...and by fandom, I really mean "pet owls" because Harry Potter fans are growing quite sick of having owls as pets and are now inundating British bird sanctuaries with scores of the poor, unwanted avians.
No doubt memes like this also contributed to the pet owl fad.
At the (hor)crux of the matter is the fact that owls make terrible pets, no matter how adorable and helpful they might appear in the books and movies. Yet during the decade of unbridled Pottermania, fans ignored the fact that the nocturnal avians would rather remove a stray finger or unguarded eyeball than deliver the mail and began paying top
galleon dollar to secure one as a trendy housepet.
After the novelty of owning an owl wears off and the reality of dealing with piles of owl pellets sets in, fans became eager to dispose of their once-beloved Hedwigs and Pigwidgeons.
Speaking on behalf of The Owlcenter in Carwen, Wales, one Miss Pam Toothill summarizes this fad perfectly, "People saw Harry's owl in the movies and thought how cute and cuddly they looked. Now they are bored and fed-up with all the work involved looking after an owl..."
In addition to having a name perfect for an adjunct professor at Hogwarts, Ms. Toothill also happens to have a very good point: owls require a lot of work, a lot of mice, and a lot of ice cream* to be content and happy. There's a very good reason why more people didn't have owls as pets before the movies, and it probably wasn't because of their well-documented plans to kill Simon Cowell:
*- Or so I assume. I am not (and never claimed to be) an owlologist, so you may want to check wikipedia on that one.