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
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
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
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)
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
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
Predation Limitation Hypothesis NOBO Productivity NT T
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
37 site-year combinations when MMTR occurred 20 site-year combinations when MMTR did not occur Site Years monitored Years trapped Tall Timbers 2000-2006 2004-2006 Red Hills Plantation 1 2002-2005 2002-2005 Red Hills Plantation 2 2000-2006 2001-2003 Albany Plantation 1 1999-2006 1999-2006 Albany Plantation 2 2000-2006 2001-2003 Albany Plantation 3 2000-2006 2004-2006 Albany Plantation 4 1999-2004 1999-2004 Georgia Plantation 1 2003-2004 2003-2004 Georgia Plantation 2 2003-2004 2003-2004 Alabama Plantation 1 2003-2005 -- Alabama Plantation 2 2003-2006 2004-2006
Bobwhite Demographics From 1999-2006, 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
Model Construction GLMMs used to evaluate relationships between: MMTR and bobwhite reproduction metrics Site treated as a random effect in all models
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 1999-2006
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
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
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
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
MMTR 0.53 0.53 0 FP FP tsurv BP t BP tsurv t FP t+1 BP tfec YY t YY tsurv 0.37 Harvest
Fecundity Female Chicks per Hen (CPH) With MMTR: 2.13 CPH Without MMTR: 1.59 CPH
Density Dependence Incorporated density dependence into survival and fecundity Implemented 4 forms Convex Sigmoid Concave Weak Linear
Convex Sigmoid Concave Weak Linear
Harvest Fully Compensatory Partially Compensatory Fully Additive 10, 20, 30, 40, and 50% Harvest 15 Harvest Scenarios Cumulative Harvest
Stochastic Figures
Abundance Convex Sigmoid Concave Weak Linear
Cumulative Harvest Convex Sigmoid Concave Weak Linear
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
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
Questions?
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?
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
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
Growth Rate: 10% Harvest, Partially Compensatory Chick and Breeding Season Survival Chick and Non-breeding Season Survival
Cumulative Harvest: 10% Harvest, Partially Compensatory Chick and Breeding Season Survival Chick and Non-breeding Season Survival