Friday, 1 December 2006

Swanning around

I had to visit the optometrist today for a check up. (And the bad news, which wasn't news because I had a pretty good idea, is that I need reading glasses.) Anyway, my ophthalmic challenges are neither here nor there but the relevance is that the optometrist is in Williamstown, so after the appointment I drove back along the Strand.

The tide was in so the waterbirds were on the basalt boulders and the last strip of beach. Black swans (Cygnus atratus) were having an after lunch nap, oblivious to the silver gulls (Larus novaehollandiae) on the rocks around them. One of the birds wore a ring. I don't know anything about banding so I'm not sure whether this individual has done a runner or is part of a research program. Can you real bird-watchers tell me something about the ring?

A pied cormorant (Phalacrocorax varius) was preening itself on a boulder close to shore. I mentioned in an earlier post the all five cormorant species occur along the south coast (although not all of them are found in Port Phillip Bay). Three of them have black and white plumage but are easy to tell apart:
  • pied cormorant has a yellow face and black garters
  • little pied cormorant (P. melanoleucus) has a white face and no garters
  • black-faced cormorant (P. fuscescens) has a black face and garters

A handful of crested terns (Sternus bergii) mixed in with the gulls. And some grey teal (Anas gracilis) perched on rocks a bit further out. I was a bit surprised to see a masked lapwing (Vanellus miles) skulking around on the mud. They're more often spotted on grassed areas—especially roadside verges and suburban parks.

Not a bad haul, I thought, for a small patch of mud and rocks in an urban area.


PBD said...

Something interesting about black swans-
"Some black swans of Australia form sexually active male-male mated pairs and steal nests, or form temporary threesomes with females to obtain eggs, driving away the female after she lays the eggs. More of their cygnets survive to adulthood than those of different-sex pairs possibly due to their superior ability to defend large portions of land."

I think I read from another source that the same-sex pairs are close to half of the population?

Darky said...

The Emu, Dromaius novaehollandiae, male incubates exclusively after driving the female off the nest. He neither eats nor squits for the duration.
Birds display a big range of alloparenting behaviours. Externally developing eggs would make flexibility around parenting very easy, what?

Kraaijeveld and Mulder are the current investigators into Cygnus atratus behaviour.
I have no access via my public library membership to all online references, and a decreasing access to university journals sections - - a uni library these days is like the offices of some corporation, complete with armed goons - - and so readers will have to go it alone for full references, but the Oxford Journals online is very generous, and the Lake Wendourie swan stuff is free online
For example: their study of social mating behaviours.
Black Swan pens on Lake Wendourie compete for cobs more than females of most species compete for males - and are agonistic over grazing rights in about the same way as Moorhens, Gallinula chloropus, are and it's interesting that both species have a marked lack of sexual dimorphism wrt sexual selection finery - even though other differences such as size remain.

The Wikipedia line is throw-away and sloppy. More of their cygnets survive to adulthood than those of different-sex pairs possibly due to their superior ability to defend large portions of land. This isn't anywhere in the literature. More male/male pair broods than in other species survive, certainly, but there's nothing anywhere I have read that says male/male C atratus broods survive better always than male/female ones. The whole tone of the article there is low, Discovery Channel Wow! Kids. I'm sympathetic with the proselytising efforts of people wanting greater acceptance of difference in sexuality in humans, but I cringe at this pop science justification kind of screed.

I can recommend Partnerships in Birds: The Study of Monogamy ed JM Black, OUP.

Monogamy - in the sense of single partner fidelity, both with insemination and pair behaviour, throughout life - is not the mode in sexually reproducing animals. I favour the idea that in long-lived species, fidelity would pay off in the accumulation of experience. Swans, geese, vultures are all very long-lived and all display mate fidelity. Black Vultures are at the conservative end of marriage behaviour; not only do they mate heterosexually for life, they also have a social rule that forbids any sexual activity except in the privacy of the nest.
abstract online, phew. And there I was thinking that vultures did some pretty disgusting things with corpses. Prudery is as prudery thinks, I suppose.

jj said...

Thanks for a most interesting introduction to a whole new area of information for me.