Rock wrens preferentially use song types that improve long distance signal transmission during natural singing bouts

Abstract

When animals are capable of producing variable signals they may preferentially use some signal types over others. Among songbirds, individuals are known to alter song type form and usage patterns in contest and mating situations, but studies have not examined how song choice improves signal efficacy during broadcast song. For this study we investigated rock wren Salpinctes obsoletus song type use rates during natural singing bouts. We tested three hypotheses for adaptive song use during broadcast song: 1) birds improve signal content by increasing the use of high quality songs, 2) birds optimize for signal propagation by preferentially using songs that transmit well, and 3) birds maintain energy by reducing the use of costly songs. The study included 19 058 songs sung by 12 individuals, each of which had a measured song repertoire of between 52 and 117 song types which were produced at highly variable rates. Results indicated that rock wrens did not preferentially sing song types with shorter durations or fewer frequency switches, as would be expected if they selected song types to minimize delivery costs. They also did not favor songs with more rapid trills or more frequency switches, as would be expected if they adjusted song use primarily to indicate quality. Focal birds did preferentially sing significantly longer songs with lower bandwidths, lower frequencies, and slower trill rates. Results suggest that natural broadcast singing patterns are shaped more by the benefits of long distance transmission than by the benefits of advertising performance ability or the costs of song production.

Form and Function Predict Acoustic Transmission Properties of the Songs of Male and Female Canyon Wrens

“…Theory suggests that buzzy female canyon wren songs should travel a limited distance, allowing signalers to communicate effectively with rivals and avoid eavesdropping (Vargas-Castro et al, 2017). The pure-toned notes of male canyon wren song cascades, in contrast, are expected to carry long distances, broadcasting male presence across widely spaced territories (Warning et al, 2015;Benedict and Warning, 2017). Interestingly, when male canyon wrens are challenged in aggressive confrontations, they adjust their songs to reduce the length of the cascade and to add or increase the number of terminal "cheet" notes .…”

Are quartzite scree slopes used by birds to promote sound transmission in the Mediterranean forest?

“…In order to promote sound transmission, birds use different strategies, such as singing on perches high up in the vegetation (Catchpole and Slater, 2008;Barker et al, 2009). Some studies show that the benefits of long-distance transmission are more relevant to the birds than the benefits of advertising performance ability or the costs of song production (Benedict and Warning, 2017).…”

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“…Theory suggests that buzzy female canyon wren songs should travel a limited distance, allowing signalers to communicate effectively with rivals and avoid eavesdropping (Vargas-Castro et al, 2017). The pure-toned notes of male canyon wren song cascades, in contrast, are expected to carry long distances, broadcasting male presence across widely spaced territories (Warning et al, 2015;Benedict and Warning, 2017). Interestingly, when male canyon wrens are challenged in aggressive confrontations, they adjust their songs to reduce the length of the cascade and to add or increase the number of terminal "cheet" notes .…”