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USGS2012

Collecting a sample of loggerhead sea turtle hatchlings before a natural emergence does not reduce nest productivity

In numerous studies involving hatchling sea turtles, researchers have collected small numbers of hatchlings from nests a few hours before the turtles would otherwise have emerged naturally. This procedure makes it possible to do experiments in which the behavioral or physiological responses of numerous hatchlings must be tested in a limited period of time, and also allows hatchlings to be released back into the sea in time to migrate offshore before dawn. In principle, however, the procedure might inadvertently reduce nest productivity (the number of hatchlings that successfully leave the nest), if digging into a nest prior to emergence somehow reduces the ability of the remaining turtles to emerge. We compared nest productivity in 67 experimental loggerhead nests, from which we removed 10 hatchlings before a natural emergence, to 95 control nests left undisturbed before a natural emergence. The 2 groups showed no statistical differences in productivity. We conclude that taking a few hatchlings from a loggerhead nest shortly before a natural emergence has no negative impact on hatchling production if sampling is done with care at locations where there are few nest predators, and at sites where an emergence can be predicted because nest deposition dates are known.

Florida↗

USGS2021

Revising the marine range of the endangered black-capped petrel Pterodroma hasitata: occurrence in the northern Gulf of Mexico and exposure to conservation threats

The black-capped petrel Pterodroma hasitata is an Endangered seabird endemic to the western North Atlantic. Although estimated at ~1000 breeding pairs, only ~100 nests have been located at 2 sites in Haiti and 3 sites in the Dominican Republic. At sea, the species primarily occupies waters of the western Gulf Stream in the Atlantic and the Caribbean Sea. Due to limited data, there is currently no consensus on the geographic marine range of the species although no current proposed ranges include the Gulf of Mexico. Here, we report on observations of black-capped petrels during 2 vessel-based survey efforts throughout the northern Gulf of Mexico from 2010-2011 and 2017-2019. During 558 d and ~54700 km of surveys, we tallied 40 black-capped petrels. Most observations occurred in the eastern Gulf, although birds were observed over much of the east-west and north-south footprint of the survey area. Predictive models indicated that habitat suitability for black-capped petrels was highest in areas associated with dynamic waters of the Loop Current. We used the extent of occurrence and area of occupancy concepts to delimit the geographic range of the species within the northern Gulf. We suggest that the marine range for black-capped petrels be modified to include the northern Gulf of Mexico, recognizing that distribution may be more clumped in the eastern Gulf and that occurrence in the southern Gulf remains unknown due to a lack of surveys there. To date, however, it remains unclear which nesting areas are linked to the Gulf of Mexico.

Northern Gulf of Mexico↗

USGS2024

Spatial segregation between phenotypes of the diablotin black-capped petrel Pterodroma hasitata during the non-breeding period

Despite growing support for ecosystem-based approaches, conservation is mostly implemented at the species level. However, genetic differentiation exists within this taxonomic level, putting genetically distinct populations at risk of local extinction. In the diablotin black-capped petrel Pterodroma hasitata , an endangered gadfly petrel endemic to the Caribbean, 2 phenotypes have been described: a smaller dark form and a heavier light form, which are genetically distinct. To assess possible differences in the marine distributions of phenotypes, in May 2019, we captured 5 adult black-capped petrels of each phenotype at sea in the western North Atlantic and equipped them with satellite transmitters. We used generalized linear mixed models to test the importance of phenotype on geographic distribution. Using kernel density estimations, we located use areas, quantified spatial overlap between forms, and assessed form-specific exposure to marine threats. Petrels were tracked for 11 to 255 d ( mean ± SD: 102.1 ± 74.2 d). During the non-breeding period, all individuals ranged from 28.4 to 43.0° latitude. Phenotypes had significantly distinct non-breeding distributions, independent of time of year. The dark form used waters of the Carolinian marine ecoregion, and the light form used pelagic waters of the Virginian ecoregion, to the north. The dark form was more exposed to marine threats than the light form, in particular to mercury, microplastics, and marine traffic. The light form overlapped with proposed wind energy areas off the central US coast. These differences in exposure suggest possible differences in vulnerability, which can have repercussions on the viability of this imperiled species.

