Territorial reactions of male Yellowhammers (Emberiza citrinella) toward a specific song structure

Male songbirds assess their rivals by listening to their songs and, in some species, are especially sensitive to certain parts of the song. Yellowhammers (Emberiza citrinella) sing songs with different structures consisting of an initial phrase of stereotyped and repeated notes in a trill, and a terminal phrase, present or not, which consists of low or high frequency whistles that we called elements. We analyzed 1,055 songs from 25 different males and found that four different structures could be distinguished in a French Yellowhammer population. We found that the frequency ranges of the elements were more constant across individuals than the ranges of the notes, and among them, the low frequency element was nearly twice as conserved as the high frequency element. Then, in the wild, we tested the territorial responses of males to the four different structures and found that the full song structure, which is composed of the initial phrase followed by a high frequency element and a low frequency element, induced stronger territory defence responses from the males than any of the other structures. As only the structure containing the initial phrase and the low frequency element also induced a strong response, we propose that the main element responsible for the enhanced reaction of the males is the low frequency element, which is consistent with the fact that it is more conserved than the other constituents.