1294 



HORMONAL REGULATION OF BEHAVIOR 



gesterone induces incubation behavior by a 

 means other than the stimulation of pitui- 

 tary prolactin, and that the prolactin is 

 secreted as a result of participation in in- 

 cubation (see below). We will recall Mar- 

 shall and Serventy's (1956) observation 

 that in several species of seasonal-breeding 

 wild birds, the lipid metamorphosis of the 

 testis tubules coincides with the onset of 

 incubation duties in a species in which the 

 male takes part in incubation, and does not 

 take place until some weeks later in a spe- 

 cies in which the male does not take part in 

 incubation. Paper chromatographic analysis 

 by Lofts and Marshall (1957) indicates that 

 the lipid contents of these metamorphosed 

 tubules contain progesterone. Lofts and 

 Marshall suggested that the postnuptial 

 avian testis tubule may possess an endocrine 

 function similar to that of the mammalian 

 corpus luteum. At any rate, the association 

 of progesterone with incubation behavior in- 

 dependently of prolactin, at least in some 

 types of birds, needs to be taken seriously. 



3. Interaction between Internal and Exter- 

 nal Environments in the Regulation of 

 Incubation Behavior 



Induction of incubation behavior by ex- 

 ternal stimuli. Male and female ring doves 

 are brought into readiness to incubate by 

 stimuli provided to each other, and by stim- 

 ulation coming from the presence of the 

 nesting material and/or nest bowl, even in 

 the absence of eggs (Lehrman, 1958a, 

 1959b). Although doves kept singly in cages 

 containing a nest with 2 eggs will show no 

 interest in the eggs during a 6-week test 

 period, pairs of birds kept in a cage with a 

 nest bowl and nesting material will imme- 

 diately sit upon eggs introduced into the 

 cage by the experimenter after 7 days. If a 

 pair of birds is kept together in a cage, but 

 without a nest bowl or nesting material, 

 they will, for the most part, not subse- 

 quently be ready to sit on eggs until after 

 a short period of nest-building activity. 

 Lehrman, Brody and Wortis (1961) tested 

 doves for their response to eggs after vary- 

 ing periods in the cage with a mate or with 

 a mate and nesting material. These birds 

 were killed for autopsy immediately after 

 the test. The data indicate that stimuli from 



the male induce growth of the ovary and 

 o^•iduct in the female and that this growth is 

 additionally fostered by the presence of 

 nesting material. Further, differences be- 

 tween the rates of oviduct growth in birds 

 kept in the cage with and without nesting 

 material closely parallel differences with 

 respect to the rate of onset of incubation 

 behavior. In addition, the onset of incuba- 

 tion behavior is closely related to the oc- 

 currence of ovulation, which conforms with 

 and strengthens our earlier suggestion that 

 l^rogesterone is involved in the beginning of 

 incubation behavior in this species (Lehr- 

 man, 1959a, b). 



Stimulation provided l)y the egg seems to 

 play a considerable role in the maintenance 

 of incubation behavior in many species of 

 birds. In an often quoted but rather casual 

 experiment Taibell (1928) forced 2 male 

 turkeys to stay on a nest with eggs by hold- 

 ing them down by a cloth bag. These birds 

 developed complete incubation behavior, 

 including delicate treading on the nest, set- 

 tling on the eggs, etc., in 1 to 4 days. On the 

 other hand, Collias (1950) reported that 

 confinement with eggs is relatively inef- 

 fective in stimulating incubation behavior 

 in hens. 



The importance of the egg in maintaining 

 and stimulating incubation behavior can be 

 seen from the fact that, when the eggs fail 

 to hatch at the end of the normal incubation 

 period, the bird will often continue sitting 

 for a considerable time. Domestic hens will 

 sit on sterile eggs up to 44 days, which is 

 more than twice the normal incubation pe- 

 riod (Saeki and Tanabe, 1954). Other ob- 

 servers (quoted by Katz, 1937) have found 

 incubating hens sitting on artificial eggs for 

 u]) to 4 months. Night herons breeding in 

 captivity sit on sterile eggs for 40 to 51 days, 

 as compared with the normal incubation 

 period of 22 to 24 days (Noble and Wurm, 

 1942). Herring gulls, which normally incu- 

 bate 26 to 27 days, will incubate 56 to 75 

 days on infertile eggs (Paludan, 1951). The 

 sitting period of domestic pigeons can simi- 

 larly be extended from 18 to 25 days (Ko- 

 bayashi, 1953a). These data are especially 

 interesting in view of the fact that, in a nor- 

 mal reproductive cycle, there is a rather 

 striking change in the behavior of incubat- 



