The pigeon chested ones were the first people ever to be discovered as being immune to the powers of the brainwashing powers of the curlew. With such an immunity the pigeon chested ones are a capable threat to the power of the curlew. Therefore meaning anybody of the pigeon chested status is in serious danger of being attacked by these creatures from outer space.
A pigeon chested one can be recognised by an indent in their chest. It is rumoured that this only occurs in males but recently discovered information has shown it is also possible in females as well.