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VAEYING FECUNDITY IN BIRDS. 

 By W. Stores Fox, M.A. 



In a very interesting article in the December number of 

 1 The Zoologist,' Mr. Basil Davies attempts to explain why 

 some species of birds lay more eggs than others. Personally I 

 feel grateful to him for suggesting this enquiry, and for the 

 reasons he assigns for the remarkable diversity in the number of 

 eggs laid by different species. If, therefore, I criticise to some 

 extent the theory which he propounds, I hope that it will be un- 

 derstood that I do so in no unfriendly spirit. 



Mr. Davies compares the reproduction of birds and mammals. 

 He says : ' ; Birds feel it their duty not only to produce a certain 

 number of offspring each year, but also to bring a certain number 

 to maturity." To illustrate this he compares the Cat and the 

 Nightingale. The former breeds at stated periods whether you 

 destroy her offspring or not ; but the latter at once prepares to 

 produce a second brood if the first is destroyed. The truth is 

 that the main object of every organism is to reproduce itself. 

 Each species has its own method of bringing this about. The 

 Cat provides for the peopling of the world by future Cats as 

 thoroughly as the Nightingale provides against the extermination 

 of its kind. These facts are familiar to us, but it is not easy to 

 explain them. Under natural conditions the Indian Elephant 

 does not become exterminated, nor the Brown Bat exceed certain 

 limits. On the one hand, with the former the period of gestation 

 is about nineteen months, and rarely is more than one produced 

 at a birth (Roy. Nat. Hist. vol. ii. p. 536 ; Darwin estimated 

 that though a pair might live to be one hundred years old, their 

 offspring would probably average only six, ' Origin of Species,' 

 6th edit. p. 51) ; whereas the Rat bears "four or five times in 

 the year from four to ten blind and naked young, which are in 

 their turn able to breed at an age of about six months, the time 

 of gestation being about twenty days " (Flower and Lydekker's 



