Bird nests come in many different styles, and we could find many different ways to categorize them. Typically, we organize them based on their type or style. So, here they are.
Adherent. These nests are made of mud and built against a surface, such as a cliff, tree, or under the eaves of a house. Some are shaped like a cone, some are globular and nearly round, while others are shaped more like a hemisphere. Mud or dirt is collected and added to the nest, where it is allowed to dry before more is added. In some cases, dirt is mixed with saliva to create the mud for the nest.
Aquatic. These nests are built out in the water. In some species, a foundation of sticks, rocks and vegetation is build to the level of the water, and the actual nest is then build on top of this foundation. In other species, the nest actually floats on top of the water. Others will build a nest in shallow water, where the nest is basically floating, but is anchored in one or more places.
Burrow. As the name implies, these nests are built by burrowing into the ground. Depending on the species, these burrows may be made horizontally into a vertical cliff face, or vertically into the ground. There is a chamber either off of or at the end of the tunnel, which can vary in length depending on the species. Since birds don’t have shovels, they rely on their beaks and feet to build a burrow.
Cavity. These nests are similar to a borrow, except that they are made in trees. A small hole leads a short way to a chamber where the eggs are laid. Although many species nest in cavities, very few can actually excavate their own. Of those that can, they either chisel an opening with their strong beaks, or chew an opening in soft deadwood. Those that can’t will use natural cavities, or those excavated by another bird. In many cases, they will also use man-made bird houses.
Cup. Perhaps the most famous type of nest, a cup is made of grasses, thin twigs, lichen, spider webs and mud. It contains a deep depression in the middle to hold the eggs. These nests are typically nestled in the fork of a tree, but can certainly appear anywhere an industrious bird feels safe. These are built by collecting the building materials and flying it to the nest, where it is applied. Mud or spider webs may be used to adhere the building materials together.
Enclosed. Similar in build to a cup nest, but with bigger walls, a roof, and a small entrance hole.
Mound. These nests basically amount to a compost pile made of twigs, leaves, grasses and soil. Eggs are laid inside the mound, and as the material decomposes it generates heat to keep the eggs warm. To build a mound, most species will use their feet to collect and pile up debris.
Pendant. These are hanging nests, woven from grasses and other plants, and suspended from a tree branch. The nest itself is either a cup nest or a completely enclosed sack with a single entrance hole. The birds that build these are very skilled, indeed.
Plate. A plate nest is similar to a cup nest, but has a very shallow depression.
Platform. While most nests are just big enough for eggs and the incubating mother, platform nests are very large, often many times bigger than the birds that build them.
Scrape. Very simply, a scrape is a very shallow cup made in soil or vegetation, usually just deep enough to keep the eggs from rolling away. Sometimes these nests are lined with grasses, bits of shells, or feathers. There are various methods used to build these types of nests. Some birds will roll their bodies into soft sand or vegetation, others will use their feet to dig out a little depression.
For those of you in North America, A Guide to the Nests, Eggs, and Nestlings of North American Birds (Princeton Field Guides)
