Measuring Conservation Trade-offs: Demographic Models Provide Critical Context to Empirical Studies

Calvert, Anna M.; Taylor, Philip D.

doi:10.5751/ace-00470-060202

Cited by 7 publications

(15 citation statements)

References 9 publications

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“…There are at least two ways in which the presence of the predator may increase the risk of abandonment. First, if a predator removes one adult, the energetic demands of continued incubation and subsequent brood-rearing may be too great for the remaining parent (Calvert and Taylor 2011), which could lead to nest abandonment. Abandonment by the remaining bird following the mortality of its mate has been observed in a banded population of Piping Plovers in the Great Lakes region (Roche et al 2010), although it remains unclear that the disappearance of a mate caused abandonment.…”

Section: Discussionmentioning

confidence: 99%

“…As with other species, nest exclosures increase plover hatching success, but are also associated with higher rates of adult mortality and nest abandonment (Neuman et al 2004). This is cause for concern as increased adult mortality, in particular, can have significant impacts on population growth (Calvert and Taylor 2011;Watts et al 2012) and therefore poses a greater risk to species persistence than the loss of eggs (Isaksson et al 2007). Thus, determining if exclosures affect the behaviour of adult plovers or their predators in ways that increase mortality and nest abandonment is required to determine if the continued use of this management tool is warranted.…”

Section: Introductionmentioning

confidence: 96%

“…As such, the use of nest exclosures may result in a trade-off between the protection of eggs and the increased loss of adults to predation and nests to abandonment. Indeed, this trade-off is a significant consideration in the protection and recovery of endangered species such as the Piping Plover (Charadrius melodus Ord, 1824; Mabee and Estelle 2000;Calvert and Taylor 2011), where nest predation has been identified as a major limiting factor in recovery (Goossen et al 2002;Stewart et al 2008).…”

Section: Introductionmentioning

confidence: 98%

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Do nest exclosures affect the behaviour of Piping Plovers (Charadriusmelodus melodus) and their predators?

BeaulieuG.

AustinD.

2014

Can. J. Zool.

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Predators are a threat to many ground-nesting shorebirds; however, nest exclosures are a tool used by managers to reduce nest predation. Others have found that nest exclosures increase hatching success, but there has been concern that they may also increase adult mortality and nest abandonment. We examined the effects of nest exclosures on the behaviour of incubating Piping Plovers (Charadrius melodus melodus Ord, 1824) and their predators on nesting beaches in eastern Canada. Using a combination of field observations, video monitoring, and an artificial nest experiment, we found that adult incubation behaviour did not differ between exclosed and unexclosed nests. Predators, however, visited exclosed nests more often than unexclosed nests and spent more time in the vicinity of exclosed nests than unexclosed nests at one of our sites. These findings suggest that concerns over increased adult mortality and nest abandonment are plausible and require further study. Résumé :Les prédateurs sont une menace pour plusieurs espèces de limicoles nichant au sol et sont souvent contrôlés par des méthodes de gestion comme les exclos. Les exclos agissent comme barrières contre les prédateurs sur les nids et augmentent le niveau d'éclosion. Par contre, ils sont aussi associés avec un tôt plus élevé de mortalité chez les adultes et d'abandon des nids. Nous avons examiné les effets des exclos sur le comportement du pluvier siffleur (Charadrius melodus melodus Ord, 1824) nicheur et de leurs prédateurs sur les plages de nidification de l'Est du Canada. En combinant nos observations sur le terrain et la surveillance par vidéo tout en faisant une expérience de nids artificiels, nous avons trouvé que le comportement du pluvier siffleur nichant n'est pas différent entre les nids protégés par exclos et les non-protégés. Les prédateurs ont cependant visité les nids protégés par exclos plus souvent que les nids non-protégés et ils ont aussi passé plus de temps près des exclos que des nids sans exclos. Ces résultats pourraient aider à expliquer le lien entre la protection des nids par exclos et le tôt plus élevé de mortalité chez les adultes et d'abandon de nids.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 98%

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Do nest exclosures affect the behaviour of Piping Plovers (Charadriusmelodus melodus) and their predators?

