Roles of syntax information in directing song development in white-crowned sparrows (Zonotrichia leucophrys)

Abstract

Syntactical cues play an important role in song learning in songbirds. White-crowned sparrows (Zonotrichia leucophrys), whose song typically consists of four to five different phrases, fail to construct normal songs if exposed to all phrase types presented singly (Plamondon, Goller, & Rose, 2008; Soha & Marler 2001b). The specific role of acquired syntax information in guiding ontogenetic trajectories of syntax, however, and the respective contributions of instructive and selective processes to syntax ontogeny remain unknown. We tutored white-crowned sparrows with syntax information ranging from acoustic isolation to full song. Manipulation of tutor syntax influenced developmental trajectories of syntax assembly, suggesting that instructive processes contribute to syntax ontogeny. Early in development, birds tutored with full song or phrase pairs preferentially produced phrase pairings matching tutor syntax. Birds tutored with single phrases showed decreased diversity of pairwise syntactical combinations immediately after tutoring compared with other tutor groups, further illustrating the role of instructive processes. Overproduction of song material was also observed, suggesting that selective forces play a role in syntax development as well. Finally, consistent with the notion that innate influences guide syntax ontogeny, birds from all groups exhibited many similarities in trajectories of syntax assembly.

Figure 1

Spectrogram of a white-crowned sparrow song used to generate tutor models. This particular dialect of white-crowned sparrow song consists of five phrases: a whistle (A), a trilled note complex (B), a high-pitched buzz (C), a lower-pitched buzz (D), and a second note complex (E).

Figure 2

Spectrograms of crystallized songs of birds raised in acoustic isolation. Isolate birds crystallized songs containing whistles, frequency modulated whistles (wc04, first phrase; wc16, first and third phrases; wc18, second, fourth, and fifth phrases), a note complex (wc05, final phrase), buzzes (wc04, final two phrases), and trills (wc11, and wc16, final phrase).

Figure 3

Spectrograms of vocalizations produced at various developmental time points by representative birds from four tutor groups. Spectrograms shown are from a bird tutored with full forward song (a), reverse pairs (b), single phrases (c), and an acoustically isolated bird (d). Numbers in brackets indicate the bird’s identification number, while numbers to the left of each spectrogram indicate days post-tutoring. In the case of wc05 (d), which was not tutored, numbers to the left of each spectrogram (and all indications of days post-tutoring for isolate birds in the following figures) represent days elapsed from September 15 of the year of capture (see Methods). For early time points, song renditions shown are not typical of a bird’s repertoire at that time (see Results), but were chosen to illustrate that each bird produced some renditions of what would eventually become its crystallized song very early in development.

Figure 4

Proportion of groupings of 1 to 5 phrases (mean ± 95% CI) versus days post-tutoring. Relative proportions of phrase bout sizes are shown for birds tutored with full song (a, c), phrase pairs (b, d), single phrases (e), and isolate birds (f). Phrases were considered to be grouped if less than 250 ms transpired between the end of one phrase and the beginning of the subsequent phrase. Purple lines indicate phases in which production of phrase pairs predominate.

Figure 5

Pairwise phrase syntax diversity (mean ± 95% CI) for birds tutored with full song (black), phrase pairs (hatched), and single phrases (striped) in the first 10 days post-tutoring.

Figure 6

Relative production of phrase types (A, B, C, D, and E; mean ± 95% CI) versus days post-tutoring. Birds tutored with single phrases did not produce C and E phrases during the first 10 days after tutoring and for the majority of development (c), while birds tutored with full song sang all five phrase types throughout development (a). Birds tutored with phrase pairs also sang all phrase types, with the exception of the ‘E’ phrase early in development (b).

Figure 7

Emergence of phrase pairings of A and B phrase types. Proportion of tutor or crystallized order (dark blue lines), nontutor or noncrystallized order (red lines) and reversed order (light blue lines) phrase pairings of A and B phrase types (mean ± 95% CI) over developmental time for birds tutored with forward syntax (full song and phrase pairs; a-b), reverse syntax (full song and phrase pairs; c-d), single phrases (e) and isolate birds (f).

Figure 8

Emergence of phrase pairings of D and E phrase types. Proportion of tutor order (dark blue lines), nontutor order (red lines) and reversed tutor order (light blue lines) phrase pairings of D and E type phrases (mean ± 95% CI) over developmental time for birds tutored with full forward syntax (a), and reverse syntax (full song and phrase pairs; b-c). Birds tutored with forward-order phrase pairs did not crystallize E type phrases and therefore are not shown.

Figure 9

Emergence of phrase pairings of B and C phrase types. Proportion of tutor order (dark blue lines), nontutor order (red lines) and reversed tutor order (light blue lines) phrase pairings of B and C type phrases (mean ± 95% CI) over developmental time for birds tutored with forward syntax (full song and phrase pairs; a-b), and reverse full song (c). Birds tutored with reversed-order phrase pairs did not crystallize CB phrase pairings and therefore are not shown.

Figure 10

Emergence of phrase pairings of C and D phrase types. Proportion of tutor order (dark blue lines), nontutor order (red lines) and reversed tutor order (light blue lines) phrase pairings of C and D type phrases (mean ± 95% CI) over developmental time for birds tutored with forward syntax (full song and phrase pairs; a-b), and reverse full song (c). Birds tutored with reversed-order phrase pairs did not crystallize DC phrase pairings and therefore are not shown.

Figure 11

Temporal coupling of A and B phrase types. Temporal coupling was measured over development for birds tutored with forward syntax (full song and pairs; a-b), reverse syntax (full song and phrase pairs; c-d), single phrases (e) and isolate birds (f).