North Carolina↗

USGS2021

Statistical methods used in research concerning endangered and threatened animal species of Puerto Rico: A meta-study

A concern about statistics in wildlife studies, particularly of endangered and threatened species, is whether the data collected meet the assumptions necessary for the use of parametric statistics. This study identified published papers on the nine endangered and six threatened species found only on Puerto Rico using five different databases. The results from the Zoological Record database identified the most articles, including all identified by the other databases. Of the 222 identified articles, 108 included some form of statistics, 26 used only descriptive statistics, 34 included only parametric statistics, 26 used only nonparametric statistics, and 22 reported both parametric and nonparametric statistical analyses. This meta-study showed that the percentage of articles with no statistical treatment decreased in the most recent 20 years, and that although parametric statistics continue to be the most commonly used in published wildlife studies of Puerto Rican wildlife, there has been a distinct increase in the use of nonparametric statistics over time.

Caribbean Journal of Science↗

USGS2010

Effects of subsidized predators, resource variability, and human population density on desert tortoise populations in the Mojave Desert, USA

Understanding predator–prey relationships can be pivotal in the conservation of species. For 2 decades, desert tortoise Gopherus agassizii populations have declined, yet quantitative evidence regarding the causes of declines is scarce. In 2005, Ft. Irwin National Training Center, California, USA, implemented a translocation project including 2 yr of baseline monitoring of desert tortoises. Unusually high predation on tortoises was observed after translocation occurred. We conducted a retrospective analysis of predation and found that translocation did not affect the probability of predation: translocated, resident, and control tortoises all had similar levels of predation. However, predation rates were higher near human population concentrations, at lower elevation sites, and for smaller tortoises and females. Furthermore, high mortality rates were not limited to the National Training Center. In 2008, elevated mortality (as high as 43%) occurred throughout the listed range of the desert tortoise. Although no temporal prey base data are available for analysis from any of the study sites, we hypothesize that low population levels of typical coyote Canis latrans prey (i.e. jackrabbits Lepus californicus and other small animals) due to drought conditions influenced high predation rates in previous years. Predation may have been exacerbated in areas with high levels of subsidized predators. Many historical reports of increased predation, and our observation of a range-wide pattern, may indicate that high predation rates are more common than generally considered and may impact recovery of the desert tortoise throughout its range.

Endangered Species Research↗

USGS2011

Sea otter mortality in fish and shellfish traps: Estimating potential impacts and exploring possible solutions

Sea otters Enhydra lutris can be bycaught and drowned in fishing pots and traps, which may pose a threat to the welfare of otter populations. We explored this potential problem and its solutions using a wide variety of analyses. We exposed live California (USA) sea otters to finfish traps, lobster traps, and mock Dungeness crab traps in captive trials and found that the animals attempted to enter the circular and rectangular fyke openings, with some becoming entrapped. Using both live and dead sea otters, we found that a 3 × 9 inch (7.6 × 22.9 cm) fyke opening (1 inch narrower than the 4 × 9 inch [10.2 × 22.9 cm] openings currently used in California’s commercial Dungeness crab fishery) would exclude most free-living (i.e. weaned from their mothers) otters while permitting the undiminished capture of crabs. Observer programs do not currently exist in California for these fisheries, so we calculated the effort required by an observer program to document sea otter bycatch over a range of hypothetical levels and evaluated the impact of those mortality rates on population growth. These analyses demonstrate that significant mortality from bycatch might easily go undetected, even with seemingly high levels of observer effort. As sea otters reoccupy portions of their former habitat in California, co-occurrence with finfish and shellfish traps with relatively large fyke openings will increase.

