Social information trumps vegetation structure in breeding-site selection by a migrant songbird

Abstract

To maximize fitness, organisms must assess and select suitable habitat. Early research studying birds suggested that organisms consider primarily vegetation structural cues in their habitat choices. We show that experimental exposure to singing in the post-breeding period provides a social cue that is used for habitat selection the following year by a migrant songbird, the black-throated blue warbler (Dendroica caerulescens). Our experimental social cues coerced individuals to adopt territories in areas of very poor habitat quality where individuals typically do not occur. This indicates that social information can override typical associations with vegetation structure. We demonstrate that a strong settlement response was elicited because post-breeding song at a site is highly correlated with reproductive success. These results constitute a previously undocumented, but highly parsimonious mechanism for the inadvertent transfer of reproductive (public) information from successful breeders to dispersers. We hypothesize that post-breeding song is a pervasive and reliable cue for species that communicate vocally, inhabit temporally autocorrelated environments, produce young asynchronously and/or abandon territories after reproductive failure.

Figure 1

Relation between treatment (‘C’: control, ‘PI’: public information, ‘LC’: location cues) and (a) the proportion of sites where prospecting black-throated blue warblers were detected in the post-breeding season of the treatment year, (b) the proportion of sites settled by males in the following spring and (c) the proportion of sites settled by females in the following spring. Error bars represent±1 s.e. Lower case letters represent results of multiple comparisons tests. Values below error bars indicate number of sites occupied. n=18 for each treatment.

Figure 2

Proportion of sites occupied by black-throated blue warbler males as a function of time during the settlement period (date in May) and treatment (triangles, location cues; open circles, PI; filled circles, controls). Values below data points indicate the number of sites occupied. n=18 for each treatment.

Figure 3

Relation between shrub abundance (L, low (0–5% cover); M, medium (greater than 5–80% cover; H, high (greater than 80% cover)) and the proportion of sites settled by black-throated blue warblers in the following spring (triangles, location cues; open circles, PI; filled circles, controls). Error bars show s.e. Values adjacent to error bars indicate sample size in each category.

Figure 4

Singing frequency of male black-throated blue warblers as a function of time during the post-breeding season (19–31 July). Circles are fitted values (±95% CI) of the GLMM: song frequency=treatment (fledged (open circles) versus failed (filled circles))×time.