Animal Conservation最新文献

Northwest African cheetah populations have declined precipitously, with expert opinion estimating that <420 individuals persist across parts of Algeria, Benin, Burkina Faso, Chad, Niger and Mali. However, no reliable density estimates exist in the remaining subspecies strongholds throughout the Sudano-Sahel Zone, including the W-Arly-Pendjari Complex and Greater Zakouma Ecosystem within the Bahr/Salamat landscape. Camera trap surveys were combined with spatially explicit capture–recapture methodologies in both regions to estimate the cheetah density and detectable demographic composition of these populations. Following 15 429 camera trap nights, we detected nine individuals during the dry season and four individuals during the wet season in Pendjari (2021), nine individuals (dry season; 2023) in Zakouma and none in Siniaka Minia. Cheetah densities were thus estimated at 0.17–0.24 and 0.37 cheetah per 100 km² in Pendjari and Zakouma, respectively. While marginally higher than predicted, such low-density estimates are concerning in the last remaining habitats harbouring this critically endangered subspecies. Considering the substantial contraction of regional cheetah distribution, we estimate an overall population size of 68 ± 29 individuals across the studied areas. These novel estimates are among the lowest formally determined densities throughout cheetah range in Africa, where a high frequency of people and livestock detected on camera traps highlight the ongoing risks to large carnivores in these protected areas. Subsequent management recommendations include implementation of the established regional conservation strategies that encompass the distributional range of these cheetah, continuous monitoring of populations, genetic analyses to inform management, curbing illegal trade and increasing international awareness around the plight of the subspecies.

Measures to boost populations can help ensure population persistence in the short-term while longer-term conservation interventions take effect. Headstarting, involving the collection of wild early life-stage individuals, rearing in captivity, and release into a new or existing population once independent, has recently been identified as a potential translocation technique to assist small breeding populations of waders declining due to low levels of productivity. However, the demographic rates of headstarted individuals have not been quantified, and their impact on target populations not understood, which is required to determine the efficacy of this technique as a tool for species recovery. Between 2017 and 2022, headstarting was trialled as a tool to supplement the critically small sub-population of black-tailed godwit (Limosa limosa limosa) breeding at the Ouse Washes, Eastern England. We demonstrate that a high survival rate for eggs and chicks can be achieved through artificial incubation and hand-rearing, and that headstarting can substantially increase the overall productivity of a small population. Using survival analysis and mixed effects modelling, we show that apparent survival and breeding success of headstarted individuals is comparable to wild-reared conspecifics. The survival rate of released birds was sufficient to significantly boost the breeding population, reaching over five times the number of breeding pairs at the release site during the trial. Providing demographic rates remain the same, the number of godwits breeding at the Ouse Washes is predicted to continue to increase moderately over the next 20 years. This study highlights the potential of headstarting to boost small populations of breeding waders, and demonstrates the value of this technique to assist with the recovery of threatened populations when there is a clear justification that headstarting can negate the effects of population limiting factors.

Turtles and tortoises (Order Testudines) are facing an extinction crisis, and ecosystems are at risk of collapsing with the loss of key roles they play. Hatching failure is a crucial barrier to population growth and persistence, but its causes are poorly understood, and it is unknown whether fertilization rates are declining as many populations become smaller and more female-biased. Here, we show that very few studies of turtle and tortoise hatching success consider fertilization rates, and those that do use unreliable methods to determine egg fertility. We also show that studies of hatching success are biased towards marine turtles, as opposed to freshwater and terrestrial species, and wild rather than captive populations. To address the lack of reliable methods for assessing fertilization rates in turtles and tortoises, a microscopy-based method (originally designed for bird eggs) for detecting perivitelline membrane (PVM) bound sperm and embryonic nuclei in the germinal disc of unhatched eggs has been developed and tested (in turtle and tortoise eggs). We demonstrate that this method provides unequivocal evidence of egg fertilization in five different turtle and tortoise species from both captive and wild populations, even after eggs have been left in wild nests for the full incubation period. This methodological approach represents a valuable tool for monitoring egg fertility and embryo survival rates in turtles and tortoises, with the potential to provide important insights into the underlying drivers of reproductive failure in threatened captive and wild populations.

Recovery of endangered species is challenging and lengthy, especially when it involves reintroduction and dynamic environmental conditions. Because managers often need to decide between many management strategies with uncertain outcomes, periodically assessing progress toward recovery using population viability analysis (PVA) can help guide decision-making. We developed a PVA for the critically endangered Puerto Rican parrot (Amazona vittata) to evaluate current status and potential future management strategies to reach goals set in the Recovery Plan. Having grown from their nadir of 13 birds in 1976 to 686 in 2021, the recovery effort has made great progress. Using 15 years of data, we built an individual-based PVA that included interactions between two captive and three wild populations connected via annual releases. If management continues as planned, the wild populations have no to moderate risks of extinction (0–32%) over the next 100 years. However, wild populations remain dependent on releases to sustain growth, and recovery targets for stable population growth and connectivity have not yet been reached. Our analysis suggests that hurricanes are an impediment to reaching recovery targets and impact some wild populations more than others based on geography. Projections with climate-change-induced higher hurricane impact resulted in wild populations being less likely to stabilize. We identified demographic rates and associated management strategies that could positively impact wild populations: increasing reproduction (e.g., via increasing artificial nests, improving nest success) and decreasing first-year mortality (e.g., via targeted predator control). Based on our current understanding of Puerto Rican parrot demographics, species recovery will continue to be management-dependent unless demographic rates can be altered. As more data are gathered, especially for data-sparse populations and in the face of environmental change, future iterations of this model can re-evaluate progress, update management strategies, and provide support for deciding if and when to delist this iconic species.

