One must examine birds one intends to eat to ensure that they
are of a kosher species. This is comparable to the way in which
animals must be so inspected, as in Mitzvah #153. The reason for
this mitzvah is the same as for Mitzvah #153: Just as certain
foods are bad for us physically, God knows which things are bad
for us spiritually. He has therefore warned us not to eat these
things and instructed us to inspect animals and birds to ensure
that they are kosher. The Ramban (Nachmanides) does not include
examining animals or birds among the 613 mitzvos, considering
this a necessary precaution to avoid eating non-kosher creatures
rather than a separate commandment. This mitzvah applies in all
times and places. It is discussed in the Talmud in the tractate
Chulin on pages 61a-64b. It is codified in the Shulchan Aruch in
Yoreh Deah 82. This mitzvah is #150 of the 248 positive mitzvos
in the Rambam’s Sefer HaMitzvos; it is not listed in the Sefer
HaMitzvos HaKatzar of the Chofetz Chaim.