Dominance and geographic information contained within black-capped chickadee (Poecile atricapillus) song

Abstract

In songbirds, male song is an acoustic signal used to attract mates and defend territories. Typically, song is an acoustically complex signal; however, the fee-bee song of the black-capped chickadee is relatively simple. Despite this relative simplicity, two previous studies (Christie et al., 2004b; Hoeschele et al., 2010) found acoustic features within the fee-bee song that contain information regarding an individual’s dominance rank; however each of these studies reported a different dominance-related acoustic cue. Specifically, the relative amplitude of the two notes differed between the songs of dominant and subordinate males from northern British Columbia, while the interval pitch ratio differed between the songs of dominant and subordinate males from eastern Ontario. In the current study, we examined six acoustic features within songs from both of the chickadee populations (northern British Columbia and eastern Ontario) examined in these previous studies and used bioacoustic analyses and discriminant function analyses to determine whether there is a consistent dominance-related acoustic cue across both, or in each of these populations. Consistent with the previous findings, the current results indicate that relative amplitude differs based on dominance status in the songs from British Columbia; however, our results failed to reach significance with songs from Ontario. These results suggest that acoustic cues that signal a male’s dominance in this species vary with geographic location. Furthermore, examining songs from these two locations and one additional location in northern British Columbia, we found that discriminant function analyses could correctly classify songs based on geographic location. Considering the broad extent of the species’ range, black-capped chickadee song is considered relatively invariant; however, our results suggest that there is geographic variation in songs, although the differences are subtle compared to geographic song variation in other species.

Black-capped chickadees categorize songs based on features that vary geographically

“…We changed the start frequency of the fee note to match the start frequency of the fee note that was being replaced in the song using the 'sliding time scale/pitch shift' effect in Audacity 1.3.12 (http://audacity.sourceforge.net). This manipulation resulted in songs with a mean ± SD internote interval frequency ratio of 1.13 ± 0.036 (range 1.07-1.186), which corresponds to the internote interval ratios found in a larger sample of songs (N = 360) from these two geographical locations (mean ± SD =1.13 ± 0.022; range1.047-1.206; Hahn et al, 2013a) and corresponds to the average internote interval ratio reported previously (i.e. 1.13; Weisman et al, 1990).…”

“…Although the black-capped chickadees' range extends across most of North America (Smith, 1991), little geographical variation has been described in this song (although, variation has been found in geographically isolated populations of chickadees, where some animals produce unusual songs; see Gammon & Baker, 2004;Kroodsma et al, 1999). Recently, Hahn et al (2013a) conducted a bioacoustic analysis on songs produced by birds from different geographical locations (northern British Columbia and eastern Ontario). For this bioacoustic analysis, six acoustic features were analysed, similar to previous bioacoustic analyses of fee-bee songs (e.g.…”

“…end frequency of the fee note divided by the start frequency of the bee note), (5) the relative amplitude of the two notes and (6) the relative loudness of the fee note to the entire song. Using a permuted discriminant function analysis (Mundry & Sommer, 2007) to determine which acoustic features vary with geographical location, Hahn et al (2013a) found that birds from northern British Columbia produced songs that were longer in total duration compared to birds from eastern Ontario. In addition, the acoustic cues that are associated with a male's dominance rank vary between these two locations (i.e.…”

“…In addition, the acoustic cues that are associated with a male's dominance rank vary between these two locations (i.e. variation in the consistency of the interval ratio in songs from Ontario: Christie et al, 2004b; variation in the consistency of the relative amplitude in songs from British Columbia: Hahn et al, 2013a;Hoeschele et al, 2010), indicating that additional geographical variation occurs in fee-bee songs.…”

“…Specifically, we wanted to examine whether birds used the overall song duration (i.e. the acoustic feature that shows the most variation between these populations; Hahn et al, 2013a) as a cue when discriminating. We also examined whether birds used acoustic features within either the first (i.e.…”