Endangered Species Research↗

USGS2012

Heterogeneous detection probabilities for imperiled Missouri River fishes: implications for large-river monitoring programs

Occupancy modeling was used to determine (1) if detection probabilities (p) for 7 regionally imperiled Missouri River fishes (Scaphirhynchus albus, Scaphirhynchus platorynchus, Cycleptus elongatus, Sander canadensis, Macrhybopsis aestivalis, Macrhybopsis gelida, and Macrhybopsis meeki) differed among gear types (i.e. stationary gill nets, drifted trammel nets, and otter trawls), and (2) how detection probabilities were affected by habitat (i.e. pool, bar, and open water), longitudinal position (five 189 to 367 rkm long segments), sampling year (2003 to 2006), and season (July 1 to October 30 and October 31 to June 30). Adult, large-bodied fishes were best detected with gill nets (p: 0.02–0.74), but most juvenile large-bodied and all small-bodied species were best detected with otter trawls (p: 0.02–0.58). Trammel nets may be a redundant sampling gear for imperiled fishes in the lower Missouri River because most species had greater detection probabilities with gill nets or otter trawls. Detection probabilities varied with river segment for S. platorynchus, C. elongatus, and all small-bodied fishes, suggesting that changes in habitat influenced gear efficiency or abundance changes among river segments. Detection probabilities varied by habitat for adult S. albus and S. canadensis, year for juvenile S. albus, C. elongatus, and S. canadensis, and season for adult S. albus. Concentrating sampling effort on gears with the greatest detection probabilities may increase species detections to better monitor a population's response to environmental change and the effects of management actions on large-river fishes.

Endangered Species Research↗

USGS2012

Habitat and prey availability attributes associated with juvenile and early adult pallid sturgeon occurrence in the Missouri River, USA

The pallid sturgeon Scaphirhynchus albus is a federally endangered species native to the Missouri and lower Mississippi Rivers, USA. As part of recovery efforts, over 360000 pallid sturgeon have been stocked into the Missouri River since 1994, and a standardized, long-term monitoring program was initiated in 2003. Understanding the distribution and habitat requirements of juvenile and early adult pallid sturgeon (fork length <720 mm, age <10 yr) is an important goal of the monitoring and recovery programs. In this study, we collected information on habitat characteristics and prey availability from the upper Missouri River along the Nebraska-South Dakota border and compared these attributes between capture (present) and non-capture (absent) locations (N = 59). To evaluate the relative influence of habitat and prey availability on pallid sturgeon occurrence, we examined several candidate models using an information-theoretic approach. A prey availability model had the most support and included site-specific information on Diptera and Ephemeroptera abundance. A habitat-based model showed that juveniles and early adults were found in relatively deeper water and avoided areas where bottom velocities were greater than 1.2 m s −1 . Although not as well supported as the prey-effects model (evidence ratio = 6.4), habitat features also provided a plausible model for predicting occurrence. The models developed here could be used to evaluate pallid sturgeon habitat potential in the Missouri River basin and help guide future monitoring and conservation management of this endangered species.

Missouri River↗

USGS2013

Is there room for all of us? Renewable energy and Xerospermophilus mohavensis

Mohave ground squirrels Xerospermophilus mohavensis Merriam are small ground-dwelling rodents that have a highly restricted range in the northwest Mojave Desert, California, USA. Their small natural range is further reduced by habitat loss from agriculture, urban development, military training and recreational activities. Development of wind and solar resources for renewable energy has the potential to further reduce existing habitat. We used maximum entropy habitat models with observation data to describe current potential habitat in the context of future renewable energy development in the region. While 16% of historic habitat has been impacted by, or lost to, urbanization at present, an additional 10% may be affected by renewable energy development in the near future. Our models show that X. mohavensis habitat suitability is higher in areas slated for renewable energy development than in surrounding areas. We provide habitat maps that can be used to develop sampling designs, evaluate conservation corridors and inform development planning in the region.

