A top-fill hummingbird feeder has a generally upstanding liquid container with a large opening at its top end that is closed and sealed by a removable top or cap. The cap has a two-part construction including an outer shell and an inner sealing member. The inner sealing member includes a sealing element in the form of a vertically elongated, reinforced sealing ring that is received within the top of the container with a friction fit to automatically form a cork-type seal when the outer shell is threaded onto the container. Unthreading of the outer shell pulls the sealing ring out of engagement with the container to remove the cap.