Soft Release Technique Research Articles

Establishment success of the reinforced population of Gran Canaria Blue Chaffinch Fringilla polatzeki

The Gran Canaria Blue Chaffinch is the rarest forest passerine in the western Palaearctic with a population reduced to a single locality, Inagua, in the west of the island. After a forest fire, some birds were established in another location and a reinforcement programme was launched with the aim of consolidating this new population. Between 2010 and 2019, 194 Blue Chaffinches were released in the pine forest of La Cumbre, in the centre of the island and at a higher altitude than the previous one. Birds of two origins were used for this action: captive-bred birds were released using “soft” release methods, and wild-caught birds from the Inagua source population were released using “hard” release methods. Survival of radio-tagged birds (20–42 days of battery life) was high and similar between the two groups. Wild-caught birds occupied 12–15 times more surface area than captive-bred birds that remained close to supplementary feeding sites. All translocated birds displayed breeding behaviour in the following breeding season, although the rate of contribution to the new population was significantly lower for wild-caught birds (21% compared to 54% for captive-bred birds). This disparity can be partly attributed to nearly one-fifth of the wild-caught birds returning to Inagua. We conclude that the establishment phase of the Blue Chaffinch reinforced program in Gran Canaria has been successful. To retain wild-caught birds and deter their return to the source population, we recommend employing methods akin to the soft-release techniques utilized for captive-bred birds. Ongoing monitoring of the enhanced population, collecting data on survival and breeding success, will enable the evaluation of the long-term success of the translocation program.

Translocation of southern mountain caribou using a soft-release technique

Southern mountain caribou (Rangifer tarandus caribou, SMC) in British Columbia, Canada, are experiencing a precipitous population decline and range recession. In 2019, the two southernmost herds, the South Selkirks and the Purcells-South herds, were functionally extirpated and facing imminent extinction. To rescue the remaining animals, a translocation into the Columbia North herd range was performed using a soft-release method. The translocated animals were released alongside a captive-reared yearling and a resident adult female from the Columbia North SMC herd. A comparison of habitat selection behaviours at the 2nd order of selection demonstrated that the released animals responded to habitat and elevational conditions similarly to resident caribou. The translocation and soft release of Purcells-South and South Selkirks individuals demonstrates that soft release of wild translocated and captive-reared SMC can be successful and should be considered where and when feasible.

Assessing translocation effects on the spatial ecology and survival of muskrats Ondatra zibethicus

Muskrats Ondatra zibethicus are semiaquatic herbivores experiencing long-term and widespread population declines across North America. Translocation may be a viable tool to bolster or reestablish local populations; however, subsequent effects of translocation on muskrats are unknown. We live-trapped and translocated radiomarked muskrats (n = 65) during the summers of 2018–2019 in Voyageurs National Park, MN, USA and assessed post-translocation effects on weekly survival probabilities and space-use patterns. We did not observe homing behavior, though individuals moved an average of 2.2 km (SE = 0.30 km) from release sites and established home ranges within ∼8 days (SE = 1.16 days) post-translocation. Weekly post-translocation survival probabilities (0.95, SE = 0.001) and average home-range sizes (2.52 ha, SE = 0.44 ha) were similar to other studies of non-translocated muskrats. Our most-supported known-fate survival model revealed muskrats using beaver Castor canadensis lodges had greater weekly survival probabilities. Additionally, weekly muskrat survival varied between years suggesting a positive response to a novel soft-release technique applied in 2019. Our study provides the first empirical assessment of translocation effects on muskrats and suggests translocation may be effective for establishing or enhancing local muskrat populations. Additionally, our study suggests beaver lodges may confer fitness benefits to sympatric muskrats particularly during dispersal.

