Two crows after the rain

Murder of crows’ cacophony decoded as researchers eavesdrop on conversation

Image credit: Dreamstime

Scientists at the University of Washington Bothell have covered their school’s roof with audio recording equipment in order to attempt to make sense of the cacophony of noise produced by congregating crows.

Thousands of crows gather on campus at the university and produce an enormous amount of noise before and after sleeping. Given the intelligence of the birds, it is unsurprising that the researchers on the ground began to question what the crows may be trying to communicate.

“[The crows] are incredibly raucous, and make this cacophony every night, and people wonder: what are they saying? And that’s a great question to ask on this campus,” said Professor Douglas Wacker, a biologist who has been studying the local population of crows with undergraduate students at the University of Washington Bothell.

According to Professor Wacker, crows are capable of making a wide range of noises, some of which have functions which are understood. However, the typical “caw” sounds made by crows are not well understood.

“If a bee can do a dance to tell other bees where food is located, then certainly a highly intelligent bird – in a family with other bird species that are capable of insight learning, recognising themselves in a mirror, recognising faces and passing that information on to subsequent generations – could be capable of communicating complex information,” he said.

In order to better understand what the crows were communicating with these sounds, Professor Wacker joined forces with acoustics expert Professor Shima Abadi on a project to perform “a sort of computerised eavesdropping” on the crows.

This was to prove a challenge: the researchers had to identify the sounds in a chaotic environment, where it was difficult to separate individual caws from the sounds made by other birds and other surrounding noises. In addition to this, the intelligence of crows must not be underestimated: they are known to change their behaviour when they suspect they are being observed.

In order to circumvent these complications, the researchers experimented with different arrangements for their equipment. In a car park, they placed four audio recorders in a square and played recorded crow sounds for them to detect. Using precise time stamps gathered by the equipment, the source of the noise could be pinpointed.

The researchers were able to optimise the precision of this method such that they were able to determine the source of a caw to within 15-30cm, approximately the size of a single bird.

“With audio alone, our team is able to localise and record the birds remotely, and in dim light that makes this situation less suitable for video tracking,” said Professor Abadi. “It’s still a challenging task, but we can use the audio signals to look for patterns and learn more about what the birds may be communicating.”

Now, the researchers are working on the development of a user interface and computational methods to single out the calls of individual crows in order to streamline the tedious analysis of their recordings by identifying noteworthy events.

Eventually, they hope to be able to combine their audio recordings with video recordings, such that they can study how the birds respond to specific calls, and consequently determine some meaning behind these calls.

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