Gay penguins and bisexual bonobos

The Natural History Museum at the University of Oslo (Norway) has recently opened a remarkable exhibition devoted to homosexuality in the animal kingdom. As the museum explains on its website, one of its aims in documenting some of the hundreds of species where same-sex short and long-term relationships have been observed is to counter the all too familiar claim that such relationships are a crime 'against nature' (hence the title of the exposition, Against nature?).