Bird Nests – How Do Birds Protect Them?

Keeping Nestlings Safe From Predators and Other Dangers

Oct 9, 2009

A bird's nest is meant to be a safe place for eggs and young. Adult birds use location, camouflage, design, odor, deception, and renewal to ward off various threats.

With the exception of breeding bird colonies, where bird nests are hard to miss, people generally come upon nesting birds by chance. Once discovered, a nest may appear vulnerable and exposed, but birds have evolved a number of ways to protect their nests from predators, weather, and disease.

Location is Important for a Bird's Nest

The best location is one that can’t be reached by predators. Nests built off the ground are out of reach. When they are suspended from twigs and thin braches, like the nests of oropendolas and some orioles, they are even harder to get at.

Other locations, such as tree cavities, burrows, and the interior of dense and thorny thickets or cacti are difficult to find and easy to defend. Some birds build domed nests of vegetation that simulate a cavity, while others, such as Cliff Swallows and the Rufous Hornero build round hollow nests of mud like little artificial caves.

Many birds, of course, select caves, hidden crevices, the insides of hollow trees or chimneys, cliff faces, and holes in the sides of buildings as good places to nest.

Some birds protect their nests from sun or wind by orienting the nest opening appropriately, or taking advantage of sheltering features in the landscape. Horned Larks, for example, tend to build on the north side of a tuft of grass: the nest is shaded in the afternoon and cooled by afternoon wind, but protected from the colder southerly winds of evening.

Having a colony of wasps, bees, or ants near a nest can actually be a good thing for nesting birds. These insects deter other pests such as botflies and mites, but they don’t harm birds and nestlings.

Camouflage Can Hide a Nest From Danger

It’s amazing how well some birds' nests blend in with their surroundings. Materials such as lichen and spider web not only camouflage the nest but give it strength and help repel water. Pebbles and other ornaments collected from the ground nearby can make a nest on the ground become almost invisible. And a nest constructed of twigs, leaves and mosses, situated among the same materials is almost impossible to spot.

Nest Design Protects Eggs and Nestlings

Many birds use design features to hide or protect the nest. Cavity nests are an obvious example, where the nest is hidden away with only a small opening to the outside world. This feature appears in birds' nests in wide variation. Other birds build nests that dangle from tree limbs (see location, above) or include materials that put predators off (see odor, below).

In hornbills, which nest in cavities, the female bird goes inside and seals the opening with mud and droppings, leaving only a narrow opening.

Odor Can Deter Nest Predators and Pests

When added to the nest material, aromatic plants ward off pests, parasites, and even bacteria that pose a health risk to nestlings. Blue Tits, European Starlings, Purple Martins and many other species use fresh plant material and even replace it when it gets stale. Plants used include lavender, mint, curry, oak, yarrow, and cedar bark.

A different kind of odor results from adding animal dung to the nest. Common Waxbills add the dung of carnivores, and Burrowing Owls use droppings from grazing animals. This probably disguises the scent of the birds from hunting predators and may have other functions as well.

Nesting shorebirds, such as sandpipers, actually change the way they smell during nesting: their preen glands secrete an altered composition of preen wax at this time which probably makes the nest more difficult for predators to detect.

Deception Works to Protect Birds' Nests

Nesting birds may deceive predators by mimicking another predator, luring a predator away from the nest by pretending to be injured, or laying a false trail. Some species of wrens build many nests each breeding season. Most remain empty but may keep predators busy and divert them from the real nest.

The Great Crested Flycatcher, which breeds in North America, places a piece of shed snakeskin in its nest, presumably to deter predators. Similarly, wrynecks actually pretend to be a snake when threatened.

Renewal – Birds Build Nests Every Year

Some birds use the name nesting site year after year, but most build a new nest for each breeding season, thereby ensuring strong construction and leaving nest parasites behind.

Sources

Firefly Encyclopedia of Birds. Perrins, Christopher ed. Buffalo: Firefly Books, 2003

“Birds as Builders of Homes” Ramel, Gordon. The Earthlife Web, Earthlife.net

The copyright of the article Bird Nests – How Do Birds Protect Them? in Bird Habitats is owned by Rosemary Drisdelle. Permission to republish Bird Nests – How Do Birds Protect Them? in print or online must be granted by the author in writing.