A top-fill hummingbird feeder is provided having a liquid container with a liquid flow opening at a lower end and a removable cap at an upper end, a feeding basin positioned below the liquid container, and a sealing mechanism associated with the liquid flow opening and the feeding basin. The sealing mechanism includes a bottle seal assembly configured for removable coupling with a base of the feeding basin, and a float valve captured by said bottle seal assembly to prevent rotation thereof while allowing the float valve to move upwardly and downwardly with changing nectar levels in the feeding basin. The feeding basin is filled by gravity feed of the liquid in the container through the liquid flow opening when the sealing mechanism is open. When the feeding basin reaches a full position, the liquid nectar raises the float valve which, in turn, acts to close the liquid flow opening.