Document Type

Dissertation - Open Access

Award Date

2023

Degree Name

Doctor of Philosophy (PhD)

Department / School

Natural Resource Management

First Advisor

Joshua D. Stafford

Second Advisor

Aaron Pearse

Keywords

Mesopredator, nest survival, Prairie Pothole Region, South Dakota, step-selection functions, waterfowl

Abstract

As conversion of native grasslands and wetlands to croplands continues in the Prairie Pothole Region (PPR), managers are tasked with maintaining sustainable waterfowl populations. Mesopredator community dynamics is a hypothesized mechanism driving spatiotemporal variation of waterfowl nest survival in the PPR, yet studies often lack detailed information on mesopredator species occurrence and abundance. Therefore, understanding spatial and temporal variation in behaviors of mesopredators provides valuable insights for understanding predator-prey interactions between mesopredators and upland duck nests. Further, differences in a predator community resulting from lethal removal of dominant species may influence composition and space use patterns of subordinate and non-target mesopredators, potentially affecting prey through mesopredator release. Our study was conducted in two counties in eastern South Dakota, one with ongoing standardized annual coyote removal (i.e., Faulk; the treatment county) for the last 30 years, and the other receiving no standardized coyote removal (i.e., Hand; the control county). To quantify the nest predator community and potential interactions among mesopredators, I deployed 4 camera trapping surveys, each 3 weeks in length, conducted during the nesting seasons each year (i.e., May–July, 2018–2020). I evaluated species-specific detection and occupancy patterns, then explored co-occupancy relationships among mesopredator species (i.e., coyotes [Canis latrans], striped skunks [Mephitis mephitis], raccoons [Procyon lotor], and American badger [Taxidea taxus]). To evaluate spatiotemporal changes in resource selection and movements, I used integrated step-selection functions from radio-marked mesopredators. Lastly, I simultaneously searched for and monitored nests, and incorporated developed predator-derived covariates from occupancy models and integrated step-selection functions with associated landscape characteristics to compare with direct nest site metrics in logistic exposure nest survival models to understand predator-prey interactions. We found that mesopredators increased movement rates and home range size during periods when common resources were in shorter supply. Across the study area, detection probabilities of mesopredators were 1.7-7.1 times greater in 2018, when duck nest densities were lowest, and 5.2-7.1 times higher during early-season surveys (May) when food resources (i.e., nests, small mammals, invertebrates, vegetation) were expected to be sparse compared to summer. These results suggest individuals increased movement frequencies or distances to locate sufficient food resources or to avoid negative interspecific interactions. Observed elevated detection rates at times of lower food resources (i.e., early spring and in 2018) coincided with greater average step lengths and daily movement rates of radio-marked raccoons and striped skunks during the prenesting period compared to other times of the year, as well as greater average home range size and daily movement rates of raccoons in 2018 compared with subsequent years. Similarly, 2018 was associated with greatest probabilities of mesopredator co-occurrence, suggesting that low food resource availability may aggregate sympatric species. Coexistence of mesopredators corresponded with spatiotemporal segregation of similar selection and movement patterns by sympatric mesopredator species throughout the nesting periods and in both counties for landscape characteristics associated with waterfowl nest site selection and high nest density. Further, direct species overlap of space use was mostly observed during the post-nesting period, when food resource abundances were suspected to be highest. Mesopredators would behave similarly in relation to a landscape characteristic but in different counties or different nesting periods which allowed for niche partitioning, avoidance of negative interspecific species interactions via increased movements, or both, allowing for sympatric species to coexist when food resources are scarce and presents an elevated risk of nest failure earlier in the nesting season. Because our study area comprised two counties with suspected differences in coyote densities due to the presence/absence of active coyote removal management (i.e., coyote occupancy in the treatment county was 44% lower compared to the control county), it allowed an opportunity to test predictions of the mesopredator release hypothesis. This hypothesis predicts that if densities of the dominant predator are reduced (e.g., annual lethal removal of coyotes), densities or movements of subordinate predators should increase since the need to alter behaviors to avoid negative interactions is comparatively reduced. Raccoon occupancy probability was 30% greater in the treatment compared to the control county. Average home range size and daily movements of raccoons and coyotes were greater in the treatment county than in the control county. Additionally, in the treatment county, detection probability of a member of the nest predator guild was not different when a coyote was present or absent nor if a coyote was detected or not, potentially implying the reduced density, distribution, and/or movements of coyotes did not influence those of other mesopredators. Further, spatiotemporal differences in selection and movement between coyotes and smaller mesopredators (e.g., raccoons and striped skunks) were largely not observed in the treatment county, indicating coyotes were not depressing or influencing the behaviors of other mesopredator species which would thereby suggest a presence of mesopredator release. Alternatively, in the control county, spatiotemporal differences in selection and movement between coyotes and smaller mesopredators were widely observed and indicate that subordinate species may have altered their space use to avoid or decrease encounters when coyotes were at greater densities. Such behavior would presumably minimize a predation risk effect as a result of higher coyote densities that were due to a lack of standardized coyote removal management. Importantly, our study provided support that standardized annual coyote removal (i.e., the treatment county) induced mesopredator release and indirectly reduced nest survival via increased occupancy, greater movements, more extensive space use by subordinate mesopredators due to decreased interspecific competition. To this end, daily duck nest survival rates were 0.965 (95% CI = 0.961, 0.969) in the treatment county compared to 0.974 (95% CI = 0.971, 0.978) in the control county. Finally, our study revealed that, in the context of a productive landscape with ample and evenly distributed food resources and seasonal nest success rates that exceed sustainable management levels (i.e., all county and waterfowl species estimates were >25%), direct nest site metrics were sufficient in quantifying landscape and patch characteristics that influence nest survival. Although predator-derived covariates better explained variation in daily nest survival for distance to nearest surface water and patch area landscape characteristics compared to direct nest site metrics, predator-derived covariates were not present in the most supported nest survival model. However, our findings reflected those from other studies; the relationship between nest survival and fate of nearest neighboring nest at time of the nest searching effort, as well as observed and common prey searching behavior of mesopredators during the core nesting period and in relation to landscape characteristics associated with increased food resource availability and nest site selection by ducks (i.e., based on habitat characteristics and or on the local density of conspecifics), suggests that mesopredators may key in on specific prey once encountering it and congregate in areas of high nest density. Our results also support previous studies in that nest depredation events are diluted in patches with higher nest densities as well as camouflaged from mesopredators when patches have taller grass heights around the nest. By investigating and evaluating mechanisms that drive nest survival, I hope our research helps to inform future management endeavors to be efficient and effective. Further, while several studies have found that removing predators from the landscape resulted in increased duck nest survival, our study will help guide and inform management decisions on focal predator species, timing, and associated landscape characteristics of such strategies. And lastly, by overlaying simultaneous predator-prey geospatial data, our project can assist in the prioritization of patches for habitat management and restoration efforts that benefit upland game bird productivity.

Library of Congress Subject Headings

Ducks -- Nests -- South Dakota.
Ducks -- Predators of -- Control -- South Dakota.
Predatory animals -- Ecology.
Predation (Biology)

Publisher

South Dakota State University

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Rights Statement

In Copyright