Gemara

138b (Mishnah): Shilu'ach ha'Kan does not apply to Mezuman (what a person owns).

Geese or chickens that nested in an orchard are not Mezuman;

One is exempt if they nested in his house, and from sending domestic doves.

139a - Question: A verse taught that the Mitzvah does not apply to Kodshim. What is the case?

If one was Makdish a bird in his house, he is exempt. "Ki Yikarei" excludes Mezuman!

Answer #1: He lifted the chicks, was Makdish them, then put them back.

Rejection: Even if they were Chulin, he would not have to send the mother!

(Mishnah): If one took the chicks and returned them to the nest, and the mother returned, he need not send it.

Answer #2 (Rav and Shmuel): He was Makdish his bird, and then it fled (and now he recognizes it, and it sits on its young).

139b (Beraisa): "Lefanacha ba'Derech" teaches that the Mitzvah applies only to cases similar to "ba'Derech," i.e. it is not Mezuman;

This is the source to obligate (sending) doves that nested in a dovecote or attic, birds that nested in a hole in a wall or in a tower, and chickens and geese that nested in an orchard, but not birds that nested in a house or domestic doves.

141a (Mishnah): If one sent the mother and it returned, he must send it again, even four or five times - "Shale'ach Teshalach."

141b - Question (a man): What is the law regarding Teimah (a Tahor bird)? Perhaps it lays only one egg at a time!

Answer (Rava - Mishnah): One must send the mother even if there is only one egg or chick in the nest.

The man sent it. Rava set a trap and caught it.

Question: Rava should have been concerned lest the man suspect that Rava obligated him to send it for Rava's own gain!

Answer: He trapped it kil'Acher Yad (far away, so the man would not see).

(Beraisa): If doves nested in a dovecote or attic, one must send the mother. One may not take, due to Darchei Shalom (to avoid ill will).

Question: R. Yosi b'Rebbi Chanina taught that a Chatzer (or attic or any land) acquires for its owner without his knowledge. If so, he owns the eggs, so it is Mezuman. He should be exempt from sending the mother!

Answer: Since one may not acquire the eggs, the Chatzer does not acquire them for the owner (of the Chatzer);

(Rav Yehudah): One may not acquire eggs while the mother is on them.

Levi bar Simon transferred ownership of the yield of his dovecote to Rav Yehudah. Shmuel instructed Levi to hit the nest, so the mother will jump up, allowing Levi to acquire so he can transfer ownership of them to Rav Yehudah.

Rishonim

Rambam (Hilchos Shechitah 13:5): One holds the mother by its wings and makes it fly away. If he sent it and it returned, even four or five times, he must send it, for it says "Shale'ach Teshalach."

Rambam (7): If one took the children and afterwards the mother returned, he is exempt from sending her. The Torah forbids only trapping her so she cannot fly away due to her children, over which she hovers, lest they be taken - "the mother crouching on the chicks." If he expelled her from his hand and then he trapped her, it is permitted.

Radvaz: The Gemara says that Rava seized the bird kil'Acher Yad. This was so there would not be suspicion. When there is no suspicion, one may overtly trap it.

Kesef Mishneh: The Rambam learns from the case of Rava. He holds that there is no difference between the one who sent it and anyone else. (Anyone may take it afterwards.)

Rambam (8): Shilu'ach ha'Kan applies only to Eino Mezuman, e.g. doves of a dovecote or Aliyah, or birds that nested in an orchard, for it says "Ki Yikra." One need not send Mezuman, e.g. geese and chickens and doves that nested in the house.

Rambam (18): One may not acquire the eggs as long as the mother is on them. Therefore, even if it was lying on eggs or chicks in one's Aliyah or dovecote, they are not Mezumanim. Just like he cannot acquire them for others, his Chatzer does not acquire for him. Therefore, he must send it.

Kesef Mishneh: It should say 'just like he cannot acquire them, his Chatzer...' The words 'for others' are a printing mistake.

