1142 



SUBMAMMALIAX VERTEBRATES 



as low as — 20°F., resulted in earlier produc- 

 tion of sperm with high fertilizing capacity 

 (Burrows and Kosin, 1953; Kosin, Mitchell 

 and St. Pierre, 1955a I. On the other hand, 

 "cooling" the toms to 65°r. in the period 

 May to July, when outside temperatures 

 may range between 60° and 100°F., pre- 

 vented the drop in sjiermatogenesis and fer- 

 tility experienced by toms kept outside 

 (Kosin, Mitchell and St. Pierre, 1955b; Law 

 and Kosin, 1958). Kosin (1958) established 

 that the respiration rate of turkey semen, 

 especially during the second hour of incuba- 

 tion, was affected by the environment in 

 which the donors were kept. The respiration 

 rate was higher for semen from toms kept 

 at 65°F., especially during the summer, sug- 

 gesting that high temperatures may be more 

 harmful than low temperatures. In view of 

 the fact that body temperatures rose in the 

 toms kept outside during the summer (Ko- 

 sin, Mitchell and St. Pierre, 1955b), it seems 

 that the higher body temperature may have 

 affected spermatogenesis, as discussed in the 

 beginning of the present chapter. Constant 

 temperature 50° ± 5°F. depressed over-all 

 egg production by turkey hens (Mitchell 

 and Kosin, 1954). Preheated (50° ± 5°F.) 

 hens laid initially at a somewhat higher rate 

 than the hens kept outside, where temi)era- 

 tures were as low as 10°F., but the birds kept 

 in the constant environment had a greater 

 tendency to become broody with an accom- 

 panying decrease in the rate of lay (INIitchell 

 and Kosin, 1954; Kosin, Mitchell and St. 

 Pierre, 1955a). Eggs from turkey hens in 

 the constant environment were significantly 

 smaller (84.5 versus 96.7 gm.) than those 

 from hens kept outside. 



4. Rainfall 



Marshall (1959) reviewed the evidence 

 that rainfall may be involved in regulation 

 of the breeding cycles. Serventy and Mar- 

 shall (1957) observed that unseasonal pre- 

 cipitation in Australia was followed by the 

 appearance of spermatogenesis in a large 

 number of terrestrial as well as aquatic spe- 

 cies. Marshall and Disney (1957) analyzed 

 experimentally in what manner the rain or 

 increased humidity had its effect. Rainfall 

 induced adult nonbreeding Quelea quelea 

 to molt from one breeding plumage dress 



to the other without the normally interven- 

 ing neutral dress. The urge to build nests 

 was also stimulated by rainfall or humidity, 

 but for the construction to be successful 

 long green grass was reciuired. This grass 

 normally becomes available after the rain. 

 After the nests are built, breeding can pro- 

 ceed; at the same time the seed heads, the 

 staple food of the nestlings, normally ap- 

 pear in the grass. Whether the relationship 

 between the initiation of ovulations and ap- 

 pearance of seed heads is coincidental was 

 not determined. These results suggest that 

 rainfall affects the breeding cycle directly 

 and also indirectly by making suitable nest- 

 ing material (and food?) available so that 

 reproduction can occur. 



5. Food 



The a\-ailability of food may affect breed- 

 ing success, but no evidence is available that 

 demonstrates that a specific food supply reg- 

 ulates the ))r('C(ling cvcle of birds (Marshall, 

 1959). 



6'. \'ocalizatio»s 



Vaugien (1951) found that female bud- 

 gerigars, Melop.slftacits inuhilatus, would 

 lay in complete darkness, provided they 

 could hear the vocalizations of courting 

 pairs of budgerigars in the aviary. Ficken, 

 van Tienhoven, Ficken and Sibley (1960) 

 investigated the effects of vocalizations by 

 the birds' own mates on gametogenesis. The 

 gonads of pairs isolated from hearing other 

 pairs remained inactive, w^hereas pairs which 

 could hear others showed full spermatogene- 

 sis and ovulations, whether or not they could 

 see the other pairs. No quantitative investi- 

 gations were made to determine how many 

 pairs were reciuired to start tlie chain of 

 events. 



7. Xesting Site 



Marshall (1952) reported that arctic birds 

 of a variety of species seem to be adversely 

 affected by lack of nesting sites. A rather 

 detailed investigation of nonbreeding, or 

 rather decreased laying, has been made by 

 Barry (1960) for the brant, Branta berniela 

 hrota, and blue and snow geese, CheJi caeru- 

 lescens. The data from the two species agree 

 closely enough to be treated here as one 



