PARENTAL BEHAVIOR 



1295. 



ing birds when tlie eggs hatch (see below, 

 page 1300. 



Adjustment of incubntlon behavior to the 

 immediate stimulus situation. The hormo- 

 nally induced modification of the ventral 

 apterium (defeatherization, vascularization, 

 edema) into the incubation patch, which, as 

 we have noted, develops in most types 

 of birds during the egg-laying period, is 

 adapted for the production of localized 

 higher skin temperatures and the transfer 

 of heat between the bird and the eggs. There 

 is much evidence that temperature regula- 

 tion does in fact play a role in the regula- 

 tion of the birds' behavior toward the eggs. 

 Many field observations of wild birds in- 

 dicate that the time spent sitting on the 

 eggs is greater at lower ambient tempera- 

 tures than at higher (Nice, 1937; Weston, 

 1947; Nice and Thomas, 1948; Skutch, 

 1957). Simmons (1954) found that the eggs 

 of the graceful warbler are covered only 

 9 per cent of the time at an ambient tem- 

 perature of 90°F., but 57 per cent of the 

 time when the ambient temperature is 60 to 

 70°F. In the European wren the correlation 

 between air temperature and the time spent 

 on the eggs is -0.74 (P < 0.01) (White- 

 house and Armstrong, 1953; Armstrong, 

 1955). On very hot days, some birds may 

 stand over the eggs without being in actual 

 contact with them (Brackbill, 1958; Weller, 

 1958). Weller measured the temperature 

 under an incubating nighthawk sitting on 

 its eggs on the bare roof of a building (this 

 species does not build a nest) and found 

 that, during a very hot day, the tempera- 

 ture under the bird was lower than the tem- 

 perature on the bare roof, indicating that 

 the bird actually cooled the eggs by stand- 

 ing over them. At night, when the bird sat 

 closely on the eggs, the egg temperatures 

 were warmer than the temperatures on the 

 bare roof. Irving and Krog (1956) found 

 tiiat the average temperatures of eggs and 

 young of various species of birds in the 

 Arctic, measured in the nest, were about 

 the same as those found in milder climates, 

 indicating that the varying behavior of the 

 parent in different climates tends to pro- 

 duce regulation of nest temperatures to 

 about the same optimum. 



Baerends (1959) experimentally altered 



the temperatures of artificial eggs being in- 

 cubated by herring gulls in the wild, by 

 running water of various temperatures 

 through tubes imbedded in the eggs. He 

 found that temperature changes in the eggs 

 (while ambient temperatures remain con- 

 stant) induce temperature-regulating be- 

 havior of the bird {e.g., shivering, panting,, 

 increase or decrease of body surface by 

 erection or sleeking of feathers, etc.), as 

 well as restlessness expressed by increased 

 preening and "displacement nest-building," 

 the latter resulting in improvement of the 

 nest structure. In addition, abnormal egg 

 temperatures induce movements which in- 

 crease the isolation of the eggs from the 

 surrounding air and improve the contact be- 

 tween the eggs and the incubation patches. 

 For example, the bird wobbles from side to 

 side on the eggs, resettles itself on the eggs, 

 shifts the eggs with its bill, etc. Similar be- 

 havior is sometimes seen to increase on very 

 hot days (Deusing, 1939). 



Behavior which regulates the temperature 

 of the eggs is not restricted to those birds 

 having an incubation patch. The megapodes 

 or mound- builders build large mounds of 

 plant material, sometimes up to 35 feet in 

 diameter and 15 feet high, and lay their 

 eggs in holes dug in these mounds, which are 

 then filled in. Incubation is accomplished 

 by the heat produced by the rotting and 

 fermentation of the materials of which the 

 mound is built (Frith, 1956b). In one genus 

 {Alectura) , the male works continuously to 

 regulate the temperature, by digging holes 

 in the mound, ramming his head into the 

 hole (apparently to test the temperature), 

 and then adding material (which raises the 

 temperature) or digging oft' material from 

 the top (which cools the mound), depending 

 upon the temperature in the mound. The 

 skin of the head and upper neck in this spe- 

 cies is naked, and, in the male, turns bril- 

 liant red at the beginning of the breeding 

 season (Frith, 1956a). It seems not unrea- 

 sonable to suggest that this change is in- 

 duced by changes in endocrine secretion, 

 and that these changes in vascularity (and 

 probably other characteristics) of this skin 

 area make it more capable of serving as a 

 temperature-sensing mechanism. 



Physiologic effects of stimuli arising from 



