Research
Topics
1. Red & grey squirrel interactions
Both our native red squirrels and the introduced grey squirrels occupy a similar ecological niche being small tree dwelling mammals using tree seeds, berries and nuts as their principle foods.
The grey squirrel however has a competitive edge as it can digest large seeds from deciduous trees, such as oak, before they are fully ripe. In this way greys out-compete the red squirrels in mixed and broadleaved woodland resulting in loss of condition and reduced breeding success of the reds (Kenward & Holm, 1993, Kenward et. al, 1995 see References).
Grey squirrel control for red squirrel conservation. A study in Thetford Forest. No 453 English Nature Research Reports (2002).
A study on the effects of grey squirrel control on red squirrel conservation was conducted in a part of Thetford forest, East Anglia, from 1998 - 2001. Previous field trials in the 1990's had demonstrated that red squirrels appeared to benefit from active grey squirrel removal. In this study, using live trapping, the level of control effort was insufficient to reduce grey squirrel numbers significantly, highlighting how labour and cost intensive a grey squirrel control programme could be. (Gurnell & Steele, 2002). For a full report contact English Nature, Northminster House, Peterborough PE1 1UA.
Red squirrel Scuirus vulgaris L. conservation on Anglesey, North Wales (2002)
In 1998 Menter Môn carried out grey squirrel control on Anglesey to conserve the few remaining red squirrels on the island. Cage trapping of grey squirrels proved highly successful in a plantation trial, at Mynydd Lywydiarth, and the red squirrel population doubled by spring 2000 from 43 to 82. It has now reached over 100 (2002) with some red squirrels reported to have moved into neighbouring broadleaved areas for the first time in recent years.
A re-introduction study is underway in Newborough forest, in the hope of re-establishing red squirrel across a wider area of Anglesey. Other projects include an assessment of the value of nest boxes as a tool to monitor red squirrels and an examination of the effect of population reduction upon the sera-prevalence of squirrel poxvirus within grey squirrels.
2. Poxvirus research
The impact of grey squirrels on reds is exacerbated by the fact that the grey squirrels are thought to be hosts and carrier of the squirrel poxvirus (SQPV) which is fatal for red squirrels and has been implicated in many population crashes and local extinctions.
A novel poxvirus lethal to red squirrels (Sciurus vulgaris)(2003)
A study into the genetics of the virus causing this disease suggests that instead of the parapoxvirus as initially described, it may be a previously unknown genus of the chordopoxvirus family, i.e. a poxvirus. Further work is needed to verify this and throughout this site the disease will be referred to as squirrel poxvirus (SQPV) (Thomas, et al. 2003). This paper can be viewed from the Advice notes section.
Parapoxvirus causes a deleterious disease in red squirrels assiciated with UK population declines (2001)
A recent paper modelling red and grey squirrel populations suggests that transmission of poxvirus by grey squirrels has been a crucial factor in the decline of red squirrels and explains the speed of replacement of reds by greys. See references for details of this paper.
In the last three years two sero-positive grey squirrels have been found in the borders region of Scotland. This is the first indication that the virus has moved north into Scotland, but as yet no red squirrels showing poxvirus symptoms have been reported in this region. This suggests that de-fragmentation of forests and creation of habitat corridors, which could be used by greys to extend their range into red squirrel areas, will ensure the further spread of the disease.
3. Habitat management
A drive to increase biodiversity in many of our plantation forests, by planting broad leaved trees may have a significant negative impact on red squirrel populations. Although the exactmechanism by which greys replace red squirrels has still not been identified it is clear that grey squirrels are more proficient at recruiting juveniles except in coniferous woods (of 2000ha plus) (Pepper& Patterson, 1998 see link below). In large continuous conifer forests red squirrels have a competitive advantage, being more adapted to foraging in the canopy where the heavier greys are unsuited. Planting large seeded broadleaved trees amongst these plantations may inadvertently attract and subsequently support grey squirrels and open up a route for possible disease transmission. (Lurz et al 2003).
4. Grey squirrel control - research into a contraceptive for grey squirrels
Novel methods of grey squirrel control are constantly being sought and an innovative approach to contraception pioneered by Professor Harry Moore of Sheffield University was tested a few years ago. The technique, known as immunocontraception, involved treating squirrels with a vaccine that would trigger the grey squirrel females' immune systems to reject the males' sperm, thereby preventing pregnancy.
The process developed by Professor Moore utilises antigens developed from naturally occurring proteins in sperm cells; when fed to squirrels, the antigens elicit an immune response in the female reproductive tract, causing egg cells to reject sperm. Although immuno-contraceptive techniques using other types of antigen have been successfully developed, the sperm antigen approach offers the prospect of a species-specific vaccine that could be delivered in treated food without causing any effects on non-target animals.
Laboratory trials initially proved promising with an immune response created in treated females. Studies progressed to enclosures large enough for squirrels to conduct their normal mating behaviour, and the first trial showed a significant reduction in pregnancy rates among treated squirrels. Two further enclosure trials and a subsequent field trial in the wild failed to produce an immune response that was powerful or long-lasting enough to validate the results.
It was concluded that further field tests with animals were not justified until more fundamental research on reproductive biology, immunology and delivery systems could be carried out. However, the research proved that an immune response could be induced in treated animals, although it wasn't powerful or long-lasting enough to cause a reliable reduction in fertility. Unfortunately, funding was not available to progress this work.
Studies on the use of fertility control for wildlife management using various approaches are ongoing in other parts of the world, so with further research fertility control may one day provide an option for humane control of grey squirrels in the future.
Researchers in other countries are carrying out similar work with other invasive non-native species. For example, see the work of the New Zealand Biocontrol programme developing biological control of their introduced possums, from Austrialia, which occupy 95% of the country and are causing large damage to the native woodland.
5. Monitoring red squirrels
National Monitoring Development
Scotland Squirrel Survey Co-ordinator
- For more information see the Scottish Squirrel Group.
Northern Ireland monitoring
EHS recently commissioned a study into the trends in red squirrel distribution in Northern Ireland and to follow up the previous study by O'Teangana (1999) that estimated red squirrel population size in Northern Ireland. The report showed that grey squirrels are continuing to expand and long term red squirrel survival is now only likely in large conifer woodlands. To find out more please see the EHS web site, publication section.