Experimental Evidence That Distinct Song Phrases in the Grey-Cheeked Fulvetta Alcippe Morrisonia Permit Species and Local Dialect Recognition
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Ibis (2013), 155,32–41 Experimental evidence that distinct song phrases in the Grey-cheeked Fulvetta Alcippe morrisonia permit species and local dialect recognition BAO-SEN SHIEH,1* SHIH-HSIUNG LIANG,2 HSIAO-WEI YUAN3 & CHAO-CHIEH CHEN1 1Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, 100 Shihchuan 1st Road, Kaohsiung, 807, Taiwan 2Department of Biotechnology, National Kaohsiung Normal University, 62 Sanchung Road, Yanchao Township, Kaohsiung, 824, Taiwan 3School of Forestry and Resource Conservation, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106, Taiwan Birds with small song repertoires have a limited number of song types which may serve multiple functions. The Grey-cheeked Fulvetta Alcippe morrisonia is a non-migratory spe- cies of lowland forests in Taiwan. Its song consists of two distinct phrases: a whistled phrase and a harmonic one. Each individual usually sings only one type of whistled phrase, and the geographical patterns of songs can be distinguished by the motif of this phrase. We proposed a dual adaptation hypothesis for the functions of these two phrases. Playback experiments including six sound stimuli (familiar whistled phrases, familiar har- monic phrases familiar complete songs, foreign whistled phrases, foreign harmonic phrases and foreign complete songs) were conducted at 12 sites in the Shoushan Nature Park of Kaohsiung, Taiwan. Grey-cheeked Fulvettas came closer to the playback speaker and increased counter-singing more in response to the familiar whistled phrase (local dialect) than to a foreign whistled phrase (distant dialect). However, birds responded equally to the playback of harmonic stimuli from familiar and foreign sources. We suggest that in this species, whistled phrases are used for local recognition and harmonic phrases are used for species recognition in short-range communication. Keywords: communication, experiment, repertoire, Taiwan. Adaptation to function and environmental context 1988). Songs are also used for territory defence have been identified as the primary drivers of the and mate attraction, and both of these functions evolution of bird song acoustics (Kroodsma & may require the recognition of individuals and Miller 1982, Boncoraglio & Saino 2007). One local populations (Catchpole & Slater 1995). The important function of song is to enable birds to simultaneous need for both species specificity and recognize individuals of their own species (Catch- individual variability places potentially conflicting pole & Slater 1995). Features such as syntax, ele- demands on the evolution of bird songs (Marler ment structure and frequency, which vary little 1960). and are relatively constant among individuals of For species with medium to large song reper- the same species, have been shown to be the most toires (i.e. 6–200 song types) (Stoddard et al. important cues for species recognition in several 1991), different song types may be used to meet bird species (Becker 1982). For example, fre- the respective needs of species specificity and indi- quency changes are important in species recogni- vidual variability. Geographically widely distrib- tion among Field Sparrows Spizella pusilla (Nelson uted song types are typically those that function in species recognition (Becker 1982). For birds with *Corresponding author. small repertoires (i.e. only one or two song types), Email: [email protected] songs with different functions involve different © 2012 British Ornithologists’ Union Grey-cheeked Fulvetta song recognition 33 patterning and organization instead of distinct song proposed that tonal, frequency-modulated signals types. For example, the Chestnut-sided Warbler are optimal for long-range communication, and Dendroica pensylvanica has two song patterns: that wide-spectrum sounds with sharp amplitude accented, which contains a distinctive ending, and modulation and limited frequency modulation are unaccented, which does not (Kroodsma et al. optimal for short-range communication. 