Song sparrows do not learn more songs from aggressive tutors

Natural noise affects conspecific signal detection and territorial defense behaviors in songbirds

Recent research suggests that anthropogenic noise can substantially alter animal behavior. Although there are many sources of natural background noise, the relative influence of these sounds on behavior has received much less attention. Using landscape-scale playbacks of rushing rivers and crashing ocean surf, we investigated how habitat appropriate natural noise alters territorial defense behaviors in lazuli buntings (Passerina amoena) occupying riparian areas and spotted towhees (Pipilo maculatus) in riparian and coastal areas when exposed to simulated intruder song. We also incorporated naturally occurring cicada noise as an acoustic source influencing lazuli bunting behavior. Both songbird species possess songs that share substantial spectral overlap with low-frequency, water-generated noise, and lazuli bunting song shares an additional high-frequency overlap with cicada calls. Thus, there is potential for background acoustic conditions to mask conspecific signals. We found that detection and discrimination of conspecific playback occurred more slowly for both species as background sound levels increased. Lazuli buntings also exhibited complex flight behavior in noise, suggesting they respond differently depending on the amplitude and type of background noise (with versus without cicada calls). Our results suggest natural noise can impair territorial defense behaviors in songbirds, highlighting natural soundscapes as an under-appreciated axis of the environment.

Social factors in bird-song development: Learning to sing with friends and rivals

Laboratory studies have revealed that social factors are key in bird-song learning. Nevertheless, little is known about how or why birds choose the songs they do learn from the many they will hear under natural conditions. We focus on various theories concerning social song learning that have been offered to date, with special attention paid to two axes of social factors. First, does song learning occur via direct interaction of the young bird with song tutors, or via social eavesdropping by the young bird on interacting singers (social modeling of song)? Social modeling, a hypothesis first proposed by Pepperberg (Zeitschrift für Tierpsychologie, 55(2), 139-160, 1981), and direct interaction are not mutually exclusive hypotheses, and the evidence we review suggests both play a role in song learning. Second, does song learning occur via interactions with rivals (territorial competitors) or with friends (mutually tolerant or even cooperative territorial neighbors). These are largely mutually exclusive hypotheses, and can really only be tested in the field. There is little evidence on this contrast to date. We review our recent study on song sparrows, which indicates that both the young bird and his primary tutor may benefit from song learning/tutoring. If this mutual benefit result is confirmed by further studies, we believe that song "tutoring" in these cases may be more than a term of convenience: that it may qualify as true teaching.

The fitness consequences of honesty: Under-signalers have a survival advantage in song sparrows

How honest or reliable signaling can evolve and be maintained has been a major question in evolutionary biology. The question is especially puzzling for a particular class of signals used in aggressive interactions: threat signals. Here, we report a study on song sparrows (Melospiza melodia) in which we assayed males with playbacks on their territories to quantify their aggressiveness (flights and close proximity) and aggressive signaling levels (rates of soft song, a close-range signal reliably predicting attack) and asked whether these traits affect individuals' survival on territory. We found that the effect of aggressive signaling via soft song interacted with aggressive behaviors such that there was a negative correlational selection: among males with low aggression, those males that signaled at higher levels (over-signalers) had higher survival whereas among males with high aggression those that signaled at low levels (under-signalers) survived longer. In other words, males that deviate from reliable signaling have a survival advantage. These results, along with previous research that suggested most of the deviation from reliable signaling in this system is in the form of under-signaling (high-aggression males signaling at low levels) pose a puzzle for future research on how this reliable signaling system is maintained.