WI LDL I F E


CONT ROL L ING SQUI R R E LS


Squirrel Control S


SWA member Geoffrey White asks what measures are being taken to combat grey squirrels


hould woodland owners aware of present rates of debarking be in depressed acceptance? It is a constant


reminder to walk in the wood and see tops of young oak dying from ring debarking and see heavy branches from mature beech and sycamore fallen from mechanical failure as debarked branch wood rots. What can we do and what should be done? In my wood I have gone through a sequence of control methods, changing from one to another for good reasons. I started with Warfarin- laced grain served in hoppers, fitting hinged barriers within them to prevent a kill of other animals, which is the standard requirement now. For a few years squirrels ate progressively less of this grain, presumably because they were building up an awareness of the danger, and so I was obliged to seek another way.


Drey shooting An annual winter drey shoot reduces their number, but only with varying success. The 2007-8 winter shoot was affected by high winds blowing out most dreys so that too few squirrels were shot, and debarking occurred in the summer.


I bought some Kania traps, and killed one squirrel but unfortunately also one greater spotted woodpecker. I do not want to risk killing any such landmark species and have ceased to


Red squirrels


Forestry Commission Scotland is planning to create 18 stronghold forests of about 2000ha each to protect red squirrels. The idea will be to protect cone-bearing conifers as a food source for reds, while restricting food sources for greys from large-seeded broadleaves. A stakeholder group of landowners and managers is currently being formed to take the plans forward. "Fortunately, much of the north of Scotland and Dumfries and Galloway are still grey- free," said Ron McDonald of Scottish Natural Heritage. "But with sightings of greys becoming more frequent even in some of these areas, it's essential we act quickly to protect the red squirrels."


Forest Research's new free


use the Kanias. Instead I decided to try out a cage trap, but the associated rules render it unsuitable to use. Such traps have to be visited daily. If there is a trapped squirrel there are restrictions on the disposal of the animal. One cannot drown it, one cannot release it elsewhere. It can be shot or killed with a blow to the head. I live several miles from my wood and it is not practical to visit it more than once a week. For many years there has been talk of biological control, ie. contraception, achieved by giving food laced not with a poison, but


Fresh grey


squirrel damage on a beech tree in the New Forest (above). A grey squirrel approaching a hopper (above right), and a grey squirrel drey in branches of a tree (right)


with additive that renders squirrels infertile. They would live without breeding success. I had thought that research was progressing along these lines, so it is with surprise and dismay that I found, on enquiry, that this is not the case, probably due to lack of funding. This is unsatisfactory. Gill Petrokofsky of Oxford


University has been involved in a survey of some people concerned in forestry practice. The first of the top 10 questions intended to be directed at forestry research is summarised as: ‘What are the most technically and cost effective ways of identifying, monitoring and controlling invasive species, pests and disease?’ I wonder how many actual


woodland owners were asked. I don’t think I was, and I suspect many of us were not. [Actually we did report on Gill Petrokofsky’s survey, inviting woodland owners to take part. We don’t know how many did participate. From what we were sent we found it


16 Smallwoods Spring 2010 www.smallwoods.org.uk


Practice Note recommends surveying squirrel densities if you have reds, if you want to protect reds from greys, or if your trees are suffering from grey damage and you want to establish an appropriate method of control. There are a number of ways of monitoring squirrels, but according to this report visual sighting is probably the most suitable for the majority of woodland owners. To make a visual survey you simply count the number of squirrel sightings along a 500m line through your wood. Do this early in the morning when squirrels are most active. This will give you a rough estimate of how many squirrels you have per hectare (though the guide isn't very clear how to use the numbers you count).


very difficult to understand what she was trying to achieve, but there was certainly an invitation in Smallwoods.] This summary seems to imply that biological control of squirrels has not been on the minds of foresters and researchers before. This is not so.