Hatchling short-necked turtles (Emydura macquarii) select aquatic vegetation habitats, but not after one month in captivity

Knowledge of turtle hatchling ecology is fundamental for managing wild populations. Information on habitat selection by turtle hatchlings is particularly important to ensure that conservation programmes that release hatchlings into the wild give them the best chances of surviving to adulthood. Currently, knowledge of the ecology of turtle hatchlings worldwide is limited, which restricts evidence-based management for threatened species. Here, we used laboratory and field experiments to test for effects of captivity on habitat selection, movement, and short-term survival of Murray River turtle hatchlings (Emydura macquarii). This species has declined > 60% since the 1970s, and a conservation plan is urgently needed to manage their recovery. In both the laboratory and field, we found that hatchlings select aquatic vegetation when it is available. Hatchlings raised in captivity for a month, however, were radio-tracked in habitats significantly further from vegetation after release, and over three times as many of these hatchlings were attacked by predators, compared to those released immediately after hatching. Aquatic vegetation is clearly an important habitat for hatchling E. macquarii, and therefore, (i) hatchling conservation should prioritise areas with appropriate aquatic vegetation, and (ii) aquatic vegetation restoration should be prioritised to ensure E. macquarii hatchling survival in the wild. Moreover, since captivity affects hatchling habitat selection, E. macquarii hatchlings should be released immediately upon hatching. Further research on soft release techniques and longer-term captivity is required to determine whether the impact of captivity can be reduced.

Reintroducing Cuvier’s gazelle. Better than expected from captive-bred founders

The use of captive-bred animals as founder stock for reintroduction is sometimes discouraged due to their low genetic diversity and even accumulation of deleterious alleles. In October 2016, 43 Cuvier’s gazelles (12 males and 31 females), managed under a European Endangered Species Programme (EEP) and housed in captivity, formed the base of a reintroduction project in Tunisia. The project approach used soft-release techniques. Upon arrival, animals were released in acclimatisation pens, so they could adjust to the new conditions gradually before true release. This study reports on the three-year period gazelles were in the acclimatisation pens before release into the wild. To assess the suitability of captive-bred Cuvier’s gazelles as founder stock for reintroduction, the demographic parameters of the reintroduced population were studied for three reproductive seasons in Tunisia (2017–2019). The demographic parameters of the reintroduced population were also compared to those from the source captive population as a control during the first breeding season. If the animals used as founders were unsuited, a decrease in demographic parameters could be expected over time in the reintroduced population, as well as lower demographic variables compared to the source population. Contrary to expectations, during the three-year study period, all demographic variables increased in the population reintroduced in Tunisia, except juvenile mortality, which decreased. Moreover, none of the demographic values of the gazelles in Tunisia were significantly different from the source population. We hypothesize that in the extremely bottlenecked captive Cuvier’s gazelle population used as founder stock, genetic diversity was still high enough to surmount the presumably deleterious effects of inbreeding. This is probably due to very high heritability (h2), a parameter providing information on the quantitative genetic variation associated with multi-locus quantitative traits previously found in this population. Although reintroduction programs have traditionally been undertaken purely as management exercises, ours was designed to meet a research objective as well. We wanted to find out the adaptive variation in sex ratio in offspring of female Cuvier’s gazelles using the size of the enclosure as a proxy reflecting their body condition. As found in captivity using consanguinity level as a proxy of body condition, in the reintroduced population, mothers in large enclosures produced more daughters while those in the small ones produced more sons, which supports adaptive manipulation of the birth sex ratio favoured by natural selection in reintroduced Cuvier’s gazelles.