California, Nevada↗

USGS2014

Space use and resource selection by foraging Indiana bats at the northern edge of their distribution

Despite 4 decades of conservation concern, managing endangered Indiana bat ( Myotis sodalis ) populations remains a difficult wildlife resource issue facing natural resource managers in the eastern United States. After small signs of population recovery, the recent emergence of white-nose syndrome has led to concerns of local and/or regional extirpation of the species. Where Indiana bats persist, retaining high-quality foraging areas will be critical to meet physiological needs and ensure successful recruitment and overwinter survival. However, insight into foraging behavior has been lacking in the Northeast of the USA. We radio-tracked 12 Indiana bats over 2 summers at Fort Drum, New York, to evaluate factors influencing Indiana bat resource selection during night-time foraging. We found that foraging space use decreased 2% for every 100 m increase in distance to water and 6% for every 100 m away from the forest edge. This suggests high use of riparian areas in close proximity to forest and is somewhat consistent with the species’ foraging ecology in the Midwest and upper South. Given the importance of providing access to high-quality foraging areas during the summer maternity season, Indiana bat conservation at the northern extent of the species’ range will be linked to retention of forested habitat in close proximity to riparian zones.

Endangered Species Research↗

USGS2015

Chilled frogs are hot: hibernation and reproduction of the Endangered mountain yellow-legged frog Rana muscosa

In the face of the sixth great extinction crisis, it is imperative to establish effective breeding protocols for amphibian conservation breeding programs. Captive efforts should not proceed by trial and error, nor should they jump prematurely to assisted reproduction techniques, which can be invasive, difficult, costly, and, at times, counterproductive. Instead, conservation practitioners should first look to nature for guidance, and replicate key conditions found in nature in the captive environment, according to the ecological and behavioral requirements of the species. We tested the effect of a natural hibernation regime on reproductive behaviors and body condition in the Endangered mountain yellow-legged frog Rana muscosa . Hibernation had a clear positive effect on reproductive behavior, manifesting in vocal advertisement signaling, female receptivity, amplexus, and oviposition. These behaviors are critical components of courtship that lead to successful reproduction. Our main finding was that captive R. muscosa require a hibernation period for successful reproduction, as only hibernated females produced eggs and only hibernated males successfully fertilized eggs. Although hibernation also resulted in a reduced body condition, the reduction appeared to be minimal with no associated mortality. The importance of hibernation for reproduction is not surprising, since it is a major component of the conditions that R. muscosa experiences in the wild. Other amphibian conservation breeding programs can also benefit from a scientific approach that tests the effect of natural ecological conditions on reproduction. This will ensure that captive colonies maximize their role in providing genetic reservoirs for assurance and reintroduction efforts.

Endangered Species Research↗

USGS2016

Predictive habitat models derived from nest-box occupancy for the endangered Carolina northern flying squirrel in the southern Appalachians

In the southern Appalachians, artificial nest-boxes are used to survey for the endangered Carolina northern flying squirrel (CNFS; Glaucomys sabrinus coloratus ), a disjunct subspecies associated with high elevation (>1385 m) forests. Using environmental parameters diagnostic of squirrel habitat, we created 35 a priori occupancy models in the program PRESENCE for boxes surveyed in western North Carolina, 1996-2011. Our best approximating model showed CNFS denning associated with sheltered landforms and montane conifers, primarily red spruce Picea rubens . As sheltering decreased, decreasing distance to conifers was important. Area with a high probability (>0.5) of occupancy was distributed over 18662 ha of habitat, mostly across 10 mountain ranges. Because nest-box surveys underrepresented areas >1750 m and CNFS forage in conifers, we combined areas of high occupancy with conifer GIS coverages to create an additional distribution model of likely habitat. Regionally, above 1385 m, we determined that 31795 ha could be occupied by CNFS. Known occupied patches ranged from

North Carolina, Tennessee, Virginia↗

USGS2015

Severe mortality of a population of threatened Agassiz’s desert tortoises: the American badger as a potential predator

In the Mojave Desert of the southwestern United States, adult Agassiz’s desert tortoises Gopherus agassizii typically experience high survival, but population declines associated with anthropogenic impacts led to their listing as a threatened Species under the US Endangered Species Act in 1990. Predation of adult tortoises is not often considered a significant threat as they are adapted to deter most predation attempts. Despite these adaptations, some populations have experienced elevated mortality attributed to predators, suggesting that predation pressure may occasionally increase. During the tortoise activity seasons of 2012 and 2013, we observed unsustainably high mortality in 1 of 4 populations of adult desert tortoises (22 and 84%, respectively) in the western Mojave Desert in the vicinity of Barstow, CA. Photographic evidence from trail cameras and examination of carcass condition suggest that American badgers Taxidea taxus— a sometimes cited but unconfirmed predator of adult tortoises — may have been responsible for some of the mortality observed. We discuss the American badger as a plausible predator of a local tortoise population, but recommend further investigation into these events and the impacts such mortality can have on tortoise persistence.

