Aircraft events correspond with vocal behavior in a passerine

Airports can affect birds by hindering acoustic communication. Here, we investigated the impacts of aircraft events on vocal behavior in wood thrush (Hylocichla mustelina) breeding one mile from an airport in Ithaca, NY, USA. We identified the number of wood thrush songs between 0500 and 0800 h at various distances from the airport and on days with various morning flight schedules. We also analyzed the number of sites from which birds sang during the peak of aircraft events (proxy of number of wood thrush). We found that birds sang more from 0600 to 0640 h when there were aircraft events during this period. This increased vocal behavior is likely explained by increased song output per individual wood thrush, rather than more wood thrush vocalizing. Increased song rate may negatively affect wood thrush fitness through increased energetic demands and/or time tradeoffs with other important behaviors, such as foraging. Identifying the noise thresholds associated with fitness costs (if any) and how different behavioral strategies (i.e. changing the pattern of vocalizations) may allow individuals to evade these costs would be useful for establishing conservation policy in breeding habitats used by passerines, such as the wood thrush.

Full life course analysis of birdsong reveals maturation and senescence of highly repeatable song characteristics

Signalers may benefit in some contexts from advertising their ages, for example in courting potential mates. Receivers in turn may benefit from assessing a signaler’s age, even in cases where their doing so is against the signaler’s interests. Indicators of age contained in signals thus may have important fitness consequences for both signalers and receivers. In birds, males of many species have been shown to display delayed maturation of their songs, resulting in older males singing songs that are higher in quality in one or more characteristics. Conversely, it seems possible that songs might eventually deteriorate with age as an aspect behavioral senescence. Studies of birdsong long enough to test both possibilities are quite uncommon, with nearly all studies aspect of age-dependent changes in birdsong spanning 3 or fewer years of males’ lives. Here, we present the longest longitudinal analysis of male birdsong to date, in which we analyze songs recorded for 4–11 years of the lives of captive male swamp sparrows. We find that males displayed delayed maturation of three song characteristics: song rate, song length, and consistency between songs. Delayed maturation was followed by behavioral senescence of three characteristics: song rate, stereotypy within songs, and consistency between songs. Because song quality declined in males beyond 2 years of age, this evidence is inconsistent with a signaling system in which females both prefer increasingly older males and are able to accurately determine male age through song assessment. Rather, our evidence suggests that swamp sparrows should be able to use song to distinguish intermediate-aged males from 1-year-old and very old males.

Prenatal environment affects embryonic response to song

Early environmental enrichment improves postnatal cognition in animals and humans. Here, we examined the effects of the prenatal acoustic environment (parental song rate) on prenatal attention in superb fairy-wren ( Malurus cyaneus ) embryos, the only songbird species with evidence of prenatal discrimination of maternal calls and in ovo call learning. Because both adults also sing throughout the incubation phase, we broadcast songs to embryos and measured their heart rate response in relation to parental song rate and tutor identity (familiarity, sex). Embryos from acoustically active families (high parental song rate) had the strongest response to songs. Embryos responded (i) strongest to male songs irrespective of familiarity with the singer, and (ii) strongest if their father had a high song rate during incubation. This is the first evidence for a prenatal physiological response to particular songs (potential tutors) in the egg, in relation to the prenatal acoustic environment, and before the sensitive period for song learning.