John H. Giudice

Comparison of avian communities on restored and natural wetlands in north and south Dakota

We compared avian use of 39 restored and 39 natural wetlands in North and South Dakota during spring and summer of 1997 and 1998. Wetlands were widely distributed, but restored- and natural-wetland pairs were from the same geographic locale and had similar characteristics, including wetland size. We conducted paired comparisons between restored and natural wetlands for wetland-bird density, waterfowl-breeding pairs, and wetland-avian abundance, species richness, and diversity. We also compared abundance, species richness, and diversity of birds on upland areas adjacent to wetlands. Canada goose (avian scientific names in Appendix A), mallard, redhead, and ruddy duck had higher densities on restored wetlands. We failed to detect differences in overall avian abundance, species richness, or diversity between restored and natural wetlands. We conclude that restored wetlands in the Prairie Pothole Region supported similar avian communities with equal or higher abundances than those of natural wetlands.

Variance of stratified survey estimators with probability of detection adjustments

Abstract Estimates of wildlife population sizes are frequently constructed by combining counts of observed animals from a stratified survey of aerial sampling units with an estimated probability of detecting animals. Unlike traditional stratified survey designs, stratum-specific estimates of population size will be correlated if a common detection model is used to adjust counts for undetected animals in all strata. We illustrate this concept in the context of aerial surveys, considering 2 cases: 1) a single-detection parameter is estimated under the assumption of constant detection probabilities, and 2) a logistic-regression model is used to estimate heterogeneous detection probabilities. Naïve estimates of variance formed by summing stratum-specific estimates of variance may result in significant bias, particularly if there are a large number of strata, if detection probabilities are small, or if estimates of detection probabilities are imprecise.

Survival and recovery of Mallards and Gadwalls banded in eastern Washington, 1981-1998

Abstract Current estimates of annual survival, an important process affecting population dynamics, are lacking for breeding-waterfowl populations in Washington. I used hunting-season recoveries in conjunction with band-recovery models (program MARK) to estimate survival and recovery probabilities of Mallards (Anas platyrhynchos) and Gadwalls (A. strepera) banded in eastern Washington during 1981–1998. I also evaluated hypotheses about sources of variation in these rates and described the geographical and temporal distribution of band recoveries. Mallard survival and recovery probabilities were sex and age-specific, and recovery rates were year-specific but not strongly correlated with harvest regulations. Survival probability of Mallards was 0.661 for adult males, 0.660 for immature females, 0.606 for adult females, and 0.560 for immature males. Average recovery rates were generally highest for immature males (0.083) followed by adult males (0.050), immature females (0.050), and adult females (0.029). Survival and recovery rates of Gadwalls were 0.576 and 0.054, respectively, but sample size was small (52 recoveries from 436 banded birds) and sex-age classes were pooled prior to analysis. Seventy-two percent of Mallards banded in eastern Washington were recovered in the Columbia Basin of central Washington. The proportion of adult-male recoveries decreased in the Columbia Basin (from 75% in 1981–84 to 54% in 1995–98) and increased in California (from 4% to 22%). The distribution of direct recoveries of Gadwalls was similar to Mallards. My data suggest that annual survival of Mallards and Gadwalls banded in eastern Washington was similar to or slightly higher than survival probabilities in other North America populations.

Cost and Precision Functions for Aerial Quadrat Surveys: a Case Study of Ring-Necked Ducks in Minnesota

Abstract Cost considerations may be as important as precision when making survey-design choices, and the ability to accurately estimate survey costs will be essential if survey budgets become more constrained. We used data from a survey of ring-necked ducks (Aythya collaris) to illustrate how simple distance formulas can be used to construct a cost function for aerial quadrat surveys. Our cost function provided reasonable estimates of effort (hr) and costs, and allowed us to evaluate plot-size choices in terms of expected cost-precision tradeoffs. Although factors influencing costs in wildlife surveys can be complicated, we believe that cost functions deserve more attention and should be routinely considered in conjunction with traditional power analyses.

A comparison of models using removal effort to estimate animal abundance

This paper compares methods for modeling the probability of removal when variable amounts of removal effort are present. A hierarchical modeling framework can produce estimates of animal abundance and detection from replicated removal counts taken at different locations in a region of interest. A common method of specifying variation in detection probabilities across locations or replicates is with a logistic model that incorporates relevant detection covariates. As an alternative to this logistic model, we propose using a catch–effort (CE) model to account for heterogeneity in detection when a measure of removal effort is available for each removal count. This method models the probability of detection as a nonlinear function of removal effort and a removal probability parameter that can vary spatially. Simulation results demonstrate that the CE model can effectively estimate abundance and removal probabilities when average removal rates are large but both the CE and logistic models tend to produce biased estimates as average removal rates decrease. We also found that the CE model fits better than logistic models when estimating wild turkey abundance using harvest and hunter counts collected by the Minnesota Department of Natural Resources during the spring turkey hunting season.