Bird Nesting

Nest building is one of the most remarkable behaviors of birds. Nearly all species create some form of nest to lay their eggs and raise their young. The nest provides protection, insulation, and camouflage – playing an essential role in birds’ breeding success and survival.

There is tremendous diversity among bird nests. They can be found in all shapes and sizes, from hummingbirds’ small delicate cup nests to the enormous mound nests of the Marabou Stork, reaching over 10 feet wide and deep. Nests can be crafted from a variety of materials including twigs, grasses, lichens, spider silk, feathers, mud, and even paper or plastic if available.

The location and placement of nests are another key element. Some species are cavity nesters, using holes in trees, crevices, burrows, or nest boxes. Others build exposed surface nests on the ground, in shrubs and trees, or in man-made structures like buildings or bridges. Certain seabirds nest in remote and rugged island cliffs for protection.

Birds have evolved specialized nesting behaviors and roles between genders. In most species, the female does the majority of nest construction, though the male may supply some materials. Incubation duties are shared in some species, like the Laysan Albatross, but left predominantly to the female in others. Parental care also varies, with precocial young able to feed themselves soon after hatching, while altricial young require extensive feeding and brooding.

This article will provide a comprehensive overview of the diverse world of bird nesting, covering nest-building techniques, incubation, rearing young, defending the nest site, and profiles of notable and unique nests across the avian world. Understanding nesting ecology and behavior provides vital insights into our feathered friends’ evolution and life history strategies.

Nest Building

Bird nest construction is a complex process that varies extensively across species. The type of nest built depends on the materials available, nesting location, and unique traits and behaviors of the bird. Birds have evolved specialized skills, techniques, and tools to craft remarkable nest structures.

Nest Materials

Birds use a diverse array of materials to build their nests:

• Twigs, stems, branches – Most common nesting material. Sources include trees, shrubs, and vines. Allows weaving and support.
• Grasses and leaves – Softer lining materials. Provides insulation. Common in cup nests.
• Mud or clay – Used in mound and bowl nests for structural support. Allows shaping.
• Feathers and down – Soft inner lining for insulation and padding eggs. Plucked from own breast.
• Spider silk and cocoons – Incredibly strong. Used for structural support and adhesion.
• Moss and lichens – Natural spongy materials to regulate moisture and insulation.
• Trash and debris – Some species incorporate litter like cigarette butts, plastic, and paper into nests.

Nest Locations

• Cavities – Protected sites in trees, cliffs, banks, caves, crevices, holes. Examples are woodpeckers, owls, and parrots.
• Cups – Shallow bowl nests built on branches, cliff ledges, and poles. Robins, jays, doves.
• Scrapes – Simple depressions scratched into the ground. Examples are shorebirds like plovers.
• Platforms – Larger nests built by raptors high in trees or cliffs. Provide visibility.
• Burrows and mounds – Tunnels dug into banks or soil for nesting chambers. Made by kingfishers, bank swallows.
• Floating nests – Buoyant nests anchored among reeds near water. Built by grebes and coots.

Construction Techniques

• Weaving – Intertwining flexible materials to form a felted mat. Done by weaver birds orioles.
• Sewing – Stitching materials together with stalks or spider silk. Tailorbirds sew leaves together.
• Cementing – Using mud or saliva to cement materials. Swiftlets build edible saliva nests.
• Molding – Pushing and molding soft materials into shape. Seen in ovenbirds and woodpeckers.
• Patchwork – Adding materials in layers or patches. Wrens continuously add lining as eggs are laid.

Unique Nests

• Pendulant – Hanging woven nests built by orioles and weaverbirds. Have a downward-facing entrance.
• Igloos – Domed nests from mud or snow built by Victoria crowned pigeons and ptarmigans.
• Communal – Shared nests housing 100s of pairs. Found in sociable weaver colonies.
• Decorated – Nests adorned with found objects like feathers, trash, and bones. Bowerbirds are master decorators.
• Parasitic – No nest building at all. Eggs are laid in other bird nests by cowbirds and cuckoos.

