"I was getting really worried when you didn't answer any of my letters. I thought it was Errol's fault at first ... Our owl. He's ancient. It wouldn't be the first time he'd collapsed on a delivery."
-- Ron Weasley (CS3)
Errol is an elderly owl owned by the Weasley family. Post owl deliveries are difficult for Errol at his age, but he does his best. When Mr. Weasley sent Harry an “enormous fruitcake and assorted meat pies,” the poor owl needed five days to recover (GF3).
Rowling on Errol:
Poor exhausted Errol is a Great Gray, which in my opinion is the most comical-looking owl in the world – just Google the Great Gray to see what I mean (JKR).
When I dreamed up Errol, the aged, long-suffering and overworked Weasley family owl, I had in mind a picture I thought I had seen, which featured a very comical, large, fluffy, grey, bewildered-looking bird whose breed I had never known. In fact, I wondered whether it had been a real photograph, or whether imagination was distorting the image. It was with sheer delight, therefore, that I rounded a corner on my first ever visit to the aviary at Leavesden Studios, where they were filming Harry Potter and the Philosopher's Stone, and saw a line of big, grey, fluffy, bewildered-looking owls blinking back at me, each an exact replica of the half-remembered picture I thought I might have dreamed. They were all playing Errol, and they are Great Greys (Pm).