Endangered Species Research↗

USGS2015

Microsatellite variation and rare alleles in a bottlenecked Hawaiian Islands endemic: implications for reintroductions

Conservation of genetic biodiversity in endangered wildlife populations is an important challenge to address since the loss of alleles and genetic drift may influence future adaptability. Reintroduction aims to re-establish species to restored or protected ecosystems; however, moving a subset of individuals may result in loss of gene variants during the management-induced bottleneck (i.e. translocation). The endangered Laysan teal Anas laysanensis was once widespread across the Hawaiian archipelago, but became isolated on Laysan Island (415 ha) from the mid-1800s until 2004 when a translocation to Midway Atoll (596 ha) was undertaken to reduce extinction risks. We compared genetic diversity and quantified variation at microsatellite loci sampled from 230 individuals from the wild populations at Laysan (1999 to 2009) and Midway (2007 to 2010; n = 133 Laysan, n = 96 Midway birds). We identified polymorphic markers by screening nuclear microsatellites (N = 83). Low nuclear variation was detected, consistent with the species’ insular isolation and historical bottleneck. Six of 83 microsatellites were polymorphic. We found limited but similar estimates of allelic richness (2.58 alleles per locus) and heterozygosity within populations. However, 2 rare alleles found in the Laysan source population were not present in Midway’s reintroduced population, and a unique allele was discovered in an individual on Midway. Differentiation between island populations was low ( F ST = 0.6%), but statistically significant. Our results indicate that genetic drift had little effect on offspring generations 3 to 6 yr post-release and demonstrate the utility of using known founder events to help quantify genetic capture during translocations and to inform management decisions.

Endangered Species Research↗

USGS2015

Dim ultraviolet light as a means of deterring activity by the Hawaiian hoary bat Lasiurus cinereus semotus

Widespread bat fatalities at industrial wind turbines are a conservation issue with the potential to inhibit efficient use of an abundant source of energy. Bat fatalities can be reduced by altering turbine operations, but such curtailment decreases turbine efficiency. If additional ways of reducing bat fatalities at wind turbines were available such tradeoffs might not be needed. Based on the facts that bats perceive distant objects primarily through vision and can see in very dim lighting conditions, and the possibility that bats might interact with turbines after approaching them as they would trees, we propose a novel method of reducing bat activity at wind turbines: illumination of the structure with dim light. As a first step toward assessing this approach, we illuminated trees with dim flickering ultraviolet (UV) light in areas frequented by Hawaiian hoary bats Lasiurus cinereus semotus , an endangered subspecies affected by wind turbines. We used a repeated-measures design to quantify bat activity near trees with acoustic detectors and thermal video cameras in the presence and absence of UV illumination, while concurrently monitoring insect numbers. Results indicate that dim UV reduces bat activity despite an increase in insect numbers. Experimental treatment did not completely inhibit bat activity near trees, nor did all measures of bat activity show statistically significant differences due to high variance in bat activity among sites. However, the observed decreases in bat activity with dim UV illumination justify further testing of this method as a means to reduce bat fatalities at wind turbines.

