|Red-billed Buffal0-weaver, Naabi Gate, Serengeti NP, Jan 2011|
The nests of this species are called compound nests, as several 'pairs' share the same walls, with typically several nests within the same overall nest structure. I say 'pairs' in quotes, because these are seriously polyandrous birds. Each compund nest is defended by a group of resident males, and each nest within the compond nest is likely to have two or more males assoiated with it (but just the one female). What's more, if you look at the genetics involved in parternity within the nests, you'll find that more often than not the actual father of some of the yound in the nest isn't even one of the resident males, but one of the non-territorial individuals hanging around the edge of the colony, so it seems that a lot of the time the female sneaks off and finds non-territorial males to father young too.
|Red-billed Buffalo-weaver nests, near Arusha, Nov 2009|
It follows that there's a lot of competition among males to be fathers, even though genetics again tells us that the cooperating territorial males sharing a female are at least sometimes related (though not usually close elatives). What the phalliod organ actually does isn't entirely clear - it's not the route for sperm to flow through - but apparently it needs stimulation before females can be inseminated by the male, and they're the only birds to experience anything that looks rather like an orgasm (but only after repeated copulation), and only at the point of orgasm (who's main effect seems to be pulling the female closer to the male) is sperm transferred to the female, so we think it must be related. What's more, some rather interested scientsts have demonstrated that if you manually stimulate the organ on a bird, you can induce orgasm and sperm transfer (the description in the paper isn't detailed enough to say exactly how the manual stimulation too place, but you can leave that to your imagination).
Interesting things huh (you can read more about it here? In fact, it goes on - they've got some remarkably evolved sperm too, to deal with the considerable post-copulatory competition between sperm from different males within the female, all trying to fertilise the same egg.Can't find a picture just now, but trust me - theyre turbo-powered!