Recreational noise pollution of traditional festivals reduces the juvenile productivity of an avian urban bioindicator.

Noise is a pollutant of emergent concern for ecologists and conservation biologists. Recreational noise pollution, especially unpredictable and intermittent sounds, and its effects on wildlife and biodiversity have been poorly studied. Researchers have paid very little attention to the effect of noisy traditional festivals (fireworks and powder-guns). This study aimed to explore the effect of these recreational activities on the juvenile productivity of an urban avian bioindicator: the house sparrow. We studied five pairs of localities in the Valencia Region (E Spain) with noisy traditional festivals. Each pair was composed of one locality with festivals during the breeding season and the closest similar locality, but with festivals outside the reproductive period (controls). Both locality types were sampled twice each spring (May-June of 2019 and 2020). Sampling dates were selected as 15 and 30 days after noisy festivals ended, while the control localities were sampled 1 day after the census of their correspondent town pair with noisy breeding season festivals. The ratio of the juveniles/adults detected during surveys in the influence area of festivals (100-m buffer around the parades route) was used as a house sparrow breeding success proxy. Data were analysed using GLMM: year (2019/2020), festivals season (breeding/non-breeding), survey (15/30 days), and their interactions were included as fixed factors. Pair of localities and locality nested within the pair were random factors. In 2019, juvenile productivity was lower in the towns with noisy traditional festivals during the breeding season than in the control towns. The 2020 festivals were cancelled due to COVID-19. In spring 2020, house sparrow juvenile productivity was the same in both town groups. Lockdown did not increase this species' juvenile productivity in the control localities in 2020 versus 2019.