Two-toed sloths are nocturnal and arboreal mammals whose survival depends on remaining inconspicuous. Their slow movement, energy-conserving metabolism and mottled coloration help them blend into trees, while their associated communities of algae, insects and other organisms can further disguise their bodies against a forest background. Yet this stealth offers little protection from terrestrial predators if a sloth comes down to the ground. Coastal Ecuador is also home to potential predators such as pumas, ocelots and tayras. Consequently, a released animal faces unfamiliar dangers including predation, human activity, accidents and behavioral deficits during the period when it must learn to feed, navigate and remain hidden effectively.

Bravo entered the Mansión Mascota wildlife clinic in Guayaquil in March 2021, weighing only 750 grams at one to two months of age. He received intensive care, individual support from a caregiver and veterinary treatment when unusual behavior or reduced food intake required it. Rehabilitation also involved exposing the young sloth to a complex enclosure containing branches and small trees, feeding him native leaves with their attached invertebrates, allowing controlled contact with other two-toed sloths, and assessing his responses to people and dogs at a safe distance. By the time he was evaluated for release, Bravo weighed 3.8 kilograms, moved competently through trees, could occasionally crawl on the ground, sought food in both arboreal and terrestrial settings, interacted with other sloths and avoided predator-like stimuli.

Independent veterinarians concluded that Bravo was fit for release. The site selected was the 323-hectave Bosque Protector Prosperina, a restored dry tropical forest within the Polytechnic University of Guayaquil. The reserve is connected to the much larger Cerro Blanco Protected Forest Reserve and contains mature patches linked to secondary growth. The release took place during the rainy season, when leaf abundance and food availability are higher than during the dry period. Surveys covering 11 kilometers led to the selection of a release point with important food trees, including bototillo, ceibo, saman and jocote, as well as canopy layers ranging from about six to 22 meters and routes connecting the area to taller surrounding forest.

Because the release site lies within a university precinct, the team also prepared the people who might encounter the sloth. Security personnel received a six-hour course on empathy-based wildlife management, with about one-third of the instruction devoted to two-toed sloths. These guards already handled around two sloth rescues or translocations each year in collaboration with the university’s Biodiversity Unit, and they participated in the release. Their familiarity with the project meant they could respond appropriately if they located Bravo. The sloth was transported 11.1 kilometers from the clinic in a kennel fitted with a transverse branch that he could grasp, a measure intended to reduce stress during the journey.

The field team monitored Bravo every night, generally beginning between 17:30 and 18:00 and continuing until 04:00 to 06:00. Direct observation was used to record movement, feeding, posture, vocalizations and unusual events. When he could not be found, teams searched the forest in daylight and darkness, sometimes for as long as seven hours, while resting during periods when sloths are generally less active. Torches were used sparingly and at standardized intervals to limit disturbance to Bravo and other wildlife. Over 167 hours of observation, the sloth was directly detected for 62 hours. He began moving at 20:00 and 21:00 on the first two nights, then usually began around 19:00 to 19:30, with 75% of the remaining records showing this pattern.

Bravo’s movements covered approximately 0.12 hectares during the first 10 days and involved 19 trees. He fed on bototillo leaves, saman leaves or insects and the leaves of lianas. The number of trees used each day increased after the first five days, suggesting that he was beginning to explore a wider portion of the forest. On the eighth day, carers placed feeding support about one meter from his resting position, but he ignored it. Analysis also identified a relationship between movement and the likelihood that the monitoring team could detect him. The highest combined rates of movement and detection occurred around 19:00, while a smaller movement peak appeared between 02:00 and 04:00. The movement and detection data were normally distributed, and their Pearson correlation was positive and statistically suggestive, with a reported value of p = 0.06.

Despite the favorable results, the sixth night brought a dramatic and potentially dangerous encounter. A masked owl, Pulsatrix perspicillata, called from within roughly 10 meters of Bravo. The sloth became motionless in a defensive posture and fell from the tree, but a caregiver reached him quickly. After resting briefly, he became highly active, moved rapidly toward the source of the owl calls and then returned to the canopy on his own. The researchers inferred antagonistic behavior involving the owl, although they could not establish whether the bird attempted predation, was displaced by Bravo, or was reacting to him. The encounter is notable because motionless defense had not previously been reported in this context for Choloepus hoffmanni. Bravo also descended to the ground to feed that night, highlighting the vulnerability faced by a sloth away from the canopy.

