There are many types of birds that dig holes in the ground to make their nests. Some of the most common hole-nesting birds include kingfishers, parrots, owls, puffins, sand martins, bee-eaters, and woodpeckers. The specific type of hole-nesting bird depends on the region, habitat, and size of the bird. For example, kingfishers nest in burrows along riverbanks, while burrowing owls nest in prairie dog holes in grasslands. Regardless of habitat, these cavity-nesting birds share common traits and behaviors when it comes to selecting nest sites, excavating cavities, and raising young.
Hole-nesting offers several advantages over building an open nest. Underground burrows provide shelter from predators and extreme weather. They also help regulate temperature and humidity levels for eggs and chicks. However, digging a nest requires specialized skills and adaptations. Strong legs and sharp, chisel-like bills allow certain species to tunnel into dirt, sand, or wood. Nest excavation can take days or even weeks of hard work. Both males and females participate in the digging, though the male often takes the lead role.
Reasons Birds Dig Holes for Nests
There are several key reasons why some bird species build nesting burrows rather than open-topped nests:
Protection from Predators
A burrow deep underground helps conceal the nest from predators like snakes, foxes, raccoons, and hawks that cannot reach eggs and chicks easily. Being underground and out of sight provides a major advantage over exposed nests in trees and shrubs.
Shelter from Weather
The insulating properties of soil help regulate temperatures inside the burrow. This protects eggs and nestlings from overheating on hot days and from cold exposure. Burrows maintain higher humidity levels as well which is better for incubation and chick development.
Stable Environment
An underground burrow provides a stable nest site that remains fixed in place. It does not sway or bounce in windy conditions like a tree nest might. This reduces the chance of knocking eggs and chicks out of the nest accidentally.
Reuse and Expansion
Many hole-nesting birds reuse the same burrows year after year for breeding. Some expand their holes over successive years. This saves energy compared to building a new nest from scratch each season.
Limited Nesting Sites
In certain habitats like plains, prairies, and beaches, there are few trees suitable for nesting. Digging a burrow may be the only option available to breed. Birds like puffins and sand martins rely completely on tunnel nests.
Escape from Parasites
Enclosed burrows help keep nests free of parasites like fleas, mites, and ticks. Birds can better defend a small opening compared to an open nest. Cleaning out old nest materials further reduces parasites.
Major Types of Hole-Nesting Birds
Kingfishers
Kingfishers are medium-sized birds that nest in burrows dug into vertical riverbanks and cliffs. Both parents work together to dig a tunnel that leads to a nest chamber. Kingfishers have sturdy, pointed bills adapted to chiseling into dirt and sandstone. Popular kingfisher species include belted kingfishers and ringed kingfishers.
Parrots
Many parrot species nest in tree cavities, but others dig their own burrows. Monk parakeets are known for excavating nest tunnels of tightly packed sticks and mud in embankments or the ground. The Australian burrowing parrot digs holes with its strong legs and massive bill. Its fluffy feathers line the interior nesting chamber.
Owls
Small owl species like burrowing owls and elf owls nest underground. Burrowing owls move into existing holes made by prairie dogs or other animals. Elf owls excavate their own nests in rotten saplings or dirt banks. Their long legs allow forceful digging.
Puffins
Atlantic puffins and other puffin species nest in underground burrows on islands and seaside cliffs. They use their stocky bodies, short wings, and webbed feet to dig burrows up to 8 feet deep. Both parents work together and reuse burrows over successive seasons.
Sand Martins
The sand martin, also called bank swallow, is a small migratory songbird that breeds across Europe, Asia, and North America. Colonies nest together, excavating tunnels in sandy banks and cliffs near water. Sand martins have adapted to carry away excavated dirt and evenly reinforce burrow walls.
Bee-Eaters
These slender, brightly colored birds dig nest burrows up to 6 feet long in sandy banks and open flat land in Europe, Asia and Africa. Bee-eaters have pointed bills to chisel into the ground, spearing dirt away with their bills. Both parents work on excavation.
