MENTAL QUALITIES. 253 



Passeres, Scansores, Columbines and Raptores leave the egg mem- 

 branes very early (altrices) ; they are naked, or only covered with 

 down in places, and incapable of free locomotion or of feeding them- 

 selves, and remain for some time in the nest, in which they are fed 

 and tended by their parents. 



The mental qualities of Birds are incomparably higher than those 

 of Reptiles. The high development of the senses (sight) renders 

 them capable of a sharp discernment, with which is combined a good 

 memory. Under the guidance of its parents the Bird gr dually 

 learns to fly and sing ; it collects experiences, which it combines so as 

 to arrive at judgments and conclusions ; it recognises the surround- 

 ings 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 especially 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 exceptionally in the middle of winter. 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 (winter plumage, breeding plum- 

 age) and song, the whole behaviour of Birds is modified under the 

 influence of sexual excitement (love-gestures, etc). 



With the exception of Fowls, Pheasants, etc., Birds are mono- 

 gamous ; they pair only for the breeding time, and collect together 

 later, and migrate in larger flocks. There are, however, some instances 

 of the migration of single pairs. 



Most Birds build nests, and seek for this purpose a suitable place 

 in the district they inhabit. Only a few Birds (Goat-suckers, etc.) 

 are content simply to lay their eggs on the ground, others (Skua, 

 Terns, Ostrich) scoop out a pit or make a depression in moss and 

 grass (Tetraonidce). The most skilfully constructed, however, are the 



* Cf. A. E. Brehm's " Illustrirtes Thierleben," Tom IV.. V. and VI, 



