As someone who pays a lot of attention to animal behavior, I cringe when I read false conclusions like this from common animal behaviors.  When male lions mount another male, it is more to show domination so would be more appropriately called rape.  When killer whales form pods of males, it is for hunting...not for sexual encounters.  And to say that gulls are lesbians, etc is a causation fallacy and more anthropomorphication than science.  

But what is sad in all this is that people are forced through the discrimination of others to try to prove that a lifestyle is acceptable.  A lifestyle that brings two people in love together, promotes happiness and does nothing to affect the lives of those who try to tear down their happiness.  Why prove it is natural or unnatural?  Just because some bible thumper with nothing more to go on that what their preacher told them is doubting your choice?  Here is a word to the wise...nothing you say, even if you prove it through science eventually, will change their minds.