Lechem Mishneh: The Gemara said 'just like he cannot acquire them, his Chatzer...' It did not mention others. It seems (i.e. one might have thought) that he can acquire for himself, for no one else may take them from his Chatzer. One may not take them until sending the mother. If he sends the mother, this is absolute theft (to take the young), for the Chatzer already acquired it. Therefore, the Rambam says that even though others cannot acquire them, he (the owner of the Chatzer) cannot be Makneh (transfer ownership of) them as long as the mother was on the eggs, like we find that Levi bar Simon could not be Makneh them as long as the mother was on the eggs.

Ran (48a DH she'Kanenu): The birds fled and left the house and do not return. They become wild. The orchard is not Mezuman, for they can flee from there.

Ran (DH she'Hayu): We do not say that since they were initially Mezuman before they fled, also now he is exempt.

Ran (DH Yonei): If one hit the nest and the mother went up, his Chatzer acquires the eggs, so it is Mezuman and he is exempt. The Mitzvah applies to doves of a dovecote when he never lifted the mother above her young from when she laid the eggs, for then his Chatzer did not acquire.

Poskim

Shulchan Aruch (YD 292:2): If a Kan is Mezuman, e.g. doves that normally grow among people in houses, one is exempt (from sending). However, one must send doves of a dovecote or Aliyah, or birds that nested in Tapichim (earthenware Kelim built into houses for birds to nest in) or towers, and geese or chickens that nested in an orchard. This is if the mother never was lifted above the eggs from when she laid them. If she was lifted above them and one owns the place of the nest, his Chatzer acquired for him so this is Mezuman, and he is exempt.

Beis Yosef (DH u'Mah she'Chasav v'Eino): Rashi explains that if birds that nested in an orchard fled, they no longer belong to you.

Shach (3): Rashi connotes that they are not guarded in the orchard. If they are guarded, he is exempt. R. Yerucham agrees. In such a case, it is like in one's house.

Beis Yosef (DH u'Mah she'Chasav v'Eino): Rashi explains that after one sent it out of his hand, if he can catch it again, it is permitted. We find that Rava trapped a bird after someone else sent it away.

Shach (5): We must say that he elevated the bird and it left his hand. If not, since he could not acquire it, since it did not leave his hand and he did not fulfill the Mitzvah, his Chatzer does not acquire for him. Alternatively, it lifted itself. Therefore, it suffices if it is not touching the Kan, like the case of hovering (Sa'if 11).

Shach (6): One's Chatzer acquires for him even without his knowledge.

Shulchan Aruch (4): One must send the mother until it leaves his hand, and then he may take the children. After it leaves his hand he may take it if he wants.

Bach (4): Rashi holds that the Mishnah obligates sending it four or five times only if it never left his hand. If it left his hand once and returned, he may take it. He need not send it again. He may sieze it, since it returned by itself. If it did not return, he may not sieze it, since it did not return. Someone else may sieze it, like the case of Rava. The Rambam explains that even from when he first sends the mother, he may sieze her after she left his hand. The Tur explains that there are two connotations. One may not take the mother on the children, rather, one must send her until she leaves his hand. If she did not left his hand and returned, he may not take her. He must send her even 100 times, until she left his hand. Afterwards, he may take her. The other connotation is that if he sent her and she did not leave his hand, he may not take the children. First, he must send her out of his hand, and then he may take the children.

Bach (1 DH u'Mah she'Chasav Afilu): One must send doves of a dovecote or Aliyah if they are wild doves that nested in his dovecote or Aliyah. The same applies to birds that nested in Tapichim or towers, i.e. if they never were lifted above the eggs from when they laid them.

Bach (DH u'Mah she'Chasav v'Avazin): Geese or chickens that nested in the house are exempt if they never fled. If they once fled, they are like wild birds that nested in a dovecote or Aliyah. One must send them.

Shach (8): Even if he did not take the children, since it left his hand, it is by itself, so he may take what he wants.