The Bluetooth tracker supplied an additional layer of support. The 34-gram device was carried in a flexible, semi-leather backpack sealed with a cardboard slide and four Velcro junctions designed to decay without manual removal. Bravo underwent five habituation sessions with the apparatus, although he detached it on three earlier occasions after one to four days. The pack eventually remained on his body for 54 days until humidity degraded its cardboard components, and it was successfully refitted 14 days before release. On the sixth night after liberation, heavy moisture caused the same junctions to fail and the tracker slipped away. While attached, the device’s nominal open-range reach was 120 meters, and its signal was used to identify the tree holding the strongest signal, with positions checked using a Garmin GPS receiver of about three-meter accuracy. The tracker allowed the team to find Bravo during searches, including a low-visibility encounter on day 10, when observers had difficulty seeing the motionless animal in the forest.

The episode highlights both the promise and the limits of inexpensive wildlife monitoring. Bluetooth devices cannot provide the continuous movement tracks available from satellite or radio telemetry, and Bravo’s observation period was too short to prove permanent establishment. Previous work on other arboreal mammals suggests that a follow-up period of about a month, combined with several months of tracking, would provide stronger evidence that an animal has settled successfully. Nevertheless, Bravo fed on several tree species, moved through the forest, left feces, recovered from his fall and climbed back into the canopy unaided. The study’s central lesson is that successful rehabilitation cannot be demonstrated by releasing an animal alone: its health, behavior, feeding and ability to avoid detection must be checked afterward. For scarce and difficult-to-observe species, biodegradable Bluetooth packs offer an affordable way to combine field support with direct observation, while more extensive evaluation is needed to establish their limits and improve post-release survival.

Subject of Research: Post-release monitoring of a rehabilitated two-toed sloth using direct observation and Bluetooth tracking

Article Title: Release and follow-up of a rehabilitated two-toed sloth ( Choloepus hoffmanni ) in a tropical dry forest in Ecuador

Article References: Villalba-Briones, R., Jiménez, E. R., & Monros, J. S. (2022). Release and follow-up of a rehabilitated two-toed sloth (Choloepus hoffmanni) in a tropical dry forest in Ecuador. Neotropical Biology and Conservation, 17(4), 253-267. https://doi.org/10.3897/neotropical.17.e91332

Image Credits: AI Generated

DOI: 10.3897/neotropical.17.e91332

Keywords: two-toed sloth, animal rehabilitation, post-release monitoring, Bluetooth tracking, wildlife conservation, tropical dry forest, Choloepus hoffmanni, masked owl, Ecuador, animal telemetry, Release, follow-up

The study addresses a stubborn gap in conservation practice. Rehabilitation and release of injured wildlife is common, but assessing whether those releases actually succeed is difficult, particularly for nocturnal felids that are almost never seen after the transport box opens. Post-release monitoring data for rehabilitated Leopardus species fitted with GPS devices is scant, and past efforts have often ended early when the animal died or had to be recaptured. Costa Rica has the highest wildlife roadkill incidence in Central America, and ocelots are the most common feline victims of vehicle strikes, so the pipeline from collision to rescue center to release is a busy one. Without tracking, nobody could say what happened to the cats on the other end of it. This project was designed to change that, pairing a rescue case with satellite technology capable of documenting survival, movement, and habitat choice in near real time.

The setting matters as much as the technology. The Osa Peninsula, a 1,543-square-kilometer biodiversity hotspot on Costa Rica’s southern Pacific coast, holds a unique mosaic of oil palm plantations, cattle farms, and a stable network of protected primary and secondary lowland rainforest anchored by Corcovado National Park. Camera-trap surveys have documented mammal populations recovering from historical hunting and habitat loss, and the peninsula supports a singularly dense ocelot population, with estimates reaching up to 169 individuals per 100 square kilometers. That density is a double-edged sword for any release program: prey and habitat are abundant, but a young male dropped into the landscape must contend with resident adults already holding territories. The researchers chose a hard release site near Piro Biological Station, inside a private reserve in Corcovado’s buffer zone, citing stream access, ample prey, distance from human conflict areas, and ease of monitoring access.

The ocelot’s road to release was long and deliberately hands-off. Rescued with minor injuries plus central nervous system inflammation and vestibular symptoms from the strike, he was treated for seven days and then held under rehabilitation protocols for eight months. Four health checks were performed under anesthesia to minimize human contact, and the cat repeatedly demonstrated the behaviors that made him a release candidate: fear and aggression toward people, successful hunting of live prey and fish introduced into his enclosure, and minimal pacing distress. A final veterinary workup 24 days before release included a complete blood count, ELISA screens for seven pathogens, PCR testing for feline infectious anemia, and a coprological exam. Results came back positive for Chlamydophila and Toxoplasma gondii, both pathogens wild ocelots commonly carry, and the team correctly judged that treating them was pointless when reinfection in the wild was near-certain. At that final check he weighed nine kilograms.