Role of Parents

The female predominantly does nest construction in most species, though the male assists in gathering materials. However, there are exceptions:

• Male weaverbirds and orioles do a majority of weaving and nest-building
• Both sexes contribute equally to raptors and seabirds
• Male woodpeckers roost in cavity nests they excavate

Tools for Building

Specialized tools and techniques used by birds:

• Talons to scrape depressions into dirt or sand
• Beaks to interweave and tie materials together
• Saliva to cement and bind nesting materials
• Feet to form mud and push materials into shape

Site Preparation

Some birds carefully clear or prepare the nest site first:

• Removing loose materials or obstructions
• Lining depressions with soft materials
• Building canopy covers above nests for shelter

Maintenance

Birds actively maintain and improve their nests:

• Relining the interior with fresh soft materials
• Securing nests to branches with new sticks and silk
• Patching holes or reinforcing edges
• Expanding size as young grow

Proper nest building is vital to the breeding success of birds. The diversity and complexity of avian nests is a testament to our feathered friends’ evolutionary pressures and ingenuity.

Eggs and Incubation

Bird eggs come in a remarkable variety of shapes, sizes, colors, and quantities. The egg stage represents a critical phase of avian reproduction – ensuring chicks’ proper incubation and hatching.

Egg Anatomy and Variation

While varying greatly across species, all bird eggs share key anatomical features:

• Shell – The Calcite barrier protects and contains the embryo. Porosity allows air exchange.
• Yolk – A primary food source for the developing embryo. More significant in precocial chicks.
• Albumen – Protein-rich white provides additional nutrition, water, and cushioning.
• Chalaza – Twists the yolk to center yolk and stabilize it.
• Air cell – Pocket of air that enlarges as the embryo breathes. Site of external pipping.

Size – Ranges from tiny hummingbird eggs measuring 0.3 inches long to ostrich eggs over 6 inches long. More prominent in precocial young.

Shape – Mostly elliptical, but some species have more rounded or conical eggs.

Color– Depending on pigments, color – White, brown, blue, green, and pink eggs. Camouflage important.

Numbers – Clutch sizes range from 1 egg in condors to 20 eggs for ostriches and may lay multiple clutches.

Incubation Periods

• Small songbirds – 11 to 15 days
• Raptors and seabirds – Around five weeks
• Large flightless birds – 35 to 90 days
• Megapodes – Eggs left to develop entirely buried externally

Parental Roles

• Most species share incubation duties, but some have division of labor:
  • Male-only incubation in waterfowl and shorebirds
  • Female-only incubation in falcons, eagles, owls
• Both parents develop brood patches – bare vascularized skin that transfers warmth.

Incubation Behaviors

• Turning/Rotating – Parents often turn eggs for even heating and development.
• Shading – Adults shade eggs from excessive sun exposure.
• Hydration – Water applied to eggs by parents ensures proper humidity.
• Nest Maintenance – Adults keep the nest clean and make repairs during incubation.

Hatching Synchrony

• Many species hatch eggs together for uniform brood care.
• Others have staggered hatching, leading to size disparity.

Nest Attendance

• One parent incubates while the other provides food. Shift duties throughout the day.
• Attentiveness increases as hatching approaches. Some species rarely leave a nest.

Precocial vs Altricial Young

• Precocial chicks can walk and feed quickly after hatching. Have more parental independence. Typical of ducks, chickens, shorebirds.
• Altricial chicks are helpless, blind, and require extensive parental care. Songbirds and raptors are generally altricial.

Bird eggs and incubation strategies are remarkably diverse, reflecting complex reproductive systems tailored to environments and resources. Proper incubation is vital to developing healthy hatchlings and continuing the avian life cycle.

Parenting

Once birds hatch, parents take on the crucial tasks of raising and protecting the young through the fledging stage. The parenting strategies of birds are remarkably diverse.

