habían serenado
-they/you had calmed
Past perfect ellos/ellas/ustedes conjugation of serenar.

serenar

Los árboles, in­quietos por la brisa, se preparaban para pasar la noche; también ellos se habían serenado; los pájaros acudían en busca de refugio nocturno entre el denso follaje de esos árboles.
The trees made restless by the breeze were settling down for the night; they too had become quiet; the birds were coming in, taking shelter for the night among the trees that had thick foliage.
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