[Heb., sis].

One of the fastest of all flying birds, regularly attaining speeds of over 100 km/​hr (60 mph) and capable of bursts of speed probably of 200 km/​hr (120 mph) or more. It uses its long, thin scythelike wings energetically and with seeming tirelessness as it swoops and darts after insect prey, which it engulfs while on the wing. Of the four varieties of swifts to be seen in Israel, the Alpine swift (Apus melba) is the largest and is distinguished by its white underparts. It is the first of the migrating swifts to appear in Palestine at the approach of spring, followed shortly thereafter by long streams of common swifts (Apus apus). Their nests are built in dark places, often under the eaves of roofs, and sometimes inside hollow trees or on the sides of cliffs, and are formed of straw and feathers cemented together with the sticky saliva that the bird’s glands produce. The swift’s feet are evidently not structurally designed to allow for walking or perching, so the bird obtains all its food and nest materials while in flight and even drinks by skimming over the surface of the water; it rests by clinging to vertical surfaces. The swift’s cry has a somewhat wailing, melancholy note.

That the Hebrew sis identifies the swift is indicated by the use of the same name in Arabic for that bird. The name is suggested by some scholars to indicate a rushing sound; but others consider the name to represent the shrill si-si-si cry of the swift.

Hezekiah, upon recovering from illness, said in a thoughtful composition that he ‘kept chirping like the swift,’ evidently in a melancholy way, and the prophet Jeremiah used the migratory swift as an example when rebuking the people of Judah for not discerning the time of God’s judgment.​—Isa 38:14; Jer 8:7.