Maple is the type of tree that spreads TONS of seed in the hope that a few will have ideal genetics and land in an ideal place where it doesn't get eaten.
What I do is wait until the strongest few of them are clearly head and shoulders above the rest, then pull the rest out by the roots. [I don't recommend letting these best ones get more than a foot tall before thinning, their root system is expansive. I never had that problem though, because 'winners' always clearly showed themselves by that height for me.]
The winners get to live on and become a coppice feedstock [either for fodder or
compost and for fuel], while the losers are fed to livestock or allowed to dry out and then added to a compost pile.
As for what eats maple seedlings, a better question is what doesn't. Cows, Goats, Sheep,
Rabbits, Ducks and Chickens and Pigs all seem to enjoy them.
EDIT: and apparently people too. That's a new one for me, might try it next spring.