlighted the importance of wetland basins and wet-dry episodes to duck nest survival in the PPR. Current habitat conservation efforts focus on landscapes with numerous wetland basins and a high proportion of herbaceous perennial vegetation. Our results suggest that future conservation efforts should focus on preserving high-density wetland complexes across as large a geographic extent as possible even in cropland-dominated landscapes.

Wind Power and Biofuels: A Green Dilemma for Wildlife Conservation

Renewable or green energy is defined as energy generated from natural processes that are replenished over time; it includes electricity and heat generated from solar, wind, hydropower, biomass, geothermal resources, and biofuels derived from renewable resources. In 2006, around 18 percent of global energy use was derived from renewable sources (REN21 2008). The Obama Administration has made the development of renewable energy a top priority for economic expansion, to reduce U.S. dependence on fossil fuels and to lower greenhouse gas emissions contributing to climate change. More than twenty states have enacted laws requiring that a portion of the electricity supply come from renewable energy (American Wind Energy Association 2006). The U.S. Department of Energy (2008a) reports that it is technically feasible to generate 20 percent of the nation’s electricity by 2030 from wind energy, and there is a goal of replacing 30 percent of transportation fuel consumption with renewable fuels by the year 2030. Although developing renewable energy sources is generally considered environmentally friendly, impacts on wildlife and their habitats can be associated with many forms of renewable energy (McDonald et al.2009). With the expected increase in renewable energy, careful planning is needed to avoid conflicts between the development of green energy and concerns with wildlife impacts.

Influence of Wind Turbines on Presence of Willet, Marbled Godwit, Wilson's Phalarope and Black Tern on Wetlands in the Prairie Pothole Region of North Dakota and South Dakota

Abstract. The millions of wetlands that define the Prairie Pothole Region (PPR) harbor large proportions of continental populations of several species of North American waterfowl, waterbirds, and shorebirds. The PPR also has some of the highest wind energy potential in the United States. Thousands of wind turbines are being erected in the PPR to produce electricity and have the potential to affect migratory bird populations through collisions, displacement, barriers to movement, habitat fragmentation, and habitat loss. We assessed occurrence of waterbirds and shorebirds from 2008 through 2010 on wetlands in two wind energy development sites, defined as wetlands within 805 m of a wind turbine, and two reference sites in the PPR of North and South Dakota. We conducted 10,321 wetland visits on 3,542 individual wetland basins and related bird occurrence to wetland characteristics, upland characteristics, survey type (roadside vs. off-road), seasonal timing of sampling, year of sampling, and site type (wind energy development vs. reference). Models characterizing occurrence of Willet (Catoptrophorus semipalmatus), Marbled Godwit (Limosa fedoa), Wilsons Phalarope (Phalaropus tricolor) and Black Tern (Chlidonias niger) indicated that occurrence varied with wetland characteristics and among sites and years, was not substantially reduced on either wind energy site, but was slightly and consistently lower on one of the wind energy sites for the three shorebird species. Our results suggest that wetlands have conservation value for these species when wind turbines are present, but additional sampling across time and space will be necessary to understand the effects of wind turbines on shorebird and waterbird presence, density, survival, and reproductive success.

Temporal and multi-spatial environmental drivers of duck nest survival

ABSTRACT Nest survival is determined in part by a combination of large-scale environmental factors and local nest-site characteristics. Because predation is the primary cause of nest failure, those drivers likely operate by influencing predator abundance, behavior, and/or nest detectability. For example, fluctuations in landscape productivity have the potential to alter predator and prey abundance, whereas nest vegetation and patterns of nest spacing may influence predator behavior. We used 8 yr of site-specific environmental data coupled with data collected from 11,547 duck nests to evaluate the relative importance of large-scale and local factors on nest survival. We found that higher values of gross primary productivity, basins, and pond counts were associated with higher nest survival in a given year, but were associated with lower nest survival the following 2 yr. Taken in combination with the literature, our interpretation is that productive environmental conditions can result in time-lagged increases in predator abundance, leading to higher levels of nest predation in subsequent years. Local factors were generally less important than large-scale covariates in determining duck nest survival, but we found that nests laid earlier, in thicker vegetation, and with closer nearest neighbors had higher survival rates. However, as the season progressed, nests with closer nearest neighbors had lower survival rates (significant initiation date*distance interaction), suggesting predators may eventually aggregate in areas of higher nest density. Our results highlight the importance of both large-scale and local factors as they affect duck nest survival, and suggest several hypotheses about predator numerical and aggregative responses that are ripe for empirical testing.

Skewed Age Ratios of Breeding Mallards in the Nebraska Sandhills

Abstract Understanding demographic structures of populations allows managers to better evaluate factors affecting populations and increase efficiency of conservation efforts. Recent studies suggest low productivity, but high survival characterizes mallard (Anas platyrhnchos) populations in the Nebraska Sandhills. We studied age ratios of decoy-trapped and observer-shot mallards in the Sandhills during 2007–2008. Observed age distribution (second-year:after-second-year) of mallards was 2.8:1 for females and 0.8:1 for males. Age ratios of trapped females were skewed towards young females relative to other studies, and the age ratio of trapped females was not different than the age ratio of the sample we collected by shooting. The skewed age ratios we observed provide additional context to the low reproductive success that has been reported for nesting mallards in the Sandhills. Second-year mallard females tend to invest fewer resources and take fewer risks associated with nesting. As a result the Sandhills population may not contribute significantly to productivity of the continental mallard population but act as a reservoir of young female mallards available to disperse to more productive breeding areas in future years.