Devarim 22:6,7 records that if a person is going along a road, and happens to find a nest with a mother bird and her young (either eggs or babies), then he/ she cannot take all of the birds. He/ she must send away the mother bird, and then takes the eggs or the baby birds. Upon speaking to people, I realize that there has developed a misunderstanding concerning this law. Some people believe that the law is that whenever one comes upon a nest, he/ she must send away the mother bird. This is not the law, just an act of cruelty. A person only sends away the mother bird if he/ she wants to take the young birds. If the person has no desire to take any of the birds, then he/ she can keep right on walking without sending off the mother bird.
The law also only applies if the person happens to find this nest, but does not apply if the person raises birds, as then a person can take both the mother and her young together. It is not clear to me if the law applies if a person specifically goes searching to find nests, and he/ she wants all of the birds in the nest. In this case, the birds are wild birds, but then his/ her finding is not a chance occasion.
Why is the mother bird released or chased away? Rashbam (on 22:6) compares this law to the law in Vayikra 22:28, not to kill a mother cow or sheep with their young, and writes that taking both the mother and her young is cruel and gluttonous. With regard to the second idea, this might be gluttonous, but this cannot be the reason it is forbidden since one can eat the mother and young together if one raises them.
Ibn Ezra (on 22:6) and the Rambam (Moreh III:48) also write that it is cruel to take the mother with her young. The Rambam writes "if then the mother is let go and escapes of her own accord, she will not be pained by seeing that the young are taken away (Pines' translation, 1963, p. 600). Yet, does she really go away? Most likely she flies above and still sees her young being taken away. Finally, the sending away itself is also cruel, and if the mother bird really goes away, when she comes back and sees the empty nest, she will be "sad." In addition, if this act is really so cruel that it is forbidden, why then can one take the mother and her young when they are being raised in a bird coop?
Ramban writes that the law is not for the sake of the birds, but to teach people not to be cruel. Presumably the idea is that if one is concerned for the feelings of the mother bird, then one will be concerned for humans. Yet, again the act of sending away the mother bird is cruel and the mother bird can continue to see her young being taken away from above. Furthermore, again why then is it allowed to take the mother and young when you raise the birds in a bird coop?
Ramban (also see Abravanel) adds that maybe the goal is maintain the species since the mother bird can reproduce elsewhere. However, this seems to be quite coincidental that the person happened to come across a species that was on the verge of being extinct. Furthermore, with this reason it is not clear why the person can eat the young.
My understanding is that the goal of the law is that a person should not act like an animal. If an animal is walking along and saw the nest, the animal, say a cat, would pounce on the mother bird, and then afterwards eat the young. A person is commanded to act in manner different from animals to show that people are not animals since people have G-d's image within them (Bereshit 1:26). With this idea, we understand why it is permitted to take the mother and young when they are being raised in a bird coop since when a person raises birds, he/ she is not acting like an animal.