!92o J Grinnell, Sequestration Notes. 85 



A seemingly adequate method of deciding upon the meaning 

 of bird voices is to note as accurately as possible (1) the exact nature 

 of the sounds produced in all particulars, and at the same time (2) 

 the behavior of the bird when uttering each kind of note, and (3) 

 the conditions obtaining with respect to all extraneous factors such 

 as relate to activities of other individual birds in the vicinity, other 

 animals, cover, and foi'age. The degree of reliance upon the infer- 

 ences from such observations will increase with the number of 

 times these observations are repeated. The final and satisfac- 

 tory explanation will not be forthcoming at once, though it is 

 well to hold whatever meaning presents itself even from the outset 

 as a tentative hypothesis. 



Some years ago the attention of the present writer became 

 directed to the behavior and notes of certain non-flocking passer- 

 ine birds as exhibited during the winter season. Dearth of other 

 ornithological features of interest at that season was probably the 

 circumstance which favored the development of the following ideas. 

 The particular class of notes here to be considered are those of the 

 category commonly called "location" or simply "call" notes, and 

 are uttered at irregular intervals by certain birds when foraging 

 singly under normal conditions. 



To be more explicit, the birds in the writer's experience especially 

 concerned are the Ruby-crowned Kinglet (Regidus calendula) and 

 Audubon's Warbler (Dcndroica auduboni). The common winter 

 call-note of the former is the familiar rachety, tone-less noise, of 

 three or more sections or syllables. The usual call-note of the 

 latter is the rather sharp single syllable, tsip. The notable thing 

 with both species is that their notes are uttered at rather frequent 

 intervals, though irregular ones, by each individual as it forages 

 alone. There are often to be heard in the distance, many trees 

 away perhaps, other individuals of the same species; but a point 

 of importance here is the essentially non-flocking habit in both the 

 species under consideration. 



I am aware that Ruby-crowned Kinglets do occasionally assemble 

 to a limited extent in winter; for example when "mobbing" an owl. 

 Or, late in the afternoon, as many as five or six individuals may be 

 found in the same tree on a sunny upper hill-slope, especially if the 

 trees be scattering. Also, Audubon's Warblers sometimes collect 