The collar itself was engineered around the constraints of tracking a small cat. Weighing less than five percent of the ocelot’s body mass, the Telonics unit was programmed to collect a GPS fix every five hours, transmit data every five days, and emit a VHF beacon daily for real-time tracking when needed. Critically, during the final months of rehabilitation the cat wore a non-functional collar of identical size and weight, so the device was already familiar on release day. He was chemically immobilized, fitted with the working unit one day before release, and set free at 08:00 local time on January 4, 2023. The collar achieved an 81 percent fix success rate, averaging 3.9 locations per day, a dataset dense enough to reconstruct daily movement but frugal enough to stretch the battery across the monitoring window.

The movement data split cleanly into two phases. For the first 75 days the ocelot kept moving away from the release point, covering an average daily displacement of 1.05 kilometers, with single-day displacements ranging from five meters up to 5.4 kilometers and total daily movement reaching 7.5 kilometers. Then the track tightened. Average daily displacement fell by 46 percent, from 1.82 kilometers per day in the exploratory period to 0.99 kilometers per day once the animal settled, and the track began repeatedly revisiting the same locations, which the researchers defined as territory establishment. Two veterinarians visually confirmed the cat once, 43 days after release, noting he displayed fear of humans and ran off quickly, an encouraging sign that rehabilitation had not habituated him to people.

The habitat findings were the surprise. Although the release site sat in primary forest and high-quality forest was available nearby, the ocelot spent progressively more time in grassland, pasture, and other disturbed habitats as the months passed. A resource selection function, built with 100 pseudo-absences per location and weighted logistic regression, found strong statistical support for selection of grassland, palm plantations, open and urban areas, and secondary forest relative to primary forest, with only mangroves ranking lower than the baseline habitat. Camera traps deployed for 30 days around day 105 confirmed that known ocelot prey, including Central American agouti, white-nosed coati, and raccoon, were present in the settled area, and residents of two nearby properties reported seeing a collared ocelot passing through without distress, though no photograph was ever obtained.

Why would a wild cat released into pristine forest choose the farmland? The authors offer two non-exclusive explanations. First, competition: camera-trap surveys have documented high densities of resident ocelots around the release area, and this young male was likely pushed out of prime territory by established adults, relegated to grasslands until a vacancy opened. Second, familiarity: the area around his collision site is dominated by agriculture, so he may have carried a learned preference for disturbed habitats, or an acquired taste for domestic prey such as chickens, and sought out a landscape that felt like home. The pattern also fits natal habitat preference induction, the phenomenon in which animals settle in habitats resembling those they grew up in. Either way, the flexible habitat and diet requirements that make ocelots generalists appear to have carried this individual through a difficult transition.

The lessons for future releases are practical. Release-site assessments should weigh the existing density of conspecifics and sympatric carnivores, since intraspecific competition can shape long-term success, and generalist species like ocelots may actually be well suited to mixed-use matrices where varied prey and habitat compensate for competitive pressure. The study also exposes the trade-offs of collar-based monitoring: six months is likely an underestimate of true integration, given that subadult ocelot dispersal can take up to 18 months and post-translocation vulnerability up to four years, but longer tracking demands heavier batteries or sparser data for a nine-kilogram cat. Camera traps, despite their popularity, proved nearly useless for finding a single individual in dense forest. As a single-animal study, the work cannot settle whether competition or preference drove the habitat choice, but it demonstrates that rehabilitation centers and researchers, working together with satellite collars, can finally measure what happens after the release door opens, one of the first fine-scale GPS assessments of its kind for a rehabilitated Neotropical felid.

Subject of Research: Post-translocation GPS monitoring of a rehabilitated ocelot on the Osa Peninsula, Costa Rica

Article Title: Back to the wild: Post-translocation GPS monitoring of a rehabilitated ocelot ( Leopardus pardalis ) in a forest-agriculture matrix in the Osa Peninsula, Costa Rica

Article References: Wicks, S., Beirne, C., Azzopardi Schellmann, C., Flatt, E., Quirós Beita, S., Pereira Rocha, R., & Whitworth, A. (2024). Back to the wild: Post-translocation GPS monitoring of a rehabilitated ocelot (Leopardus pardalis) in a forest-agriculture matrix in the Osa Peninsula, Costa Rica. Neotropical Biology and Conservation, 19(3), 379-392. https://doi.org/10.3897/neotropical.19.e124324

