Chest-spot on Long-tailed Field Mouse

NOTES

ON T H E CHEST-SPOT ON LONG-TAILED FIELDMOUSE (Apodemus s. sylvaticus Linn.)

THE

THE garden at Great Glemham House consists of a walled garden and some 5 acres of what before the war was shrubbery and lawns, now mainly better described as rough grass and woodland.

It is situated in the middle of a small park which is itself surrounded by woodland, mostly coppice and oak Standards ; Apodemus sylvaticus is of course abundant throughout the whole wooded area.

Apodemus does not seem to travel far from its nest and the minimum distance of some 150 yards which separates the garden and an adjacent copse from the woodland surrounding the park is probably far enough to ensure that the population found in t h e garden is a self-contained Community so far as breeding is concerned. T h e ehest spot of A. sylvaticus varies considerably in size : it is sometimes absent but usually consists of a larger o r smaller buffish longitudinal patch between the forelegs, occasionally spreading sideways, sometimes far enough to form a complete collar.

There is in the garden a small population of the Yellow-necked woodmouse (A. flavicollis wintoni Barret-Hamilton). Apart f r o m those mentioned below, I have examined 6 or 8 individuals over the last 5 years, mainly brought into the house by cats, a n d in all the ehest spot was large, forming a complete collar, often extending backwards towards the belly as a wider or narrower median stripe. A. flavicollis is a decidedly larger animal than A. sylvaticus with a hindfoot of 23-27 mm. as opposed to 21-23mm.

It has been suggested that A. sylvaticus and flavicollis are not speeifieally distinet and may interbreed in the wild, though so far as I am aware they have never been induced to do so in captivity. If interbreeding did occur in the relatively isolated populations in the garden at Great Glemham House it would seem that it might show itself amongst the A. sylvaticus in agreater average size of the ehest spot and of individual speeimens absolutely. Düring the latter half of December, 1953, and again in March, 1954, traps were set in the garden and in a wood 500 yards away in which no A. flavicollis have been found. T h e results are set out below :— Garden. Wood.

Spot absent or minute, at most a few buff coloured hairs Spot small, less than 10 mm. long Spot medium, 10-20 mm. long Spot forming a collar A. flavicollis

7 34 3 —

6

8 18 20 1 —

CHEST-SPOT ON THE LONG-TAILED FIELD MOUSE

33

In all the A. sylvaticus caught, save the one from the wood with a complete collar, the ehest spot was a stripe of greater or less width, i.e., in no other case did it show any sign of spreading sideways to form a collar. All six A. flavicollis had complete collars, in four cases the patch extended backwards as a median line, in three almost to the breastbone, in the other far back along the belly. There was no difference in size between the adult individuals of A. sylvaticus captured in the two localities, the hind feet of all being 21-22 mm. T h e hind feet of three A. flavicollis kept were 25, 25 and 24 mm., the others measured alive and released, were about the same.

T h e incisive foramen of A. flavicollis is shorter than that of A. sylvaticus and in all the speeimens from Gt. Glemham that I have handled terminates distinctly in front of the roots of the two first molars : 15 skulls of A. sylvaticus from the garden were examined, in each case the incisive foramen reached as far back as the first molars.

From the above xesults it will be seen that the A. sylvaticus in the garden are no more like A. flavicollis than are those living in the wood, indeed the only difference between them is that the former, occupying the same habitat as A. flavicollis, have a significantly smaller average size of ehest spot. This indication that local strains of A. sylvaticus may vary in colouration seems worthy of further investigation.

C.

YOUNG FIELD VOLES FROM BIRTH TO WEANING ON July 18th, 1954, an obviously pregnant Field Vole (Microtus agrestis) was captured and put into a large glass case w ith a sod of clovery turf in it and with a 1-lb. glass jam jar as a nest. T h e grass on the turf was soon eaten down and handfuls of assorted green stuff pulled from meadowland were thereafter supplied as food. Clover seemed to be the favourite food but lucerne, grass, hawkweed, plaintain, yarrow and cinquefoil were all eaten readily as were runner beans, peas, carrots and apples. Twigs and leaves were usually left untouched. A mixture of oats, wheat and maize was kept continually available but though grain was regularly eaten in small quantities, green foodstuffs were obviously preferred. One day a moth was dropped in accidentally with a