Definition of "shrilly"

[T]he thwarted Hawk circled above, calling shrilly.

1948, Alec H. Chisholm, Bird Wonders of Australia, page 96

The night—its silence—its rest, was rent in twain by a savage, a sharp, a shrilly sound that ran from end to end of Thornfield Hall.

1847, Charlotte Brontë, Jane Eyre

Yet there they sat, as stones, silent and still. / Sudden a voice, a feeble shrilly voice, / Rose from the inner tent […]

1860, Robert Stafford, Enoch, a Poem in Three Books