“Cavity Nesting” refers to the behaviour of birds that create nests, lay eggs, and rear their young inside protected chambers or cavities. This term is specific to birds that do not construct entirely enclosed nests but rely on pre-existing sheltered spaces, like natural cavities in trees, to build their nests and raise their offspring. These hidden chambers serve as crucial homes for cavity nesting birds. The species that exhibit this behavior are often associated with particular types of trees, such as the birds nest spruce, which provides suitable nesting logs and sites for cavity nester birds.
These cavity nesting birds display a unique nesting strategy, utilizing available cavities in trees or other appropriate structures. Their nesting products vary, and their ability to adapt to different nesting sites is vital for their reproductive success. The nesting logs involve
- selecting an appropriate cavity,
- preparing it for nesting,
- laying eggs,
- incubating them, and
- ultimately caring for the young until they fledge.
Understanding the nesting habits and preferences of cavity-nesting birds is essential for conservation efforts and ensuring suitable habitats for these fascinating avian creatures.
Types of Cavity Nesters
When it comes to cavity nesting birds, there are two primary categories based on how they secure a suitable nesting site:
- Primary cavity-nesting birds: These birds can excavate their nesting cavities. Woodpeckers, for instance, demonstrate this behavior by drilling chambers into appropriate trees, while ground-nesting species may dig burrows into riverbanks. The labor involved in creating a new cavity varies, lasting several days or even weeks, depending on the nesting requirements of the bird.
- Secondary cavity nesting birds: Species in this category capitalize on existing natural cavities or take over abandoned ones. In some cases, they may even forcibly acquire these cavities from other birds through aggressive intrusion. While they may make minor adjustments to the hole, such as modifying the entrance or adding or removing nesting logs and material, they do not significantly alter the cavity’s structure.
In Alberta, the practice of cavity nesting is prevalent. A cavity nest is a chamber typically hollowed out in a dead tree snag, serving as a bird nesting site. The birds creating these nests are termed “Primary Cavity Nesters.” This endeavor is a substantial undertaking for the birds, often lasting several days to a week.
However, some bird species, either unable or indolent in hollowing out trees, opt to inhabit these cavities after the primary cavity nesters have vacated them. These occupants are known as “Secondary Cavity Nesters.”
Primary Cavity Nesters
Only a select few species possess the capability to excavate their nests. Examples include woodpeckers, trogons, and certain nuthatches. The nests they create are typically excavated on the underside of a tree branch, possibly to minimize visibility to predators and reduce exposure to rainfall. Some species have adapted defense mechanisms due to their vulnerability to predators cornering them inside the cavity. For instance, Red-breasted Nuthatches spread sap around the entrance to their nests, while white-breasted nuthatches surround theirs with noxious insects. Most species use the hole only once, leaving it available for other species to utilize in subsequent breeding seasons.
Secondary Cavity Nesters
Secondary cavity nesting birds utilize existing or abandoned cavities, sometimes displacing other species. Common secondary cavity nesters include Mountain Bluebirds, Tree Swallows, House Wrens, and certain owl species. They typically leave the cavity relatively unchanged, with minor modifications such as adding fur, grass, or moss to the excavated hole. Additionally, other species, including Northern Flying Squirrels, may also opportunistically make use of these cavities.
Cavities Birds Use
Cavities’ dimensions, structure, and positioning vary according to the specific bird species and their unique nesting requirements. The types of chambers that birds may utilize encompass a range of options, including:
- Holes excavated in dead or decaying trees, stumps, nesting logs, poles, or large cacti
- Burrows in soft, vertical riverbanks, dirt mounds, dunes, or similar banks (cavity nests)
- Rock niches or crevices, either in natural cliffs or stone walls and structures
- Exposed pipes, chimneys, or similar artificial cavities
- Supplemental nesting boxes and birdhouses (nesting products)
Birds exhibit varying behaviors regarding chamber preparation: while some birds prefer a bare, empty chamber, others embellish the interior with grass, twigs, wood chips, feathers, fur, or other materials. Certain birds go as far as crafting an entire nest within the chamber, tailoring it to their needs and preferences.
Familiar Cavity Nesting Birds
Numerous birds will readily nest in cavities; many bird families have at least a few cavity nesters. Familiar examples include woodpeckers, chickadees, parrots, nuthatches, trogons, flycatchers, wrens, and bluebirds. Some ducks, such as the mandarin duck and wood duck, nest in cavities, as do smaller raptors and owls. The American kestrel, barn owl, purple martin, great tit, and European robin are common cavity nesters birds.
Attracting Birds With Nesting Sites
Backyard birding enthusiasts can attract these birds by providing suitable nesting logs. Preserving old trees and dead snags available for primary cavity nester birds can be successful, and introducing birdhouses or nest boxes will help attract many secondary cavity nesters. Supplying appropriate nesting products for birds in spring will also encourage nesting activity nearby.
It’s also crucial to be vigilant about birds using unsuitable cavities, such as dryer vents, chimneys, pipes, or other unsafe locations. In those cases, it may be best to discourage nesting birds while encouraging them to use safer, more appropriate sites.
If birds reside in a backyard cavity, whether a natural hole or a birdhouse, it’s important to take steps to protect the nest from predators. Backyard birders may also want to monitor birdhouses to track which birds nest successfully, and witnessing a bird raise its family in the yard can be an enriching experience.
What are sisal nesting logs made from?
Sisal nesting logs are crafted from Agave sisalana, a plant native to Central America. In South Africa, however, the sisal plant has become a nuisance, rapidly spreading across the landscape. Once the sisal plant has bloomed and produced seeds, it completes its life cycle, leaving behind the stalks, ideal shelters for nesting birds.
Elaine’s Birding has ingeniously designed its nesting logs by incorporating protective caps, enhancing their durability and longevity.
What type of birds can I expect to attract with a nesting log?
Primary cavity nesting birds actively excavate their nesting cavities, crafting suitable shelter for themselves. On the other hand, secondary cavity nesters’ birds rely on abandoned pre-excavated or natural holes, adapting and utilizing what is available.
Examples of common primary cavity nesting species include:
- Barbets
- Cardinal Woodpecker
Among the common secondary cavity nesting species are:
- Cape Glossy Starling
- Green hoopoes
- Grey Hornbills
- Sparrows
When is the best time to hang up nesting logs?
They can be easily hung up at any time throughout the year. However, we strongly advise placing them during winter, allowing the birds ample time to acclimate and become familiar with the nesting logs, preparing for the upcoming breeding season in spring.
Where and how do I mount my nesting log?
Select a serene, shaded location, away from potential predators like cats and dogs, and near a consistent source of fresh food and water.
Securely mount the log beneath a gently sloping branch or trunk using wire or rope.
Ensure the branch or trunk chosen for mounting is of comparable thickness to the nesting log.
When mounting, position the hole at the top of the nesting log.
Place the nesting log at a height between 2m-4m from the ground, oriented away from direct sunlight.
Consider situating the opening of the nesting log in an area or direction that protects rain exposure.
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