APPENDIX. 369 



selected and profitable modification, or to acquired and 

 inherited habit. In the same manner, as the northern and 

 southern thrushes have largely inherited their instinctive 

 modification from a common parent, so no doubt the thrush 

 and blackbird have likewise inherited much from their 

 common progenitor, but with somewhat more considerable 

 modifications of instinct in one or both species, from that of 

 their ancient and unknown ancestor. 



We -nill now consider the variability of the nesting-instinct. The eases,, 

 no doubt, would have been far more numerous, had the subject been attended 

 to in other countries with the same care as in Great Britain and the United 

 States, From the general miiformity of the nests of each species, we clearly 

 see that even trifling details, such as the materials used and the situation 

 chosen on a high or low branch, on a bank or on level ground, whether 

 sohtary or in communities, are not due to chance, or to intelligence, but to 

 instinct. The Sylvia stflvlcola, for instance, can be distinguished from two- 

 closely allied wrens more readily by its nest being lined with feathers than by 

 almost any other character. (" YarreU's British Bii'ds.") 



Necessity or compulsion often leads birds to change the situation of their 

 nests : numerous instances could be given in various parts of the world of 

 birds breeding in trees, but in treeless countries on the ground, or amoniisfc 

 rocks. Audubon (quoted in " Boston Journ. Nat. Hist.," vol. iv, p. 249) 

 states that the G-ulls on an islet off Labrador, " in consequence of the perse- 

 cution wliich they have met with, now build in trees," instead of in the rocks. 

 Mr. Couch ("Illustrations of Instinct," p. 218) states that three or four- 

 successive layings of the sparrow {F. dornesticus) having been destroyed, 

 " the whole colony, as if by mutual agreement, quitted the place and settled 

 themselves amongst some trees at a distance — a situation which, though 

 common in some districts, neither they nor their ancestors had ever before 

 occupied here, where their nests became objects of curiosity." The sparrow 

 builds in holes in walls, on high branches, in ivy, under rooks' nests, in the 

 holes made by the sand-martins, and often seizes on the nest made by the 

 house-martin : "the nest also varies greatly according to the place" (Mon- 

 tague, "Ornitho. Dict.,"p. 482). The Heron (Macgillivray, " Brit. Birds," 

 vol. iv, p. 446: W. Thompson, "Nat. Hist. Ireland," vol. ii, p. 146) builds 

 in trees, on precipitous sea-cUffs, and amongst heath on the ground. In the 

 United States the Ardea lierodias (Peabody in " Boston Journal Nat. Hist.," 

 vol. iii, p. 209) likewise builds ia tall or low trees, or on the ground ; and^ 

 which is more remarkable, sometimes in communities or heronries, and 

 sometimes solitarily. 



Convenience comes into play : we have seen that the Taylor-bird in 

 India uses artificial thread instead of weaving it. A wild Gold-finch 

 (Bolton's Harmon ia Rural is, vol. i, p. 492) first took wool, then cotton, 

 and then down, which was placed near its nest. The common Kobin 

 will often build imder sheds, four cases having been observed in one season 

 at one place (W. Thompson, "Nat. Hist. Ireland," vol. i, p. 14). In Wales- 

 the Martin {H. nrbica) builds against perpendicular cliffs, but all over the 

 lowlands of England against houses ; and this must have prodigiously in- 

 creased its range and numbers. In Arctic America in lS2o Hinmdo luni- 

 from (Richardson, " Fauna Boreali-Amercani,"p. 331) for the first time built 

 against houses ; and the nests, instead of being clustered and each having a 

 tubidar entrance, were biult imder the eaves in a single line and without th& 



2 A 



