A (2018) Data and code from "Sub-species status and methodological choices explain strength of territorial response to local versus foreign song by oscine birds in meta-analysis." Open Science Framework.

To understand the implications of geographical variation in vocal culture in songbirds, researchers have often compared territorial responses to playback of local songs versus responses to playback of songs from ‘foreign’ conspecifics. This body of work has the potential to help us move towards a general understanding of factors driving divergence in signal recognition. We conducted a systematic review and meta-analysis of 57 playback studies to explain variation in strength of response to local versus foreign songs. Studies with incomplete reporting of results had elevated effects due to selective reporting. Studies that used small numbers of stimuli as exemplars (pseudoreplication) had more variable effects than studies without severe pseudoreplication. Whether or not we controlled for pseudoreplication, we found greater response to playback of local song than to foreign song. In investigating potential biological drivers of the variation in strength of experimental effects, we found that the difference in territorial response to local versus foreign song was stronger if the foreign song was recorded from another subspecies than if the foreign song was recorded from the same subspecies as the focal individuals. Indexes of risk of accidental response to heterospecific song did not coherently explain response to foreign conspecific songs, nor did factors expected to influence individual experience with foreign conspecific songs. Thus, although oscine songbirds clearly react more aggressively to local song than to foreign song and variation in the strength of this effect is influenced by methodological choices and subspecies status, considerable variation in the strength of response to local versus foreign song playback remains to be explained.

In many songbird species, young individuals learn songs from neighbors and then settle nearby, thus creating neighborhoods of conformity to local vocal culture. In some species, individuals appear to postpone song learning until after dispersal, possibly to facilitate conformity to local dialects. Despite decades of study, we still lack a consensus regarding the selective pressures driving this delayed song learning. Two common hypothetical benefits to conformity, and thus delayed song learning, are rooted in territorial interactions; individuals preferentially produce local song either to avoid detection as new arrivals (deceptive mimicry) or to be more effectively recognized as conspecific territory holders. The dickcissel (Spiza americana) is an ideal species in which to study these hypotheses. Males of this species appear to delay song learning until they arrive at their first adult territory, each individual sings a single song type, and conformity to the local song culture is high. Using playback, we contradicted both of the territorial hypotheses described above; male dickcissels did not respond differentially to local vs foreign song playback treatment. We are confident in this lack of difference because dickcissels clearly responded less strongly to a third treatment, neighbor song, than to the other two treatments, demonstrating sufficient power in our experimental design (and providing the first evidence of the dear‐enemy effect in dickcissels). Our results raise the question of why dickcissels respond equally aggressively to both local and foreign songs when other bird species often show reduced aggression toward foreign song. If reduced aggression to foreign song is not ubiquitous in species that achieve conformity through delayed learning, then selection from aggressive territorial interaction seems unlikely to be a general explanation for such delayed learning. Reduced aggression in response to foreign songs in other species may be due to reduced exposure to the stimulus of foreign song or to different cost‐benefit trade‐offs when responding to songs that deviate from the local average.

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