Birds build nests for a variety of reasons, but the main purpose is to lay eggs and raise baby birds. Nest building is an intricate process that varies by species, though all birds employ beak and body to construct interwoven nest materials into a secure shelter.
Why do birds build nests?
Birds build nests to provide a safe place to lay eggs and raise young. Nests protect eggs and chicks from predators and harsh weather while providing a comfortable place for parents to incubate eggs. The structure and placement of nests depends on the species’ habits and needs.
When do birds build nests?
Most birds build nests during breeding season in anticipation of egg laying. However, some species build nests year-round for roosting or resting. Resident birds may repair or maintain old nests throughout the year. Migratory birds generally build fresh nests upon arriving at breeding grounds each spring.
Types of Bird Nests
Birds construct diverse nest types using various materials. Nest architecture falls into a few broad categories:
Cup Nests
Cup nests are small, round structures made of interwoven grasses, twigs and other flexible materials. They are often lined with soft feathers, hair or moss and built in the branches of trees and shrubs. Familiar cup nesters include robins, cardinals and sparrows.
Platform Nests
Platform nests take the shape of shallow baskets situated on a relatively flat, sturdy surface. They may be situated on the ground, in tree forks, on building ledges, or atop poles. Examples include hawk, eagle, osprey and crow nests.
Burrow or Cavity Nests
Burrow nesting birds excavate tunnels into sand, soil or wood to create sheltered breeding chambers. Cavity nesters utilize natural or abandoned hollows in live or deteriorating trees, cliffs and banks. Examples include kingfishers, owls, woodpeckers and puffins.
Ground Nests
Ground nests are shallow scrapes or depressions made on bare ground, often with a partial overhead canopy for protection. Some shorebirds employ this simple open style. Other ground nesting species include gulls, terns, snipes and plovers.
Mud Nests
A few species mold globular mud nests, attaching them to crags, tree limbs, manmade structures or cave walls. The chimney swift is named for nesting in old chimneys. Cliff swallows affix mud flask-shaped nests under overhangs.
Specialty Nests
More complex nest building occurs among weaverbirds, which stitch elaborate hanging nests, and brush turkeys, which construct enormous incubating mounds. Large raptor species occasionally build huge platform stick nests called aeries.
Nesting Materials and Construction
Bird nest construction requires gathering, transporting and skillfully weaving appropriate nesting materials. Different species have evolved specialized beak and body adaptations to aid nest building.
Gathering
Birds use their beaks and feet to gather materials from their environment. Most haul one item at a time. Gathered supplies may include:
- Twigs
- Grasses
- Mud
- Spider silk
- Feathers
- Leaves
- Pine needles
- Moss
- Roots
- Lichen
- Paper
- String
- Plastic
Transporting
Birds employ specialized techniques to efficiently convey material to the nest site:
- Grasping in beak – Most common method
- Clasping between mandibles – For more unwieldy items
- Clutching in feet – Allows birds to reuse grasp of beak
- Wedging underneath feathers – To carry soft lining materials
A few species, like the male weaverbird, can remarkably transport huge loads of grasses between extended mandibles and feet.
Weaving
At the nest site, birds skillfully weave materials into place using only their beaks and feet. Weaving techniques include:
- Hooking materials through the substrate
- Threading items through others
- Interlocking crossed sticks and grasses
- Intricate sewing or stitching
- Knotting fibers
- Wrapping supple materials
Birds may incorporate weatherproofing by matting plant down, feathers or fur into the inner nest. Some species also add binding agents like mud or spider silk to stick elements together.
Nest Locations
Bird nest placement largely depends on species habits and habitat. Nest height, concealment and attachment vary across different kinds of birds.
Tree Nesters
Tree branches provide excellent nesting opportunities. Arboreal nests may be situated:
- In a fork
- Out on a limb
- Against the trunk
Nests are lodged securely in place through weaving, bonding, or balancing. Height ranges from lower branches to the highest tree tops.
Shrub Nesters
Low shrubs offer convenient sites for small, well-camouflaged nests. Protection comes from surrounding vegetation.
Ground Nesters
Some species nest on the ground, relying on surrounding cover for concealment. Ground nests may be dug into burrows or built into surface scrapes.
Cavity Nesters
Natural tree cavities and woodpecker holes provide shelter for cavity nesting species. Others utilize rocky crevices, dense brush piles, reedbeds, mammal burrows or manmade sites like nest boxes.
