The primary song identifies the singer as a male Bell Vireo. It aids in securing a mate and in warning potential adversaries; also, the song is a signal in certain situations and serves to locate the male. TABLE 1. REPRESENTATIVE SINGING RATES OF BREEDING BELL VIREOS. ALL RATES WERE AT AIR TEMPERATURES LESS THAN 86° F. EACH INSTANCE REPRESENTS APPROXIMATELY 30 MINUTES OF OBSERVATION. ==================================================================== | | Average Circumstance | Instances | rate per | | minute ----------------------------------------------+-----------+--------- Attraction of mate | 2 | 6.3 Territorial dispute | 5 | 12.8 Nestbuilding | 6 | 7.0 Egglaying | 1 | 3.0 Incubation | 6 | 3.9 Exchange of partners in the incubation period | 1 | 4.0[A] Foraging | 2 | 2.2 "Morning" song | 1 | 28.6[A] "Evening" song | 1 | 1.9[A] ----------------------------------------------+-----------+--------- Over-all average rate per minute 6.3 [A] Not sustained; data representative of periods less than 5 minutes in length. 2. Courtship song. It is here termed the "congested" song and is comparable to the adult "run-on" song mentioned by Nolan (1960:240). The congested song is a squeaky version of the primary song and is given when birds are engaged in pair-formation, nestbuilding, and egglaying. The delivery is rapid and the sound can be likened to that made by rapidly scraping a bow across a taut violin string. Nolan (_in_ Mumford, 1952:230) is probably speaking of this song when he describes a "tuneless" song that "had a jerky, sputtering quality that characterizes part of the song of the Ruby-crowned Kinglet (_Regulus calendula_)." More recently (1960:240) he applies the adjectives "twanging," "Bobolink-like," "bubbling," "jerky," and "squeaky." This song is often blended with the primary song and is audible for 75 feet. A specialized version of the congested song is associated with pre-and post-copulatory display but differs from the typical squeaky performance in terminating in two ascending notes reminiscent of the ascending phrase of the primary song.