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It's Valentine's Day, and many people are planning to celebrate with that special someone. It's also a good excuse to look at lovin' in nature. While humans may value monogamy, it turns out to be quite rare among animals in the wild.

The National Science Foundation provides a few fun facts about monogamy and wildlife (if you like animals, you have to the NSF put together to accompany these stats):

1) Not a single mammal species has, thus far, been definitively shown to be truly monogamous. (Nevertheless, individual pairs of mammals may be truly monogamous.) Scientists now estimate that only about three to five percent of the approximately 4,000⁺ mammal species on Earth practice any form of monogamy.

2) Before the advent of DNA fingerprinting, scientists believed that about 90 percent of bird species were truly monogamous. But paternity testing suggests that the reverse is true: Scientists now believe that about 90 percent of bird species are socially monogamous, and that true monogamy among birds is the exception rather than the rule.

3) Some insects, including cockroaches, are monogamous.

4) Any form of monogamy among fish and amphibians is exceedingly rare.

In hisof Bernd Heinrich's excellent book, The Nesting Season, Wayne Mones addresses the question: What good is monogamy anyway?

The answers depend on conditions. Heinrich cites the example of screech owls, which are typically monogamous throughout their lifetimes. But when food is plentiful and nest density is high, males can easily provision more than one nest, so they become polygynous. And when food is readily available, females need less parenting investment from males. On the other hand, when food is widely scattered, so are nests and females. In these instances, females benefit most from increased help in parenting, which means males can maximize their reproductive success only by devoting themselves to a single mate and a single nest.

And finally, take a look at ±¬ÁϹ«Éç associate editor 's compilation of .