Human perception of avian biodiversity in naturalistic auditory scenes.

Natural environments are filled with a diverse array of sound sources, from bird vocalizations and insect stridulations to waterfalls and wind noise. The sounds often co-occur, arriving at the ear of human listeners as a mixture of the different sources. The auditory system is tasked with segregating the individual sound sources of the mixture into meaningful representations. In contrast with human auditory perception in urban environments, which include speech and music, little is known about our capacity to segregate mixtures common in natural environments. Here, we report on the capacities of the human auditory system when presented with mixtures of bird vocalizations - that is, scenes common in natural environments - by systematically varying the number of vocalizations from the same species and from different species. We found that humans could discriminate mixtures but only up until around 8 individuals of the same species beyond which mixtures may rely on a time-averaged summary statistic. Furthermore, humans appear to segregate mixtures of different species based on the disparities in their summary statistics. The results suggest that humans analyse natural auditory scenes using the same segregation mechanisms as for sounds produced by humans and other geophysical sounds.