麻豆淫院

New research finds that territorial behavior and diet help explain why some birds sing more often at dawn, challenging traditional theories about dawn choruses.

The was published June 12 in the Philosophical Transactions of the Royal Society B.

Scientists from the Cornell Lab of Ornithology's K. Lisa Yang Center for Conservation Bioacoustics and Project Dhvani in India studied 69 bird species in India's Western Ghats mountain range, one of the world's biodiversity hotspots, to understand why birds sing more or less at different times of the day.

To collect the data, the team placed microphones throughout the forest to automatically record bird vocalizations throughout the day鈥攖echnology often referred to as passive acoustic monitoring. It records audio that researchers later listen to and catalog which species vocalized during the day.

"Passive acoustic monitoring allowed us to collect simultaneous acoustic data for 43 locations, over several months. We could not have done this study without it because we needed a lot of data to answer our questions," said lead author Vijay Ramesh, postdoctoral researcher at the K. Lisa Yang Center.

The team found that 20 bird species had substantially higher vocal activity at dawn compared to dusk. These dawn singers included species such as gray-headed canary-flycatcher, greater racket-tailed drongo and large-billed leaf warbler. Only one species, the dark-fronted babbler, sang more often at dusk than dawn.

Ramesh and his colleagues examined four possible theories to explain why several of the species they studied sang more at dawn compared to dusk. Existing theories suggest that dawn singing is more prevalent due to microclimate conditions such as wind speed and air temperature that would allow birds with high-pitched songs to be heard more clearly over longer distances.

Other theories suggest that birds sing more at dawn to defend their territories, or to maximize foraging opportunities later in the day when there is more light, or more insect activity. The team gathered additional data from existing literature, such as degree of territoriality and diet, to examine these four theories alongside the acoustic data they collected in the field.

"We found that highly territorial birds and omnivorous species were much more likely to be active singers during dawn hours," said Ramesh. Singing in the early morning hours, the authors suggest, is important for territorial species to advertise and protect their locations.

Species that eat insects and fruit鈥攖hat is, omnivores鈥攁lso showed prevalence for singing more at dawn. Ramesh suspects that's because these species are often members of mixed-species foraging flocks, in which vocal communication is essential for finding food and for warning group members about potential predators nearby. But additional research that includes visual observations is needed to confirm his speculation, Ramesh said.

The other environmental factors the team examined, such as light levels and sound transmission conditions, did not significantly influence when birds sang, challenging previous theories about why birds tend to vocalize more at dawn.

"Our findings demonstrate that social factors, particularly territoriality and feeding habits, are more important in driving dawn singing behavior than environmental conditions," Ramesh said.