Feeding Hatchlings

• Parents initially feed many altricial songbirds regurgitated food, then progress to whole items as they grow.
• Fish-eating birds like herons and egrets bring whole fish to the nest to tear up and feed young.
• Seed-eating parents collect and deposit seeds or fruit directly into the nest for young.
• Insectivores deliver a wide variety of invertebrates to feed growing chicks.
• Some seabirds like petrels and albatrosses have an extremely nutrient-rich oil that they regurgitate to fatten chicks rapidly.

Brooding and Sheltering

• Young chicks cannot thermoregulate initially, requiring extensive brooding by parents sitting over them or tucking them under their wings.
• Parents also provide shelter from precipitation and sun exposure:
  • Positioning themselves over chicks
  • Shading with outstretched wings
  • Utilizing vegetation or nest structure

Sanitation

• Adults keep the nest clean by consuming or removing chick waste.
• Which helps avoid predators being attracted to nest sites.
• Some birds carry away fecal sacs to dispose of them at a distance.

Predator Defense

• Parents are very aggressive in defending nests from potential predators.
• Distraction displays like injury feigning lure predators away.
• Direct attacks with wings, claws, and beaks to drive away threats.

Nest Maintenance

• Parents continue to maintain and improve nests as the chicks grow:
  • Expanding size
  • Reinforcing edges
  • Adding fresh lining
  • Building protective canopy

Fledging

The transition from nest to flight is a vulnerable stage:

• Nestlings make initial short flights to nearby branches while parents monitor.
• Young are fed and accompanied by parents during the post-fledging period.
• Birds with precocial young, like ducks, lead them to water soon after hatching.

Empty Nest Stage

• After young fledge, adults undergo complete feather molt and rest phase.
• Some long-lived birds remain with fledglings for extended periods to teach them how to forage and migrate.
• Most temperate species are single-brooded, while tropical birds can have multiple broods per year.

Cooperative Breeding

• In some species, non-parent helpers also assist in feeding and protecting young, which occurs in certain jays, bee-eaters, and babblers.

Proper parenting is essential for developing foraging skills, flight capability, and independence in juvenile birds. It requires extensive energy investment by avian parents.

Nest Defense

Birds have evolved strategies and behaviors to defend their nests from predators and threats. Protecting the eggs and chicks is an extremely high priority for parent birds.

Warning Calls

• Sentry birds use loud alarm calls to signal danger to the colony. Examples are gulls, terns, and crows.
• Warning calls prompt other birds to take evasive action or mob predators.
• Specific threat calls may differentiate ground vs. aerial predators.

Distraction Displays

Visual displays draw predators away from the nest by feigning vulnerability:

• Injury-feigning – Fluttering on the ground as if wounded. Used by plovers, killdeer.
• Rodent runs – Dragging wings as if an easy target. Performed by wrens pipits.

Auditory distractions like harsh mobbing calls also focus attention away from the nest.

Camouflage

Well-hidden nests avoid detection from many predators. Strategies include:

• Cryptic coloration and materials
• Concealed locations like cavities or dense foliage
• Nest shapes blend into the surroundings
• Nest coverings like lichens or spiderwebs

Aggressive Defense

• Large territorial species like hawks, crows, jays, and blackbirds use dive-bombing intruders.
• Smaller birds harass predators with swarming attacks.
• Physical strikes with wings, pecks, claw raking, and biting.
• High-risk defense behaviors are reserved for critical threats.

Nest Placement

Site selection for safety is the first line of nest defense. Examples:

• Cavities safe from most predators
• Spiny trees deter climbing snakes and mammals
• High up in trees away from ground threats
• Overwater, where fewer predators travel

Group Mobbing

• Cooperative mobbing by multiple birds drives predators away through persistence and disorientation.
• Used against larger threats like foxes, cats, and stoats.

Chemical Deterrents

• Foul-smelling midden heaps at nest entrances deter investigating mammals.
• Rancid oils in regurgitated food can repel predators.
• Vultures urinate down their legs to ward off enemies.

