Mark White's inspiring picture is of a White-Tailed Tropic Bird high over Kauai, Hawaii..
A N.N. Taleb aphorism says: "Asking science to explain life and vital matters is equivalent to asking a grammarian to explain poetry." So, any Wiki description of Tropic Birds pales in comparison to Hopkin's ode to a bird that soars "upon the rein of a wimpling wind in his ecstasy!"
Gerard Manley Hopkins (1844–89). Poems. 1918.
The Windhover
To Christ our Lord
I caught this morning morning’s minion, king-
dom of daylight’s dauphin, dapple-dawn-drawn Falcon, in his riding
Of the rolling level underneath him steady air, and striding
High there, how he rung upon the rein of a wimpling wing
In his ecstasy! then off, off forth on swing,
As a skate’s heel sweeps smooth on a bow-bend: the hurl and gliding
Rebuffed the big wind. My heart in hiding
Stirred for a bird,—the achieve of; the mastery of the thing!
Brute beauty and valour and act, oh, air, pride, plume, here
Buckle! AND the fire that breaks from thee then, a billion
Times told lovelier, more dangerous, O my chevalier!
No wonder of it: shéer plód makes plough down sillion
Shine, and blue-bleak embers, ah my dear,
Fall, gall themselves, and gash gold-vermillion.