ArrEXDix. 3G9 



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 will now consider the yariability of the nesting-instinct. The cases, 

 D i doubt, wouM bare 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 uniformity 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 

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

 instinct. The Si/lcia tylvicola, for instance, can bedistingnished from two 

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

 almost any other character. (" Yarrell's British Birds.") 



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

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

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

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

 it itrs that the Gulls on an islet off Labrador, " in consequence of the perse- 

 cution which they have met with, now build in trees," instead of in the r< 

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

 successive layings of the sparrow (F. domesticus) 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 lure, where their nests became objeots of curiosity." The sparrow 



builds in holes in walls, on high branches, in ivy, under rooks' nc.-ts, in the 

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

 house-martin: "the nest, also varii s greatly according to the place" (Mon- 

 b, "Ornitho. Diet.," p. 462). The Heron (Macgillivray, "Brit, lord-," 

 vol iv, p. 1 16 : W.Thompson, "Nat. Hist. Ireland," rol. ii, p. L46) builds 

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

 United States the Ardea he •odiat ( Pea body in " Boston Journal Nat. Hist.," 

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

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



sometimes solitarily. 



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

 India uses artificial thread instead of wearing it. A wild Gold-linch 

 (Bolton's Harmonia Bara&t, vol. i, p. 402) Bret t"ok wool, then cotton, 



Mi.l then down, which was placed near its ne-t. The common Robin 



will often build under sheds, four eases baring been observed in one 



nt one place (W. Thompson, "Nat. Hist. Ireland," vol. i. I 1 1 IK In Wale.-' 



the Ifartin {II. urbiett) builds against perpendicular cliffs, bul all over the 

 lowlands of England ■gains! bouses | and tins must have prodigiously in* 

 ed its range and numbers. In Arctic America in 1 3 -'•"> Hirundo luni- 

 front (Richardson, " fauna Boreali-Amercani,"p. 881) tor tin- flrsl tunc built 

 against bouses i and the nests, instead of being clustered and each bavii i 



tubular entrance, waff built under the Bares in ■ sil gle hue and without the 



