PARENTAL BEHAVIOR 



1.301 



latod by the change from the presence of 

 eggs to the presence of young. Striking 

 changes in behavior can be observed at the 

 time of hatching. For example, a female 

 duck sitting on eggs is very silent. As soon 

 as the eggs are chipped, indicating the onset 

 of hatching, frequent calls can be heard from 

 the mother (Collias and Collias, 1956). It 

 is often reported that in species in which the 

 male takes no part in incubation, but does 

 participate in the feeding of the yovmg, 

 abrupt changes in behavior take place at 

 the time of hatching. The male suddenly 

 begins to spend much more time near the 

 nest and to bring food to the young (Blan- 

 chard, 1941; Davis, 1941). Skutch (1953b) 

 pointed out that the males of many species 

 bring food to the female during the incuba- 

 tion period, or carry nesting material to- 

 ward the nest, etc. thus maintaining a 

 contact with the nest which provides the 

 background for parental feeding by the 

 male. In those species in which the male 

 brings no food or other objects to the nest 

 during the incubation period, he does not 

 begin to bring food to the nest until he has 

 seen the new nestlings, the sight of which 

 stimulates the change in his activity. In the 

 case of the tricolored red-winged blackbird 

 the male leaves the colony area at the be- 

 ginning of incubation, which is carried out 

 entirely by the female, and then reappears 

 after the eggs have hatched to participate 

 in feeding the young (Emlen, 1941). 



Observations of wild birds reveal that 

 newly hatched young often interfere with 

 the incubation of eggs not yet hatched. 

 When the eggs of gulls hatch, for example, 

 the parents appear at first to continue to 

 treat the young just as they did the eggs, 

 but the intensity of this incubation behavior 

 is Cjuickly reduced by the behavior of the 

 young, which crawl about in spite of the 

 parent's effort to push them under its body 

 (Paludan, 1951; Tinbergen 1953; Ytreberg, 

 1956). If there is a substantial interval be- 

 tween the hatching of the first and the third 

 (last) egg, the incubation of the last egg 

 may be interrupted, and it may die during 

 the hatching process (James-Veitch and 

 Booth, 1954; Ytreberg, 1956). The Ameri- 

 can coot, an aquatic bird which liuilds a 

 number of nest-platforms in its marshy 



territory, often broods the (precocial) 

 young in a "brood nest" built when the eggs 

 hatch and which is separate from the "egg 

 nest." These birds often desert some of the 

 eggs in the egg nest when enough of them 

 have hatched to stimulate the beginning of 

 brooding at the separate brood nest. The 

 calls of the young appear to stimulate the 

 adults to brood them instead of incubating 

 the eggs (Gullion, 1954). 



Stimulation of broodiness by the chicks. 

 Broody behavior toward the chicks is in- 

 duced in domestic hens by keeping them 

 closely confined with the chicks (Burrows 

 and Byerly, 1938; Collias, 1946; Ramsay, 

 19531. Broodiness induced by this method 

 develops rather gradually, the bird first 

 showing an incipient brooding posture, then 

 clucking, then showing full broodiness in- 

 cluding clucking and hovering over the 

 young, and finally leading them to food, etc. 

 (Ramsay, 1953). Confinement with the 

 young also induces broody behavior in ca- 

 pons (Goodale, 1916) and immature hens, 

 although in the latter the broody behavior 

 develops more slowly than in adult birds 

 (Saeki and Tanabe, 1955). Stanford (1952) 

 induced adult bobwhite quail to become 

 broody toward chicks by confining them in 

 small cardboard boxes. In his experiment 

 more of the males (46.7 per cent) than of 

 the females (23.1 per cent) accepted the 

 young. 



In domestic chickens, the development of 

 broodiness appears to be facilitated by 

 keeping the birds in warm (80 to 90°r.), 

 dark coops (Burrows and Byerly, 1938; 

 Yamashina, 1952; Saeki and Tanabe, 1955). 



Collias (1946) kept domestic hens brood- 

 ing for months by repeatedly substituting 

 young chicks for the growing chicks of the 

 previous brood. (Older chicks are less ef- 

 fective in inducing broodiness than are 

 newly hatched birds.) Emlen (1941) ex- 

 tended the parental feeding behavior of tri- 

 colored red-winged blackbirds from the nor- 

 mal 11 days to about 17 days by replacing 

 the nestlings with younger birds. On the 

 other hand, attempts to extend the period 

 of crop-milk formation in pigeons by giving 

 newly hatched squabs to the parents to re- 

 place the older birds which they were feed- 

 ing have been unsuccessful (Patel, 1936). 



