Chamber of Secrets

Errol appears at the Burrow a couple of days after Harry's arrival there, when Percy Weasley nearly sits on him at breakfast. Harry initially thinks it's a moulting grey feather duster, but then notices it's breathing. Ron says that he's finally brought an answer from Hermione, that Ron had told her that they were planning to rescue Harry. Ron tries to put Errol on a perch by the door, but he just flops off, so eventually, he leaves Errol on the draining board. Hermione suggests in the letter that Ron should probably try to find a different owl, the trip seems to have almost killed this one.

We next see Errol when he brings a Howler for Ron on the first day of school. He falls into the jug on the table, spraying milk on Hermione. Ron seems horrified, so Hermione points out that Errol is still breathing, but it is the Howler that Ron is scared of.

Prisoner of Azkaban

Errol delivers a birthday present to Harry from Ron, or tries to. The first we see of Errol, he is being essentially dragged through the sky by Hedwig and one of the school's barn owls, having tried to fly all the way from Egypt and not been up to the task. Harry tries to put Errol on the perch in Hedwig's cage, but he falls right off again. A few hours later, when Harry gets up, Errol has recovered enough that he is able to stand on the perch, and he and Hedwig are both asleep. Shortly, though, Harry has to send them both away to The Burrow, as he has agreed to act entirely normal for a week while Aunt Marge is there.

Goblet of Fire

Order of the Phoenix

Half-Blood Prince

Deathly Hallows