ADAPTATION'S AND DISTRIBUTION 



ture relations uncertain. Oliscrvcd only a few times. I^reeding pattern, xeric. 

 (Figs. 14, 16, 19, 30.) 



Some Details of Breeding Habits 



A return to the consideration of the hehavior ot lUito and Scaphiopus 

 as they approach a breeding site proves especially interesting. Individuals of 

 Scaphiopus are outstanding in the marked attraction of the male's breeding 

 call for individuals of either sex. The first spadefoot male to reach a pool 

 begins calling and others of either sex within hearing distance hurry toward 

 the sound. In studying S. bombijrons and S. hammondii, I have frequently 

 observed pools in late afternoon without evidence of a single anmal but at ten 

 to eleven o'clock the same night there were hundreds present and others still 

 migrating in. Not only this, but in at least ten instances with S. bombijrons, 

 I have watched the progressive development of such a congress. In all cases, 

 ther were only a few males to be found in the early phases; later, here and 

 there a new voice was heard and individuals could be found on the bank 

 and by another half hour the area within two hundred yards of the pool in 

 all directions was swarming with spadefoots migrating toward the water. 

 Clasping pairs are often found in such large aggregations as early as ten p.m. 

 and most eggs that will be laid at any one site under the influence of a single 

 rain are produced on the first night. Less extensive observations of the same 

 type have been made upon S. couchii and S. hurterii, but they indicate that 

 these species undoubtedly follow the same general pattern. 



Members of the genus Bufo in Oklahoma differ more, interspecifically, 

 than members of Scaphiopus in these matters. As stated above, all tend to 

 use shallow water and the calls of the first males to arrive at a pool attract 

 other individuals. It has been shown, however (Bragg, 1940), that, with B. 

 cognatus, the place where eggs are to be laid is largely determined by the 

 behavior of the female rather than by the place where the male calls. Males 

 call from any temporary water that they may find but females pay little at- 

 tention to them unless the water is six inches to one foot in depth. When 

 males about shallow pools fail to find females, they migrate to larger pools 

 where others are calling. Thus, during the first night a huge chorus con- 

 sisting of most of the adult male population of an area of some acres becomes 

 congregated in one or a few pools. Females during this time are often in- 

 active, sometimes in nearby pools (Bragg, 1937) although a few may go to 

 the males and actually produce eggs. Most often daylight comes with hun- 

 dreds of males, and at most only an incidental female, in the congress. In 

 cases where several pools of the proper types are available within a given area, 

 several correspondingly smaller congresses inay, of course, develop. In any 

 case, the typical result of the first night's activity is ( 1 ) huge numbers of avail- 

 able males in a small area, (2) females in abundance near the pool (usually 

 not in it), and (3) a very small amount of actual reproduction, often none 

 at all. 



The approach of daylight typically stops the calling, although several 



79 



