EVEN nature’s fiercest rivals can sometimes live in harmony. Researchers have
found a small corner of Scotland where red and grey squirrels, usually
irreconcilable, are getting along splendidly.
Since the grey squirrel (Sciurus carolinensis) was introduced from
North America in 1876, it has driven out the native red squirrel (Sciurus
vulgaris) from most of England and Wales. The number of greys has risen to
over 2.5 million, while reds have dwindled from a few million to 160 000,
three-quarters of which are in Scotland. Reds die in the winter or fail to breed
because they are deprived of food by greys, which can eat a wider range of
seeds. Greys find it easier to digest acorns, and can eat hazelnuts earlier in
the season than reds.
But researchers from two government agencies, the Forestry Commission and
Scottish Natural Heritage, have found stable populations of reds and greys
living together in Craigvinean Forest, near Dunkeld in Perthshire. Using radio
collars to track the animals’ movements within an 80-hectare section of the
forest, they have been able to prove that the two species share the same
Simon Hodge, head of woodland ecology at the Forestry Commission, says that
reds favour the Norway spruce and Scots pine trees on the hillsides, while greys
prefer the beech and Douglas firs down by the River Tay. But both make nests,
known as dreys, in each other’s territory and use the same feeding
grounds—and seem to have been doing so for the past 20 years.
Hodge suspects that a poor supply of beech mast may limit the number of greys
while a good supply of seeds from Norway spruces may benefit the reds. Norway
spruces produce cones almost every year at Craigvinean, compared to every three
or four years elsewhere, and reds find it easier to eat their small seeds than
do greys. Hodge argues that understanding why squirrels cohabit at Craigvinean
could help schemes to conserve reds throughout Britain.
HATA wapinzani wakali zaidi wa asili nyakati nyingine wanaweza kuishi kwa upatano. Watafiti wamegundua eneo dogo nchini Scotland ambapo vipepeo wa rangi nyekundu na wa rangi ya kijivu, ambao kwa kawaida hawapatani, wanaelewana vizuri. Tangu kuingizwa kwa squirrel ya kijivu (Sciurus carolinensis) kutoka Amerika Kaskazini mnamo 1876, imemfukuza squirrel nyekundu (Sciurus vulgaris) kutoka sehemu kubwa ya Uingereza na Wales. Idadi ya watu wenye rangi ya kijivu imeongezeka hadi zaidi ya milioni 2.5 wakati idadi ya watu wenye rangi nyekundu imepungua kutoka milioni chache hadi 160,000, na robo tatu ya watu hao ni watu wa Scotland. Nyekundu hufa wakati wa majira ya baridi kali au kushindwa kuzaliana kwa sababu wanakosa chakula na kijivu, ambacho kinaweza kula aina mbalimbali za mbegu. Wanyama wa rangi ya kijivu hupata ni rahisi kumeng'enya matango, na wanaweza kula hazelnuts mapema katika msimu kuliko nyekundu. Watafiti kutoka mashirika mawili ya serikali, Tume ya Misitu na Urithi wa Asili wa Scotland, wamegundua idadi thabiti ya nyekundu na kijivu wanaoishi pamoja katika Msitu wa Craigvinian, karibu na Dunkeld, Perthshire. "Kwa kutumia collars za redio kufuatilia harakati za wanyama katika sehemu ya hekta 80 ya msitu, wameweza kuthibitisha kwamba spishi hizo mbili zinashiriki sawa ""Simon Hodge, mkuu wa mazingira ya misitu katika Tume ya Misitu, anasema kuwa nyekundu hupendelea Norway spruce na Scots pine miti kwenye mteremko wa milima, wakati kijivu hupendelea beech na Douglas fir chini ya Mto Tay." Lakini wote wawili hufanya viota, vinavyojulikana kama dreys, katika eneo la kila mmoja na kutumia maeneo yaleyale ya kulisha - na inaonekana wamekuwa wakifanya hivyo kwa miaka 20 iliyopita. Hodge anashuku kwamba ugavi duni wa mti wa beech unaweza kupunguza idadi ya kijivu wakati ugavi mzuri wa mbegu kutoka Norway spruces inaweza kufaidika na nyekundu. Mti wa Norway huzaana kila mwaka katika eneo la Craigvinian, ikilinganishwa na kila baada ya miaka mitatu au minne mahali pengine, na mti wa Norway hupata urahisi zaidi kula mbegu zao ndogo kuliko mti wa kijivu. Hodge anasema kwamba kuelewa kwa nini squirrels kuishi pamoja katika Craigvinean inaweza kusaidia mipango ya kuhifadhi nyekundu kote Uingereza.