Read it through once

Tess guessed at once the meaning of this. The birds had been driven down into this corner the day before by some shooting-party; and while those that had dropped dead under the shot, or had died before nightfall, had been searched for and carried off, many badly wounded birds had escaped and hidden themselves away, or risen among the thick boughs, where they had maintained their position till they grew weaker with loss of blood in the night-time, when they had fallen one by one as she had heard them.