To exclose nests or not: structured decision making for the conservation of a threatened species

Abstract

Abstract. Decisions regarding endangered species recovery often face sparse data and multiple sources of uncertainty about the effects of management. Structured decision making (SDM) provides a framework for assembling knowledge and expert opinion and evaluating the tradeoffs between different objectives while formally incorporating uncertainty. The Atlantic Coast piping plover provides an illustrative case for the utility of SDM in endangered species management because its population growth is simple to model, most populations are monitored, decision alternatives are well defined, and many managers are open to recovery recommendations. We built a model to evaluate the decision to use nest exclosures to protect piping plover eggs from predators, where the objective was to maximize λ and the tradeoff was between nest survival and adult survival. The latter can be reduced by exclosures. We used a novel mixed multinomial logistic exposure model to predict daily nest fates and incorporated the results into a stochastic projection matrix that included renesting after nest failure, and adult mortality associated with abandonment. In our test data set (n = 329 nests from 28 sites over four years), the mean nest survival over 34 days was markedly higher for exclosed nests (0.76 ± 0.03 SE) than for unexclosed nests (0.37 ± 0.07). Abandonment rates were also higher for exclosed nests (0.092 ± 0.017) than for unexclosed nests (0.045 ± 0.017), but the difference was not statistically significant and the loss rate to "other sources" (mostly predators) was much lower for exclosed nests (0.15 ± 0.03) than for unexclosed nests (0.58 ± 0.07). Population growth rate (λ) was clearly improved by exclosure use at the sites with high background nest loss rates, but λ was still <1 with exclosure use. Where the background nest loss rates were low, the decision to use exclosures was ambiguous, and λ could benefit from reducing uncertainty in vital rates. Our process demonstrated that geographic and temporal variation in nest mortality determines whether exclosures will be useful in attaining positive population growth rates and that other management options must be considered where the background nest mortality rates are high.

A Bayesian multinomial logistic exposure model for estimating probabilities of competing sources of nest failure

“…Management recommendations should be based on demographic consequences (Calvert & Taylor , Cohen et al . ); thus, with adult mortality associated with nest abandonment but not nest predation, estimating only daily nest survival probability with exclosure use could not be used to predict population‐level effects of exclosure use. Rather, with this model we demonstrated that exclosures decreased predation probability but increased abandonment probability, and that abandonment probability with exclosure use varied among sites.…”

Managing individual nests promotes population recovery of a top predator

“…At regional scales, rare and recovering species are protected through legislation (Bottrill et al., ), fenced sanctuaries (Moseby, Hill, & Read, ; Moss, ) and other conservation reserves (Le Saout et al., ; Watson, Dudley, Segan, & Hockings, ). At more local scales, management can involve identifying and protecting individuals to safeguard them against anthropogenic disturbance, poachers or invasive predators (Cohen et al., ; Elliott, Merton, & Jansen, ). These individual‐level actions often are intended to provide higher level (i.e., population‐level) benefits.…”

Using the Value of Information to improve conservation decision making

“…Another eight (27%) papers used a unitless value that reflected a weighted response across multiple objectives (Runge et al ., ; Williams et al ., ; Smith et al ., ; Johnson et al ., , b , ; Thorne et al ., ; Williams & Johnson, ). Other papers used a range of performance metrics, namely cost ratio (Sahlin et al ., ), probability of survival of different age classes (Canessa et al ., ), population growth rate in per cent (Cohen et al ., ), species retention rate at the end of a 20‐year simulation period (Grantham et al ., ), increase in gas extraction while maintaining brook trout ( Salvelinus fontinalis ) populations (Smith et al ., ), probability of population persisting for 256 years (Tyre et al ., ), utility function reflecting both yield (kilotons) and risk of falling below critical spawning mass (Kuikka et al ., ), and proportion of maximum phylogenetic diversity retained (Hartmann & Andre, ).…”