Nearly everyone can identify a robin's cup-shaped nest, fashioned of mud and grass. The reason they are so common is that robins usually build a new nest for each brood they raise. They've even been known to build several nests at once, sometimes side by side. Whether they do this because they are confused or to confuse predators isn't known, but both parents participate in this flurry of building. Cardinals, finches, blue jays, mocking birds, crows and many other species also build some variety of the cup-shaped nest.
Hummingbirds build the tiniest nest of all, little more than an inch across.
It usually straddles a small, downward sloping branch and is easily overlooked. Female hummingbirds construct the nests and use spider webs and bits of lichen to disguise them. Because their nests are so tightly built, hummingbirds can return to them year after year. The female red-eyed vireo builds a basketlike cup that hangs by its rim from the fork of a thin branch. She often uses grapevine bark in the construction.