Abstract
Urban great tits (Parus major) sing with a higher minimum frequency than their forest conspecifics. Cultural processes may account at least in part for the song divergence in city birds as great tits learn their repertoire from conspecifics and switch to high pitch song types in presence of background noise. However, in small cities, this process of cultural divergence could be constrained because it is likely that these birds have a greater exchange of song types with the outside. We tested this prediction by recording great tit songs in a small city (Toledo, central Spain) and in a nearby forest. We found that background noise and the peak and the maximum frequency of songs were higher in the city but the minimum frequency did not differ. The pause length was also longer in forest birds. Seventy percent of the song types were shared between Toledo and the nearby forest. These results suggest that the small size of Toledo allows a homogenized cultural wealth, preventing the development of a high pitch song as observed in larger cities.
Highlights
Like many other urban bird species, urban great tits, Parus major, sing with a higher minimum frequency than their forest conspecifics (Slabbekoorn & den Boer–Visser, 2006), highlighting the role of environmental conditions on sound production
Apart from presenting a shorter pause length and a quicker song–rate in Toledo than in the forest (GLM: F1, 64 = 5.89; p = 0.02 and F1, 64 = 5.49; p = 0.02, respectively), these shared memes did not differ in minimum frequency (GLM: F1, 64 = 2.96; p = 0.09) or in peak frequency (GLM: F1, 64 = 2.56; p = 0.11); only the maximum frequency differed, being higher in Toledo than in the forest (GLM: F1, 64 = 19.82; p < 0.001; Toledo = 5,483 ± 117 Hz and Forest = 4,956 ± 57 Hz)
The minimum frequency of great tit songs did not differ between Toledo and forest, but the maximum frequency did so significantly, making bandwidth in Toledo wider
Summary
Like many other urban bird species, urban great tits, Parus major, sing with a higher minimum frequency than their forest conspecifics (Slabbekoorn & den Boer–Visser, 2006) (see table 1), highlighting the role of environmental conditions on sound production (i.e. fig. 1 in Laiolo, 2010). Experimental procedures have shown that birds can adjust their acoustic signals as a short–term response to increasing noise levels due to vocal plasticity These plastic adjustments could be mediated by an active frequency shift (Gross et al, 2010; Bermúdez–Cuamatzin et al, 2011; Hanna et al, 2011; Potvin & Mulder, 2013), by switching song types (Cardoso & Atwell, 2011a; Halfwerk & Slabekoorn, 2009), by increasing the duration of the vocalizations (Montague et al, 2012; Potvin & Mulder, 2013), or by increasing the amplitude of the songs (Brumm, 2004; Schuster et al, 2012). Such phenotypic plasticity would impede habitat–dependent selection and speciation (Baker, 2006)
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