Do monkeys pay for sex

This is also evident in penguins. The penguins nest is generally made up of pretty stones and twigs. The female penguin leaves her nest in seek of nicer stones that other male penguins have collected. She initiates sex, and receives these pretty stones as payment, sometimes she does not even have to perform the act to get payment, just show interest.

I saw this on a documentary, if anyone knows of an article based on this please provide a link.

http://www.xs4all.nl/~sbpoley/ukrbiga3.htm
The comments are funny

Thanks Aribeth.