Any bird is a non-kosher bird if it splits its toes two on each side when a thread is stretched, or if it seizes and eats its prey midair. Any bird that lives with and resembles a non-kosher species is itself non-kosher.
החסידה — This is the white stork, cigogne in old French And why is it called חסידה? Because it deals kindly (חסד) with its fellows in respect to food (Chullin 63a).
הדוכיפת — the wild cock which has a double comb (כרבלת). In O. F., herupé; (English = hoopoe). And why is its name called דוכיפת? Because its ornament (הודו) is tied tegether (כפות): this refers to its comb (which being doubled, appears to be tied up). It is also called נגר טורא, mountain-splitter, because of its doings, just as our Rabbis explained in Tractate Gittin 68b in the chapter commencing שאחזו מי.
העוף שרץ PROLIFIC CREATURES AMONGST FOWL — These are the thin, lowly creatures which move upon the ground, such as flies and hornets and gnats and grasshoppers (cf. Rashi on Genesis 1:20).
ממעל לרגליו ABOVE ITS FEET — Quite close to its neck it has something like two feet, in addition to its real feet; when it wants to fly and to spring off the ground it presses itself strongly on the ground with those two knees and so it flies. There are many of these, such, as those which we call longouste (sea-locusts), but we are not expert in regard to them, — as to which we are not permitted as food, — because four characteristic marks of cleanness are mentioned by our Rabbis in respect to them, viz., four feet, four wings, and קרסולים, i. e. the כרעים mentioned here, and that their wings cover the greater part of them. All these characteristics are present in these which are found amongst us, but there are some of them which have a long head and there are some which have no tail, matters which do not affect the question of cleanness (Chullin 59a). It is, however, necessary in order that they shall belong to the clean species that they should bear the name חגב (Chullin 55b), and in this respect we do not know how to distinguish one from another [i. e. we have no tradition as regards to these locusts whether they belong to the species which was in olden (Talmudic) times called חגב or not, and consequently in spite of the other four marks of cleanness we cannot distinguish them from unclean locusts which also show the same marks but are unclean because they do not bear the name חגב].
"Whatever God created has value." Even the animals and the insects that seem useless and noxious at first sight have a vocation to fulfil. The snail trailing a moist streak after it as it crawls, and so using up its vitality, serves as a remedy for boils. The sting of a hornet is healed by the house-fly crushed and applied to the wound. The gnat, feeble creature, taking in food but never secreting it, is a specific against the poison of a viper, and this venomous reptile itself cures eruptions, while the lizard is the antidote to the scorpion. Not only do all creatures serve man, and contribute to his comfort, but also God "teacheth us through the beasts of the earth, and maketh us wise through the fowls of heaven." He endowed many animals with admirable moral qualities as a pattern for man. If the Torah had not been revealed to us, we might have learnt regard for the decencies of life from the cat, who covers her excrement with earth; regard for the property of others from the ants, who never encroach upon one another's stores; and regard for decorous conduct from the cock, who, when he desires to unite with the hen, promises to buy her a cloak long enough to reach to the ground, and when the hen reminds him of his promise, he shakes his comb and says, "May I be deprived of my comb, if I do not buy it when I have the means." The grasshopper also has a lesson to teach to man. All the summer through it sings, until its belly bursts, and death claims it. Though it knows the fate that awaits it, yet it sings on. So man should do his duty toward God, no matter what the consequences. The stork should be taken as a model in two respects. He guards the purity of his family life zealously, and toward his fellows he is compassionate and merciful. Even the frog can be the teacher of man. By the side of the water there lives a species of animals which subsist off aquatic creatures alone. When the frog notices that one of them is hungry, he goes to it of his own accord, and offers himself as food, thus fulfilling the injunction, "If thine enemy be hungry, give him bread to eat; and if he be thirsty, give him water to drink."

