S. Nowicki et al., THE TERRITORY DEFENSE FUNCTION OF SONG IN SONG SPARROWS - A TEST WITHTHE SPEAKER OCCUPATION DESIGN, Behaviour, 135, 1998, pp. 615-628
Territory defense is considered one of the primary functions of bird s
ong. but this hypothesis has been directly tested in only a few cases.
We used the speaker replacement method to ask whether song functions
as a 'keep out' signal in song sparrows, a species for which there is
considerable evidence supporting a mate attraction and stimulation fun
ction of song, but only indirect evidence that song functions as a sig
nal to other males. We removed 11 matched pairs of male song sparrows
from their territories, replacing one male of each matched pair with l
oudspeakers broadcasting that male's song (the 'experimental' territor
y) while leaving the other male's territory silent (the 'control' terr
itory). III all cases in which encroachments or takeovers occurred, th
ese occurred first (or solely) on the control territory of a matched p
air, supporting the hypothesis that song functions in territory defens
e in this species. The incidence of intrusions on control territories
was very low, however, posing difficulties for the interpretation of s
peaker replacement experiments designed to ask more specific questions
about how song functions in male-male aggressive competition.