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ERMINE STOATS IN SUFFOLK J. R. MARTIN The Stoat (Mustela erminea) is a widespread species in Britain, and throughout most other parts of Europe. It is very similar in appearance to the Weasel (.Mustela nivalis), and in the field confusion may arise between the two unless a clear view is obtained of the tail. The tip of the Stoat's tail is always black, but the tail of the Weasel remains brown. However, in Britain there can be little confusion when the observer is fortunate enough to see an animal wearing a white coat, for normally only the Stoat turns white. White weasels are a great rarity in Britain (King, 1989) but in the northern parts of their European ränge weasels do turn white. However, caution should be exercised at all times in Britain, as the possibility of the animal being a white Ferret cannot be dismissed. The reason for the coat of the Stoat turning white is often assumed to be a reaction to immediate cold weather, but this is not the case. Harrison Matthews (1952) stated that in some parts of Britain stoats nearly always turn white in winter, although in the south there was little, if any, change at all. He reported that the white coat grows beneath the old one, before the latter is moulted in the autumn, so that when it is shed the white one is revealed. He stated that the moult takes place in just a few days, during November and December, but King (1989) stated that in mild climates the moult could take place over a period of four to six weeks. The spring moult usually starts in February but could be delayed if the spring was particularly cold (King, 1989). For those records which we have dates the most common months in which ermine stoats are recorded in Suffolk are January and March (Table. 1). Harrison Matthews stated that stoats which were exposed to cold both before and during the moult turn white, and that if a stoat is exposed to cold one winter, it will turn white the following winter even if that winter is mild. This would explain why ermine stoats are sometimes seen in mild winters. Table 1: Numbers of ermine stoats noted in Suffolk by month, including pied individuals Month No. % Month No. % October 1 2 February 10 21 November 0 March 12 28 December 4 9 April 1 2 January 16 37 July 1 2 Earliest date 29th October 1985, latest 5th April 1981 (Heathcote, 1992). Following translocation experiments in North America, King (1989) reported that heredity played an important role in coats turning white, as well as temperature. She stated that in an area where it is always sunny or very mild ft is easy to predict whether a white coat will be needed or not. She considered that only in a 'zone of indecision' is it an advantage to have a temperature 'switch' thus enabling an animal to make an adjustment one way or another. The switch may turn off the supply of melanin whilst the new fßr grows on the tail and sides; but by the time the new dorsal fßr is growing, it may be turned
Trans. Suffolk Nat. Soc. 32 (1996)