"Common swifts" refers to a type of bird called swifts that are often seen in many places. They are called "common" because they are widespread and not rare or unusual. Full definition
Brazilian free - tailed bats may have snatched the title for the fastest muscle - powered flight, outpacing even the record - holding common swift (newscientist.com)
Common swifts probably sleep and mate on the wing, and juvenile birds may fly even longer than adults — perhaps for two years non-stop (newscientist.com)
Liechti says researchers have previously asserted but never proved that newborn common swifts spend three years aloft before landing for breeding. (newscientist.com)