THE AMPHIBIA OF OKLAHOMA 



daylight choruses have been observed. Toads of both sexes remain in the 

 vicinity of the pool through the day, sometimes in the pool itself, more often 

 buried near its edge or resting in shallow burrows such as have earlier been 

 described (Bragg, 1937). With the coming of twilight (or even of more rain 

 in late afternoon) the chorus breaks out rather suddenly and within a half- 

 hour or so reaches its full development. Females react by entering the pool, 

 clasping occurs, and eggs are laid. 



Thus, most eggs are laid during the second night (Bragg, 1942b) and 

 on into the following day. During the third night or even the fourth, a few 

 males which have not succeecied in attracting females may call and, should 

 another heavy rain occur in the interim, males are further stimulated. It seems 

 probable that females are also affected, for during very frequent and heavy 

 rains in May and June, 1941, in central Oklahoma, large choruses of B. cog- 

 natus were heard practically every night for a month; and, later, young re- 

 cently metamorphosed toads of at least three different ages were collected in 

 several single breeding areas (Bragg, 1942e). 



Peculiarities in the physiological adjustment of females in this prairie 

 toad are shown by the fact that even on the nights of heaviest breeding ac- 

 tivity some females continue to feed along the roads apparently not attracted 

 by the loud clamoring of the males. This probably explains why periods of 

 breeding activity continue to occur after rains throughout the summer — not 

 all females are ready to lay eggs nor are they receptive to males at the same 

 time. This again indicates a sort of eccentric rhythm in this xeric form (and 

 possibly others). 



This typical pattern of the breeding behavior of B. cognatus is reviewed 

 here in some detail in order to compare it with that of other species. Ps. 

 clar\ii Baird behaves in much the same manner as B. cognatus in producing 

 eggs on the second night after a rain (Bragg, 1942e), often developing huge 

 congresses of males on the first night. Microhyla c. olivacea, Ps. strecl^eri , B. 

 w. woodhoHsii , B. t. americanus , and Hyla v. versicolor differ radically from 

 it. M. c. olivacea develops large congresses after rains but clasping pairs (and 

 females migrating into the pools) may be found within an hour after the first 

 calls are heard in a given place. Since in unmated females, captured as they 

 are entering pools and retained overnight, eggs do not ooze from the cloacal 

 opening, whereas in those taken from clasping males in a pool they usually 

 do so, it is probable that ovulation does not occur in this species except under 

 the influence of the male's clasp (contrary to Noble and Aronson, 1942, on 

 Kana pipiens^. Nearly all eggs are laid the first night. However, not all fe- 

 males enter pools during one night and, tor this reason, reproduction is pro- 

 longed through the summer, males calling and some females laying eggs 

 during or immediately after each rainy period, as in B. cognatus. I have 

 frequently taken clasping pairs and found eggs in pools containing well- 

 developed larvae of at least two ages and have found active breeding taking 

 place in a pool simultaneously with the emergence and metamorphosis of 

 young on two occasions. One would not {wx^X such a situation as this with a 

 mesically adapted frog such as A', ptpicns or R. catcsbeiana. 



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