I remember the proverb as something like, "Ein Spass in der Hand (versus) Ein Vögel, am Dach."
Or something like a sparrow in hand versus a bird on the roof.
The best support I could find was this link about something on the head (versus) a Spass.
I'm using a "mapping algorithm" that says that a roof may serve a similar function to a head (in being on top).
So I'm a bit confused about something in hand being compared to something on "top," as opposed to in the bush.
And a LOT more confused about the one-to-one relationship between a sparrow in hand, and the bird, or whatever, wherever.