Kevin M. Ringelman

Assessing Uncertainty in Coastal Marsh Core Sampling for Waterfowl Foods

Abstract Quantifying foraging resources available to waterfowl in different habitat types is important for estimating energetic carrying capacity. To accomplish this, most studies collect soil-core samples from the marsh substrate, sieve and sort food items, and extrapolate energy values to wetland or landscape scales. This is a costly and time-intensive process; furthermore, extrapolation methods yield energy estimates with large variances relative to the mean. From both research and management perspectives, it is important to understand sources of this variation and estimate the number of soil cores needed to reduce the variance to desired levels. Using 2,341 cores collected from freshwater and salt marsh habitats at four sites along the Atlantic Coast, we examined sampling variation and biological variation among sites and habitats. When we removed extreme outliers in the data caused by large animal food items found in a small core sample, estimates of energy density decreased by an order of magnitude ...

Dabbling Ducks Increase Nest Defense After Partial Clutch Loss

Abstract. Predation is the primary source of mortality of dabbling duck nests, so a key aspect of parental investment is defending the nest from predators. The hens presence on the nest is widely considered to be a good measure of nest defense; an incubating female camouflages the nest and may physically deter nest predators. Parental-investment theory suggests that investment should increase with the reproductive benefits expected from the current clutch of eggs. We used nest-temperature loggers to study how the rhythms of waterfowl incubation changed after the nest was partially destroyed by a predator. Contrary to the expected-benefits hypothesis, we found that hens significantly increased their investment after partial clutch loss: they took fewer recesses from incubation per day and extended their incubation by more than 200 min after a partial depredation. We suggest that when predators pose little risk to the incubating adult, those hens unable or unwilling to abandon a nest after partial clutch loss will increase parental investment to obtain at least some reproductive benefits.

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.

Estimating Waterfowl Carrying Capacity at Local Scales: A Case Study from Edwin B. Forsythe National Wildlife Refuge, New Jersey

Abstract The management of wintering North American waterfowl is based on the premise that the amount of foraging habitat can limit populations. To estimate carrying capacity of winter habitats, managers use bioenergetic models to quantify energy (food) availability and energy demand, and use results as planning tools to meet regional conservation objectives. Regional models provide only coarse estimates of carrying capacity because habitat area, habitat energy values, and temporal trends in population-level demand are difficult to quantify precisely at large scales. We took advantage of detailed data previously collected on wintering waterfowl at Edwin B. Forsythe National Wildlife Refuge and surrounding marsh, New Jersey, and created a well-constrained local model of carrying capacity. We used 1,223 core samples collected between 2006 and 2015 to estimate food availability. We used species-specific 24-h time–activity data collected between 2011 and 2013 to estimate daily energy expenditure, morphometric...

Habitat Edges Have Weak Effects on Duck Nest Survival at Local Spatial Scales

Edge effects on nesting success have been documented in breeding birds in a variety of contexts, but there is still uncertainty in how edge type and spatial scale determine the magnitude and detectability of edge effects. Habitat edges are often viewed as predator corridors that surround or penetrate core habitat and increase the risk of predation for nearby nests. We studied the effects of three different types of potential predator corridors (main perimeter roads, field boundaries, and ATV trails within fields) on waterfowl nest survival in California. We measured the distance from duck nests to the nearest edge of each type, and used distance as a covariate in a logistic exposure analysis of nest survival. We found only weak evidence for edge effects due to predation. The best supported model of nest survival included all three distance categories, and while all coefficient estimates were positive (indicating that survival increased with distance from edge), 85% coefficient confidence intervals approached or bounded zero indicating an overall weak effect of habitat edges on nest success. We suggest that given the configuration of edges at our site, there may be few areas far enough from hard edges to be considered ‘core’ habitat, making edge effects on nest survival particularly difficult to detect.