Hawaii↗

USGS2015

Population trends and survival of nesting green sea turtles Chelonia mydas on Aves Island, Venezuela

Long-term demographic data are valuable for assessing the effect of anthropogenic impacts on endangered species and evaluating recovery programs. Using a 2-state open robust design model, we analyzed mark-recapture data from green turtles Chelonia mydas sighted between 1979 and 2009 on Aves Island, Venezuela, a rookery heavily impacted by human activities before it was declared a wildlife refuge in 1972. Based on the encounter histories of 7689 nesting females, we estimated the abundance, annual survival, and remigration intervals for this population. Female survival varied from 0.14-0.91, with a mean of 0.79, which is low compared to survival of other populations from the Caribbean (mean = 0.84) and Australia (mean = 0.95), even though we partially corrected for tag loss, which is known to negatively bias survival estimates. This supports prior suggestions that Caribbean populations in general, and the Aves Island population in particular, may be more strongly impacted than populations elsewhere. It is likely that nesters from this rookery are extracted while foraging in remote feeding grounds where hunting still occurs. Despite its relatively low survival, the nesting population at Aves Island increased during the past 30 years from approx. 500 to >1000 nesting females in 2009. Thus, this population, like others in the Caribbean and the Atlantic, seems to be slowly recovering following protective management. Although these findings support the importance of long-term conservation programs aimed at protecting nesting grounds, they also highlight the need to extend management actions to foraging grounds where human activities may still impact green turtle populations.

Aves Island↗

USGS2015

First satellite tracks of the Endangered black-capped petrel

The black-capped petrel Pterodroma hasitata is an endangered seabird with fewer than 2000 breeding pairs restricted to a few breeding sites in Haiti and the Dominican Republic. To date, use areas at sea have been determined entirely from vessel-based surveys and opportunistic sightings and, as such, spatial and temporal gaps in our understanding of the species’ marine range are likely. To enhance our understanding of marine use areas, we deployed satellite tags on 3 black-capped petrels breeding on Hispaniola, representing the first tracking study for this species and one of the first published tracking studies for any breeding seabird in the Caribbean. During chick rearing, petrels primarily used marine habitats in the southern Caribbean Sea (ca. 18.0° to 11.5°N, 70.0° to 75.5°W) between the breeding site and the coasts of Venezuela and Colombia. Maximum distance from the breeding sites ranged from ca. 500 to 1500 km during the chick-rearing period. During the post-breeding period, each bird dispersed north and used waters west of the Gulf Stream offshore of the mid- and southern Atlantic coasts of the USA as well as Gulf Stream waters and deeper pelagic waters east of the Gulf Stream. Maximum distance from the breeding sites ranged from ca. 2000 to 2200 km among birds during the nonbreeding period. Petrels used waters located within 14 different exclusive economic zones, suggesting that international collaboration will benefit the development of management strategies for this species.

Endangered Species Research↗

USGS2016

Early life history and spatiotemporal changes in distribution of the rediscovered Suwannee moccasinshell Medionidus walkeri (Bivalvia: Unionidae)

Accurate distribution data are critical to the development of conservation and management strategies for imperiled species, particularly for narrow endemics with life history traits that make them vulnerable to extinction. Medionidus walkeri is a rare freshwater mussel endemic to the Suwannee River Basin in southeastern North America. This species was rediscovered in 2012 after a 16-year hiatus between collections and is currently proposed for listing under the Endangered Species Act. Our study fills knowledge gaps regarding changes in distribution and early life history requirements of M . walkeri . Spatiotemporal changes in M. walkeri distribution were displayed using a conservation status assessment map incorporating metadata from 98 historical (1916–1999) and 401 recent (2000–2015) site surveys from museums and field notes representing records for 312 specimens. Recent surveys detected M . walkeri only in the middle Suwannee subbasin (n = 86, 22 locations) and lower Santa Fe subbasin (n = 2, 2 locations), and it appears the species may be extirpated from 67% of historically occupied 10-digit HUCs. In our laboratory experiments, M . walkeri successfully metamorphosed on Percina nigrofasciata (56.2% ± 8.9) and Etheostoma edwini (16.1% ± 7.9) but not on Trinectes maculatus , Lepomis marginatus , Notropis texanus , Noturus leptacanthus , Etheostoma fusiforme , or Gambusia holbrooki . We characterize M . walkeri as a lure-displaying host fish specialist and a long-term brooder (bradytictic), gravid from fall to early summer of the following year. The early life history and distribution data presented here provide the baseline framework for listing decisions and future efforts to conserve and recover the species.

Endangered Species Research↗