Go to the Owlery.

When you step into the Owlery, you wrap your cloak tighter around yourself. The chill wind that enters from the openings in the roof cut through even that. In a gloved hand, you hold a letter to Sirius. You look around the room. There are hundreds of owl sitting in the perches that rose into the darkness above. Some of the owls are squabbling among themselves over vole carcasses, but most of them are staring down at you. A shiver runs down your spine. Owls seem intelligent at the best of times – not a human intelligence, but a wild intelligence. Here, the owls' attention seems almost alive.

"Hedwig?" you say, your voice muffled by the layers of dropping that plaster the floor, the walls and the perches.

There's not response. Hedwig doesn't swoop out of the darkness to peck affectionately at your ear. She might be hunting, or she's asleep on her regular perch. You know where it is, and you look up to see if you can see her, but the highest level, where she normally perches is lost in the gloom of the winter's day. You stare at the rickety walkway that spirals up to the top of the Owlery and shiver again. The walkway is notoriously treacherous in the winter, with sections covered in near-invisible ice.