Management of grey squirrels

 

Annual Summary of Research
1 April 2002–31 March 2003

Objectives of the programme and specific tasks to achieve these are given in the table.
Progress has been made as detailed below.

Progress to end of March 2003

Index Trapping Studies
Potential sites were identified throughout England and Wales using GIS analysis identifying compartments vulnerable to grey squirrel damage, adjacent to high-density grey squirrel habitats. Sites were visited in summer/autumn 2002 to confirm suitability and selection. 11 sites were selected and Technical Support Unit staff trained in trapping and seed sampling protocols. All sites were trapped for squirrels and sampled for natural food availability during the first 2 weeks in January. Damage assessments will be carried out in September. Control of grey squirrels is not being carried out at any of the sites. This study will continue for 3 years, with an expansion in the number of sites involved if resources allow.

Options for the identification of high risk compartments (vulnerable species and age classes adjacent to good squirrel holding habitat) using GIS have been discussed with Business Services Division, FE. The GIS maps for the Forest of Dean which were used to identify potential sites for the index trapping trial were passed to FE District staff to aid with selection of sites to target grey squirrel control.

Evaluation of impact of grey squirrel damage to oak on timber yield and quality
The final Mensurational measurements were taken during December 2002 with a final damage assessment made in January 2003. Analysis of the effect of squirrel damage on tree growth rates and timber quality is in progress. A final report will be produced for June 2003. The data will be used for a paper ‘ Grey Squirrel impacts and influences on tree growth ‘ to be presented at the Third International Tree Squirrel Colloquium in Northumberland May 2003.

A paper (Mayle and Broome) reviewing the results of various damage surveys is in preparation for publication in a trade journal.

Study tour to North America
The report on the study tour identified considerable differences in landscape, habitat quality and structure and in potential levels of competition and predation by other animals on grey squirrels in their native habitat. It is suggested that although grey squirrels have been recorded as reaching densities in these native habitats, as high as those observed in GB, that juvenile survival and recruitment to the summer population is likely to be lower. The high levels of damage observed in GB are believed to be influenced by high numbers of juveniles entering the population during late spring / early summer. In addition bark may be less easily stripped from trees growing in the dense woodland habitats observed. The potential for collaborative work with colleagues in Northeast USA will be discussed at the International Tree Squirrel Colloquium.

Investigate seasonal variation in sperm viability
Adult male squirrels have been trapped monthly for visual assessment of reproductive activity and correlation of visual assessments with sperm numbers and motility. This will provide improved information for any future studies involving assessment of male reproductive activity.

Investigate novel and develop improved methods of population control
A comparison of trap placement and bait type is underway in Thetford Forest. The aim is to improve trapping efficacy in conifer habitats (where squirrels can be particularly difficult to control). Eight compartments have been selected within 4 areas. Within each compartment, two transects), each with 5 trapping locations (ground v tree sited) have been identified. Two areas are trapped during each two-week period, using either maize bait or mixed bait. Squirrel carcasses are also assessed for reproductive activity (to provide additional data for the sperm viability study).

A review to investigate options (e.g. hormones) to improve trapping/ baiting efficacy has been completed and a report is in draft.

To investigate the impact of grey squirrels on woodland biodiversity
A review of potential biodiversity impacts of grey squirrels (funded by the Royal Forestry Society) is underway in collaboration with BTO and RSPB. Forest Research’s involvement is minimal, through comment on the initial draft and collection of evidence of grey squirrel predation on woodland bird populations. The review aims to identify research needs in this area.

A contract with Newcastle University for dietary analysis of grey squirrels using stable isotope analysis, is under discussion. This will identify the proportion of their diet that is derived from animal sources and investigate how this changes during the year.

Technology Transfer and Advice
Woodland Ecology Branch (B Mayle and Alice Broome) has attended the UK Red Squirrel Group and England and Scotland Squirrel Fora meetings (5 meetings) on behalf of FC.

Presentations on squirrel impacts and management have been given to Mammal Pests Meeting Wolverhampton (FR Research update meeting), Mammal Society Meeting, London (Proceedings in prep); Reading MSc students; Squirrel control seminar, Chilterns; Forestry and Timber Association and National Gamekeepers Organisation Field day on Vertebrate pests, Gamebirds and Forestry. A live radio interview was also given to Steve Madden, East Anglia regional radio.

Poster displays, which included squirrel management issues, were provided for the Royal Agricultural show, and the Association of Professional Foresters meetings.

A separate report will be provided on the advisory enquiries dealt with for all tree protection and wildlife management issues. This will provide details of customers and types of enquiry, and highlight any emerging issues.