Webster 1913 notes the phrase
pelican in her piety, but does not fully convey the strangeness of the
heraldic pelican. In
heraldry, a pelican is basically an
eagle. Yup. It's got a
beak like an eagle, the head of an eagle, and it's got an eagle's colours if you depict it
proper, i.e. in its "natural" colours.
A pelican is always plucking at its breast with its beak to draw blood. This is called vulning itself (= wounding). Even when you can't see its breast, when the object depicted is just a pelican's head, its head is drawn back to vuln itself.
A pelican in her piety is a pelican vulning herself while sitting in a nest with her brood of baby birds drinking the blood she's letting flow for them.
In modern depictions the pelican may be more recognizably a pelican, but is still always in its peculiar attitudes.