38 INTRODUCTION 



are said to lay fewer eggs than on the continent, and in 

 Ireland than in England. Certain butterflies, also, produce 

 a single brood in Ireland as against two in England, while 

 in others the number of males is excessive/ All the 

 facts lead him to suggest that diminished fertility occurs as 

 an exterminating factor at the outskirts of an animal's range. ■# 



As reo"ards other details, there is evidence that seasonal 

 change of domicile and the formation of nursing colonies obtains 

 in every British species of which we possess records in any 

 detail. Especially is this the case with the crowded cave 

 parties which only gather in the gloom of subterranean retreats 

 when the chilly blasts of winter drive them from the slighter 

 shelters of summer.^ In spring the caves are deserted and their 

 occupants betake themselves to holes in buildings and trees. 

 Our knowledge is most complete in the case of the Noctule, 

 which in spring forsakes the sheltering house-roof wherein it 

 has lain dormant throughout the winter, and forms, usually in 

 hollow trees, nursing colonies, which keep together until the 

 autumn. Mr Symington Grieve's description of the Water 

 Bat at Loch Dochart suggests similar habits. In the case of 

 the Noctule, segregation of the sexes is a general but not 

 invariable rule. The Lesser Horseshoes are as regular, but the 

 females of this species tolerate the males and frequently allow 

 them, both young and old, to associate with them. Less 

 clearly understood, and evidently more complicated, are the 

 summer " swarms " of Long-ears which for a few weeks — some- 

 times only days — of July or August, cluster in outhouses, where 

 they are unknown throughout the rest of the year. These 

 gatherings, as well as those of the Pipistrelle, include bats of 

 all ages and both sexes. 



The date of birth is subject to much variation : of nine 

 instances covering three species given by Mr Whitaker, the 

 earliest birth took place on 22nd June and the latest would 

 probably have occurred in August. Again, in south Wales Mr 

 Proger finds that the young of the Lesser Horseshoe and of 



' If, as has been suggested, there is a preponderance of males in British Lesser 

 Horseshoes, and that in Germany, as stated by Kuhl, there may be two young, a 

 thing unknown in France or Britain, that would be another case to the point. 



^ For Wales, see Proger, Proc. Cardiff Nat. Soc, March 1905, reprint, 4. 



