The presence of a backyard hummingbird feeder can reveal the competitive nature of hummingbirds. Notorious for chasing each other away from nectar sources, hummingbirds are territorial because they need to stay fueled. From Audobon.org:
As the world’s smallest birds, hummingbirds have a high surface-area-to-volume ratio. That means they lose a lot of heat through their skin (the same way, for example, small ice cubes melt faster than big ones). The problem is compounded by a lack of downy feathers, the fluffy insulation that keeps most birds warm. Skipping the down shaves weight, but the birds must compensate by refueling constantly, consuming two or three times their body weight every day.
High in the Talamanca Mountains of Costa Rica, where there are fewer nectar-rich flowers, there’s even more competition for food. This Untamed clip from NatGeo WILD showcases how these small but agile birds jostle for sustenance: Hummingbird Battleground.UCLA’s Hummingbird Whisperer, hummingbirds fly, shake, and drink in slow motion, hummingbird hatchlings in their nest with mother Rosie, and over 30 hummingbirds splash & chatter in a bird bath.