BeaulieuG.

AustinD.

2014

Can. J. Zool.

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“…, Roche et al . ) and thus has different demographic consequences than other nest failure types and may offset the benefits of increased hatching rates at exclosed nests (Calvert & Taylor ). In such a context, modelling nest survival alone as a function of exclosure use is not sufficient to predict population‐level consequences; more generally, if a covariate has opposing effects on different types of nest failure, then its importance can only be revealed through a multi‐fate study (Etterson et al .…”

mentioning

confidence: 99%

“…Few models have been developed to estimate separately the rates of failure due to different causes, although understanding the factors that lead to different types of nest failure can be of management interest. For example, abandonment at Piping Plover Charadrius melodus nests with wire exclosures (Melvin et al 1992) has been shown to be indicative of adult mortality due to predators targeting incubating adults as they leave exclosures (Murphy et al 2003, Barber et al 2010, Roche et al 2010) and thus has different demographic consequences than other nest failure types and may offset the benefits of increased hatching rates at exclosed nests (Calvert & Taylor 2011). In such a context, modelling nest survival alone as a function of exclosure use is not sufficient to predict population-level consequences; more generally, if a covariate has opposing effects on different types of nest failure, then its importance can only be revealed through a multi-fate study (Etterson et al 2007a).…”

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confidence: 99%

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

Darrah

Cohen

Castelli

2017

Ibis

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Understanding causes of nest loss is critical for the management of endangered bird populations. Available methods for estimating nest loss probabilities to competing sources do not allow for random effects and covariation among sources, and there are few data simulation methods or goodness-of-fit (GOF) tests for such models. We developed a Bayesian multinomial extension of the widely used logistic exposure (LE) nest survival model which can incorporate multiple random effects and fixed-effect covariates for each nest loss category. We investigated the performance of this model and the accompanying GOF test by analysing simulated nest fate datasets with and without age-biased discovery probability, and by comparing the estimates with those of traditional fixed-effects estimators. We then exemplify the use of the multinomial LE model and GOF test by analysing Piping Plover Charadrius melodus nest fate data (n = 443) to explore the effects of wire cages (exclosures) constructed around nests, which are used to protect nests from predation but can lead to increased nest abandonment rates. Mean parameter estimates of the randomeffects multinomial LE model were all within 1 sd of the true values used to simulate the datasets. Age-biased discovery probability did not result in biased parameter estimates. Traditional fixed-effects models provided estimates with a high bias of up to 43% with a mean of 71% smaller standard deviations. The GOF test identified models that were a poor fit to the simulated data. For the Piping Plover dataset, the fixed-effects model was less well-supported than the random-effects model and underestimated the risk of exclosure use by 16%. The random-effects model estimated a range of 1-6% probability of abandonment for nests not protected by exclosures across sites and 5-41% probability of abandonment for nests with exclosures, suggesting that the magnitude of exclosure-related abandonment is site-specific. Our results demonstrate that unmodelled heterogeneity can result in biased estimates potentially leading to incorrect management recommendations. The Bayesian multinomial LE model offers a flexible method of incorporating random effects into an analysis of nest failure and is robust to age-biased nest discovery probability. This model can be generalized to other staggered-entry, time-to-hazard situations.

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

Cohen

Hecht²,

Robinson

et al. 2016

Ecosphere

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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.

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Measuring Conservation Trade-offs: Demographic Models Provide Critical Context to Empirical Studies

Abstract: . 2011. Measuring conservation trade-offs: demographic models provide critical context to empirical studies. Avian Conservation and Ecology 6(2): 2. http://dx

Cited by 7 publications

References 9 publications

Do nest exclosures affect the behaviour of Piping Plovers (Charadriusmelodus melodus) and their predators?

Do nest exclosures affect the behaviour of Piping Plovers (Charadriusmelodus melodus) and their predators?

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

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

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