MIGRATION AND SEX RECOGNITION IN FROGS 335 



male spring peeper, represent frogs migrating between 9 p.m. of 

 March 31st and 8 a.m. of April 1st. Throughout March 31st, 

 beginning at 9 :30 a.m. the leopard frogs were croaking, the swamp 

 tree frogs began at 10 a.m., and in the evening the other two 

 species started their chorus. All four species called during the 

 night. Comparison may be made with the catch of March 

 27th, a day characterized likewise by a small catch, favorable 

 weather conditions, and croaking, but differing in that it pre- 

 ceded rather than followed the day of largest total catch, March 

 30th. As on April 1st, the temperature lay within the optimum 

 range and the air was saturated to 100. The catch included 

 two male wood frogs, one female wood frog, and four male 

 swamp tree frogs, captured in the period between the evening of 

 March 26th and 8 a.m. March 27th. All afternoon and into the 

 night of March 26th the swamp tree frog and leopard frog chor- 

 used, and at 11:30 p.m. the spring peeper began to call. One of 

 the direct observations can be applied in this connection. The 

 single female leopard frog which was picked up in the field on the 

 morning of March 27th was making her way toward the pond 

 despite the fact that there was no croaking. 



To ascribe a directive function to voice seems to be unwar- 

 ranted in the light of migrations which occur without the pres- 

 ence of this suggested factor. In order to perform a directive 

 function, the chorus must be accompanied by migration, and we 

 do not always find the two coincident. On March 30th large 

 numbers of frogs migrated because of favorable climatic con- 

 ditions; warm weather had been prolonged enough to arouse them 

 and the weather conditions were such as to allow an overland 

 trip. Few individuals migrated on April 1st; the small number 

 admits of explanation on the ground that the migrator^'- climax 

 had passed, that a longer duration of warm weather would be 

 necessary to arouse the frogs remaining in less readily warmed 

 locations. The small catch of March 27th does not indicate 

 necessarily that voice was not effective, rather that up to this 

 date only those frogs in the most easily warmed situations had 

 been aroused. The immediate inception of the migratory im- 

 pulse must be intrinsic; physiological processes with which this 



THE JOURNAL OF EXPERIMENT.Uj ZOOLOGY, VOL. 30, NO. 3 



