Young Field Voles from Birth to Weaning

CHEST-SPOT ON THE LONG-TAILED FIELD MOUSE

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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

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YOUNG FIELD VOLES

handful of grass and was immediately seized and eaten. An earwig was then caught and dropped in front of the mother while she was sitting in the open holding a clover leaf in her hands and eating it: she immediately dropped the clover leaf, seized the earwig in her mouth, took it into the jam jar and ate it. Thereafter insects were thrown in at irregulär intervals. Food was sometimes eaten in the open but often carried into the jam jar or under cover: even a runner bean 6 ins. long would be dragged along until the end was in the jam jar and then pulled further in as it was eaten. This habit seemed to be entirely instinctive and in no way due to fright or only to occur when being watched. Both the mother from thefirstday and later the young seemed unable to recognise enemies through the glass, though for the first few days after leaving the nest the young were much more timid than their dam, eating under cover while she sat in the open and only venturing from cover for very short periods. The mother throughout and the young when 3 days from the nest would sit in fßll view in a corner of the case, almost touching the glass and happily eating a piece of grass while a cat patted the outside of the case with alternate paws.

On July 19th, 4 naked young were born in the jam jar. On July 20th these were removed by the mother to a nest made of grass stalks, etc., but she continued to use the jam jar to a considerable extent as her own apartment, sometimes sleeping there and often carrying food into the jar to eat.

Milk was offered on July 19th and thereafter water, but after afirstexploratory taste these were left untouched.

The young were left unexamined and hidden in their nest until July 25th when they were found to be fully haired but seemed still to be blind.

On July 26th one young was seen crawling rather unsteadily away from the nest but was seized and dragged back by the mother.

The young were not seen again until July 28th when the nest was disturbed when some food was put in. All four young crawled out of the nest but were quickly dragged back again by the mother.

On July 29th the young were seen at intervals moving about the case with relative ease and on July 30th, after a fresh sod had been put in, were almost as active as their mother eating grass and clover leaves as they ran about, though they seemed to eat more grass roots than did the older animal.

On July 3Ist the young werefirstseen to eat oats and to take food from the open under cover to eat. Thereafter they ate more or less the same food as their mother, though they often ate clover heads which she left untouched.

YOUNG FIELD VOLES

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At no time was suckling observed, but from July 22nd squeaking was often heard from the nest when the mother went in, presumably to feed the young. On July 25th she was seen to drag some fresh grass and clover leaves into the nest and continued doing this regularly until the young ran about on their own.

Play amongst the young was first seen on July 30th : two or three would meet and roll about together like kittens for a few seconds. By August Ist this sort of play often seemed rougher and more like fighting : one or the other would run away after a rough and tumble lasting one or two seconds. On July 3Ist one was seen deliberately to turn a somersault, putting its head down between its forelegs and turning head over heels.

When they first left the nest the young were smooth coated : the longer guard hairs seemed suddenly to appear on all of them on August 2nd.

On the same day the mother started making efforts to escape, efforts which became more desperate on the following days. Voles usually settle down happily in captivity so it was presumed that she wanted to wean them and she was released on August 6th. C.