1989). The unaccented song is used primarily in The Grey-cheeked Fulvetta Alcippe morrisonia territorial defence, and the accented song is used morrisonia is a non-migratory subspecies endemic for mate attraction. to Taiwan (Collar & Robson 2007). It is found Local dialect recognition is known to play a key commonly in lowland forests (Chou et al. 1998) role in prezygotic reproductive isolation (Baker and forages in mixed-species flocks (Chen & Hsieh 1982, Danner et al. 2011). Variability in songs is 2002). The Grey-cheeked Fulvetta is monogamous required for local dialect recognition. For songbirds and sexually monomorphic, and both sexes partici- with a small repertoire, a local dialect can be rec- pate in parental care (Lin 1996, Kuo 2000). A ognized in various parts of a song (e.g. in the typical song comprises two distinct phrases: the terminal trill of the song in the Puget Sound whistled phrase and the harmonic phrase. The White-crowned Sparrow Zonotrichia leucophrys spectrogram structure of the whistled phrase is pugetensis) (Nelson & Poesel 2007) or in acoustic tonal and whistle-like, whereas the harmonic cues with different degrees of individual variation phrase has a broad frequency range with many in the song (Skierczyński & Osiejuk 2010). harmonics (Fig. 1). All the songs of this species In addition to its function, environmental fea- contain the whistled phrase, but not all of them tures such as habitat structure affect signal trans- include the harmonic phrase. Grey-cheeked Fulv- mission and thus have profound effects on the ettas usually perform a single song type based on evolution of acoustic structures in bird songs the whistled phrase (Shieh 2004), and this species (Morton 1975). Birds use songs not only for long- is therefore considered a small-repertoire species. range communication but also for short-range We propose a dual adaptation hypothesis to communication; thus, short-range songs are explain the evolution of two distinct phrases in expected to differ acoustically from long-range the songs of the Grey-cheeked Fulvetta as a result songs (Titus 1998). Wiley and Richards (1982) of adaptation to function and environment. From FT1 FT2 FT3 FT4 kHz kHz kHz kHz WH 10 10 W H 10 W H 10 WH 5 5 5 5 0.5 1.0 1.5 2.0 s 0.5 1.0 1.5 2.0 2.5 s 0.5 1.0 1.5 2.0 2.5 s 0.5 1.0 1.5 2.0 2.5 s FT5 FT6 FT7 FT8 kHz kHz kHz kHz 10 WH 10 WH10 WH 10 WH 5 5 5 5 0.5 1.0 1.5 2.0 s 0.5 1.0 1.5 2.0 2.5 s 0.5 1.0 1.5 2.0 s 0.5 1.0 1.5 2.0 2.5 3.0 s FT9 FT10 FT11 FT12 OT kHz kHz kHz kHz kHz 10 WH10 WH10 WH 10 WH 10 WH 5 5 5 5 5 0.5 1.0 1.5 2.0 s 0.5 1.0 1.5 2.0 s 0.5 1.0 1.5 2.0 s 0.5 1.0 1.5 s 0.5 1.0 1.5 2.0 2.5 s Figure 1. Sources of sound stimuli used for the playback experiments: FT1–12 were collected from 12 different sites in the study park; OT was collected from an area with a foreign dialect in Shanping. The whistled phrase is labelled with ‘W’ and the harmonic phrase with ‘H’ on the spectrogram. FT4, FT5 and FT6 have identical syllable combinations in the whistled phrase. © 2012 British Ornithologists’ Union 34 B.-S. Shieh et al. the functional adaptation perspective, we predict and harmonic phrases from 12 different sites (all at that the whistled phrase is used for local recogni- least 50 m apart) in the study park and used one of tion, due to its consistency within individuals and the most common song types from Shanping its geographical variability (Shieh 2004), and the (recorded in 2004) as the source of our ‘foreign’ harmonic phrase is used for species recognition, sound stimuli. Because the Grey-cheeked Fulvetta due to its consistency across populations in differ- defends no obvious territorial boundaries and ent locations (B.-S. Shieh, pers. obs.). We there- because the nests of different pairs can be as close as fore predict stronger individual response to 5 m (Lin 1996), to ensure that the recordings from playback of the local whistled phrase than to the the 12 sites were from 12 different birds only one playback of whistled phrases from different dia- visible singing individual was recorded at each site, lects, but similar responses to harmonic phrases and it was followed until it flew out of recording irrespective of local or foreign sources. In addition, range. From each site, we selected only one high- according to Wiley and Richards’s (1982) proposi- quality recording of a source song with three sylla- tion for environmental adaptation, we predict that bles in the harmonic phrase. Recordings of the whistled phrases are used for long-range communi- source songs were digitized and filtered at 1 kHz cation because their tonal structure transmits effi- using Avisoft-SASLab Pro software (R. Specht, Ber- ciently across long distances, and harmonic phrases lin, Germany). The spectrographic cross-correlation are used for short-range communication due to (SPCC) coefficients were computed to investigate their wide spectrum structure. That is, from the the similarities between source songs using Avisoft- environmental adaptation perspective, the two CORRELATOR (sampling rate = 22050 Hz, distinctive phrases of this species’ song are used FFT = 512, frequency tolerance deviation = 0) for long-range and short-range communication, (Specht 2010). SPCC coefficients were calculated respectively. Therefore, we also predict that the as the two spectrograms shifted incrementally past Grey-cheeked Fulvetta will respond to short-range each other along the time axis and ranged from À1 signals (i.e. harmonic phrases) with short-range to +1. A value of +1 means that the two spectro- signals, and respond to long-range signals (i.e.