Recommendations for telephoto lenses

Hello! I am looking for recommendations for telephoto lenses with adjustable zoom, especially any that go 300mm plus. My budget is around £500, ideally less but would increase if it made a massive difference. I shoot with a Canon EOS 1100D. Happy with any brand that is Canon compatible, I have been shooting for a while sporadically but would say I am still a total novice when it comes to camera equipment so any advice is appreciated! I will be using the lens for wildlife photography, particularly photographing birds. Cheers!