THE AMPHIBIA OF OKLAHOMA 



them in the general area of capture. Some also were preserved for later study. 

 By repeated collections in the same general area, data were secured as to 

 size and variation of individuals in each population so treated. By interpreting 

 the results in the light of observations on breeding dates, breeding sites, and 

 habits of movement of the toads in feeding, a fair idea could be secured as 

 to growth rates of the toads in each area for the seasons studied. 



The age at sexual maturity was not so easily obtained. Several methods, 

 none of them perfect, were utilized. (1) The smallest toads in breeding con- 

 gresses were compared with others feeding but not breeding on the same 

 nights. By examining hundreds of such toads we could at least find the small- 

 est probable size attained before breeding activity commenced. (2) Male toads 

 develop secondary sex characters by which they may be distinguished easily 

 from females. By watching for the beginnings of such differentiations and 

 comparing the sizes and stages of development of small toads taken from 

 breeding congresses with those of others taken feeding but not breeding, 

 some idea of age at sexual maturity of males could be obtained. Females do 

 not show secondary sex characters clearly until maturity, but one behavior 

 character of the male may be used beyond a certain size limit to distinguish 

 the sexes. This is the protesting note which males, but not females, give when 

 handled or otherwise disturbed. Any healthy and unfatigued individual be- 

 yond 60 mm. in size which does not "protest" when handled may safely be 

 inferred to be a female. Below this size females cannot certainly be separated 

 from males except, of course, as males may show the beginning of other sec- 

 ondary sex characters. It follows that males may be distinguished clearly at 

 an earlier age and at a smaller size than females, and that our methods could 

 teach us more about the former than the latter. 



As background for our interpretations, data on sizes of adults are given 

 in Table I. These came from measurements recorded over several years, some 

 from preserved and others from living specimens. Table II treats breeding 

 adults in the same manner except that all were alive when measured. A 

 resume is given below of our observations on breeding dates, characteristic 

 breeding sites, the degree of success in breeding each year, and characteristic 

 movements of both young and adults while feeding. Unless otherwise stated 

 all data apply specifically to B. cognatus in Cleveland County and mostly 

 from an area within four miles from the center of the city of Norman. For 

 details of breeding habits here, see Bragg ( 1940). 



Bujo cognatus breeds only after rains, typically of one-half inch or more, 

 from March to August (observed) and perhaps later. Breeding activity is 

 inhibited by air temperatures below 12 °C. Therefore, the distribution of 

 temperature and rainfall within the warmer months (rather than a limited 

 breeding season) determines largely how much breeding there will be and 

 also whether it will be successful. Spring rains in central Oklahoma are com- 

 monly accompanied by falling temperatures, often by temperatures too low 

 for breeding. 



Should a given spring be exceptionally tlry during March, April, and 

 early May, or if all early rains fall while the temperature is too low for breed- 



48 



