Bald patch on ear - any guesses?

Once again, I seek out the wide knowledge/ experience of the great people on the forum. So Calvin has this little bald spot on his ear and am wondering what it may be. He's been with us for a month now and a week or so ago I saw this little spot and it seemed that the fur in the area was stuck together as if he had got into something sticky. Unfortunately, I did not think much of it and realized that since he gets into water so much, he'll end up washing it off. Then I did not see anything alarming and had forgotten about it since nothing out of the ordinry was visible. Today I see that the little bit of fur sticking together there is missing and there is this little spot. I will call the vet's office but was wondering if anyone wanted to weigh in what it could be. He otherwise does not have any other issues and since he's been here, his fur's been growing and feels thick and soft. Here's a pic attached - it's on the left ear.
Thanks.

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Perhaps he pulled out the hair that was stuck together trying to clean it? If it's in the same place, he probably just kept rubbing at it. Don't know if it's worth taking him to the vet to get a skin scraping or not. I'd definitely call the vet, but my guess is they'll ask you to keep an eye on it.

Chumley had a bald spot on his hear, but it was rectangular, so we figured he must have scraped it on something. We searched around, and finally found a small piece of metal sticking out from a bench at cat-head height. He'd just been to the vet, and we'd had a skin scraping done for a spot on his back he'd been itching, so we knew he didn't have a skin condition or something.

Thanks LDG. I hope that that's what it is -the hair came off when he tried to clean it. Will call the vet's office and see. We hae an appointment with them to get Calvin microchipped this coming weekend and if they are not concerned, will show it to them then.