Baby birds stay safe and warm in a nest.
A nest and a perch are two very different things, although birds use both and in some cases birds use both depending on the situation and their needs. Simply put, a nest is a built space that birds can sit or crouch on, while a perch is a perch that a bird must hold on to in order to sit. Nests and perches are used for sleeping and protection from predators, but only one nest can be used to incubate the eggs.
When birds produce eggs, they must be kept warm until they hatch.
When birds build a nest, they collect materials to create a structure and line it or to line an existing space. Depending on the species, these materials can include twigs, feathers, grasses, animal hair, scraps of paper, and a wide variety of other things. Many nests are built in sheltered, hidden areas, allowing the birds to hide in the nest. This is extremely important as the nests are used to incubate the eggs.
Only passerines can perch, as they have feet that allow them to grab things.
When birds breed and produce eggs, they must be kept warm until they hatch. This usually means that one or both parents must sit on the eggs for a set period of time, allowing the embryos to develop into baby birds. The eggs obviously cannot balance on a perch, so a nest must be built to contain them during the incubation period and to protect the young birds until they are old enough to fly.
A hanger, on the other hand, is simply a hanger. Many birds perch to sleep, fly into trees and perch on twigs and twigs for protection from predators on the ground. Birds also stay on perches to keep an eye out for potential prey and stay out of reach of predators. Often a nest and perch are close together, providing options for birds as they breed and raise chicks.
Another crucial difference between a nest and a perch is that while most birds build nests of various types, not all birds nest. Only passerine birds can perch, as they have specifically developed feet that allow them to grasp things. Passerines have three fingers facing forward and one finger facing the other direction, creating a pincer that can be used to hold the bird on a branch even while sleeping, while other birds do not have this ability.