Song types and their structural features are associated with specific contexts in the banded wren

Abstract

We studied the use of song types and their acoustic features in different social contexts in the banded wren (Thryothorus pleurostictus), a resident tropical songbird in which males possess about 20 distinctive song types varying in duration, bandwidth, note composition, and trill structure. We recorded six focal males intensively for four days each while we observed context information such as during versus after dawn chorus, presence of the female, counter-versus solo-singing, location at the edge versus centre of the territory, and proximity to the nest. All males used at least some song types differentially during each of these pairs of alternative contexts. Males also preferentially used the song types they shared with a given neighbour when interacting with that bird. Songs delivered during dawn chorus were significantly longer, wider in bandwidth, often compound (double songs), and more likely to contain a rattle or buzz and an up-sweeping trill, compared to songs delivered after dawn chorus. Similar features were also more commonly observed when birds were engaged in intense male-male interactions and boundary disputes after dawn chorus, especially when countersinging at the edge of the territory. The presence of the female caused the male to deliver song types with narrower whole-song and trill bandwidth and fewer rattles and buzzes, and song-type diversity and fraction of compound songs were higher when the female was present. Thus, in addition to using type matching and variations in song-type switching and diversity to signal different levels of aggressive intention, male banded wrens also select song types based on their acoustic structure in different social contexts.

Figure 1

Maps of study areas showing first and last days’ territory boundaries and sequential nest site locations for the six focal males in the Santa Rosa population (a) and the Cerco de Piedra population (b). The solid black outlines shows the initial territory area determined from focal bird activity on the first day of observation, and black dots show nest locations in the same period. The dashed outlines and white dots show the territory boundaries and nest locations toward the end of the season. The approximate locations of neighbour territories are shown in grey ovals. The four nest sites for Male O’s neighbour Y are also shown in colors associated with male O’s boundary positions; male Y’s boundary nest caused the boundary shift between these two males. Arrows indicate the nests that caused boundary shifts and the direction of the shift. Male T1 occupied Male T’s territory on the first recording day. Each square is 50 m on a side. Trails are drawn with thin dashed lines, and streams, roads and buildings are also indicated.

Figure 2

Single-song repertoire of focal bird O, compound songs not shown. Spectrogram of each song type identified by number. Rattles can be seen in song types 1, 206, 209, and 220, buzzes in song types 193, 213, 214, and 234. Song types with up-sweeping trill notes include 103, 201, 202, 206, 213, 222, 223; down-sweeping trills include 6, 9, 21,193, 205, 214, 232, 234; hook-note trills include 118, 203, 210, 212, 217; flat trills include 1 and 209; types 130 and 220 have no trill.

Figure 3

Significant main effects of time of day on a) song duration, b) song bandwidth, c) fraction of songs with rattle or buzz, and d) fraction of compound songs. Bars show least-squares means and standard errors (corrected for bird ID and other effects in the model) for the period during dawn chorus (before 0600) and after dawn chorus (after 0600).

Figure 4

Main effects of each of the four contexts on the percentage of flat-, down-, hook- and up-note trills delivered. Bars show the mean ± SE of the percent of songs of each trill type for the six focal males. a) during versus after dawn chorus, b) countersinging versus solo singing, c) singing from the territory edge versus centre, and d) female present versus absent (after dawn chorus). Results of nominal logistic regression analysis of trill type presented in Table 5.

Figure 5

Interaction effects between singing state and location on territory (least-squares means ± SE) for a) song duration and b) song bandwidth. Star indicates significant post hoc contrast between least-squares means (P < 0.05).

Figure 6

Significant effects of female presence on acoustic parameters in different contexts (least squares means ± SE) for a) song bandwidth, b) fraction rattle or buzz songs, c) fraction compound songs, d) song-type diversity, and e) trill bandwidth (star shows significant pairwise effect).