I spotted this herring gull sitting on (I think) its eggs in the corner of the top deck of a parking garage in Portland today. It’s not the most secure spot to raise offspring, but I suppose you make do with the options presented when you’re a expectant gull. The Cornell Lab of Ornithology, my go-to for bird facts has this to say.
Several days before egg-laying, pairs hollow out up to four depressions 10–15 inches across with central depressions 4–8 inches wide and about the depth of an egg. They line the scrapes with vegetation, feathers, plastic, rope, or other materials. The pair chooses the final nest from these alternates. After the female lays her eggs, the pair continues to add vegetation to this nest throughout the monthlong incubation. Sand nests are sometimes left unlined or only sparsely lined.
It also says that after the chicks hatch, both parents will feed them day and night for up to 12 weeks, splitting foraging shifts to offer each chick up to half a pound of food per day. So, this gull’s work is just starting. Good luck!