88 The Wood-frog, Rana sylvatica LeConlc. 



THE VOICE. 



The croak of Rana sylvaticais higher-pitched than that of Rana clamata 

 and not so strong in volume or carrying quality. It can be heard only 

 a short distance from the pond whence it comes. In chorus it is 

 more of a rattle than in any of the other frogs. When held in the 

 hand and squeezed, the male can make a very grating noise. The 

 croak would be confused only with that of Rana pipiens, for at this 

 season no other Rana would make itself heard. The wood-frog's 

 note is shorter, less sustained, and not as loud or as deep as that of Rana 

 pipiens. The meadow-frog's note may be several short croaks followed 

 by two or more longer ones, or vice versa, or the shorts and longs may 

 be interspersed in other fashions a prolonged croak; while the wood- 

 frog's note is very short, not always a succession of croaks a sharp and 

 snappy clack. At times, however, 2 to 4 or 6 notes may be given in 

 rapid succession ; and when close at hand they sound high and grating 

 in character. The croak of the meadow-frog may take 6 seconds if the 

 succession be given, or less than one second if only one croak be sounded; 

 but that of the wood-frog never extends over a second. The croaking 

 begins the latter part of March and may reach to April 15. The 

 records for several years show an average date of April 9, the mode 

 April 6. The latest dates for several years are: April 16, 1900; April 

 13, 1901; April 14, 1909; April 13, 1911. 



When croaking, they are at the surface or in shallow water, where the 

 air-temperatures may play an influencing role. A consideration of 16 

 records of the species at croaking periods shows a range of maximum air- 

 temperatures from 52 to 80 degrees, averaging 62 degrees. In 1910 

 and 1911 surface-temperatures of the water were taken whenever the 

 species was heard; the range was from 47 to 60 degrees, with an average 

 of 53 degrees. Between the lowest air-temperature (52 degrees) and 

 the lowest water-surface temperature we have only 5 degrees, and no 

 doubt the two are the respective limiting temperatures for this shy 

 species. At all seasons, except the breeding time, the wood-frog is 

 silent and retiring. In water at the spring congress they are difficult 

 of approach. At ordinary approach the best one can hope for is only a 

 series of surface ripples. We have observed several concourses at noon- 

 day with opera-glasses. Such assemblies may not last more than a 

 day or so each year and careful watching is necessary to secure the 

 opportunity. Usually, by approaching flat on ground, using elbows to 

 move along, and stopping from time to time to look with bird-glasses, 

 one can reach the very edge of the pond where the croakers are. Any- 

 where from 50 to 200 males have thus been observed floating at the 

 surface. The scene resembles a small toad assembly in which there is 

 the same scrabbling and zeal of mating. They disappear simultane- 

 ously, on seeing anyone and, going through the pond a minute later, one 

 would wonder where the 200 males could be, to say nothing of the 

 females. 