Woodpeckers
Woodpeckers like the downy and red-bellied woodpecker nest inside cavities they chisel out of dead trees. However, a few species dig nest holes in softer wood, earthen banks, or even termite nests. The giant woodpecker of South America is one example. Its powerful bill hammers out deep holes in trees.
Nest Digging Adaptations
Hole-nesting birds possess specialized physical and behavioral adaptations that allow them to excavate burrows for nesting and breeding:
Chisel-like Bill
A narrow, chisel-shaped bill helps concentrate digging forces into a smaller area, chipping away wood, soil, or loose substrate. Kingfishers, bee-eaters, and woodpeckers have particularly pointed bills.
Strong Legs
Robust leg muscles provide force and stability during the digging process. Species like burrowing owls and sand martins have long legs optimized for chipping and scraping.
Coordinated Digging
Mates take turns carefully excavating the hole to avoid collapse. One bird digs at the burrow face while the partner carries away debris. They dig alternating short shifts.
Debris Removal
Continuously removing loose dirt prevents cave-ins. Parents carry material away from the burrow in their bills or feet, even using their wings to sweep debris out.
Hole Reinforcement
Some species reinforce burrow walls with sticks, grasses, or secretions. This prevents inward collapse. Parrots build walls with interwoven sticks cemented by saliva.
Clutch Size
Hole nesters lay smaller clutches of only 2-6 eggs. A tight space limits brood size compared to open nests. Smaller broods require less food delivery.
Reuse and Expansion
Some birds return to the same burrows year after year. They dig out accumulated debris or expand chambers over successive seasons.
Nesting Process
Digging a nesting burrow is demanding work and follows a typical series of steps:
Site Selection
The male and female inspect potential nest sites together and jointly choose a spot. Ideal locations have vertical, stable ground at the right depth. Some birds reuse family burrows across generations.
Hole Excavation
Both birds dig into the substrate using coordinated shifts. This prevents tunnel collapse. Soil consistency and hardness determine digging duration. Soft sand may take 1-2 days while hard wood can require up to three weeks. Holes range from 1-8 feet deep.
Burrow Shaping
The burrow shaft leads down at an angle to an enlarged nesting chamber. Birds continually remove debris and use beaks and feet to shape the cavity into a rounded, smooth interior.
Tunnel Reinforcing
Some species stabilize burrow walls with secretions or by interweaving sticks into a secure matrix. This provides structural support. The tunnel entrance may be partially concealed with debris for camouflage.
Nest Material Addition
The female lines the interior with soft materials like grass, feathers, fur, or even fish bones. These add comfort and help secure the eggs.
Egg Laying and Incubation
The female lays a small clutch, often of bright white eggs. Both parents share incubation duties, frequently for up to 3 weeks. One bird remains at the nest at all times.
Nestling Care
After hatching, both parents feed and care for altricial chicks. Young fledge in 3-7 weeks, depending on species. Parents continue providing for fledglings until independence.
Burrow Reuse
In future years, parents may return to the same burrow, digging it out again. Some expand rear chambers to accommodate larger broods over time.
Conclusion
While most birds construct open nests in trees and shrubs, some unique species go to great lengths to excavate underground burrows for breeding. Cavity-nesting adaptations like sharp bills and muscular legs allow birds to chisel into substrates like soil, sand, and wood. Nest burrows provide major advantages of protection, stable environments, and concealment from predators. Careful excavation by mated pairs involves coordinated digging shifts and debris removal to create secure nesting chambers. Underground nest sites are reused and expanded over successive seasons. Diverse bird groups around the world rely completely on dug burrow nests as part of their breeding ecology and behavior.
Bird Type | Example Species | Nest Location |
---|---|---|
Kingfishers | Belted kingfisher | Riverbanks |
Parrots | Monk parakeet | Embankments |
Owls | Burrowing owl | Prairie dog burrows |
Puffins | Atlantic puffin | Island cliffs |
Sand martins | Bank swallow | Sandy banks |
Bee-eaters | European bee-eater | Sandy banks |
Woodpeckers | Downy woodpecker | Tree cavities |