1907. Moffat. — The Problems of a?i Isla?id Fauna. 141 



parts ; and if that were so, it would lead to wholesale exter- 

 mination of such species, whenever areas within the outer- 

 most parts of their ranges were converted into islands. 



I will mention a few of the class of facts to which I refer. 

 I have examined the contents of a good many nests of the 

 Dipper on Irish streams, and have never found one where the 

 number of eggs was more than four, though English ornitho- 

 logical writers speak of the normal number as five or six. 

 Mr. Ussher has obtained clutches of five, but he agrees with 

 me that four in Ireland is the usual number, and he has told 

 me in conversation on the subject that a good many kinds of 

 birds produce, on the average, smaller clutches in Ireland than 

 in England. Then we know that the Crossbill, which twenty 

 years ago made a vigorous effort to establish itself as a resi- 

 dent breeding species in Ireland, suffered in some seasons 

 from wholesale infertility, laying only addled eggs, and it still 

 remains to be seen whether the establishment, reduced as it 

 already is to a very small garrison, will become permanent. 

 The Cuckoo must also, I think, lay fewer eggs in Ireland than 

 in England ; for very few Cuckoos' eggs seem to be found by 

 the most sedulous collectors in this country, and even the 

 young birds, though they are not by any means silent crea- 

 tures, are not, I think, very often observed. 



Turning next to mammals, we find an extraordinary con- 

 trast between what British — or rather " Britannic "—and Con- 

 tinental writers say about the rate of productiveness in Bats. 

 According to Continental writers the usual number of young 

 at a birth is two ; but English and Irish zoologists — there is 

 no difference in this case between the larger and the smaller 

 island — have made most careful inquiries into this subject, and 

 the researches of Dr. Daniell in the south of England, of 

 Thompson's correspondent Hyndman in Ireland, and quite 

 lately of Mr. Arthur Whitaker in the north of England 1 , 

 all point to the unanimous verdict— as regards, at any rate, 

 the Pipistrelle and the Noctule— that the number produced is 

 only one. I confess that this seems to me almost too great a 

 difference to be credible ; but some higher degree of fertility 

 must exist among Continental Bats to explain the differences 

 in what has been observed. 



1 The Naturalist, November, 1905. 



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