MIGRATION AND SEX RECOGNITION IN FROGS 329 



Extracts from field notes, March 23rd to April 3rd, inclusive 



March 23rd. The southern two-thirds of observation pond was free 

 from ice, while other ponds in wood were entirely frozen over. 



March 34th. A film of ice had frozen over the observation pond 

 during the night. By 3 o'clock in the afternoon this film was melted 

 with the exception of a thin strip along the west edge of the pond. In 

 the afternoon three specimens of the swamp tree frog were observed. 

 One of them was first noticed in the grass at edge of water; when 

 startled it jumped into the pond, swam for a few inches and then bur- 

 rowed into the mud. The other two were first observed swimming; 

 they were caught and proved to be male and female. 



March 25th. Two leopard frogs, sexes undetermined, were first noted 

 in the grass on west side of pond. When startled they jumped into the 

 water. Four swamp tree frogs were seen. All six frogs were observed 

 in the afternoon as on the preceding day, the morning having been too 

 cool for them to be active. 



March 26th. In the early morning there was a heavy mist, followed 

 in the late morning by a hard rain which lasted until about 1 p.m. At 

 11:15 A.M., during the rain, a single swamp tree frog croaked inter- 

 mittently for about an hour. At 1 p.m. the voice of one swamp tree 

 frog was noted; it continued for 45 minutes, when two other frogs 

 took up the chorus. Their voices continued throughout the after- 

 noon. All afternoon, too, the voice of the leopard frog was evident. 

 Apparently a number of individuals were croaking. At 11 a.m. three 

 leopard frogs were seen in the water at west edge of pond, at 1 :45 four 

 of this species, and in the late afternoon about ten individuals. None 

 were collected. 



March 27th. There was a rain throughout the preceding night. 

 The air was cool and no frogs were seen or heard. 



March 28th. There was no croaking during the morning, but for a 

 half-hour in the afternoon a few isolated calls of the swamp tree frog 

 were heard. The following leopard frogs were caught in the pond: at 

 11:30 A.M., three males and five females, which included one clasping 

 pair; at 1:45 p.m., one clasping pair, and in the late afternoon one male 

 and four females. 



March 29th. There was no croaking during the morning until about 

 11 a.m., when the occasional calls of the leopard frog were noted. Occa- 

 sionally through the afternoon a call of this species, of the wood frog, 

 and of the spring peeper was heard, but there were no calls in the 



1 Temperature and humidity records were obtained through the courtesy of 

 Professor Hussey, Director of the University of Michigan Observatory. These 

 records were made by instruments situated at a distance of over two miles from 

 the breeding pond and at a higher elevation. The temperature records in general 

 correspond with readings made at the pond; no instrument for humidity records 

 was available for use at the pond. 



