PARENTAL BEHAVIOR 



1357 



results with young curve-billed thrashers: 

 the greater the amount of care devoted to 

 the birds, the longer the period of begging. 

 Craig (1908) stated that the first learning 

 of young pigeons to differentiate individuals 

 comes about because the mother becomes 

 unwilling to feed the young long before 

 the father does so. Petersen (1955) ob- 

 served that the first flights of nestling bank 

 swallows were induced in part by the in- 

 creasing reluctance of the parents to feed 

 them. 



Of course, these may be largely effects on 

 the rate of development of the change from 

 begging to independent feeding, which 

 change may nevertheless occur without be- 

 ing stimulated by any change in the par- 

 ent's behavior. Miller (1921) found that 

 young house finches being reared by hand 

 abruptly changed from begging to self-feed- 

 ing without any change in the treatment 

 which they were getting. 



Young birds of many species apparently 

 become conditioned to follow parents having 

 particular characteristics by means of a 

 very rapid learning process occurring during 

 a particularly sensitive period shortly after 

 hatching. This is the phenomenon of "im- 

 printing" (Lorenz, 1935; Hinde, Thorpe 

 and Vince, 1956; Hess, 1959). 



The experiences of young birds with their 

 l)arents sometimes also contribute to the 

 nature of their mating preferences in later 

 life, although it has not yet been demon- 

 strated that this effect depends upon as 

 sharp a critical period of learning as does 

 the development of the following response 

 of the young birds themselves. Craig ( 1914) 

 noted that male ring doves reared by hu- 

 man keepers directed their courtship dis- 

 l-)lays toward men, and particularly toward 

 the human hand. When later allowed to as- 

 sociate with doves, they gave up their at- 

 tachment to humans very slowly and in- 

 completely, and not in all cases. Nicolai 

 (1956) found that bullfinches reared in 

 isolation accept a human keeper as the 

 "mate." This attachment can be reversed 

 during the bird's first autumn and winter 

 if it meets other bullfinches, but becomes 

 irreversible during the first mating season. 

 The importance of such learned attachments 

 to individuals of the species, based upon 



early experience with the parent, has been 

 pointed out by a number of authors (Cush- 

 ing, 1941; Cushing and Ramsay, 1949; 

 Beach and Jaynes, 1954) . 



In some species of birds, such as the chaf- 

 finch, young birds appear to learn several 

 aspects of the species' song through pa- 

 rental example (Thorpe, 1954, 1958), even 

 though the actual expression of the song 

 may not appear until much later, under the 

 influence of androgenic hormone (Poulsen, 

 1953a). Frisch (1959) found that young 

 redshanks reared from the egg by lapwing 

 foster-parents learned to respond appro- 

 priately to the calls of the foster species. 



Naturally, the actual physical survival 

 of the young depends on the display of 

 appropriate parental behavior by the par- 

 ents. Leopold (1944) found a much higher 

 survival ratio among young wild turkeys, 

 whose mothers squat and crouch at the 

 approach of man, than among liberated 

 domestic turkeys in which the mothers 

 scold and noisily herd their young away at 

 the approach of humans. Nalbandov and 

 Card (1945) found that, when young do- 

 mestic chicks were being cared for by males 

 which had been made "broody" by pro- 

 lactin injection, the young tended to die of 

 neglect or of attack after the cessation of 

 the injections. This point is so obvious that 

 it requires no further discussion. 



2. In Mammals 



Although many young mammals at first 

 attempt to suck whatever object they come 

 in contact with after birth (Colhasj 19561, 

 the establishment of a suckling relation- 

 ship with a particular mother, or even a 

 particular nipple, is accomplished very 

 rapidly (Ewer, 1959). Collias (1956) points 

 out that the repeated making and break- 

 ing of contact with the nipple during the 

 first hours of the young goat's life seems 

 to facilitate the learning of both the mother 

 and the kid. Frank (1952) noted that young 

 common voles resist being retrieved by 

 other than their own mothers, apparently 

 basing the discrimination on olfactory stim- 

 uli. King (quoted by Scott, 1953) found 

 that guinea pigs removed from their moth- 

 ers immediately after birth, and then re- 

 placed after 3 days can no longer develop 



