N O T E S O N B R I T I S H MAMMALS-NO. 1 2 221

pockets dotted about in wood mouse habitat and nobody has yet investigated the pattern and persistence of these pockets.

The general trend is seen in Table 11. These mice were not uncommon in April 1957, had vanished completely from the catch in the following autumn and stayed at a low level through to 1959, after which they gradually increased. This disappearance in the middle of the series of trappings enables us to judge whether reoccupation was at the same sites as before.

All the possibilities were recorded over these five years. Line I showed the establishment of a new pocket around trap-points 3 to 6 and 10 to 12, which were all in a group (Fig. 1). On the other hand, on line I1 yellow-necked mice were caught at trap-point 2 in April 1957 and October 1958, after which they vanished. Line IV is particularly interesting because in April 1957 these mice were caught at points 6 and also at 11 and 12; then there was an interval of three years with no records and, finally, in 1960, both these areas were reoccupied. Line I11 shows a similar gap in the records (autumn, 1957 and autumn, 1958) but afterwards sporadic reoccupation took place all along the trap-line. The picture is one of scattered focal points, some vanishing and some appearing and yet others preserving continuity even through a period of apparent temporary extinction. This might well be based on the waxing and waning of family units, some more durable than others.

Habitat preferences observed Line I has mainly bare ground beneath a dense shrub canopy of rhododendron, holly and

bamboo. The two species of wood mouse never composed less than 80 % of the catch in any year. Line I1 had big patches of rhododendron and bamboo interspersed with smaller areas of scrub, mainly bracken and brambles. On the whole the wood mouse predominated here, though not so much as on line I. The short-tailed vole declined and vanished as the few grassy parts were invaded by brambles and, at the same time, bank voles increased slightly.

On lines 111 and IV the interspersion of bare and densely covered ground made them equally attractive to wood mice and bank voles, which have oscillated about an equilibrium of equal numbers (Fig. 2). This area formed the stronghold of yellow-necked mice and 23 out of a total of 33 were caught here.

We may conclude that there is much of interest to be learned about changes in rodent populations by simple operations of this kind.

Mr John Clegg, then Curator of the Haslemere Educational Museum, was unremitting in his interest, encouragement and help. I also wish to thank specially all the students who assisted with, as well as learned from, the trap-rounds and who did not mind being bitten in a good cause.

H. N. SOUTHERN Bureau of Animal Population, University of Oxford

Harvestfrnites on bank voles that have lost a leg This note is submitted to record evidence of the harmful effects on small rodents of

banding them with metal rings (see Fullagar & Jewell, 1965). In 1961 and 1962 I banded over 1700 bank voles, Clethrionomys glareolus, and wood

mice, Apodemtrs sylvaticus, in Wytham Woods, near Oxford. Sometimes I applied the ring

222 N O T E S O N B R I T I S H M A M M A L S - N O . 1 2

too tightly and did not allow enough room for growth, or too loosely, and it slipped over the heel and caught on the foot. Either way, if the ring became too tight it caused the leg to swell, and this happened at least 40 times even though each time I recaptured a banded animal I checked the ring and replaced it if it seemed that it would possibly have become too tight.

If an animal with a swollen leg was not caught in time and its ring removed, the swollen part dropped off. At least some animals survived this, however, and at least one three- legged female continued to bear young. But in September 1961 , five bank voles which had each lost a hind foot were found each with a large naked patch on and immediately behind the shoulder on the same side as the missing leg, and with heavy infestations of larval harvest mites, Trombiculu autumnalis Shaw, around the patch. These mites are common on bank voles in the late autumn (Elton & Keay, 1936), and are normally most noticeable in the ears, around the anus and external genitalia and, on females, around the nipples. It seems possible that the maimed bank voles became heavily infested where they could no longer groom with their hind feet; the mites may have damaged the skin (Jones, 1950), and a subsequent infection caused the hair to fall out.

Murray (1961) showed that house mice, Mus musculus, comb lice, Polyplax serruta (Burm.), from their coats with their lower incisors. All lice except first stage larvae are almost confined to those parts of the mouse’s body which it cannot reach with its mouth; the first stage larvae are too small to be combed out and occur all over the mouse. (Birds with broken, deformed or amputated beaks have also been found to be unusually lousy (Pomeroy, 1962).) If bank voles, like house mice, can comb out lice with their teeth, why can they not control harvest mites in the same way, even without the help of the feet?

There are at least two possible answers. The first is that larval harvest mites are too small to be combed out, since they are even smaller than first stage larval lice. The second is that the mites, unlike lice, feed continuously, close to the skin, and cannot be reached with the teeth; they can therefore be dislodged only with a good scratch.

REFERENCES Elton, C. & Keay, G. (1936). The seasonal occurrence of harvest mites (Trombiculu autumnalis Shaw) on voles

Fullagar, P. J. & Jewell, P. A. (1965). Marking small rodents and the difficulties of using leg rings. J. Zoo/. 147:

Jones, B. M. (1950). The penetration of the host tissue by the harvest mite, Trombiculuuutumnulis Shaw. Parasitologj.

Murray, M. D. (1961). The ecology of the louse Polyp1u.x serratu (Burm.) on the mouse Mus rnusculus L. Aust. J .

Pomeroy, D. E. (1962). Birds with abnormal bills. Br. Birds 55: 49-72.

and mice near Oxford. Parasitology 28: 110-114,

224-228.

40: 247-260.

ZOO^. 9: 1-13.

MICHAEL SMYTH Bureau of Animal Population, University of Oxford