An aerial grid‐based sampling method to estimate nonbreeding duck abundance

Abstract

Probability-based sampling designs for aerial surveys are useful for estimating wintering waterfowl abundances in large areas with contiguous habitat (e.g., Mississippi Alluvial Valley). The effectiveness of these approaches for estimating abundance of nonbreeding waterfowl in small areas with discontinuous habitat has rarely been assessed. Surveys conducted within riverine areas introduce sampling design difficulties because of discontinuous bottomland habitat and irregularity of flooding events. Therefore, we implemented and evaluated a generalizable grid-based, stratified random sampling design to estimate weekly duck abundance within the Wabash River floodplain in southeastern Illinois and southwestern Indiana, USA, during midwinter and early spring 2012 and 2013. We used aerial and ground-based counts to generate abundance estimates and evaluate within-week variation of counts. Peak duck abundance totaled 279,717 (SE ¼ 69,101) in 2012 and 742,027 (SE ¼ 296,563) in 2013. Dabbling ducks were the most abundant duck guild detected and abundance estimates for this group met our precision goal (CV 0.25) in 4 of 18 surveys ( x ¼ 0.33, range ¼ 0.20-0.51). We compared the grid-based approach with a traditional aerial inventory and found that estimates from the grid-based approach were on average 75,175 (SE ¼ 46,768) greater than inventory counts. Desired levels of precision were often not met, yet design improvements in 2013 notably increased precision, suggesting that further modifications may allow this method to be useful in riverine areas with discontinuous and ephemeral habitat. Ó 2017 The Wildlife Society.

Understanding implications of detection heterogeneity in wildlife abundance estimation

“…An alternative is to base estimation on mark‐recapture distance sampling to remove residual heterogeneity resulting from distance between the animal and sampler. Hennig and Schoenecker (2023) found that mark‐recapture distance sampling was more cost‐effective and less invasive for aerial surveys of wild burros than methods that included a sample of telemetered animals (Hennig et al 2022), which are similar to what we have described and recommended here. Researchers should always be cognizant of heterogeneity in detection probability in the selection and implementation of the sampling method and analysis approaches for their data.…”

Worth the reward? An experimental assessment of risk‐taking behavior along a life history gradient

“…Although we used a random selection protocol to select individuals on which to conduct behavior samples, ducks were not marked, therefore, it is possible that the same individual may have been sampled multiple times. However, this is unlikely because hundreds of thousands of ducks migrate through this region during spring (Hennig et al ) and generally ducks were in large flocks (mean = 64 individuals) so the probability of sampling the same bird twice, using our random selection protocol, was low.…”

Methods for surveying and estimating breeding waterfowl populations in the Prairie Pothole Region of Iowa

“…Previous research has demonstrated that different wetland sampling strategies can influence population estimates from waterfowl surveys (Rutherford and Hayes 1973, Pearse et al 2009, Hennig et al 2017, highlighting the need to carefully investigate different sampling strategies when designing waterfowl surveys. Using individual wetlands as our sampling unit, we evaluated the influence of different sampling strategies on the accuracy and precision of breeding waterfowl abundance estimates in the Iowa PPR.…”

“…We demonstrated that the Neyman sampling strategy consistently produced estimates that were not significantly different from predicted abundances for all species but were less precise than estimates from the other two sampling strategies. Other studies, primarily evaluating the influence of sampling strategies during winter waterfowl surveys, have also shown the value of optimal sampling strategies such as the Neyman strategy for obtaining accurate population estimates , Pearse et al 2009, Hennig et al 2017.…”

“…Information gained from these surveys is used for annually informing harvest management decisions and guiding habitat conservation efforts, two critical tasks for managers charged with maintaining sustainable populations of these socially-and economicallyimportant birds. Not surprisingly, optimal survey design for waterfowl has been the subject of considerable field research and has illuminated many important design considerations such as survey method and timing , sampling design (Rutherford and Hayes 1973, Pearse et al 2009, Hennig et al 2017, and imperfect detection . This research has also clearly demonstrated that there is no "one-size-fits-all" approach and that optimal survey design for breeding waterfowl depends largely on the area and habitat to be surveyed as well as the species of interest.…”