86 Mr. W. Evans on the Periods 



A glance at the Table reveals a host of discrepancies, many 

 of which it is impossible,, in the present state of our know- 

 ledge, to reconcile or account for. Regarding the periods 

 obtained by observation of the nests, an obvious source of 

 error lies in the difficulty of determining when the birds 

 really begin to sit. A very natural point to reckon from is 

 the date of laying of the last egg ; but this frequently leads 

 to serious error, as many species habitually, and others occa- 

 sionally, sit before the last egg has been laid ; while others, 

 again, either do not sit at all, or only partially, for some time 

 afterwards. As examples of the extent of the error involved 

 in this way of reckoning, I would point to the cases in my 

 own experience of the Long-tailed Tit and the Starling, the 

 former not hatching for fully 16 days from the laying of the 

 last egg, while the latter were out, in one instance, in little 

 more than 11. Neither is it safe to count to the hatching 

 of the last of the young, unless each egg be numbered when 

 laid, as the last laid egg is often unfertile. By means of the 

 incubator all these difficulties are overcome. 



It seems quite unnecessary for me to discuss in detail the 

 contents of the Table, but a few remarks upon each of the 

 Orders may not be deemed out of place. 



In the Order Passeres — among the European species, at 

 any rate — we may take it as well-nigh certain that the 

 normal period ranges from about 12 days in the case of 

 the smallest (the Goldcrests), to 19 or 20 days in the 

 case of the largest (the Raven). 13 to 14 days is a very 

 common period among the great majority of the smaller 

 members of the Order ; and even the Thrushes require no 

 more than from 14 to 15 days, a remarkably short period 

 when we consider the size of their eggs as compared, for 

 example, with those of the Wren, which I have shown require 

 about 13 days. The Starling is another example of very rapid 

 development. Owen gives 10 days as the time for the Wren ; 

 but this is not borne out by my observations. The shortest 

 period I have seen recorded is that of the tiny New-Zealand 

 Zosterops ccBrulescens, namely, 9 to 10 days, as given by 

 Buller on the authority of Mr. Potts, evidently a careful and 

 systematic observer. The Coividce stand quite alone in the 



