Answer: I don't think that would be the maple seeds, they generally stay within the samara or helicopter and are not round. If there are caterpillars in the tree, then that could explain it, yes. However, that sounds a bit large to be caterpillar waste -- generally this is dark but smaller than the head of a match. Perhaps there is a small animal running on the deck at night? Or, perhaps they are seeds from some other plant that is being eaten by birds or squirrels in the tree? I'm sorry I can't be more specific for you.
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