The Auk 122(2):593–607, 2005 © The American Ornithologists’ Union, 2005. Printed in USA.
SONG STRUCTURE AND MICROGEOGRAPHIC SONG VARIATION IN WEDGE-TAILED SABREWINGS (CAMPYLOPTERUS CURVIPENNIS) IN VERACRUZ, MEXICO C G J F O 1 Departamento de Biología Evolutiva, Instituto de Ecología, A.C., Km 2.5 Carretera Antigua a Coatepec No. 351, Congregación El Haya, Apdo. Postal 63, Xalapa, Veracruz 91070, México
A .—We studied the songs of Wedge-tailed Sabrewings (Campylopterus curvipennis) in six localities from central Veracruz, Mexico, to document structure and variation within and between singing groups in the same geographic region. Wedgetailed Sabrewing songs were acoustically, structurally, and behaviorally complex, rivaling those of other taxa with complex signals. Songs of individual birds were composed of >45 well-differentiated and structurally complex syllables. We found 239 different syllable types across eight recorded singing groups of Wedge-tailed Sabrewings (∼20 syllable types per singing group), with the greatest versatility recorded in hummingbirds to date. The acoustic variation (15 variables) was summarized in three principal components (58% of acoustic variation), in which intragroup variability accounted for most of the observed variation. We found significant differences between and within groups in terms of syllable sharing (Jaccard’s similarity coefficient). Individuals generally shared >50% of syllable types within groups, whereas syllable sharing was 45 sílabas complejas y bien diferenciadas. Encontramos 239 tipos de sílabas diferentes a través de ocho grupos grabados de C. curvipennis (~20 tipos de sílabas en cada grupo), con la mayor versatilidad registrada a la fecha para colibríes. La variación acústica (15 variables) fue resumida en tres componentes principales (58% de la variación), en donde la mayor parte de la variación observada se atribuye a variación intragrupo.
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Address correspondence to this author. E-mail:
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Encontramos diferencias significativas dentro y entre grupos en los tipos de sílaba compartidos (coeficiente de similitud de Jaccard). Los individuos generalmente compartieron >50% de tipos de sílaba dentro de cada grupo, pero 7 kHz), composed of >45 well-differentiated (depending on the singing group), structurally complex syllables sung at a high rate (5 syllables per second) (Table 1). We found 239 different syllable types across the eight singing groups (Fig. 4) and commonly >20 syllable types per individual (Table 1). Acoustic structure of syllables was very complex and variable. Syllables lasted 1.5), which accounted for about one-half (57.7%) the variation recorded in Wedge-tailed Sabrewing songs (Table 2).
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F. 4. Spectrograms (first 2.5 s) of individuals from each singing group, showing the great variation and structural complexity of syllable types, and some of their respective alphabetical codes. Syllables can be separated into one or several notes with diverse structure (including trills, short bursts, harmonics), with rapid or slow frequency modulations, and lacking pure tones. (Continued on next page.) Principal component 1 (29% of the variance) exhibited positive loadings for total song duration, number of syllables, number of different syllables, and number of transitions from one syllable type to another. Principal component 2 (18.5% of the variance) was mainly explained by duration and number of notes of the introductory syllable. Principal component 3 (10.2% of the variance) represented a pitch element explained by maximum and minimum frequencies (Table 2). Although factor scores differed significantly among groups for PC 3 (KruskalWallis ANOVA; PC 1: χ2 = 3.14, df = 7, P = 0.87; PC 2: χ2 = 10.87, df = 7, P = 0.14; PC 3: χ2 = 18.77,
df = 7, P = 0.008), the lack of group discrimination in the PC 1 versus PC 2 scaerplot indicates that intragroup variability accounted for much of the observed acoustic variation (Fig. 6). Jaccard’s similarity coefficient averaged 0.12 ± 0.04 (mean ± SD) between-group comparisons (n = 446) and 0.45 ± 0.19 within-group comparisons (n = 50). The UPGMA analysis clearly clustered 32 individuals into seven groups based on syllable sharing (Fig. 7). Clustering at a higher level was less apparent in the analysis. One individual of the CLA2 singing group was separated from the cluster, and individuals of MAC1 and MAC2 (which may have included some of the
