284 BULLETIN 19 7, UNITED STATES NATIONAL MUSEUM 



some apparent when we listen carefully to the bird, others appearing 

 only when the song is recorded and studied. 



"The yellow-throated vireo's song is slower than those of the other 

 vireos, the pauses between phrases being longer. The quality of the 

 sound is rather reedy and less clear than the others. The pitch is 

 lower. The number of different phrases is less, and the bird is in- 

 clined to repeat two to four of them in a regular order. The notes 

 of the phrases are usually slurred together, so that they sound like 

 eeyay^ ayo^ or ahweeo^ etc. 



"In the records I have of 52 different birds the pitch varies from 

 C ' ' ' 'toB ' '. Only one bird sang to C ' ' ' ', the majority hav- 

 ing A ' ' ' or G ' ' ' for the highest note. The rate of singing 

 varied from one phrase every four-fifths of a second to one every 2 

 seconds. Individuals possess five to nine different phrases, but fre- 

 quently sing only two or three of them for so long a time that patient 

 listening is required to get them all. The phrases are commonly of 

 two or three notes. In all my records there are just two phrases of 

 four notes, and none with more than that. Two-note phrases that slur 

 downward are much commoner than those that slur upward; that is, 

 ayoh is a commoner phrase than oway. In the same manner in 3-note 

 phrases, such a phrase as oweeaJi is commoner than eeoway. 



"The period of song is from arrival early in spring to early in 

 August. The song is revived again late in August or early in Sep- 

 tember. It is impossible to give definite dates of cessation, for though 

 each individual stops singing for a time, that time is so short, and 

 the difference in individuals so great, that there is no certain period 

 of complete silence for the species, and one cannot be sure, when birds 

 are heard in mid-August, whether it is the last of the regular period 

 or the beginning of the revival. The song is not heard in September 

 every year, but in 14 years in which I have definite dates, the average 

 is September 8, and the latest September 18, 1939. 



"The yellow-throated vireo has a soft musical call note running 

 down in pitch, and with a trilly sound. I have written it in my notes 

 as whree-whree-orrrr. An alarm note is a series of notes, also descend- 

 ing in pitch, chi-chi-cha-cha-chu-chu. Both of these notes bear a 

 strong resemblance to corresponding calls used by the blue-headed 

 vireo." 



Mr. Skutch writes to me from Costa Kica : "Like the blue-headed 

 vireo, the yellow-throat sings much in its winter home. It is in a song- 

 fid mood upon its arrival late in September or October ; and although 

 it may fall silent during the wet closing months of the year, from Jan- 

 uary until its departure in late March or April, it frequently delivers 

 its queer, halting song. Indeed, in many parts of its winter range, the 

 species is so rare that it would probably be overlooked but for its habit 



