452 AVES. 



collects experiences, which it combines so as to arrive at judg- 

 ments and conclusions ; it recognises the surroundings of its 

 nest, distinguishes between friends and foes, and selects the 

 proper means both for the preservation of its existence and for 

 the care of its brood. In some birds the capacity for profiting 

 by instruction and the faculty of imitation are extraordinarily 

 developed (starling, parrot). The emotional side appears no 

 less developed, as may be inferred not only from their general 

 behaviour and the varying expression of their song, but especi- 

 ally from the behaviour of the two sexes at the breeding season. 

 Their instinctive actions are directed to the preservation of the 

 individual, and as in insects, but in a far higher degree, to the 

 care of their offspring. 



In general the manifestations of intelligence as well as of 

 instinct attain their maximum at the time of reproduction, 

 which in the temperate and colder climates usually takes place 

 in the spring (in the crossbill at almost any time of the year). 

 The voice is clearer and richer in the breeding season ; the male 

 endeavours to excite the female by his song and the beauty of 

 his plumage. In addition to the changes of plumage and song, 

 the whole behaviour of birds is modified under the influence of 

 sexual excitement (love-gestures, etc.). 



Most birds build nests, and seek for this purpose a suitable 

 place in the district they inliabit. Only a few birds (goat- 

 suckers, stone-curlew, Alcidae) make no sort of nest, but those 

 which breed on the ground (Laridae, Limicolae, Galli, and 

 Ratitae) scoop out a pit or make a depression in moss and grass. 

 The most skilfully constructed, however, are the nests of those 

 birds which glue particles of extraneous matter together with 

 their sticky saliva or which weave fine tressworks of moss, wool 

 and grass-stalks (weavers). As a rule it is the female alone 

 which builds the nest, the male merely helping in collecting the 

 materials. There are, however, instances in which the male 

 takes a share in the construction (swallows, weavers) ; while in 

 other cases (Galli, chaffinch) the male takes no share at all in 

 building the nest. Many sea-birds, as the auks and penguins, 

 lay but one egg, and most of the large birds of prey, pigeons, 

 and humming-birds, lay two eggs. The number of eggs is larger 

 in the singing birds and still greater in the swimming birds of 

 ponds and rivers, and in the fowls and ostriches. The duration 



