Feather Maintenance
Preening is an important aspect of feather maintenance. In the capture, a male Tree Swallow [one of our native bird species] runs a flight feather through its beak during the act of feather grooming. By doing so, the swallow is more than likely anointing the plume with oil from its uropygial gland [oil gland] or it may be simply re-conforming the feather’s structure … or both.
~ Anecdote and Tree Swallow capture, Feather Maintenance © Jerry L. Ferrara