Predator visits to acclimatization pens: implications for the soft-release of gallinaceous birds

AbstractPredator visitation to acclimatization or soft-release pens containing captive translocated animals has the potential to cause sub-lethal effects or physical injury that could influence post-release survival and establishment. No previous study has examined potential interactions between captive and resident animals during pre-release holding periods. We monitored seven holding pens containing wild-caught northern bobwhite Colinus virginianus or scaled quail Callipepla squamata in the Rolling Plains Ecoregion of Texas, USA, using remote camera systems. Our objectives were to determine if resident predator species and conspecifics visited holding pens, and to characterize visits by species, frequency, duration and behaviour. We recorded visitation to holding pens by four potential predator species. Although most visits by mammalian predators were short in duration, northern raccoons Procyon lotor were observed spending extended periods of time at holding pens. We also recorded resident scaled quail and northern bobwhite quail visiting holding pens containing conspecifics. We recommend that future studies using a soft-release technique in which captive animals are held at the release site consider the potential impacts of predator visitation to holding pens, and methods to mitigate those impacts.

Spatial organization and social relations in a reintroduced population of Endangered Iberian lynx Lynx pardinus

AbstractIn 2015 10 Iberian lynxes Lynx pardinus were released in south-eastern Portugal, within the framework of a Spanish–Portuguese reintroduction project. We examined each individual's use of space and social interactions during the first year after their release. Lynxes were selected for reintroduction according to behavioural, genetic and health criteria and fitted with collars with VHF and global positioning systems. Both males and females went through an exploratory phase that lasted 65–105 days. The lynxes did not exhibit any movement directionality from the release site during the exploratory period. During August–December 2015 a stable nucleus comprising seven individuals (four males, three females) was established south-west of the release enclosure. Although the males had a slightly larger mean home range (11.18 ± SE 1.36 km2) than females (9.87 ± SE 8.71 km2), the difference was not significant. The knowledge obtained during the first year of the lynx reintroduction project in Portugal is critical to support the future of this reintroduction strategy. Our results suggest that once the soft release technique is no longer possible because of logistical constraints on the construction of more enclosures, new individuals should be released in unoccupied areas surrounded by occupied territories. This will promote strong social ties to the resident population and prevent lynx dispersal.

Avian Restoration in the Prairie-Oak Ecosystem: A Reintroduction Case Study of Western Bluebirds to San Juan Island, Washington

Abstract Avian reintroductions are an important conservation tool, but landbird reintroductions are substantially underrepresented compared to other avian taxa, which hinders progress in improving the value and efficacy of landbird reintroductions. We document an ongoing reintroduction of Western bluebirds (Sialis mexicana) to their historic range in the prairie-oak ecosystem on San Juan Island, Washington. Further, we assess the success of preliminary reintroductions and discuss the feasibility of further landbird reintroductions in this threatened ecosystem in the Pacific Northwest. We released 80 adults and 26 juveniles from 2007 to 2010 using a variety of soft-release techniques, and we collected demographic data on the reintroduced population. The program achieved preliminary criteria of success: individuals were safely translocated to the release site, and released individuals established breeding territories; both translocated individuals and their offspring reproduced successfully; and the reintro...

Survivorship of Rehabilitated Juvenile Tawny Owls (Strix Aluco) released without Support Food, A Radio Tracking Study

We investigated the survival of 57 rehabilitated juvenile Tawny Owls ( Strix aluco) that were ‘hard released’ (without the provision of a release aviary or support food) by means of radio tracking. The birds were released in the month of August in three consecutive years: 2005, 2006 and 2007, in the counties of Somerset and Hampshire, United Kingdom. Tracking of the owls was successfully carried out for between three and 160 days. Mortality was recorded for 16 birds (28%). The transmitter was shed by 24 (42%) owls, the signal was lost for 12 (21%) and tracking was ceased for five (9%) owls. Survival of the owls was compared with results from previous studies on wild Tawny Owls and also rehabilitated ‘soft released’ Tawny Owls (released with provision of food and shelter after release) and found to be similar. This study suggests that employing costly and time-consuming soft release techniques may be unnecessary for juvenile Tawny Owls as their survival is not significantly reduced using hard-release methods. Measuring post-release success of rehabilitated birds of prey is discussed in relation to benchmarks used in previous studies.

