This is a signed painting by a well known British ornithologist and artist. Information about the painter and a handwritten note from him are shown on the back. You can read more about the artist at https://www.henrywilliamson.co.uk/?view=article&id=382:r-a-richardson&catid=65:bibliography and at http://pennyshotbirdingandlife.blogspot.com/2022/05/my-childhood-memories-of-richard.html
It is 18" wide by 15" tall.