Yes, this bird is peeing. “Don’t they normally use the cloaca?” you might ask. Well, hummingbirds expel a lot of their body weight in clear urine daily. Because their diet consists entirely of massive amounts of water-heavy nectar, their kidneys filter excess liquid to keep them lightweight enough to fly.

Source: https://www.audubon.org/magazine/do-birds-pee-hummingbirds-do-lot