This is a tall order because Hughes' poem and Hardy's poem are nothing alike in mood, tone, theme, metaphor, emotional impact or imagery. However, let's give it a go. One similarity is that in both poems, there is listening. In Hughes' "Full Moon and Little Freida," the narrator says Little Frieda is listening ("And you listening") after having listed the sounds she hears, sounds that define the night because the perfect darkness veils all sight ("a dog bark and the clank of a bucket"). In Hardy's "The Voice" the poetic speaker (in this case, Hardy himself) says that he hears the woman he has lost to death calling to him ("how you call to me, call to me, / ... / Can it be you that I hear?"). A common poetic device they both use is the poetic technique of metaphor. Hughes uses a metaphor to compare the walking cows to a "dark river" and "boulders," and Hardy uses a metaphor to compare the north wind to ooze, a liquid that moves slowly through small narrow places, like barren "thorn" branches.
Hughes employs nature imagery related to a farm on a pleasant though dark evening, mentioning "spider's web," "dew," stars, "Cows," a lane, "hedges," "wreaths of breath." Finally the "Moon! Moon!" appears to light the night and give Little Frieda a happy thrill before bedtime. Hardy employs nature imagery related to a desolate barren meadow swept by a cold northern wind, implying spring time ("when our day was fair"), a road leading to a town ("I drew near the town"), mist ("wan wistlessness") and mentioning "breeze," "wet mead" [meadow]), leaves of late autumn or early winter ("leaves around me falling"), north wind and barren thorn bushes ("Wind oozing thin through the thorn from norward").