There is a Biblical command to send away a mother bird before taking the eggs from the nest. This Misva is subject to numerous different conditions, including the requirement that the nest does not belong to the individual. The Torah (Debarim 22:6) introduces this Misva by describing a case where "a bird’s nest happens to be before you," indicating that the eggs do not belong to the person. Only in such a case does the obligation of "Shilu’ah Ha’ken" apply.
This gives rise to the question of under which circumstances a person can perform this Misva with a nest in his property, such as on his porch or in his yard. Do the bird and eggs belong to him, such that the Misva does not apply, or do we view them as ownerless, thus allowing one to perform the Misva?
Generally speaking, Halacha grants a person legal ownership over everything in his domain. In principle, then, the presence of eggs in one’s property automatically results in his ownership over them. In practice, however, the status of the eggs depends upon the mother bird. So long as the mother has never left the eggs, and has been continuously sitting on them, the eggs are considered part of the mother. And since the mother can fly away at any moment, it is not considered under the person’s ownership. By extension, then, the birds are likewise considered public property, and the Misva applies. It is only after the mother leaves the eggs that they enter the person’s possession, at which point he can no longer fulfill the Misva.
Therefore, a person with a bird’s nest in his property must carefully monitor the situation to determine whether the Misva is in effect. He can fulfill the Misva of sending away the mother bird only if the mother had not yet left the eggs.
Some proposed the idea of issuing a verbal declaration that one does not wish to acquire ownership over the eggs. According to this argument, one acquires ownership over objects in his property only by consent; if he expresses his refusal to obtain ownership, then the objects in question remain ownerless. Hence, by making this declaration, one avoids acquiring ownership over the eggs, and he can therefore fulfill the Misva even after the mother bird leaves the nest. However, Rav Shlomo Zalman Auerbach (Israel, 1910-1995) rejected this theory, and held that such a declaration will have no bearing on the obligation of Shilu’ah Ha’ken. The obligation does not apply once the mother bird leaves the nest, even if one issues a declaration in an attempt to prevent his ownership over the eggs.
Summary: The obligation to send away the mother bird before taking the eggs does not apply if one owns the eggs. If one has a bird’s nest in his property, he can fulfill the Misva only until the mother bird flies away from the nest. Once the mother flies away, one cannot fulfill the Misva when it returns.