Practical Considerations for the Reintroduction of Large, Terrestrial,Mammalian Predators Based on Reintroductions to South Africa's Eastern Cape Province

The expansion of conservation estate in South Africa has seen large predators increasingly reintroduced in or- der to restore ecological integrity, conserve threatened species and maximise tourism. Reintroductions occurred at fenced, ecotourism sites in South Africa's Eastern Cape Province. Lion Panthera leo reintroduction began in 2000 and has been highly successful with a population of 56 currently extant in the region arising from 35 reintroduced individuals. The Af- rican wild dog Lycaon pictus population has increased to 24 from a founder population of 11. Reintroduction of spotted hyaenas Crocuta crocuta also appears successful, although reintroductions of leopards Panthera pardus and cheetahs Aci- nonyx jubatus have been less successful. Here we review the successes and failures of the reintroductions that have oc- curred in the region and describe recommendations to assist future translocations. Ecological attributes of each species af- fected the success with which they were reintroduced. Soft-release techniques, adequate fencing, appropriate socio- economic environment, the order of predator reintroduction with subordinate species released prior to dominant ones, adequate prey base and adequate monitoring all improved the success of reintroductions. Carrying capacity for large predators is unknown and continued monitoring and, we fear, intensive management will be necessary in virtually all modern day conservation areas.

Optimising reintroduction success by delayed dispersal: Is the release protocol important for hare-wallabies?

The transfer of threatened animals from one location to another in order to benefit the species is a technique frequently used by animal conservation managers. However, very few of these relocations have experimentally assessed the relative merits and disadvantages of commonly used release techniques. The premise examined in this study was that a higher degree of site fidelity should be advantageous for an individual through a soft release protocol. Two species of hare-wallaby, mala ( Lagorchestes hirsutus) and merrnine ( Lagostrophus fasciatus), were fitted with radio-collars and reintroduced in August 2001 onto Peron Peninsula in Western Australia. These threatened species were reintroduced using two release strategies (soft versus hard release), and their movements and body condition were monitored, for a period of four weeks post-release, using radio-telemetry and trapping. Each species averaged decreases in body condition index when exposed to both experimental release protocols. A total of 11 animals (32%) emigrated from the release sites, with 10 of these animals being male. Importantly, no relationship was found between site fidelity and release method, although body condition was significantly higher in mala which dispersed, and there was observational evidence for a male-biased dispersal for merrnine. Although the number of released individuals of each species was low, this study demonstrates an interesting trend which indicates that soft release techniques do not necessarily to confer an advantage to the successful immediate establishment and survival of either hare-wallaby species in the short term. We recommend that managers involved with species reintroduction programs consider the costs and potential outcomes of designing and installing soft release enclosures.

Translocation of the socially complex Black-eared Miner Manorina melanotis: a trial using hard and soft release techniques

We translocated five colonies of the highly social and co-operatively breeding Black-eared Miner Manorina melanotis, an endangered Australian honeyeater. Two colonies were released immediately (hard release) and two colonies were housed in aviaries for up to a week on-site and then supplied with food for a further week following release (soft release), A fifth colony was released using a combination of methods. All four hard and soft released colonies contained dependent fledglings at the time of release, This appears to be the first translocation of a co-operative species where intact colonies containing multiple breeding females, each with a suite of helpers have been translocated successfully. Both hard and soft release treatments appeared equally successful during an initial monitoring period of up to two months. All four colonies maintained social cohesion, and displayed high levels of survival and site fidelity. Both hard release and one soft release colony attempted to breed within 600 m of their release site within eight weeks of release, The other soft release colony bred 12 months later. We believe the inclusion of dependent young in each translocated colony provided a focus for translocated colonies that promoted site faithfulness and colony cohesion. Results of long-term monitoring remain inconclusive and it is recommended that monitoring be repeated during several future breeding events. Given our findings, we recommend that when translocating highly social species every effort is made to translocate the entire group, hard release techniques be applied and stimuli that enhance group cohesion and site faithfulness (the presence of dependent young) be exploited.