Mountain chickadees from different elevations sing different songs: acoustic adaptation, temporal drift or signal of local adaptation?

Abstract

Song in songbirds is widely thought to function in mate choice and male–male competition. Song is also phenotypically plastic and typically learned from local adults; therefore, it varies across geographical space and can serve as a cue for an individual's location of origin, with females commonly preferring males from their respective location. Geographical variation in song dialect may reflect acoustic adaptation to different environments and/or serve as a signal of local adaptation. In montane environments, environmental differences can occur over an elevation gradient, favouring local adaptations across small spatial scales. We tested whether food caching mountain chickadees, known to exhibit elevation-related differences in food caching intensity, spatial memory and the hippocampus, also sing different dialects despite continuous distribution and close proximity. Male songs were collected from high and low elevations at two different mountains (separated by 35 km) to test whether song differs between elevations and/or between adjacent populations at each mountain. Song structure varied significantly between high and low elevation adjacent populations from the same mountain and between populations from different mountains at the same elevations, despite a continuous distribution across each mountain slope. These results suggest that elevation-related differences in song structure in chickadees might serve as a signal for local adaptation.

Do Male Mountain Chickadees Discriminate between Local and Non‐Local Elevation Intruders?

“…While it is unclear exactly how high-elevation females are able to discriminate between high-and low-elevation males, because males were not actively singing in the two-choice testing cage, our recent work showed significant differences in the song structure (e.g., differences in frequency ratio shift, note duration, and relative amplitude) of males from high vs. low elevations consistent with the local adaptation hypothesis (see Branch & Pravosudov 2015). In fact, given a pairwise preference test of an actual high-or low-elevation male, high-elevation females spent more time near high-elevation males compared to low-elevation males, while low-elevation females showed no detectable preference ).…”

“…These exact locations have been used in our previous studies, which show numerous elevation-related phenotypic differences including differences in song structure (Freas et al 2012(Freas et al , 2013aKozlovsky et al 2014Kozlovsky et al , 2015aBranch & Pravosudov 2015;Branch et al 2015a,b). These exact locations have been used in our previous studies, which show numerous elevation-related phenotypic differences including differences in song structure (Freas et al 2012(Freas et al , 2013aKozlovsky et al 2014Kozlovsky et al , 2015aBranch & Pravosudov 2015;Branch et al 2015a,b).…”

“…Playback stimuli were created from a sample of male mountain chickadee song collected in spring 2013 at our established high-and low-elevation sites in Sagehen Experimental Forest, CA; these males were included in the analyses published in Branch & Pravosudov (2015), showing significant differences in song structure. Songs of five males from low elevation and five males from high elevation were chosen at random based on minimal noise in the sound file.…”

Absence of population structure across elevational gradients despite large phenotypic variation in mountain chickadees (Poecile gambeli)

“…Previous work on this mountain chickadee system has shown that high and low elevation birds exhibit differences in spatial memory ability, hippocampal morphology, social dominance, novel environment exploration, problem solving and proactive aggression [19,31,39,98,99], as well as significant differences in mate preference [22], and male song structure [23]. In addition, several of these phenotypic differences between high and low elevation chickadees have been documented over multiple years despite large climatic variation among these years [32,54].…”

“…In the autumn of 2013, we sampled 167 birds from three pairs of high (2535–2590 m) and low elevation sites (1891–2122 m) in the Sierra Nevada (table 1); Sagehen Experimental Forest, CA (exact same locations sampled as those used in all phenotypic variation studies [19,22,23,31,32,39]), Mount Rose, NV (exact same locations sampled as those used to show male song structure variation [23]), and Red Lake Peak, CA (no phenotypic variation data have been collected from these locations) (figure 1). Birds were captured using mistnets at established feeders at Sagehen Experimental Forest; the other locations do not have a feeder system in place.…”