1288 



HORMONAL REGULATION OF BEHAVIOR 



male incubates (Araadon, 1944a j, both male 

 and female have incubation patches, again 

 unlike most members of the family (Bailey, 

 1952). Johnston (1956) collected a number 

 of California gulls in the field in May and 

 June when the breeding birds had eggs. All 

 the adult birds that he collected had incu- 

 bation patches. Of 13 subadult (3-year-old) 

 males, which can be recognized by their 

 plumage, 8 had incubation patches. This is 

 about the same proportion as the proportion 

 of subadult males that breed. Among sub- 

 adult /e//iaies,which do not breed, no incu- 

 bation patches were found. 



Skutch (1957) points out that there are 

 exceptions to the general trend, in that 

 males of some species have been found to 

 sit on the eggs, although they have no incu- 

 bation patch. In most of these cases, data 

 are lacking with respect to the details both 

 of the behavior of the male bird and of the 

 temperature of the eggs, so that it is not 

 possible to say whether such birds are ac- 

 tually incubating. A partial exception is the 

 bank swallow, in which Petersen (1955), 

 by measuring the temperature with the bulb 

 of the thermometer placed among the eggs, 

 showed that the egg temperature in one 

 nest rose substantially when the male en- 

 tered the nest-burrow in the absence of the 

 female. The male in this species has no in- 

 cubation patch. Since these birds nest in 

 deep burrows in the ground, no details are 

 available about the behavior of the male 

 bird. This observation of a single individual 

 should, of course, be regarded with some 

 caution. Kendeigh (1952) using a thermo- 

 couple in nests of the barn swallow and the 

 purple martin, two species closely related 

 to the bank swallow observed by Petersen, 

 found that, although the male often came 

 and stood over the eggs in the nest, the 

 temperature was elevated only when the fe- 

 male was sitting. 



In spite of the occasional exceptions, the 

 pattern is generally consistent, and indi- 

 cates that the physiological conditions giv- 

 ing rise to the formation of the incubation 

 patch may illuminate the background of in- 

 cubation behavior itself. 



(3) Development. In several species of 

 song birds the development of the incu- 

 bation patch may be divided into the fol- 



lowing four stages (Bailey, 1952): (a) De- 

 featherization: the down feathers of the 

 incubation patch area are molted several 

 days before the first egg is laid, (b) Vascu- 

 larization: the blood vessels of the area be- 

 gin to increase in size and in number 

 immediately after defeatherization. The 

 vascularization is complete by the time the 

 last egg is laid and incubation begins, (c) 

 Edema: during incubation, the incubation 

 patch continues to become more vascular 

 and edematous. This edematous stage con- 

 tinues throughout incubation and during the 

 period when the newly hatched young are 

 brooded by the parent, (d) Recovery: the 

 vascularity and edema in the dermis begin 

 to subside gradually, starting when the 

 young are about 4 or 5 days old. 



Petersen (1955) weighed the skin of the 

 ventral apterium in a number of bank swal- 

 lows collected during the breeding season. 

 Before egg-laying began, the average weight 

 of the ventral apterium in both males and 

 females was about 93 mg. This weight 

 stayed the same in the males throughout the 

 breeding season. In the females the weight 

 began to increase just before egg-laying, 

 reaching a maximal average weight of about 

 280 mg. during incubation. We may recall 

 that this is the species in which egg tem- 

 peratures were found to increase when a 

 male was in the nest. 



Some observers have stated that the in- 

 cubation patch develops a week or so be- 

 fore the laying of the first egg (Nice, 1937; 

 Brackbill, 1958), or that it persists through 

 the summer until the fall molt (Odum, 

 1941). However, except for those by Bailey 

 and Petersen, the observations on the incu- 

 bation patch have lacked histologic verifica- 

 tion. It is quite probable that observers re- 

 porting different time-relationships between 

 the development of the incubation patch 

 and of the ovary are merely referring to the 

 loss of feathers, rather than to the develop- 

 ment of vascularity and edema. 



(4) Hormonal basis. Bailey (1952) stud- 

 ied the hormonal induction of the incuba- 

 tion patch in several species of sparrows and 

 finches. He found that testosterone pro- 

 pionate, administered as pellets, had no ef- 

 fect on the development of the incubation 

 patch. Hypophysectomized birds treated 



