Abstract
Senescence is widespread in nature, often resulting in diminishing survival or reproduction with age, but its role in age-dependent variation in sexual traits is often poorly understood. One reason is that few studies of sexual traits consider non-linear relationships with age, or only consider a narrow range of years relative to the life span of the species. Birdsong has evolved to allow assessment of conspecific quality in numerous bird species. Whilst theory and empirical work suggests that song may become more elaborate with age, there are a paucity of long-term studies testing whether song is associated with age or longevity. In particular, the occurrence of song senescence has rarely been demonstrated. Using an exceptional long-term dataset for the Seychelles warbler (Acrocephalus sechellensis), we analysed relationships between male song, age, survival, and longevity. This species is a long-lived songbird with early life increases, followed by senescent declines, in survival and reproduction. The study population (Cousin Island, Seychelles) is a closed population, with no depredation of adults, providing an excellent opportunity to study senescence in free-living animals. We tested whether song traits were related to age at recording, future survival, longevity, and territory quality. We found age-dependent changes in five song traits (duration, maximum frequency, peak frequency of songs, and duration and frequency bandwidth of trills). Relationships with age were quadratic, indicating reversal in the expression of song coinciding with the onset of senescence in reproduction and survival in this species. One song trait (trill bandwidth) had a quadratic relationship with future survival, but no song traits were related to longevity, suggesting age-related patterns were not the result of selective disappearance. Our study provides one of the first examples of functional senescence in song, offering new insights into avian senescence. Late-life declines in avian song, and possibly other sexual traits, may be more common than currently known, and may play a fundamental role in age-dependent changes in reproductive success.
Highlights
Vocal communication plays an integral role in mate attraction, male-male competition, territory defence, and identification of c onspecifics[1,2,3,4]
Possible senescence in bird song has only been documented in four species previously[8,20,26,27,28]. Three of these species were studied using songs recorded in captive populations, and documented late life deterioration of (i) repertoire size in female European starlings (Sturnus vulgaris)[26], (ii) tempo and frequency parameters of song in male Bengalese finches (Lonchura striata)[20], and (iii) song rate, stereotypy within songs, song consistency, and response elicited by song playback in swamp sparrows (Melospiza georgiana)[27,28]
We found no age-related changes in vocal deviation of trills, minimum vocal deviation, mean male vocal deviation (Fig. 1d), or repertoire size (Fig. 1e)
Summary
Vocal communication plays an integral role in mate attraction, male-male competition, territory defence, and identification of c onspecifics[1,2,3,4]. The unique long-term monitoring and closed island populations of the Seychelles warbler mean that unusually powerful tests of how song changes with age, or whether song traits can predict survival or longevity, are possible. We used historical song r ecordings[36] from the Cousin population of Seychelles warblers to test for both linear and quadratic relationships between male song traits and (i) age of each male at time of recording, (ii) years until death of each male at time recording, and (iii) longevity (life span) of each male. We hypothesised that territory quality would be related to acoustic parameters of song, such that high quality males would both hold high quality territories and produce more elaborate song traits
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
