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Grey Killers

Report points the finger at Grey Squirrels

Grey Squirrels may be at least partly to blame for woodland bird declines ? by eating eggs and young chicks, taking over nest sites and eating seeds and nuts which would otherwise be eaten by birds.

In their paper Possible impacts of Grey Squirrels on birds and other wildlife, in the February issue of British Wildlife, Chris Hewson, a research ecologist at the British Trust for Ornithology and Rob Fuller Director of Habitats Research at the British Trust for Ornithology, Brenda Mayle who leads the Squirrel Management Research Programme for Forest Research and Ken Smith who leads the lowland woodlands research in the Conservation Science Department of the RSPB, report on some of the consequences of the spread of the Grey Squirrel within Britain. Grey Squirrels were introduced from North America at the end of the 19th Century. In spring, there are estimated to be 2.5 million Grey Squirrels in Britain, a number which grows as youngsters are produced during the course of the year and declines with winter mortality. Speaking about the report, Dr Rob Fuller of the BTO said, Grey Squirrels live at considerably higher densities and are larger animals than the native Red Squirrel. The species is already blamed for commercial damage to forestry and linked to the demise of the Red Squirrel. In this paper we look at how the Grey Squirrel may also be affecting woodland bird species, several of which are red-listed as Birds of Conservation Concern [Woodland species such as Bullfinch, Lesser Spotted Woodpecker, Marsh Tit, Song Thrush, Spotted Flycatcher and Willow Tit have been red-listed because numbers have declined by 50% or more in the last 30 years. See www.bto.org/psob/redlist.htm and www.bto.org/psob/index.htm]Three ways in which Squirrels can affect bird populations were identified: nest predation, competition for nest sites and competition for food.

Predation seems to vary widely. The highest reported level of predation was in a particular year in a Nottinghamshire wood, when Grey Squirrels were responsible for 27% of nest failures in nesting boxes. When Grey Squirrels were controlled on one Norfolk farm, the predation rate of open nests fell from 85% to between 5 and 10%. The arrival of Grey Squirrels in Durham coincided with the decline in abundance of open-nesting species (e.g. thrushes and finches).

Competition for nest sites can affect species such as Tawny Owl, Kestrel, Jackdaw, Stock Dove and Starling. Occupation rates of suitable holes by Grey Squirrels appear to be high enough to stop some birds, such as Tawny Owl, breeding.

Competition for food may be a big problem. Squirrels are known to take over caches of hoarded food, stored away by Jays, and their diet of insects, buds and seeds brings them into conflict with species such as Nuthatch, Hawfinch and Bullfinch.Chris Hewson of the BTO said. Although there is clear evidence that Grey Squirrels may be having an impact, we need to do more research to understand just how serious the effects of Grey Squirrels are for birds, such as Hawfinch. Comparing productivity in areas with and without the animals would enable us to do this.

For further information please contact: Chris Hewson on 01842 750050 or e-mail: chris.hewson@bto.org during office hours Graham Appleton on 01842 750050, e-mail: graham.appleton@bto.org or mobile 0797 4668503

4th July 2014