Predator Removal

• Lethal nest defense is sometimes employed against persistent predators.
  • Owls and falcons kill snakes, crows, jays, and ravens.
  • Robins may kill competing house sparrows.
• Reserved for repeat nest predators.

Nest Defense Intensity

More aggressive nest defense occurs when:

• The nesting stage is advanced with more investment to lose.
• Predator is a more significant immediate threat to eggs/young.
• Prior experience with specific predator types.
• The lower reproductive potential of the season remains.
• Multiple pairs can mob predators through group response.

Bird nest defense illustrates the critical interplay between parental protective instincts, nest ecology, and predator behavior. Birds balance the risks to their survival with the drive to protect the next generation.

Notable Nests

The incredible diversity of bird nests includes many unique, specialized, and rare types that are fascinating examples of avian engineering and behavior.

Specialized Nests

• Burrow nests – Tunnel into banks, cliffs, or ground. Made by kingfishers, bank swallows, and puffins.
• Cavity nests – Holes excavated in trees, termite mounds, crevices. Used by woodpeckers parrots.
• Mound nests – Massive mounds of sticks and vegetation. Built by flamingos, vultures, and accipiters.
• Platform nests – Flat wooden platforms for large birds like eagles, ospreys, and vultures. High visibility.
• Scrapes – Shallow depressions scratched into the substrate. Simple nests of plovers, nighthawks, skimmers.
• Termite nests – Arboreal termite mounds converted. Barbets, parrots, and sparrows use them.
• Ground nests – Directly on the ground. Megapodes, curlews, hummingbirds. Vulnerable but site-limited.
• Cliff ledges – Protected rocky outcrops on cliffs. Used by gulls, cormorants, and swifts.
• Tree canopy – Heights avoid most predators. Treepies, orioles, and tanagers build them.

Bizarre Nests

• Igloos – Insulated domed nests from mud or snow. Made by emperor penguins.
• Sewn nests – Nest materials sewn together with fibers. Seen in tailorbirds and weaverbirds.
• Edible nests – Famed saliva nests of swiftlets used for bird’s nest soup.
• Decorated nests – Adorned with colorful objects by male bowerbirds to attract females.
• Reuse – Old nests reused across years or other bird species. Herons in hawk nests.
• Parasitic nests – No nest is built, and eggs are laid directly in host nests. Common cuckoos do this.
• Floating nests – Nests built to float on water for marsh birds like grebes and coots.
• Communal nests – Hundreds of birds using one massive nest. Sociable weavers do this.

Rare and Unique Nests

Some unusual nesting occurrences include:

• Cliff nesting Atlantic puffins in the unlikely habitat of storm drains.
• Wandering albatrosses nest exceptionally on rooftops and human structures on remote islands.
• Burrowing owls make their home in the discarded spray tanks of Florida citrus groves.
• Bald eagles adopt osprey nests, telephone poles, and other exposed man-made platforms without old-growth trees.
• Penguins like Yellow-eyed and Magellanic penguins burrow under forests and bushes when cliff nest sites are limited.
• The unique cooperative nest of the Social weaver, built by hundreds of birds collaboratively over generations to form massive multi-chambered structures up to 12 feet deep and wide.

The diversity of bird nest designs reflects avian behaviors’ remarkable flexibility and adaptability. From intricate woven pendants to massive mound nests, each serves the critical evolutionary purpose of protecting eggs and raising the next generation of birds.

Conclusion

Bird nesting encompasses a remarkable diversity of behaviors and strategies tailored to species and environments. From intricate woven cups to massive mounds, nest building has driven the evolution of specialized tools, techniques, and adaptations. Birds invest heavily in constructing, incubating, and defending nests to maximize reproductive success. Understanding avian nesting ecology provides insights into the life histories of birds and how they balance investments in their young. The nest is at the heart of avian reproduction, representing the next generation of birds.