Definition of "tiercel"

In this wise, the glossy bright-eyed kestrel, whom tiercels’ training could not reclaim, shook off silver bells, and velvet hood, and broidered jesses; and fled away—to consort, henceforward for evermore, with gleds, and hawks, and such birds of prey as make their nests deep in Bohemian forests, or in the desolate places of the Wilderness that girdles the frontier of the reputable world.

1866, [George Alfred Lawrence], “Evasit”, in Sans Merci; or, Kestrels and Falcons, volume III, London: Tinsley Brothers, […], page 126

He is a tiercel, lean and long and supple-winged, the first of the year.

1967, J. A. Baker, The Peregrine, page 39