better to have a small real advantage than the possibility of a greater
proverb refers back to mediaeval falconry where a bird in the hand (the
falcon) was a valuable asset and certainly worth more than two in the
bush (the prey).
first citation of the expression in print in its currently used form is
found in John Ray's A Hand-book of Proverbs, 1670, which he lists it as:
'one'] bird in the hand is worth two in the bush
much the phrase predates Ray's publishing isn't clear, as variants of it
were known for centuries before 1670. The earliest English version of
the proverb is from the Bible and was translated into English in
Wycliffe's version in 1382, although Latin texts have it from the 13th
Ecclesiastes IX - A living dog is better than a dead lion.
Alternatives that explicitly mention birds in hand come later.
term bird in hand must have been known in the USA by 1734, as that is
the date when a small town in Pennsylvania was founded with that name.