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F. 4. (Continued.) Spectrograms (first 2.5 s) of individuals from each singing group. same individuals) were found intermixed in one cluster. We found common syllables present in the song of all singing groups. The “I” syllable was the most frequently emied (8× per song on average, range = 1–24). The “C”, “D”, “P”, “I(a)”, and “I(e)” syllables were also present in the songs of every group, but not as commonly emied. The “I(a)” and “I(e)” syllables, along with other syllables, seem variants of the “I” syllable, and their presence varied among groups (Fig. 8). No significant correlation was found between song similarity and geographic distances between sites (Mantel test: r = 0.215, P = 0.12). D Song complexity and contextual use.—Wedgetailed Sabrewing songs are structurally,
acoustically, and behaviorally complex, rivaling those of passerine birds in the complexity of their signal. In contrast to the songs of other hummingbird species that produce complex acoustic signals (e.g. Blue-throated and Amethyst-throated hummingbirds; Ficken et al. 2000, Ornelas et al. 2002), Wedge-tailed Sabrewing songs are loud and long, composed of very discrete units (syllables), with a highly variable and elaborate acoustic structure. We observed Wedge-tailed Sabrewings in two ecological contexts during our study. First, several individuals were observed aggregated in areas containing flower patches, singing for long periods between foraging bouts. We believe that the observed territorial chases may be associated with defense of floral resources, of territorial singing perches, or of both. Second,
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F. 5. Complete repertoire of introductory syllables recorded from each singing group. Note that two introductory syllables were recorded from two of the groups (ORDU and MAC1). In all groups, the first note of the introductory syllable is different from the rest of the notes, and the total number of notes is variable. individuals aggregated in areas of dense vegetation, formed by small adjacent territories. Territories were defended by one individual (presumably a male) that emied the full song in flight when an intruder initially arrived and aer it arrived on the territory. Although we observed no aempted copulations, this singing behavior appears to have an intersexual display function. Because the territories did not contain any resources required by females (except per-
haps males), and because they were close to each other (∼7 m), allowing acoustic contact between neighboring territory-owners, we believe that the males’ singing and territorial behavior can be characterized as a typical lek (Payne 1984), in which the function of vocalizations remains to be investigated. The existence of elaborate acoustic signals in Wedge-tailed Sabrewings is intriguing, because most lekking species studied in detail have simple, persistent, loud
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T 2. Principal component analysis of the correlation matrix among 15 acoustic variables in eight singing groups of Wedge-tailed Sabrewings in Veracruz, Mexico. Correlation loadings above 0.50 are in boldface. Variables Total song duration Number of syllables Number of syllable types Syllable transitions Maximum frequency Minimum frequency Duration of introductory syllable Duration of first note (introductory syllable) Different notes (introductory syllable) Note types (introductory syllable) Maximum frequency (introductory syllable) Minimum frequency (introductory syllable) Duration of syllable “I” Maximum frequency (syllable “I”) Minimum frequency (syllable “I”) Variance (%)
PC 1
PC 2
PC 3
0.94 0.98 0.92 0.98 –0.14 –0.43 –0.13 0.11 0.16 –0.32 –0.18 0.02 0.07 0.12 –0.13 29
0.07 0.00 0.07 0.00 –0.00 0.23 0.82 0.81 0.89 –0.16 0.05 –0.72 0.13 0.08 0.06 18
0.02 0.00 –0.03 –0.00 –0.82 –0.01 0.13 0.04 0.01 –0.14 0.04 0.10 0.19 0.12 0.86 10
F. 6. Bivariate plot of factor scores produced by a principal component analysis of 15 acoustic variables of Wedge-tailed Sabrewing song. songs, oen audible over long distances (>100 m) (Wiley 1971, Snow 1977, Stiles and Wolf 1979, Atwood et al. 1991, Gaunt et al. 1994). Wedge-tailed Sabrewing songs have the highest versatility among hummingbirds recorded
to date (Ornelas et al. 2002; Table 1). Songs of other species in assemblies or leks consist of a single phrase, repeated without change for long periods (Stiles and Wolf 1979). We believe that the observed variability may serve not only for
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F. 7. Average Euclidean distance between clusters. Dendrogram based on 32 individual songs distinguished seven principal clusters corresponding to eight singing groups recorded. Note that MAC1 and MAC2 are in the same cluster, so they probably belong to the same singing group. The UPGMA cluster analysis revealed clear patterns of vocal similarity within groups based on shared syllable types. Note also that ORDU is clustering outside of all the other groups, except for one bird from CLA2, probably because of differences in the contextual use of vocalizations; however, a better representation of the flight context is necessary for comparisons.
