662 ANIMAL LIFE IN THE YOSEMITE 



toes and by the presence of a streak of dark color Avhich extends along the 

 side of its head, at the level of the eye, from the tip of the nose to behind 

 the ear membrane. These features are evident at all ages, from the smallest 

 individuals recently transformed from tadpoles to the largest adults. 



Many amphibians use their voices almost exclusively during the spawn- 

 ing season, but the Pacific Tree-toad is likely to be heard at any time of 

 year, being silent, if at all, only during the dry hot days of late summer. 

 Thus, in Yosemite Valley, the notes have been heard by us in February, 

 May, June, October, and December; at Snelling in January and Maj'^; at 

 Chinquapin in May and June ; about Tuolumne Meadows in July ; at Vogel- 

 sang Lake on August 30 ; and at McGee Lake and Ten Lakes in October. 

 During the fall months the single note is usually the only one heard, while 

 from January to June the two-syllabled song note, as well as the call, is 

 given commonly. 



The call-note consists of a single prolonged guttural syllable, kr-r-r-r- 

 ech, which it requires a second or two to pronounce. This note is uttered 

 at irregular intervals, by isolated individuals when in their retreats and 

 by members of a group in a pond or marsh when their song chorus has 

 been interrupted. 



The 'song' note is a two-syllabled kreck-ek given in faster time than 

 the call and repeated at short intervals. There is slightly less emphasis on 

 the second note, which drops in pitch and ends abruptly. When a number 

 of Hylas are in a marsh or pool together, their notes tend to be given in 

 unison, so that there is a continued series of notes, every alternate note 

 being slightly stressed. Such a chorus may continue for a long period, 

 but more often it is interrupted, ceasing rather abruptly and then begin- 

 ning again after a period of quiet. If a person walks out into a meadow 

 where tree-toads are chorusing, the voices soon cease. One or more call 

 notes with an interrogative inflection are given, and then there is silence. 

 If the observer stands absolutely still, the animals will shortly resume their 

 singing. The chorus begins as it ended, with a few call notes; then one 

 individual commences his song, to be quickly followed by another, and in 

 five seconds or so the place resounds with the chorus once more. 



The tree-toad is quite the strongest voiced of any of our amphibians, 

 though it is the smallest in point of body size among the tail-less forms. 

 Only the males sing, although females may give the low call note. The 

 males when held in the hand are seen to possess loose folds of black skin 

 on the throat. When the animal is singing, this skin is inflated to form 

 a pouch which swells out beyond the chin and is kept continuously inflated 

 while the notes are being given. The pouch evidently acts as a resonator 

 and helps to give volume to the sound. 



