Bird nests come in a variety of shapes and sizes, from burrows in the ground to tiny cups perched high in tree branches. We’ve rounded up photos of some of the most fascinating nests on the planet, as well as a few unusual places for a bird to build a home.

Sociable weaver nests are the largest built by any bird and often look like massive haystacks in trees. The birds construct permanent nests that house more than 100 pairs of weavers. These nests were photographed in Etosha National Park in Namibia.

Weaver birds make their nests from thin strips of leaves and reeds in Kathmandu, Nepal.

Village weavers weave together grass and strips of leaves to create their nests. The birds are colony breeders, so one tree is often home to multiple nests.

Montezuma’s oropendola is another colonial breeder that builds nests high in tree canopies. The nests are made of woven vines and fibers, and they range in size from 24 inches to 71 inches long.

Barn swallows are the most widespread species of swallows in the world. They build cup nests from mud pellets on the sides of structures like barns, which is how they earned their name.

European Penduline tits build elaborate hanging nests. The nests are tightly woven and so strong that they’ve been used as purses and children’s shoes.

Cup nests are built by several small bird species, including hummingbirds and many passerines. Most of these nests are made from pliable materials like grasses, and many birds use spider silk in their construction.

Spider silk is lightweight, flexible and sticky, which can help bind to the nest to the branch or other item to which it’s attached. Here, a black-chinned hummingbird has built her nest upon an electrical conduit.

The Harris hawk often builds nests on cacti, and it’s the largest bird that makes a home on a saguaro cactus. Nests are constructed from sticks, roots and leaves and placed about 50 feet off the ground. The hawk is able to nest on the cactus by standing on the back of its talons to avoid needles.

A sparrow feeds its young nesting in the barrel of an anti-aircraft gun at the Al-Asad Airbase in Iraq in 2004