In Macbeth we find allusion to the "falcon towering in her pride of place"; and indeed there is no prettier sport on a still day than a flight at the partridge or the heron with the noble peregrine falcon or her mate the tiercel-gentle.
"A Cotswold Village"
J. Arthur Gibbs
Tassell is a corruption of tiercel, a name given to the male peregrine, so termed, according to the legendary lore of venery- "Because he is, commonly, a third part lesse than the female."
"The Romance of Names"
Ernest Weekley