There was an old miner named Dave
who kept a dead whore in his cave
You have to admit
He hadn't much wit
But look at the money he saved!
That's right. I'm talking about necrophilia. More specifically, animal necrophilia.
Davian behavior has undoubtedly been observed for some time, but it first sparked scientific interest in 1960, when Robert Dickerman observed a male common ground squirrel in flagrante delicto with the corpse of another squirrel. The corpse was in a typical "flexed" mating position, which Dickerman speculated had triggered a mating reflex in the randy male.
After this initial report, references to Davian behavior died off for a period (Ha! Get get? Get it?). However, in 1988, Philip Lehner reported an interesting and somewhat disturbing incident involving Mallard ducks. During this incident, five drakes (male Mallards) got jiggy with the corpse of a Mallard hen that had just been pecked to death by two geese. Apparently, avians males of all sorts are rather notorious for their surprisingly Catholic sexual tastes; one study (for which, unfortunately, I cannot find a direct link) by Martin Schein and Edgar Hale found that male turkeys were willing to mount simple model heads of female turkeys.
Of course, Mallards appear to be particularly indiscriminate about their sexual partners. In a 1995 case at the Natuurmuseum Rotterdam, Kees Moeliker observed the first recorded case of avian homosexual necrophilia. Moeliker heard a loud thump against a glass window. When he went outside to investigate, he found one Mallard dead on the ground and the other vigorously enjoying the whole situation. Altogether, the enjoyment lasted 75 minutes and only ended through Moeliker's interruption. The incident won Moeliker an Ig Nobel prize for improbable research and spawned a yearly celebration: Dead Duck Day.
However, the title of king for Davian behavior has to go to the lowly anuran (frogs and toads). As reported by the blog Tetrapod Zoology, during the mating season male anurans are well-known for gripping passing objects in a tight "breeding clasp". Aided by rough pads or spines under the forearms, these clasps may last days or even weeks. The anurans are also not known for being very discriminating, grabbing anurans from other species, or even more inappropriate objects, such as human hands. Or, as the following picture shows (and as I have alluded to in a previous post), dead salamanders.
This propensity to grab any old object in a tight copulatory grasp has gotten some species of anuran into trouble; as reported by Walter Meshaka, individual Cuban tree frogs and southern toads have been observed attempting to mate with females that have already been crushed by passing automobiles.
Of course, no post on animal necrophilia would be complete without a Youtube video or three. As you can see, there's plenty of anecdotal evidence for Davian behavior in animals besides anurans, Mallards, and ground squirrels. And before you even mention it, I'll leave the sexual quirks of humans for another time.