Not to give away anything for those who haven’t read book 5 yet, but this has bothered me ever since book 3.
How is it that Hedwig (or any other owl that Harry uses) is always able to find Sirius Black to deliver messages to him, but the whole Ministry of Magic has been unable to locate him?
My response contains no Book 5 spoilers; nonetheless, I am using spoiler tags in deference to people who don’t want any aspects of Book 4, either.
[spoiler]Harry has used Hedwig, Pigwidgeon and some unnamed School owls to send mail to Sirius. I suspect Hedwig first got Sirius’s location (intended destination, actually) from Pigwidgeon, then during the summer of 1994, from the tropical birds that Sirius had been using to send letters to Privet Drive. During Sirius’s sojourn in the hills above Hogsmeade, Hedwig and Pigwidgeon could have directed the school owls that Harry used.
All of the above is, of course, predicated on the assumption that the birds used for magical postal duties are able to communicate with one another, which is purely speculation on my part.[/spoiler]
We discover that Sirius is an animagi and no one is looking for a black dog.
In book 5 (minor spoiler):
[spoiler]We find that Sirius is living back at his old place using the Fidelus charm. Dumbledore is the secret keeper and he’s not telling anyone anything.
Though it is odd that Luicus Malfoy recognizes Sirius as a dog. Maybe we’ll find out why in the next books.[/spoiler]
So in short, a wizard did it.
We’ve been told why Malfoy knew. Peter Pettigrew no doubt told Voldemort and the rest of the DE’s that Sirius is an animagus and must also have described what the form looked like. This coupled with his proximity to Harry tipped Draco off.
I always just thought the Owls were really clever…
Maybe thats a bit naive, but considering Hermiones cat, crookshanks, stupid name, imo , knew that scabbers wasnt really just a rat, I figured that wizarding pets were a bit more intelligent then usual cats/owls etc.