The future What is needed now? I rather think the Small Woods Association and the Royal Forestry Society should lead pressure for this research. Yet let us not be too academic about it; we need answers quickly, so it is urgent and of the highest priority that research commences immediately, and any funding deficiencies are resolved. Otherwise, not doubt, we will continue to lose value in our small and other-sized woods, and our forests will only achieve a fraction of their potential. Additionally there is the need to emissions. Tree growth


control CO2 naturally makes use of carbon from www.smallwoods.org.uk


the air in the making of wood, so that all trees should be enabled to grow to their maturity unhindered by any and every source of damage. Brenda Mayle at Forest Research


(FR) says that FR are indeed investigating fertility control options for grey squirrels in collaboration with Fera and NWRC. “This is long term, high risk and costly research,” she explains. “We are looking at bait-fed options as injectable options are not practical for small mammals such as squirrels. Agents currently available are not species-specific so we need to ensure delivery mechanisms achieve this. We also need to clarify what risks are posed to non-target animals.” Other agencies like MLURI,


she says, are investigating how the squirrelpox virus is transmitted and looking at vaccine development for red squirrels. The virus is fatal to reds, but is carried and transmitted by grey squirrels.


CONT ROL L ING SQUI R R E LS WI LDL I F E


FC's reply Brenda Mayle, who heads the Vertebrate Management Group at Forest Research reponds to Geoffrey White's comments


Firstly, grey squirrel populations vary considerably between years, even in the absence of any control, due to fluctuations in natural food availability. Gurnell, in 1996, showed that for one site the summer population varied from 8.7 to 17.9 and back to 10.1 squirrels per hectare over a three-year period. Two years later it went from 8.7 to 2.8 and back to 8.9 squirrels per hectare. That's a six-fold variation from lowest to highest density. This is one reason why it is very difficult to predict either the risk of damage or the control effort required in a given year. We believe damage is triggered by densities of five or more squirrels per hectare and densities in mature large-seeded broadleaved woodland are often around/above 7-9/ha. Efficacy of control should be judged upon whether


there is unacceptable damage or not related to the level of control effort applied for the current year's squirrel population. Comparing bait take between years may enable comparison of numbers of squirrels controlled between years, but does not indicate efficacy of control. For example, a given amount of bait that is enough to reduce a poplulation by 2/ha from 6/ha to 4/ha should be effective in minimising damage, but the same amount of bait reducing the population by 2/ha from 12/ha to 10/ha will be totally ineffective in terms of damage control. Another part of our research programme is focused


on developing a method to predict likely risk of damage in early January so that woodland owners can target control from mid-March onwards. The concept is to visit woods with good squirrel habitat and adjacent vulnerable stands in early January to see whether there are many squirrels around and whether there is much/ any natural food available. If so the squirrels are likely to breed in early spring and the risk of damage is likely to increase. To test this assumption we are attempting to trap squirrels in a range of sites in early January and assess their breeding condition. At the same time we are assessing natural food availability and squirrel presence in these sites. If there is no natural food we expect to be more able to catch squirrels and check whether they are breeding. The level of variation in squirrel densities and damage across sites that we have recorded has led us to extending this work for at least another year before we can develop clear guidance on this for woodland owners. Drey shooting has been shown to be of limited use to


control bark-stripping damage as animals shot during the winter are rapidly replaced, within 1-3 months, by squirrels from neighbouring areas. It is sad but interesting to read that Geoffrey White


has caught a woodpecker in a Kania trap. The risk to non-target species is always greater when with spring or kill traps, and minimising the risk with the Kania set up a tree is likely to be more difficult than for ground- placed spring traps. Wafarin bait dispensed through selective access


hoppers probably remains the most cost effective option for controlling grey squirrel damage for woodland owners outside red squirrel areas. Cage trapping (using single capture traps) is the best approach for those with red squirrels nearby.


Spring 2010 Smallwoods 17


photo: fc photo library


photo: fc photo library


photo: fc photo library


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