Yes, I agree, it has been an extremely interesting thread. It seems likely to me, based on contributions to this discussion, that the calling of CBCs has multiple purposes. I think many of us tend to fall into the trap of providing a single reason for a particular animal behaviour, but I propose that in the CBC, at least, calling has the following purposes:
1. Early in the breeding season, males call to attract a mate and to also proclaim a breeding territory. Advertising the breeding territory through calling then continues throughout the breeding period.
2. Calling and flight displays are also used to attract the attention of potential hosts (corvids, currawongs, magpies) away from their nest to allow a female to sneak in and lay her egg.
3. Later in the breeding season CBCs call to muster fledged progeny, especially if a single pair has parasitised several nests within the breeding territory.
4. Calling while in long-distance flight, either between foraging & roosting sites or on long-distance migration helps to keep the group(s) together, thus providing safety in numbers. Perhaps another way of protecting themselves, offspring and other close relatives when flying over open areas and vulnerable to predation or mobbing?
It sounds like a great opportunity for a postgraduate project. What are the purposes of the calls? Are there different calling patterns/visual displays, each serving a different purpose? What is the genetic composition of calling flocks that are on the move – are they family groups or do they comprise unrelated/distantly-related individuals?
Stephen Ambrose Ryde NSW
