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

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 signifi- cant 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 \u3c1 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

The early shorebird will catch fewer invertebrates on trampled sandy beaches

Many species of birds breeding on ocean beaches and in coastal dunes are of global conservation concern. Most of these species rely on invertebrates (e.g. insects, small crustaceans) as an irreplaceable food source, foraging primarily around the strandline on the upper beach near the dunes. Sandy beaches are also prime sites for human recreation, which impacts these food resources via negative trampling effects. We quantified acute trampling impacts on assemblages of upper shore invertebrates in a controlled experiment over a range of foot traffic intensities (up to 56 steps per square metre) on a temperate beach in Victoria, Australia. Trampling significantly altered assemblage structure (species composition and density) and was correlated with significant declines in invertebrate abundance and species richness. Trampling effects were strongest for rare species. In heavily trafficked plots the abundance of sand hoppers (Amphipoda), a principal prey item of threatened Hooded Plovers breeding on this beach, was halved. In contrast to the consistently strong effects of trampling, natural habitat attributes (e.g. sediment grain size, compactness) were much less influential predictors. If acute suppression of invertebrates caused by trampling, as demonstrated here, is more widespread on beaches it may constitute a significant threat to endangered vertebrates reliant on these invertebrates. This calls for a re-thinking of conservation actions by considering active management of food resources, possibly through enhancement of wrack or direct augmentation of prey items to breeding territories

MyLuSurvival-datadryad

encounter histories for marked individuals in the survival stud

Evidence-based recommendations for Atlantic Coast piping plover (Charadrius melodus) conservation and habitat restoration:

Conservation action and habitat restoration for threatened and endangered species are often guided by anecdotal evidence. Limited time and resources are wasted on ineffective strategies, or in some cases, on management that is detrimental to the target species. Therefore, rigorous scientific study must be easily translatable into pragmatic conservation directives. For the Atlantic Coast piping plover (Charadrius melodus), a threatened beach-nesting shorebird, two major threats exist for the recovery of the species -- habitat degradation by beach stabilization practices and human disturbance, and intense predation pressure by the introduced red fox (Vulpes vulpes). This dissertation employs robust statistical methods to: 1) analyze piping plover nesting and foraging behavior, and 2) evaluate the effectiveness of predator exclosures to present evidence-based recommendations for the restoration of breeding habitat and the optimization of reproductive success. Piping plover nests primarily occur in four distinct habitat conditions defined by percent shell and pebble cover, and distance to nearest dunes and high tide line. Characteristics also vary depending on where the nest is initiated (backshore, overwash fan, primary dune). I translate these results into practical restoration target parameters and identify threshold values to assist managers in maintaining suitable nesting habitat. Restoration projects must also include accessible high quality foraging habitat to bolster reproductive success. Plover chicks foraged at higher rates and spent less time being vigilant or fleeing from threats at restored tidal ponds than at other potential foraging habitats. This result suggests that the study ponds offered adequate prey biomass, were visited less frequently by humans, and provided proximate refuge from approaching predators. The foraging models I created were validated externally and are applicable for evaluating future restoration projects. Finally, long-term nest monitoring data indicate that predator exclosures do increase nest hatching success. Electrified exclosures are effective under certain conditions, but at sites with high fox density and human disturbance, nest abandonment becomes sizeable. While the direct cause of abandonments remains unclear, these results will assist managers in making informed decisions on using this technique. These science-based directives can help to create effective habitat designs and conservation strategies for this species.Ph.D.Includes bibliographical references (p. 91-99)by Brooke Masl

Data from: Conservation implications of ameliorating survival of little brown bats with White-Nose Syndrome

Management of wildlife populations impacted by novel threats is often challenged by a lack of data on temporal changes in demographic response. Populations may suffer rapid declines from the introduction of new stressors, but how demography changes over time is critical to determining long-term outcomes for populations. White-nose syndrome (WNS), an infectious disease of hibernating bats, has caused massive and rapid population declines in several hibernating species of bats in North America since the disease was first observed on the continent in 2006. Estimating annual survival rates and demographic trends among remnant colonies of hibernating bats that experienced mass mortality from WNS is needed to determine long-term population viability of species impacted by this disease. Using mark–recapture data on infected little brown bats (Myotis lucifugus), we estimated the first apparent annual survival rates for four years following WNS detection at a site. We found strong support for an increasing trend in annual survival, which improved from 0.68 (95% CI = 0.44–0.85) to 0.75 (95% CI = 0.51–0.89) for males and 0.65 (95% CI = 0.44–0.81) to 0.70 (95% CI = 0.50–0.84) for females. These results suggest that stabilization at remnant colonies after mass mortality from WNS may be due to improved survival and not from immigration from other areas. Despite ameliorating survival, our stochastic matrix projection model predicts continued declines for little brown bat populations (λ = 0.95), raising concern for the regional persistence of this species. We conducted a vital rate sensitivity analysis and determined that adult and juvenile survival, as opposed to fecundity, are the demographic parameters most important to target to maximize recovery potential of little brown bat populations in areas impacted by WNS

