262 N O T E S F R O M T H E M A M M A L SOCIETY-NO. 28

Temperature ("C) FIG. I . The percentage of time that different temperatures were recorded in a pipistrelle hibernaculum. The median

is shown (3.4"C).

This work was supported by the World Health Organization. I am very grateful to M r A. Harvey, who changed the thermograph charts, and to the Reverends J. G . T. Tatham and J. J . Bunting for their interest and co-operation.

P. A. RACEY, Wellcome Institute of Comparative Physiology, Zoological Societj, of London*

*Present address : Department of Zoology, University of Aberdeen, Aberdeen

Population density in the Common shrew, Sorex araneus

Introduction Michielson (1966) was only able to quote one other figure (Shillito, 1960) for the density

of a live trapped population of Sorex, though one other study (Buckner, 1969a, b) has since appeared. This note reports the results of two short mark-recapture studies on Sorex araneus, carried out at Cap Gris Nez, Pas-de Calais, France from 24 July-3 August 1964, and at Woodchester Park, Gloucestershire, England from 22-26 July 1972.

NOTES F R O M T H E M A M M A L SOCIETY-NO. 28 263

Methods Both studies used Longworth traps set in a fairly regular grid, 56 traps in 0.2475 ha at

Cap Gris Nez, 90 traps in 0.9 ha at Woodchester Park. At both sites, the vegetation was essentially rough grassland.

Shrews were marked by toe clipping, and the traps were checked every two to three hours when in use. Hayne’s (1949) method was used to calculate the populations, after aggregating the captures for each day.

Results The results of these trappings are presented in Table I , where the density is expressed in

terms of the “true trapping area” (Michielson, 1966). At Cap Gris Nez, all the shrews except one (which was deliberately killed) were immatures, and were evidently territorial. At Woodchester Park, by contrast, there were 28 immature, 9 adult male, and 8 adult female shrews, of which only the adult females appeared to be holding discrete territories. In both exercises, Sorex araneus was the only shrew trapped. In addition to live shrews, two were killed at Cap Gris Nez, and six at Woodchester Park; these have been omitted from the calculations.

T A B L E I . Shrew pupultrtiutr estiititrtes ~~

Practical True Number Population Mean territory trapping trapping Density

Habitat handled estimate length (rn) area (ha) area (ha) (shrewsiha)

Cap Gris Nez grassland 27 29 11.4 0.25 0.38 77 Woodchester Park grassland 43 75 30 (imrn) 0.9 1.8 42

38 (8) Michielsen (1966) dune scrub - -. 22-24 1.8 2.5 17-18 Shillito (1960) woodland - - 30 (imm) 1 . 1 ? 26 Buckner (1969a, b) woodland - - 60 I .96 4.0 2.2-3.2

Discussion Both densities recorded here are very high, and that at Woodchester Park, 42/ha, is

fairly close to Crowcroft’s (1957) figure of 49/ha. Crowcroft’s figure was derived by snap trapping, and could have been inflated by immigration. The same criticism could be made of our Woodchester Park density, for the recapture rate was fairly low, 24 animals only being caught once.

On the other hand, the Cap Gris Nez density of 67/ha, admittedly all immature shrews, is much higher, and more reliable. The territory length of these shrews was approximately half the mean territory diameter quoted by Michielsen, i.e. about what would be expected with a density four times greater, while the recapture rate for these shrews was much higher (only seven were not recaptured at all). Shrews were certainly more abundant in 1964 at Cap Gris Nez than they had been in 1961 or 1963, and other trapping in the area suggested that grassland habitats were much better for shrews than sand dune scrub (or the sort Michielsen was studying). It is felt that the high population estimate is real for that site at that time.

264 N O T E S F R O M T H E M A M M A L S O C I E T Y - N O . 28

Trapping at Cap Gris Nez was greatly aided by J . F. Harper, while help and Facilities were provided by, amongst others, A. Gouillart, and Messrs Gibbs, Naylor and Redman. A t Wood- chester Park, Misses s. Fargher and M. Young did much of the trapping, while M r A. R. Kelly a n d Fountain Forestry provided facilities. Thanks are gratefully offered to all these, and others unnamed, for their help.

R E F E R E N C E S

Buckner, C. H . (1969a). The Common shrew (S0re.r mwceus) as a predator of the winter moth (Oprophfwu

Buckner, C. H. (1969b). Some aspect of the population ecology of the Common shrew .SOWS uruneris near Oxford,

Crowcroft, W. P. (1957). The lije afthe shrew. London: Reinhardt. Hayne, D. W. (1949). T w o methods fot estimating populations from trapping records. J . Muniniul. 30: 399-41 I . Michielson, N. Croin, (1966). lntraspecific and interspecific competition in the shrews Sore.r urunec/.s L. and

Shillito, J. F. (1960). Thegenerulecology of’the Conimon shrew Sorex urunueiis L. Ph.D. thesis, University of Exeter

brimiutu) near Oxford, England. Cun. Ent. 101 : 370-375.

England. J . Mutnntal. 50: 326-332.

S. minictus L. Archs nPerl. Zool. 17: 73-174.

(unpubl., quoted by Michielsen 1966).

D. W. YALDEN, Departtilent of’Zoology, University of Manchester, Manchester

Ageing and assessment of reproductive status of Pipistrelle bats, Pipistrellirs pipistrellus

Introduction Several methods of determining the age of hibernating bats have been investigated in the

past. Christian (1956) found that estimates of age from annual growth rings in sections of teeth correlated with those from cusp wear. Such sectioning is, however, laborious and the method cannot be used with accuracy for older bats. The estimation of age from tooth wear is, in addition, limited by the number of distinguishable age groups---three were used by both Christian (1956) and Davis, Herreid & Short (l962), and five by Twente (1955). Sluiter (19610) and Hall, Cloutier & Griffin (1957) considered, however, that tooth wear was a highly unreliable criterion of age. Perry & Herreid (1969) compared lens weight and tooth wear methods and found only 49% coincidence. It thus appears that the only reliable method of ageing bats involved ringing juvenile animals. These are recognized by the presence of unfused and translucent phalangeal epiphyses. If such unfused epiphyses are evident when the wings are held up to the light, then the bat was born in the immediately preceding birth season. (Davis, 1963) concluded that the rate of epiphyseal fusion is de- pendent on local environmental conditions, the most important of which is food supply. As far as British species are concerned, Cranbrook & Barrett (1965) observed that the phalangeal epiphyses of noctules closed as soon as the young bats started to fly, and Kleiman (1969) noted that in captive noctules, serotines and pipistrelles, fusion of the phalangeal epiphyses took place 50-78 days after birth.

Davis & Hitchock (1965) distinguished young of the year from adults by the degree of ossification of the metacarpal-phalanges joint in the North American species, Myoris lucifugus. These authors also maintained that it is possible to separate bats of up to a