The Effects of Meso-mammal Removal on Northern Bobwhite Populations

Transcription

1 The Effects of Meso-mammal Removal on Northern Bobwhite Populations Alexander L. Jackson William E. Palmer D. Clay Sisson Theron M. Terhune II John M. Yeiser James A. Martin

2 Predation Predation is the largest source of mortality among avian populations Ground-nesting birds are highly susceptible to nest predation High levels of nest predation can limit avian recruitment and population growth

3 An Extremely Diverse Predator Community Reptiles: Gray Rat Snake Corn Snake Cottonmouth Eastern Kingsnake Black Racer Coachwhip Eastern Diamondback Timber Rattlesnake Avian: Cooper s Hawk Red-tailed Hawk Red-shouldered Hawk Barred Owl Great-horned Owl Group of interest Meso-mammals: Raccoon Nine-banded Armadillo Virginia Opossum Bobcat Red and Gray Fox Coyote

4 Predation Manipulation Indirect Methods Modify functional relationship between predator and prey Example: Habitat alteration Direct Methods Numerical changes to predator population size Example: Meso-mammal trap and removal (MMTR)

5 MMTR MMTR has had success at improving avian population performance, controversial, time consuming, expensive Few studies evaluating the response of bobwhite populations Considered a viable management practice on managed bobwhite plantations

6 Objectives Investigate possible relationships between bobwhite reproduction and MMTR Predation Limitation Hypothesis (PLH) Determine how bobwhite population performance is affected by MMTR under different harvest strategies with varying assumptions about density dependence and vital rates

7 Predation Limitation Hypothesis NOBO Productivity NT T

8 Study Area 11 privately owned bobwhite plantations 4 sites in UCP region near Albany, GA 3 sites in Red Hills region of GA, FL 2 sites in Southeast Alabama 2 sites in Georgia outside of the plantation belt

9 37 site-year combinations when MMTR occurred 20 site-year combinations when MMTR did not occur Site Years monitored Years trapped Tall Timbers Red Hills Plantation Red Hills Plantation Albany Plantation Albany Plantation Albany Plantation Albany Plantation Georgia Plantation Georgia Plantation Alabama Plantation Alabama Plantation

10 Bobwhite Demographics From , bobwhites were captured and fit with necklace-style radio transmitters (n = 3,935) Tracked via radio-telemetry 3 times per week during breeding season Nests monitored daily (n = 2,499) Demographics: Nest Success Nests per hen Broods per hen Chicks per hen

11 Model Construction GLMMs used to evaluate relationships between: MMTR and bobwhite reproduction metrics Site treated as a random effect in all models

12 MMTR and Chicks per 100 Hens Estimated number of chicks per 100 hens on trapped study sites versus non-trapped study sites in GA, FL, and AL from

13 However. Higher fecundity does not necessarily lead to increased recruitment, population growth rate, and abundance Dispersal Density dependence Do these reproductive gains translate to a population-level response? Must consider harvest effects at population-level

14 Objectives Investigate possible relationships between bobwhite reproduction and MMTR Predation Limitation Hypothesis (PLH) Determine how bobwhite population performance is affected by MMTR under different harvest strategies with competing assumptions about density dependence and vital rates

15 Population Models Evaluate specific demographic parameters and their influence on population trajectories in response to management actions Project population response Roseberry (1979) harvest Guthery et al. (2000) harvest, weather events Sandercock et al. (2008) population dynamics DeMaso et al. (2011) population dynamics Jackson et al. (TBD) harvest, MMTR

16 The Model Female-based stochastic population model Female survival and chick survival from long-term seasonal estimates from TTRS Fecundity estimates (CPH) from Part I analysis and reflected the effect of MMTR Density Dependence Harvest Effects

17 MMTR FP FP tsurv BP t BP tsurv t FP t+1 BP tfec YY t YY tsurv 0.37 Harvest

18 Fecundity Female Chicks per Hen (CPH) With MMTR: 2.13 CPH Without MMTR: 1.59 CPH

19 Density Dependence Incorporated density dependence into survival and fecundity Implemented 4 forms Convex Sigmoid Concave Weak Linear

20 Convex Sigmoid Concave Weak Linear

21 Harvest Fully Compensatory Partially Compensatory Fully Additive 10, 20, 30, 40, and 50% Harvest 15 Harvest Scenarios Cumulative Harvest

22 Stochastic Figures

23 Abundance Convex Sigmoid Concave Weak Linear

24 Cumulative Harvest Convex Sigmoid Concave Weak Linear

25 Results Summary MMTR elicited a population-level response under a variety of harvest strategies and vital rates MMTR increased cumulative harvest, but the effect size varied by harvest rate Effects of MMTR were robust to our assumptions of harvest and density dependence

26 Implications MMTR can increase abundance and cumulative harvest MMTR can help stakeholders meet their objectives; however, stakeholder values ultimately determine if MMTR is worth the cost MMTR should complement habitat management actions fundamental to bobwhite management

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28 Questions?

29 However. The stochastic model represented the effects of MMTR under average survival rates on high quality sites What happens if average survival is higher or lower? How sensitive are the effects of MMTR to changes in survival?

30 Perturbation Analysis Assess the sensitivity of effects of MMTR to changing vital rates Identify how the relative impacts of trapping may vary as vital rates reach upper and lower bounds Same population model structure, but vital rates systematically ranged from lower bounds to upper bounds in 1% increments Populations subjected to all 4 forms of density dependence and response averaged across all forms

31 Perturbation Figures The difference in λ or cumulative harvest between MMTR and no MMTR Green represents greatest differences Adult survival on y-axes Chick survival on x-axes

32 Growth Rate: 10% Harvest, Partially Compensatory Chick and Breeding Season Survival Chick and Non-breeding Season Survival

33 Cumulative Harvest: 10% Harvest, Partially Compensatory Chick and Breeding Season Survival Chick and Non-breeding Season Survival