Global Coasts: A Baroque Embarrassment of Riches

Coasts form the universal stage on which people interact with the global ocean. Our history is inextricably intertwined with the seashore, being a rich tapestry of archaeological sites that paint a vivid picture of people hunting, foraging, fishing and scavenging at the edge of the sea. Seascapes inspire diverse art forms celebrated through the ages. The world’s sandy beaches have a flummoxing duality of anthropocentric purpose—ranging from the horrors when being theatres of war to first love under a rising moon. ‘Man’s Love of the Sea’ continues to draw people towards the shore: the narrow coastal strip contains everything from holiday cottages to mega-cities. This coastal concentration of the human population is problematic when shorelines erode and move inland, a geological process fastened by climate change. Society’s response is often a heavy investment in coastal engineering to complement and enhance the natural storm protection capacity of beaches and dunes. The coast’s immense cultural, social, and economic significance are complemented by a wealth of natural riches. In the public’s eye, these ecological values can pale somewhat compared with more imminent ecosystem services, particularly protecting human properties from storm impacts. To re-balance the picture, here we illustrate how peer-reviewed science can be translated into ‘cool beach facts’, aimed at creating a broader environmental appreciation of ocean shores. The colourful kaleidoscope of coastal values faces a veritable array of anthropogenic stressors, from coastal armouring to environmental harm caused by off-road vehicles. Whilst these threats are not necessarily unique to coastal ecosystems, rarely do the winds of global change blow stiffer than at the edge of the sea, where millions of people have created their fragile homes on shifting sands now being increasingly eroded by rising seas. Natural shorelines accommodate such changing sea levels by moving landwards, a poignant and powerful reminder that protecting the remaining natural land is primus inter pares in coastal management. There is no doubt that coastal ecosystems and coastal communities face august trials to maintain essential ecosystem services in the face of global change. Whilst bureaucracies are not always well equipped to counteract environmental harm effectively, using measures carrying a social license, many communities and individuals have encouragingly deep values connected to living coastlines. Building on these values, and harnessing the fierce protective spirits of people, are pivotal to shaping fresh models that can enhance and re-build resilience for shores that will continue to be a ‘baroque embarrassment of coastal richesCoastal Engineerin

The effect of top predator removal on the distribution of a mesocarnivore and nest survival of an endangered shorebird

For trophic systems regulated by top-down processes, top carnivores may determine species composition of lower trophic levels. Removal of top predators could therefore cause a shift in community composition. If predators play a role in limiting the population of endangered prey animals, removing carnivores may have unintended consequences for conservation. Lethal predator removal to benefit prey species is a widely used management strategy. Red foxes (Vulpes vulpes) are a common nest predator of threatened piping plovers (Charadrius melodus) and are often the primary target of predator removal programs, yet predation remains the number one cause of piping plover nest loss. Predator exclusion cages (hereafter, exclosures) around nests are often used to keep foxes from eating eggs, as an alternative to predator removal. Fox removals may increase the presence or activity of smaller predators, including American mink (Neovison vison), which can enter exclosures. We predicted that when foxes were removed from plover breeding sites, mesopredator release of mink would occur and lead to increased predation levels of plover nests. Average probability of mink occupancy was higher when foxes were absent (0.26 [95% BCI = 0.16, 0.38]) than when they were present (0.04 [0.01, 0.09]). For nests not protected by exclosures, nest predation was similar at sites with (0.42 [0.12, 0.68]) and without foxes (0.38 [0.10, 0.64]). At sites where foxes were absent, however, predation rates of exclosed nests were 3-fold higher (foxes absent [0.25 {0.06, 0.52}]) compared to sites where foxes remained [0.06 {0.01, 0.18}]). Our results suggest that removal of foxes from plover breeding sites allowed American mink to expand their local range. In turn, removal of foxes led to a decrease in nest survival of an endangered ground-nesting bird. Conservation within complex trophic systems may fail if interactions among species are not well understood when implementing lethal predator removal

Appendix A. Candidate set of 24 a priori models used to examine the effects of sex, year, and a trend in survival with time since white-nose syndrome (WNS) arrival on little brown bats (Myotis lucifugus) at Hibernia Mine, Rockaway, New Jersey, USA, 2010–2013.

Candidate set of 24 a priori models used to examine the effects of sex, year, and a trend in survival with time since white-nose syndrome (WNS) arrival on little brown bats (Myotis lucifugus) at Hibernia Mine, Rockaway, New Jersey, USA, 2010–2013

High annual survival in infected wildlife populations may veil a persistent extinction risk from disease

Host response to emerging pathogens is variable, causing uncertainty about population‐level impacts and challenging effective disease management. White‐nose syndrome (WNS) has caused catastrophic declines in some bat species, while others appear less impacted. Developing predictive models based on observed survival patterns can generate testable hypotheses about mechanisms driving population dynamics and contribute to the development of targeted approaches to disease management. We conducted a mark–recapture study of federally endangered Indiana bats (Myotis sodalis) during 2011–2016. Annual survival decreased from 0.78 (95% CI: 0.59, 0.89) and 0.79 (95% CI: 0.70, 0.86) for females and males, respectively, in 2011 to 0.74 (95% CI: 0.33, 0.94) and 0.75 (95% CI: 0.53, 0.89) for females and males, respectively, in 2015. We then modeled two explanatory mechanisms potentially driving the observed patterns: (1) phased exposure to disease through the spatial spread of the pathogen within the hibernaculum; and (2) cumulative mortality risk from iterative yearly WNS infection. Under a phased exposure scenario, models suggest that infected individuals have an average survival probability of 0.68, and disease prevalence is predicted to reach 100% within 9 yr of disease emergence. Under the cumulative mortality risk hypothesis, survival probability of individuals decreases with each infection cycle. In either case, infected populations are predicted to stabilize at a negative growth rate. Results suggest that Indiana bats tolerate a pathogen load prior to onset of infection, leading to a less pronounced population decline than for other susceptible species. However, the long‐term risk of WNS to Indiana bats may be more severe than current population trends suggest. To inform current conservation management, we performed a vital rate sensitivity analysis, which suggested that modest increases in survival (4–5%) through targeted intervention may return declining populations to stability (λ = 1.0). Demographic modeling approaches coupled with continued population monitoring can highlight important differences in disease response, and ultimately extinction risk, in host species allowing conservation practitioners to tailor intervention actions so that they will be most effective