An Etymological Dictionary of the German Language/Schwalbe
Schwalbe, f.,‘swallow,’ from the equiv. MidHG. swalwe, OHG. swalawa, f.; a common Teut. term; corresponding to the equiv. Du. zwaluw, AS. swealwe, E. swallow, OIc. svala (gen. svǫlu), f., ‘swallow.’ No certain explanation can be given of the prim. form swalwôn, f.; perhaps it represents swalgwôn-, pre-Teut. swalkuân, to which Gr. ἀλκύων is also traced.