Image Credits: AI Generated

DOI: 10.3897/neotropical.19.e124324

Keywords: ocelot, Leopardus pardalis, GPS tracking, wildlife rehabilitation, post-release monitoring, translocation, Osa Peninsula, Costa Rica, habitat selection, roadkill, Neotropical felids, resource selection

Species reintroductions are a specialized form of translocation, the movement of organisms from one place to another. Where translocation can serve many purposes, a reintroduction specifically returns a species to an area it once occupied but from which it has been lost. The practice has a surprisingly long history. Australasia hosted the first recorded conservation translocations when, in the 1880s, large numbers of kakapo and kiwi were moved to an offshore island to shield New Zealand’s native birds from introduced mammalian predators. Deliberate releases aimed at restoring wild populations date back to the 1910s, but it was the successes of the 1960s and 1970s that elevated reintroduction into a mainstream conservation strategy. In the United States, a captive breeding and release program for the peregrine falcon, combined with the ban of the pesticide DDT, lifted breeding pairs from around 40 in 1975 to more than 1,600 by 1999. The Arabian oryx, extinct in the wild by the mid-1970s, was returned to Oman in 1982 from captive stock and rebuilt to a wild population of 1,100 individuals.

Formal frameworks eventually caught up with practice. The International Union for the Conservation of Nature issued its first position statement on translocations in 1987, established a dedicated specialist group within a year, and made official reintroduction guidelines policy in 1995, updated in 2013. According to the IUCN’s Conservation Translocation Specialist Group, more than 1,500 species have now been translocated worldwide. The guidelines emphasize deciding when translocation is appropriate, careful release strategy and site selection, post-release monitoring, feasibility and risk assessment, and the dissemination of results. Yet success is notoriously hard to define, because projects differ enormously in planning, methods, budgets, and monitoring. An analysis of 293 animal translocation studies by Berger-Tal and colleagues identified more than 1,200 individual difficulties, underscoring that every project faces a unique tangle of species requirements, design choices, and resource constraints. The key pillars of success emerged as good quality release habitat, deep understanding of the species’ biology and behavior, and efficient post-release monitoring.

Reintroductions also carry a well-documented taxonomic bias. Of the 293 animal translocations analyzed in one major review, 106 involved mammals and 66 birds, while only 35 involved fish. A separate study of 699 reintroductions from IUCN data confirmed that mammals and birds are overrepresented relative to their prevalence in nature while fish are underrepresented, and intriguingly, more than half of the reintroduced birds were classified as Least Concern, suggesting that national priorities rather than global extinction risk often drive these projects. Beyond taxonomy, reintroductions face recurring social and biological hazards. Disease risk must be weighed, both from released animals introducing pathogens and from parasites that might block survival in a new environment. Public attitudes can be decisive: the reintroduction of Eurasian lynx to the Vosges Massif in France between 1983 and 1993 was undermined by illegal killing that organizers had failed to anticipate because they had not adequately researched local sentiment, and the population never became self-sustaining. Climate change adds a further layer of complexity, prompting the IUCN to add new categories such as assisted colonisation and ecological replacement to its guidelines.

When the review turns specifically to fish, the record becomes both richer and more sobering. Cochran-Biederman and colleagues previously identified 260 individual fish reintroductions from 75 published studies spanning 1989 to 2013, and Pearce’s team added 64 more cases published through 2024, bringing the global total to 324 documented projects. Of the original 260 cases, 42 percent were classified as failures. Among the 64 additional cases, 39 percent were successes, 23 percent partial successes, and 17 percent failures, with 21 percent impossible to classify because published information was insufficient. Success was judged primarily on reproductive outcomes: survival of released fish for at least six months, spawning after reaching sexual maturity, and recruitment of offspring into the breeding population. Strikingly, in more than half of the partially successful cases, it was a lack of evidence for reproduction, rather than demonstrated failure, that prevented full success, pointing to chronic weaknesses in monitoring rather than necessarily in the biology.

The causes of failure were more varied than the drivers of success, but one variable towered above the rest: whether the initial cause of the species’ decline had been addressed. Among failed cases, 65 percent had not tackled the original driver of loss, while 68 percent of successful projects had. Habitat quality ranked second, with confirming the presence of required physical habitat the single most important action for avoiding spawning failure. Stocking variables mattered too, in ways that should give hatchery managers pause: 71 percent of recruitment failures were associated with hatchery-reared fish, implicating the genetics and rearing conditions of source populations. Intrinsic species traits played a role, with migratory species surviving at least six months after release more often than non-migratory ones, 94 percent versus 83 percent, but habitat and stocking variables were ultimately considered the most influential factors determining outcomes.

