A little levity
For instance, Chapter 8 -- Exhibitionist Flamingos or Transvestites, hermaphrodites and other alternative lifestyles -- includes this revelation:
Three, or four, or six is company
If you want to keep more than one mate, the important thing to remember is to treat everyone equally. The Galapagos hawk is an excellent example of this. The female Galapagos hawk lives with two (or three or four or five) males. She is careful not to play favorites. Whenever she does the rumpy-bumpy with one male, she does it with all of them.