I went looking for explanations of the term "black swan" which I've noticed on several stock market/finance sites over the last day or two. (I think it might be coming an 'in word'.)
Started off using Wikipedia to search under "Black Swans" and got no farther than a discourse on the bird.
The 'sexuality' section amazed me.
Here 'tis.
Sexuality
A recent (2007) exhibition at the University of Oslo Natural History Museum in Norway called Against Nature? explored h/omosexual behaviours in a number of species, including Black Swans.
Several swan species exhibit lifelong h/omosexual behaviours, and the same phenomenon can also be found in a number of other water-birds, notably geese and flamingos, where it serves as a flexible life strategy.
In swans, the pair is the central social unit. The birds reinforce the unit with frequent preening and sex. Should one die, the other will usually live out the remainder of its life alone. The pair builds nests, raise cygnets and defends a territory. Two cobs, being bigger and stronger than a cob and a pen, can hold down a larger territory, and provide their cygnets with more to eat.
Such h/omosexual pairs represents a major fitness bonus to a pen, and pens without partners will seek out these couples, have sex with one or other of the cobs and lay eggs in their nest. She is then chased off, not being a part of the pair, and the cobs raise the cygnets themselves. Having access to more food the brood have up to ten times the survival rate of a brood with a heterosexual swan couple. From an evolutionary point of view, this is a very rewarding strategy for the cobs as well.
This situation only holds true as long as a nest and a territory is in short supply. The two males will have a fitness loss in that they (1) have no guarantee they are the actual fathers of the cygnets (not being bonded with the female) and (2) will anyway have to split reproduction between them.
A h/omosexual lifestyle will be advantageous in some situations, but not in others. However, having a partner is a requisite for building a nest and keeping a territory, and an opposite sex partner may not always be available when forming pairs. Thus, the ability to form a h/omosexual male pair is a normal part of the Black Swans social behaviour and an example of a flexible life strategy in the species.[21]
Perhaps you're not amazed.
If you want to read the entry in full it's at http://en.wikipedia.org/wiki/Black_swans
