Post-release Monitoring of Two Translocated Red Squirrel (Sciurus vulgaris L.) Populations

Abstract

The red squirrel (Sciurus vulgaris) has suffered a 20% decline in its range in Ireland since the introduction of the grey squirrel (Sciurus carolinensis) mainly through competition. Translocation (the intentional movement of a living organism from one area to another) of red squirrels was conducted in Derryclare wood, Connemara between July and October 2005. This project has investigated the fate of this red squirrel population through post-release monitoring techniques. A second translocation to Belleek Forest Park, Co Mayo was also conducted and the establishment and subsequent well-being of this population was also investigated. The second translocation of red squirrels to Belleek was conducted in a three phase programme in 2007 and 2008. Fifteen individuals were translocated in what was designed as a soft release procedure, although there were some problems of squirrels escaping from the enclosure during the second and third phase of the translocation. A fourth phase of translocation was deemed unnecessary as the population began to breed and recruit new individuals. Initial success was recorded using short-term monitoring. Settlement patterns investigated by radio telemetry displayed a priority for locating food initially after release; individuals tracked were found to include the release enclosure and supplementary feeders within home ranges. Not all squirrels established core areas initially using their home range uniformly. However, during a second tracking session, conducted 18 months later, a pattern more in keeping with that of established squirrel populations was shown; individuals were utilising other areas of the wood including parts without supplementary feeders and all had preferred core areas within their home range. Post-release monitoring in Derryclare was mainly conducted through live trapping, between June 2008 and March 2011. It was found that the population had dispersed further into the woodland since work had finished there in 2007 and were utilising new areas. Six of the originally translocated stock were captured near to or within the Nature Reserve in which the release enclosures had been based. Both red squirrel populations at Belleek Forest Park and Derryclare wood were monitored to investigate establishment of each population and their demographics in the medium-term. Comparison between the populations in each wood showed that spread of the red squirrels was influenced by difference in habitat type. The red squirrel population at Belleek were found to have inhabited all available habitat and then increased in density, whereas, the population at Derryclare were found to have spread through the woodland as their density increased. Recruitment of individuals was high at both sites, these new squirrels were the progeny of translocated stock as both areas were isolated from the possible immigration of other red squirrels. Over the course of the study both populations showed an increase in abundance year on year. Habitat quality was also monitored at both sites. The future success of both translocations was considered and the potential threats to the populations analysed, in order to investigate the long-term prospects of both populations. At Derryclare wood, the potential impact of habitat loss was investigated. This was achieved by examining the changing squirrel carrying capacity of the woodland due to planned clear-felling procedures. It was found that if felling was conducted as planned by land-owners, then a sufficient sustainable habitat would be available for the red squirrel population in the future. However, in April 2011, 150 hectares of forest were impacted by a forest fire. The actual detrimental effects of the fire were investigated; it was found that as the fire remained on the ground, mature trees were only scorched at their base which did not affect their survival. A small area of immature trees did suffer fatally from the fire but not enough was damaged to impact upon the sustainability of the red squirrel population. At Belleek Forest Park, the potential infiltration of grey squirrels to the area was investigated. A distribution survey of red and grey squirrels in the region separating Belleek from known grey squirrel inhabited areas of the northwest of Ireland was undertaken. It was found that the red squirrel was widespread throughout the area surveyed. Only five reports of grey squirrels were received by the survey, each report was more than a year old and in each case only one squirrel had been witnessed. Although the authenticity of these grey squirrel sightings was questioned, the potential invasion of greys from these possible nearest sources of grey squirrels to Belleek was analysed. This was achieved by using a GIS based model Least Cost Pathway (LCP) from the source location to Belleek Forest Park. The LCPs were examined to determine whether such routes were viable. It was found that there was potential for grey squirrels to reach Belleek from these locations, but that the grey squirrel would have to establish itself in habitat along the way. LCP analysis also provided the potential locations of sentry posts (areas which can be observed to detect grey squirrel presence and progress towards Belleek) to use in on-going monitoring and where necessary control programmes, that will protect the area from the invasion of the grey squirrel. Overall, the project found that translocation is a feasible option for conserving the red squirrel in Ireland. It found that red squirrels can establish themselves in uninhabited woodland successfully. A recommendation from the study suggests that long-term prospects and monitoring programmes in target sites must be incorporated into feasibility plans in the preliminary stages of translocation. This includes investigation into forest sustainability and where possible models such as the LCP to assess the sites isolation from grey squirrels.