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individual or group recognition, but to establish more complicated communication networks that are not immediately apparent to human observers. Microgeographic song variation.—The acoustic characteristics (15 variables) of full songs of individuals from six localities did not differ significantly among singing groups. Songs from the same locality did not cluster together in a scaerplot of the first and second components from the PCA analysis. However, the singing groups differed markedly in general song structure and structure of the introductory syllable. Also, syllable-sharing between singing groups was significantly lower than syllable-sharing within groups (UPGMA cluster analysis). That indicates that the songs of individuals, presumably males, vary considerably, and that birds from the same singing group tend to have similar songs. We found syllables that occurred in each singing group, and the “I(a)” and “I(e)” syllables, along with others, seem variants of the “I” syllable. The variation among those syllabic elements as well as the observed variability in the structure and complexity of vocalizations within or across birds of Wedge-tailed Sabrewing singing groups can be considered evidence of song learning. Local dialects arise when shared songs differ between neighboring groups (Marler and Tamura 1962, Harbison et al. 1999), but their functional significance remains widely debated (Catchpole and Slater 1995 and references therein). In central Veracruz, singing groups gradually disintegrated as floral resources were diminished, and groups recorded in different years in Clavijero and Macuiltépetl shared few syllables across years and, therefore, were probably composed of different individuals. Lile information exists on how hummingbirds disperse, alone or in groups, or how they track floral resources through space and over time (Hobson et al. 2003). It is impossible to know whether individuals retain the same songs from year to year; however, it is likely that different groups of individuals, with different songs, assemble in the same places each year, or that the same individuals develop different songs in each group they join, or both. That songs recorded at the same location were different over two different seasons suggests that this species does not exhibit geographically distinct dialects that are consistent across time. In polygynous Yellow-rumped Caciques
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F. 8. Variants of the “I” syllable in the songs of Wedge-tailed Sabrewing singing groups that suggest song learning.
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(Cacicus cela), males in any nesting colony learn many vocalizations from each other and can change them from year to year (Trainer 1988, 1989). At the same time, groups can have “signature” notes, shared by all members of a group in any one year, like the introductory syllables of the Wedge-tailed Sabrewings. Also, we did not find any relationship between song similarity and geographic distance among song groups, and the clustering of song types (assessed by UPGMA cluster analysis) did not reflect geographic distances among sites. Therefore, the existence of song dialects with consistency across time and well-established boundaries among singing groups in Wedge-tailed Sabrewings cannot be claimed until more data become available (greater geographic scale). Nevertheless, the interplay among this species’ social system, distribution of its floral resources, and microgeographic and temporal variation of its songs are subjects for future research. A Comments by M. S. Ficken, A. Guillén, M. E. Mermoz, D. A. Nelson, S. G. Sealy, K. G. Smith, and three anonymous reviewers greatly improved a previous version of this paper. We gratefully acknowledge L. Jiménez, A. Castillo, A. L. Castillo, M. Ordano, and C. Lara for field assistance, and A. Espinosa de los Monteros, A. Hernández, D. Hernández, and C. Pye for assistance in preliminary stages of our study. Thanks to C. Rojas Nieto for helpful and enlightening discussion. This work was supported with research grants from the Consejo Nacional de Ciencia y Tecnología, México (CONACyT) (Ref. 25922-N) and Comisión para el Conocimiento y Uso de la Biodiversidad (CONABIO) (Ref. H028) to J.F.O., and the Instituto de Ecología, AC (Ref. 902-11-563). L C A , J. L., V. L. F , J. E. B . 1991. Temporal paerns of singing activity at leks of the White-bellied Emerald. Wilson Bulletin 103:373–386. B, L. F., K. L. S . 1990. Song learning in the Anna Hummingbird (Calypte anna). Ethology 84:15–26. C , P., P. L . 2001. The R PACKAGE for Multivariate and Spatial
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Associate Editor: D. A. Nelson
