I purchased a used Mansfield Hummingbird in 1976.
I have long thought it to be an Ibanez instrument based on information from various websites. While Ibanez may have supplied many of the Mansfield guitars, I believe my Hummingbird was made by the Kiso Suzuki company in Japan.
My Mansfield appears to be identical to the Suzuki Hummingbird that can be seen on various websites. Note the unique "zero fret" under the nut. This was not used by Ibanez or Gibson (at least I could not find any evidence that it was) and given the similarities of the Suzuki and the Mansfield this is almost certainly a Suzuki Hummingbird.
Notice in the Mansfield 1975 catalogue (search for Mansfield guitars) that there are two Hummingbirds shown - one with the zero fret and one without. The one without the zero fret seems to be a more accurate copy and is probably the Ibanez Hummingbird.