Me'ilah 14 - A Bird Nest Atop A Tree
A bird nest atop a tree consecrated to the Temple should not be used, by the decree of the Sages, but there is not prohibition of misappropriation. Even if we assume that it was built from the twigs that grew after consecration, they may be prohibited, but not with the serious misappropriation laws. If that nest was on top of a tree planted for worship, he should knock it down with a stick, then take it.
Rabbi Yochanan and Resh Lakish were discussing a different subject, and in doing so elucidated our ruling. If an idol broke on its own, is it permitted for use? Rabbi Yochanan said that no, because only an idol worshiper can nullify an idol. However, Resh Lakish said that yes, because the idol worshiper reasons as follows, "This idol could not save itself, how can it save me?!" - and nullifies it in his heart.
Resh Lakish then asked Rabbi Yochanan, "The nest on top of a worshiped tree was made of twigs broken off by birds, so it is the same as an idol that broke on its own, and it is nevertheless permitted!" Rabbi Yochanan replied though that the birds brought the twigs from elsewhere.
Art: Neville Henry Peniston Cayley - Kookaburras Feeding at a Nest in a Tree