Ki Seitzei, Devarim 22:7. Shiluach Hakan. Dense Fog.

Besides the spinning compass needle of whether Shiluach Hakan is a mattir for someone that needs birds or eggs, or a precious opportunity to be seized, (despite the Minchas Elazar 3:43, the Chasam Sofer's shitta is still a shittah) Shiluach Hakan generates widely disparate ideas in hashkafa as well.

The Gemora in Brochos 33b and the Mishneh in Megilla 25a say “האומר: "על קן צפור יגיעו רחמיך", ו"על טוב יזכר שמך", משתקין אותו..”  One who says ""To the nest of a bird does Your compassion reach! On the good shall Your Name be mentioned!" must be silenced.  The Gemora says two reasons; because the Mitzvos are nothing more than Gzeiros- God's decrees, and because he elicits Kina- jealousy from those that are not thus favored.

The Ramban here says that the reason for the Mitzvah is not because of the birds, but to inculcate middas rachamim in us.  

The Maharal in Tiferes Yisroel 6 argues and says that it still doesn’t explain why birds and not another creature was chosen to demonstrate this middah, so while it shtims with “gzeiros”, it’s still not like “kin’a.” 

The Rambam in Moreh 3:48 says that the reason is because Hashem is a rachamon, and we should learn from this sensitivity to a creature’s grief that we should be much more careful with people.  He then says, what about the Gemora in Brochos?  And he answers that that Gemora is only going according to Reb Yehuda in Bova Metzia 115a that “ein dorshin taima dikro”, but we hold like Reb Shimon that dorshin.  

(Harav Shimon Krasner (author of the acclaimed Nachalas Shimon on Tanach)  pointed out that the Rambam does not mention R’ Yehuda or R’ Shimon, he simply says that the Gemorah is according to those that hold that “ein ta’am lemitzvos;”  which SK says refers to the people who hold that mitzvos are for discipline and have no underlying reason at all.  However, as is evident in the Maharal and others, they learn like me.)  The Maharal also goes to town on this, and says that he cannot believe that the Mishna in Brochos, about which no tanna says a word, is only according to one shittah, and especially a shitta that we don’t hold of. 

The Magiah in the Maharal (Yad Mordechai, R’ Chaim Pardes,) brings that the Rambam really paskens like R’ Yehuda in Malveh veLoveh 3:1, but that the Lechem Mishneh there explains that he really holds like R’ Shimon.  Also, Tosfos in Sota 14a d’h Kedei Leyag’a says that R’ Yehuda only argues on R’ Shimon where the ta’am will result in a nafkeh minna lehalacha.  But where there’s no nafkeh minna, everyone darshens.  (This does not explain the Rambam in the Moreh, because obviously the Gemora in Brochos doesn’t want to darshen even here, and the Rambam says that whether you darshen is tolui in the machlokes R’Y and R’S.)  Anyway, the Maharitz Chiyos there says that the Tosfos in Sotah is the shitta of the Rambam and explains why the Rambam often gives reasons for mitzvos.  Tosfos in Megilla 25a brings a piyut from the Kallir which seems to say that it is because of rachamim, but the Maharsha says that the piyut is no raya, but then brings from a Targum Yonasan in Vayikra 22:28 that oso ve’es bno is rachamim.  Also, the Maharsha in Brochos also says that the meshaskin is only because he’s doing it in tefilla, which is matil kin’a, but the mitzvah can be because of rachamim, just like tzedaka. 

And, adding to the fogginess, the Rambam in Tefilla 9:7 and the pirush hamishne in Brochos and Megilla brings the din of meshaskin and the reason of ‘gzeiros’. 

Also, remember the Rashba in Teshuvos 4:253 (with some prefatory words of kovod to the Rambam,) that it is best to just ignore all the reasons the Rambam gives for mitzvos, because “yeish kushyos gedolos kim’at bekulan,” and only Hashem knows His reasons.

And of course, in contrast with what the Gemorah and the rishonim are mashma (that this is a mitzvah that shows rachamim), is the Zohar that says that Shiluach haKan causes grief to the mother bird, and it is me’oreir rachamim by the Ribono Shel Olam, who says, if this bird is so grief stricken at being separated from its young, how much more so am I saddened by the siluk Shechina from my children, Klal Yisroel.

There is also the Gaon in his pirush on Mishlei, 30:17, where he says that all the mitzvos of Hashem are Rachamim, and the reason meshaskin is because this particular mitzvah has an element of achzorius in it, by chasing away the mother.

Doctor Meir Zahtz suggested that a “ki yikorei” of achzorius done by a Ben Yisroel causes a revulsion and generates a reaction of rachamim.  This is like a weakened virus is injected to elicit an immune reaction which will protect the patient from more serious infection.  Here, a little achzorius elicits a flood of rachamim.