Woodland caribou (Rangifer tarandus caribou) are designated as Threatened or Endangered in Canada, with many populations being at risk of extirpation. Approaches for caribou conservation can be both invasive and expensive. For example, maternity penning involves the relocation of pregnant females to a predator-free fenced enclosure where they are held for 20–22 weeks. This activity greatly reduces the risk of predation for adult females and their dependent calves, but requires the construction, maintenance, and monitoring of a penning facility as well as the risk associated with the capture and transport of adult caribou. With only four maternity pen trials within the last decade, there has been little study of the potential influence of maternity penning on the distribution and habitat use of caribou after release. We used Brownian Bridge Movement Models to examine changes in range fidelity and overall range use of the Klinse-Za caribou herd in north-central British Columbia, Canada, following eight years of maternity penning. We generated annual home range utilisation distributions and examined the space use of caribou among years and between penned and unpenned animals, as well as pre-penning and post-penning time periods. We found that following penning, caribou shifted distribution to areas near maternity pens and expanded their overall use of range. However, caribou did not shift their distribution relative to the elevation of their mountainous habitats. Our results suggest that caribou can adapt to capture and forced displacement without altering patterns of instinctual or learned habitat use.

Electric fences are widely used in human–elephant conflict mitigation. However, elephants constantly challenge and overcome fences, which is a growing concern. We studied how elephants crossed the perimeter electric fence around the Udawalawe National Park (UWNP), Sri Lanka. Using camera traps, we monitored 18 fence posts and an open gate in the fence over 605 days from 2016 to 2019. Photographs of 3097 fence crossings were analysed to obtain demographic data for fence crossing elephants, crossing methods, and the daily and seasonal timing of fence crossing. We identified 77 adult males and 12 adult females that crossed the fence, which represent about 17% of the adult elephants in UWNP. Most of the crossings were through the open gate at night. Elephants used a variety of crossing methods, comprised of crossing at the open gate, at previously toppled posts, by crashing through wires and stepping over wires, as well as by using the trunk or forefeet to topple posts. Fence voltage was not a determinant of fence crossing. The frequency and timing of fence crossings varied between locations with later exits and less time spent outside, at crossing points bordering human dominated areas. Our results emphasis on the importance of taking into account the problem solving abilities of elephants in fence design and location, such as energising fence posts and constructing exclosure fences at the boundaries of crop fields and settlements, in employing electric fences to mitigate human-elephant conflict.

Northern bobwhites (Colinus virginianus) have become a species of great conservation priority because of widespread and ongoing population declines. Long-distance translocations are becoming increasingly used to access a source population with densities high enough to support translocation. Two key uncertainties exist regarding the efficacy of long-distance translocations: choosing a source population with adaptations that will be successful in a novel environment and mitigating the stress response common during the translocation process. We translocated bobwhites from the South Texas Plains and the Floridian Coastal Plain to a recipient site in the Floridian Coastal Plain in 2021 and 2022 to compare the survival and productivity of bobwhites translocated from two different source populations. We also evaluated how varying holding times during the translocation process influenced the success of the translocated individuals. Breeding season survival, nest propensity and fecundity were greater for Florida resident and Florida translocated bobwhites relative to Texas translocated bobwhites. We observed high rates of mortality during the transport and holding processes, but holding time did not affect breeding season survival of Texas translocated bobwhites. Both nest success and fecundity of Texas translocated bobwhites were negatively affected by holding time. Bobwhites translocated long distances may have the adaptive capacity to be successful in novel environments, but the consequences of translocation stress can be detrimental. Future translocation planning should consider choosing source populations from similar ecoregions to simultaneously decrease translocation distances and potential stress from translocation.

Fire, invasive predators and low rainfall are key disturbances that interact to negatively impact wildlife. Reptiles are a highly threatened group, yet they have rarely been the focus of threat interaction research. Research assessing the impacts of disturbance on wildlife have typically focussed on changes in species richness and abundance. However, these metrics largely overlook the non-lethal effects on individuals and populations persisting within disturbed landscapes. Body condition is an individual-level response metric that is easily obtainable and provides insight into the cumulative behavioural and morphological changes within a population. We used a landscape-scale natural experiment in southern Australia to investigate the impacts of prescribed fire severity, invasive red fox (Vulpes vulpes) control, low rainfall conditions and their interactive effects on reptile body condition. Low rainfall had pervasive negative effects on body condition, while prescribed fire had negative effects on the larger, viviparous species. We found a three-way interactive effect, whereby the negative effects of fire and low rainfall were greater in areas where red foxes were controlled. These results indicate that there are complex ecological interactions at play, potentially including intra-specific competition and interspecific interactions. Lower body condition in disturbed environments could have lasting implications for individual fitness and population persistence. For instance, species with lower body condition one-year post-fire could be more vulnerable to another fire event, compared to species that are able to maintain condition in post-fire landscapes. With reptile body condition lower in a drier year, we advise minimising additional disturbance (e.g. avoid prescribed fires) during low rainfall years and drought periods. Along with research into ecological interactions, understanding how body condition indices relate to altered fitness is a priority knowledge gap. Such research could improve the ability to predict how species and populations will respond to future disturbances, a key challenge in wildlife disturbance research.