Cliff Nesters
Steep, rocky cliffsides offer habitat for specialized nesting birds. Protected ledges or crevices hold nests built by swifts, swallows, eagles and falcons.
Aquatic Nesters
Aquatic species often nest in shoreline trees or on the ground among reeds and rushes in marshland. Some seabirds nest on remote islands and rocky shores. Others use buoyant floating nests.
Human Structures
Birds readily nest on human buildings, bridges, and other structures that mimic natural sites. Popular locations include rafters, gutters, window ledges and sheltered overhangs.
Nest Shapes
Beyond basic nest styles, bird nests can take on more specialized forms and shapes depending on materials and needs.
Cups
The simplest nest is an open cup shape woven from grasses, twigs and mosses. It creates a cozy container for eggs and chicks.
Saucers
Saucer-shaped nests have a wider, shallower basin for holding eggs and babies. They provide a sturdy, supportive platform.
Bowls
Bowl nests are similar to cups but feature thicker, more pronounced walls made of interlaced sticks, twigs or grasses. The enclosed shape provides extra protection.
Hanging Pouches
Pendulous woven pouches with side entrances are constructed by specialized weaverbirds using grasses and plant fibers. The entrance hole is intricately stitched shut after the female enters to lay eggs.
Mounds
Unique mounded nesting hills are fabricated from decomposing vegetation and earth by brush turkeys and other megapode birds for natural egg incubation.
Platforms
Platform nests built by hawks, crows and other large birds take the shape of a sturdy shallow basket able to support substantial weight without collapsing.
Scrapes
Scrape nests are mere shallow divots dug into sand or gravel and lined with bits of debris. Simple and inconspicuous but without sturdy walls.
Burrows
Some species dig out tunnel-like burrow nests in sandy banks or even woodpecker holes. The enclosed space provides temperature regulation and protection.
Nest Sizes
Nest dimensions vary greatly by species depending on body size and clutch requirements.
Species | Nest Diameter |
---|---|
Hummingbird | 2 – 5 cm |
Finch | 13 cm |
Robin | 16 – 23 cm |
Hawk | 60 – 150 cm |
Eagle | 150 – 250 cm |
Osprey | 60 – 90 cm |
Smaller birds require tiny nests sometimes only a few centimeters wide. The smallest hummingbird nests may be only 2-3 centimeters across and 2.5 centimeters deep. Small songbirds like finches build nests around 10-15 centimeters in diameter.
Mid-sized birds construct appropriately larger nests. American robin nests range from 16-23 centimeters across and 8 centimeters deep. Hawks build big sturdy nests 60-150 centimeters wide to hold themselves and raise multiple large chicks.
Massive bald eagle nests can reach 2-3 meters across and weigh over a ton! Osprey nests measure up to 90 centimeters in diameter and 30 centimeters deep. Nests sized appropriately to species provide just the right amount of room and security.
Stages of Nest Building
Nest construction occurs in a progressive sequence for most species. The main stages include:
Site Selection
Birds choose ideal nesting locations based on food availability, safety from predators and protection from the elements. Nest height, amount of surrounding cover and availability of building materials help determine the site.
Foundation
The nest starts with a foundation structure to support the bulk of the nest. This may consist of a platform of crossed sticks or twigs or a woven cup anchored to branches. Sturdy branches often provide the base.
Shaping
With basic structure in place, birds continue actively adding and weaving materials to build up side walls and create the interior shape. Nests take form as cups, bowls, saucers or spheres.
Lining
Once the main structure is complete, soft lining materials are added to cushion and insulate the inner nest. Downy feathers, soft grasses, hair and moss make cozy linings.
Finishing Touches
Final details like further weaving, camouflaging, decorating and sealing provide the perfect finishing touches. The nest reaches functional completion before egg laying.
Maintenance
Parents keep nests maintained and repaired as needed during incubation and chick rearing. Good maintenance ensures nest stability and sanitation.
Conclusion
From careful site selection to intricate weaving to diligent maintenance, nest building demonstrates a bird’s innate construction skills and instincts. Different species have evolved specialized tools and techniques to create safe, tailored nests. The variety, complexity and artistry of bird nest architecture provides insights into avian intelligence, creativity and resourcefulness in action. Whether tiny cups or massive platforms, each nest represents a unique avian achievement.