To me, 'vigilant' is a somewhat out-dated word (Biblical, old west 'vigilantes'). Your use is not incorrect, however. It will be interesting to see what other native speakers have to say.
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successorThe horse kept a careful VIGILANCE for predators while it grazed.I've never heard "vigilance" used like this. You probably mean "careful vigil".The horse could keep a constant vigilance for predators while it grazed.