How do humming birds mark their territory?

Hummingbirds are small, highly territorial birds that defend their territory against intruders. They establish territories by singing and displaying, and they will chase away any other hummingbirds that come too close. Hummingbirds also mark their territory with scent, which they produce from a gland near the base of their tail. The scent is spread when the hummingbird hovers in mid-air, and it serves as a warning to other hummingbirds that this territory is already taken.