Lack of consistent responses to aircraft noise in dawn song timing of bird populations near tropical airports

Abstract

Abstract: Birds living near airports can reduce the noise interference by advancing their dawn chorus timing and avoiding the start of airport operations. Data supporting this finding come from temperate areas, but little is known from tropical environments, where seasonal variation is lower and biodiversity is higher. Here, we investigated whether 15 tropical bird species are able to advance their dawn song and avoid aircraft noise interference. We sampled dawn song in three airports and three control sites in Brazil, using automated recording units. We found that dawn song times were not globally affected by the exposure to airport noise. Instead, changes were highly variable and species-specific, as dawn song onset was significantly advanced in two and delayed in four species. This large variation in responses was surprising given patterns found in previous studies. Indeed, this is the first time that a significant delay is reported for bird’s dawn song. We explored whether between-species differences in this response could be explained by additional variables (song frequency, degree of urbanity, and noise release), but none of them explained the direction or the strength of the changes. We suggest that earlier airport activity and shorter variations in day length and in twilight duration of tropical areas may be restricting birds’ ability to change dawn song timing. Further studies should consider these differences and analyze to what extent populational declines in noisy areas and the resultant reduced competition for acoustic space may be affecting the changes in dawn chorus onset time. Significance statement: Birds have been shown to advance the timing of their song at dawn to avoid airport noise in Europe. However, we did not find a similar pattern in the birds near three Brazilian airport-affected sites, where the tropical environment can be a key factor (higher biodiversity and lower seasonal variation). We found that of the 15 studied species, only two followed this pattern, 9 species showed no changes in their timing, and 4 species showed the opposite trend, delaying their dawn song in an apparently non-adaptive manner. Neither differences in the birds’ song frequencies and degree of urbanity nor the noise release could account for delays in dawn song. We suggest that the birds’ ability to change their song timing may be limited by shorter seasonal light variations in tropical areas and by earlier airport activity in studied sites.