May 4, 2015
Thanks to Mickey Pardo for this guest student blog post – bluebirds may all look the same to us, but they can tell one another apart, perhaps by sound.
Biologists have long known that animals prefer to help individuals who are more closely related to them. For example, male Western Bluebirds sometimes help neighboring males to raise their chicks, and they are far more likely to help their relatives—fathers, brothers, grandfathers—than unrelated males. This sort of favoritism towards kin makes sense from an evolutionary standpoint, since assisting your relatives ultimately allows them to pass on copies of the genes that they share with you. But how do the birds know who their relatives are? Researchers here at the Lab of Ornithology recently discovered that male Western Bluebirds use cues in the songs of other males to identify their kin, but the nature of those cues remained unclear. What makes the song of a relative sound different than the song of a non-relative?
To find out, the researchers recorded songs from male Western Bluebirds at Hastings Reserve in central California. This population has been continuously monitored since 1983, so the researchers knew which males were related to whom. The song of the Western Bluebird consists of two basic note types: pews and chucks. However, the pew notes especially are highly variable, and each male uses a different set of pew notes in his song.
The research team hypothesized that the songs of related males would have more pew notes in common than the songs of unrelated males. But when they analyzed the data, they were in for a surprise. Related males did indeed share more notes than unrelated males, but there was quite a bit of note sharing going on between unrelated males as well! And what is more, the note sharing only occurred between males on neighboring territories; non-neighbors never shared notes, regardless of whether or not they were related.
This led the team to conclude that note sharing is probably not the main mechanism by which Western Bluebirds recognize their relatives. It may be a piece of the puzzle, but is unlikely to be sufficient for kin recognition, because unrelated neighbors share notes as well, and related males did not share notes if they didn’t live next to each other. There may be some other cue that allows bluebirds to more reliably distinguish kin from non-kin. Alternatively, there may not be any one blanket signature that is common to all members of a family. Instead, Western Bluebirds may actually know the song of each male in their area and recognize them as individuals. If this is the case, it still begs the question of how the bluebirds learn which individuals are related to them. This remains a mystery waiting to be unraveled.
Reference: Akçay, Ç., Hambury, K. L., Arnold, J. A., Nevins, A. M., Dickinson, J. L. 2014. Song sharing with neighbours and relatives in a cooperatively breeding songbird. Animal Behaviour, 92, 55-62.