Geography matters as much as biology. North America dominates the fish reintroduction literature, accounting for 75 percent of the cases in the earlier review and 45 percent of the newer additions, with Oceania contributing 38 percent of the latter, mostly from Australia. Europe, despite having 37 percent of its freshwater fishes threatened, contributed only about 12 percent of documented cases. North American projects frequently rely on piscicides such as rotenone to remove invasive fish before native species are returned; 20 percent of the recent North American cases used a piscicide and another 24 percent used mechanical mixed methods. These chemicals can harm non-target zooplankton and macroinvertebrates and sometimes fail to eradicate the target species, and public trust in their use is fragile even where they have achieved dramatic results, such as the 95 percent reduction of invasive sea lamprey in the upper Great Lakes. European projects offer complementary lessons: German work on the European weatherfish showed the value of careful stocking strategy and habitat assessment, a central German project for the bleak demonstrated environmental DNA monitoring as an inexpensive detection tool, and Hungarian efforts combined translocation, captive breeding, and restocking to support the endemic European mudminnow.

The United Kingdom presents a distinctive case. The country has a growing reintroduction culture, from white-tailed eagles in 1975 through red kites, Eurasian beavers, pine martens, and the short-haired bumblebee, whose return required improved management of 850 hectares of flower-rich grassland that also benefited the rare shrill carder bee. Yet no extirpated fish species has ever been reintroduced to Britain. The candidate is the burbot, the only freshwater member of the cod family, which historically inhabited 42 eastern-flowing rivers in England before being driven out by widespread river channelization and the severing of river-floodplain connections that destroyed its spawning and larval habitats. The last recorded catch came from the Old West River near Aldreth, Cambridgeshire, in 1969. The obstacle is formidable: rivers in Great Britain now average one artificial barrier, whether weir, dam, or lock, for every 1.5 kilometers, leaving only about 1 percent of rivers in England, Scotland, and Wales free-flowing, and the burbot’s life cycle depends precisely on the lateral floodplain connectivity that has been lost.

The review argues that any English burbot project should follow a structured adaptive framework such as the Open Standards for the Practice of Conservation, which mirrors the IUCN’s planning and implementation stages. The groundwork is already partly laid: research since the 2000s has identified the loss of lateral floodplain spawning habitat as the cause of decline, candidate sites of sufficient quality have been identified, and the closest genetic relatives of the extinct English population have been traced to the western European subclade. Stocking strategy remains a critical open question. Continental projects show that annual releases for at least ten years are needed before the first evidence of natural reproduction appears; Belgium releases larvae annually into the Grote Nete system, trading numbers for lower rearing costs, while Germany stocks fingerlings, which survive better because of their greater swimming capacity. Monitoring will need to combine electrofishing, environmental DNA, bioacoustics, and visual surveys across life stages, a resource-intensive mix that Belgian and Dutch projects have shown is essential given how difficult spawning sites are to locate.

Ultimately, the review’s central message is that reintroductions are not short-term fixes but long-term socio-ecological investments. American projects such as the lake sturgeon and barrens topminnow reintroductions in Tennessee succeeded largely because public engagement built durable support, while the multi-state bull trout effort in the United States, organized into six recovery units and 109 core areas with structured decision-making, demonstrates the coordination that large-scale fish recovery demands. For the burbot, early national surveys found more than 90 percent of anglers supported reintroduction, but attitudes must be re-measured locally, and floodplain restoration will require engaging landowners and flood authorities, work that aligns conveniently with England’s Natural Flood Management and Environmental Land Management policies. Above all, the authors urge that findings from every project, successful or not, be shared through open conservation databases so that the hard-won lessons of three decades of fish reintroductions can finally flow into the rivers that need them most.

Subject of Research: Global fish species reintroductions and their lessons for a potential burbot reintroduction in UK rivers

Article Title: An updated review of fish species reintroductions: global lessons to inform future riverine fish conservation in the UK

Article References: Pearce, R. H., Sayer, C. D., & Chadwick, M. A. (2026). An updated review of fish species reintroductions: global lessons to inform future riverine fish conservation in the UK. Discover Conservation, 3(1), Article 2. https://doi.org/10.1007/s44353-025-00072-w

Image Credits: AI Generated

DOI: 10.1007/s44353-025-00072-w

Keywords: fish reintroduction, burbot, conservation translocation, freshwater biodiversity, UK rivers, IUCN guidelines, habitat restoration, stocking genetics, post-release monitoring, environmental DNA, rewilding, Discover Conservation