154 
The Irish Naturalist. 
points one way. In the four cases quoted we have a total 
of ninety-four Lesser Horse-shoe Bats collected by different 
observers in England, Wales, and Ireland, and of these 
eighty-six were males and only eight females — a proportion 
of practically eleven to one. 
Now there is no British mammal that could worse afford 
so anomalous a wastage. In the case of prolific creatures 
like rats and mice, a large predominance of males would be 
no impediment to the full maintenance of the numbers of 
the species. All that is necessary to keep up the number 
is that each female shall rear successfully enough young to 
include one female descendant. But unless she can do that 
the species must gradually die out. How long, then, must 
a female Lesser Horse-shoe Bat live to insure the rearing 
of one daughter ? Major Barrett -Hamilton makes it clear 
that the animal is an extremely slow breeder. Breeding 
does not begin till the third year ; and as only one young 
one is produced in a season the average age of a female 
Lesser Horse -shoe would have to exceed four years even 
if the young of both sexes came in equal proportions. But 
it would appear from the evidence as to the extraordinary 
predominance of males that she must live long enough to 
bear young in at least twelve different seasons in order to 
insure the birth of one daughter. Her minimum average 
age would therefore have to be fourteen ; and as allowance 
must be made for some mortality amongst the young, and 
also amongst the full grown, it is not unreasonable to say 
that, a natural term of twenty years must be allowed to 
this little animal's life if her species is not to disappear. 
Is it possible that there should be such a difference in the 
ages of two of our smallest mammals — the Pygmy Shrew 
and the Lesser Horse-shoe Bat — as that one of them should 
need to live twenty years to fulfil her life -task, while the 
other expires of old age at the end of one year, or at most 
fourteen months ? 
It is to be hoped that the question may be solved by 
further research in the haunts, both Irish and British, of 
Rhinolophus hipposideros. 
Dublin. 
