Tree Swallows nest in holes made by others such as woodpeckers or man. Both parents help to feed their youngsters. This is the breeding season which means that there is great deal of coming and going. Often one parent must wait at the entrance with a mouth full of food, while the other completes its feeding inside.
The parent (male?) with a mouthful of insects has waited by the cavity opening. As the other parent (female?) climbs over it, the male leans back, moves the nictitating membrane over its eyes, and clamps its bill tightly closed on the insects (although some bristles stick out). Stepping on the male’s head as it leaves, the female continues on its way to fetch more food.