Gray Squirrels Not Causing Bird Declines

The Eastern Gray Squirrel (Sciurus carolinensis) is a relatively recent addition to the fauna of the British Isles. The species's rapid spread has led to fears that it will displace native fauna that are already under pressure. According to one recent study, recent declines in the U.K.'s woodland birds are not being caused by the introduced gray squirrels.

BTO ecologists Dr Stuart Newson, Dr David Leech and Dr Chris Hewson and NE's Dr Humphrey Crick and Mr Phil Grice examined 38 bird species associated with woodland, including common starlings, wood pigeons, wrens, woodpeckers, thrushes, warblers, tits and finches....

Of the 38 bird species, a statistically significant relationship between grey squirrel and bird population sizes was found for 12 species.

Of those, squirrels appeared to have a positive impact on seven bird species, a correlation probably caused by both mammal and bird species benefiting from similar changes to their habitat.

Grey squirrels had a negative impact on just five: the common blackbird, Eurasian collared dove, green woodpecker, long-tailed tit and Eurasian jay.

"Of these species, the most convincing evidence is for blackbird and collared dove," says Dr Newson.

For these two species, the researchers found a weak but significant relationship between the abundance of grey squirrels and a failure of the birds' nests.

However, while grey squirrels may be predating on these two species, the overall number of blackbirds and collared doves has gone up nationally, and even locally where grey squirrels are common.

Of course, the study does not rule out negative effects on species not included in the study, such as hawfinches. It also does not negate the very real problems that gray squirrels are causing for Britain's native red squirrels (Sciurus vulgaris).