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Architects of Nature Series: Avian Builders and the Complexity of Bird Nests

a bald eagle perches over a nest of twigs formed in the branches of a tall tree
Crystal Bridges Museum of American Art is closed today, Monday, January 30 due to inclement weather. Any programs, tours, lectures or classes will not be held. If you are a ticket holder for a tour or an event today, we’ll contact you about rescheduling.

The Architects of Nature blog series is inspired by the outdoor exhibition Architecture at Home, located near the museum’s entrance on the Orchard Trail. This exhibition brings together a wide range of voices to explore how architecture can prompt questions about human-centered design, housing attainability, and environmentally friendly design. In this blog series, we ask ourselves: what can nature teach us about these themes? Here, we highlight the importance of bird-centric building techniques.

 

Have you ever considered the construction of a bird nest? Why do some birds use mud to make their nests while others only use sticks? Why are some round while others are oblong or amorphous?

a tit bird perches outside of a white, cotton-like nest with a false entrance made in a tall tree
Cape Penduline tit nest showing the false entrance. Credit: Dirk Heinrich, Namibian.org.

Bird nests are fascinating examples of site-specific, need-based housing. While some birds like the South African sociable weaver build communal nest sites complete with advanced ventilation systems, other birds like the Cape Penduline tit build an elaborate main entrance to throw off predators while actually using a “secret” entrance to access their home.

 

Building techniques are as unique as birds themselves and include piling up, molding, sticking together, interlocking, sewing, and weaving. While the most obvious use of nests is for laying eggs and rearing young, they also serve as protection from parasites and pathogens, insulation, and even as important parts of mating rituals.

You could say that “location, location, location” is the mantra for the (the largest member of the blackbird family). This bird is endemic to the east coast of Central America. It chooses its neighbors wisely, often selecting nesting spots near wasp nests. These wasps, with their ruthless stinging habits, tend to keep away both nest predators and parasitic insects. Additionally, the hanging nests en masse are quite the spectacle. These birds build their nests in colonies. Typically, one male mates with multiple females who are responsible for the nest building. The females are talented builders, using banana fibers, twigs, grass, and vines to weave oblong shaped nests that sway in the breeze. Not only do these unique shaped nests withstand wind, but they are also adept at protecting eggs from falling out of the nest.

 

a brown, bushy cluster of bird nests with multiple holes for openings made on a tall tree by sociable weaver birds
Sociable weaver nests. Credit: Diego Delso, CC BY-SA 4.0, via Wikimedia Commons.
a hanging tree branch with several drooping, brown, sac-looking birds nests built on the ends of the branches
Hanging nests of the Montezuma oropendola in Costa Rica. Credit: Charles J. Sharp, CC BY-SA 3.0, via Wikimedia Commons.

A great home is not only about location, but it’s also about how you make it your own. Humans paint their walls, hang art, and coordinate fabrics in their homes. Male bowerbirds, found in Australia and New Guinea, also work hard to showcase the individuality of their homes. While the structures they make are not necessarily nests, they are marvelous for their sculpture-like quality. Some of these are freestanding and comprised of two “walls” that create an oval shape in the middle, others consist of a flat platform that is flanked by two stick towers that can reach up to six feet in height. These structures are created by multiple generations of males. The oldest one found to-date is 40 years old!

But what makes these structures truly unique is how they are personalized. In an attempt to attract females, the male bowerbirds will collect colorful objects (bottle caps, colored plastic, feathers) and precisely arrange them in ways that are pleasing to the female eye. This practice takes years to perfect and often, juvenile males will work in gangs to steal trinkets from their elders while they perfect the art. Perhaps this is not a neighbor worth having.

a royal blue and black bowerbird with a yellow beak stands proudly in his vertical nest of twigs with blue and yellow items scattered on the forest floor in front of him
A male bowerbird proudly shows his building and decorating prowess. Credit: Photo by Luke Shelley/Shutterstock.

When it comes to homes, is bigger always better? If you are a bald eagle, the answer is yes. While bald eagles are known for their predatory skills, they are equally known for their giant nests. Bald eagles start their home building by carefully selecting a site that provides wide views of the surrounding landscape. This means they are looking for the tallest trees in an area, so mature or old-growth trees are particularly important for their habitat.

Being close to a food source is also important (and opportunistic) so you’ll find nests close to large bodies of water. These raptors build their nests from large sticks and cushion the inside of them with moss, grass, lichens, and seaweed. Nests can be up to six feet in diameter and three feet deep and can weigh upwards of 1,000 pounds! That’s big enough for a human to relax in. Fun fact: the largest nest found in the United States was in St. Petersburg, Florida, and measured a whopping 10 feet in diameter, 20 feet deep, and weighed over 4,400 pounds: talk about Extreme House making!

Nests get so large because eagles come back to the same nest every year, adding more material to their home with each visit. To build nests this large, you can bet it takes a team approach. Male and female pairs work together. The males gather materials to bring to the female who constructs the actual nest.

 

a bald eagle perches over a nest of twigs formed in the branches of a tall tree

The structure of bird nests is being studied by scientists who are trying to understand the building methods that create them and what gives them their strength. In using branches as a building material, certain spatial relationships must be maintained to ensure the nest remains in place and provides structural integrity.

To better understand this, one study began to deconstruct the complex, large, oval nests of Dead Sea sparrows. The study found that 66 percent of sticks were set at an angle greater than 45 degrees. This shows that birds have a very specific method that they follow while building their homes and helps to answer why nests can withstand wind damage. Perhaps the methods of our feathered friends could be useful to builders and engineers.

So next time you’re outside, look up! You never know what feat of architecture might be right above you.

 

Written by Samantha Best, outdoor interpretation specialist, Crystal Bridges.

 

Check out the rest of the Architects of Nature series: