The Wood-frog, Raria sylvatica LeConte. 



87 



LIFE-HISTORY OF THE WOOD-FROG. 



This, our smallest Rana, awakens, spawns, and disappears into the 

 woods, in such quick succession that it generally escapes notice. Often 

 our first intimation of its presence is the eggs. In fact, at Ithaca, were 

 it not for a street railway in the path of amphibian migration, this 

 frog would seldom be seen before its eggs were recorded. Even with 

 this excellent check, the two records often appear coincident, the frog 

 coming rarely more than a day previous to egg-laying. 



THE FIRST APPEARANCE. 



R. sylvatica Sip\)ea,m almost simultaneously with the meadow-frog and 

 spring-peeper. It may appear 1 to 7 days after Hyla pickeringii, but 

 averages 3 days later, and usually emerges after Rana pipiens, and 

 among our earlj^ spring records there are several instances of its being 

 seen or taken from beneath the ice of small ponds. An average of all 

 our first spring records is about April 2 ; the average for the years when 

 most intensive work was done gives March 31 ; or an average of the 

 first appearances of the frogs themselves (exclusive of first egg-records) 

 yields March 31. The first records are: 



The appearance of Rana sylvatica is mainly influenced b}^ air-temper- 

 atures. From records based upon the first appearances of the frogs 

 alone, the maximum air-temperatures for the day previous range from 

 45 to 72 degrees, the average 53 degrees; for the day of the record, from 

 41 to 62 degrees, the average 51 degrees. In this computation the 

 record of April 4, 1902, is eliminated, for it was of a frog observed 

 beneath the ice of a pond. Inasmuch as they hibernate in logs, 

 stumps, possibly beneath stones and among leaves, not in water, this 

 individual must have appeared when the pond was free of ice. A 

 cursory glance at the temperatures shows the records flanked on either 

 side by maxima of at least 41 degrees. An average of all the first 

 appearances (both frog and egg records) gives 55 degrees for the day 

 previous, and 56 degrees for the day of the record. The data seem to 

 point to an effective temperature between 51 and 56 degrees, although 

 41 to 45 degrees occasionally brings the species out. 



