As a bird owner or avid bird watcher, you may be curious if birds have the ability to carry or roll their eggs to new locations after laying them. This seemingly simple question has a surprisingly complex answer.
If you’re short on time, here’s the quick answer: most bird species cannot move their eggs once laid, but some birds have behaviors that give the appearance of purposefully relocating their eggs post-laying.
Birds That Actively Move Eggs
Grebes
Grebes are water birds that build floating nests in the water. Since their nests can drift away, grebes have evolved some amazing abilities to move their eggs. After the female lays each egg, the parents use their feet to roll the egg onto their backs.
The male and female then take turns incubating the egg under their feathers. This allows the grebes to swim away from predators while protecting their egg. If danger approaches, the parent dives underwater with the egg still balanced on its back, safe from harm.
When it’s time to hatch, the grebes will roll the egg back onto the nest. Grebe chicks can swim and dive almost immediately after hatching. However, the parents still often carry the chicks on their backs for the first few weeks to help protect them.
Megapodes
Megapodes, also called mound-builders, are found in Australia and the Pacific Islands. They have taken egg-moving to the extreme since the adults don’t actually sit on the eggs to incubate them. Instead, they bury their eggs in large mounds of decaying vegetation, which provides enough heat to incubate the eggs.
The mounds can be up to 33 feet (10 meters) wide and 6 feet (2 meters) high! 👍
Different megapode species use various techniques to regulate the egg temperature in the mound. The Australian brush-turkey, for example, uses its large feet to move material inside the mound, allowing more or less air flow to control the temperature.
The male mound-builders spend about an hour a day maintaining the mound. Some species even have a specialized feathered appendage on their wings called an incubator wing that they use to feel the mound’s temperature. Amazing!
Since megapodes don’t sit on their eggs, the chicks hatch fully independent and ready to go. As soon as they hatch, the chicks claw their way up through several feet of dirt and vegetation to reach the surface and start foraging. Incredible! 😮
Indirect Egg Movement
Nest Sanitation
Birds keep their nests clean by removing egg shells, broken eggs, chick droppings, and other debris. This nest sanitation benefits the hatchlings by reducing bacteria, fungi, and parasites. Amazingly, parent birds may carry eggs or chicks short distances if needed to discard nest waste.
For example, a mourning dove was observed transporting an egg 23 feet to sanitation sites away from the nest. This indirect egg movement maintains nest hygiene.
Egg Retrieval
If an egg rolls out of the nest, adult birds may retrieve it by carrying it back in their beak or feet. In one case, a tropical kingbird flew 50 yards to pick up a displaced egg and return it to the nest. Egg retrieval prevents losses and gives healthy embryos continued incubation.
Remarkably, bird parents distinguish their own eggs from imposter eggs in such situations based mainly on egg coloration and patterning. So while birds cannot directly move eggs inside, their ingenious instincts lead to efficient indirect adjustment.
Why Birds Don’t Usually Move Eggs
Birds rarely move their eggs once they have laid them in a nest for several important reasons related to egg development and survival. Here is an overview of the key factors that prevent birds from relocating their eggs:
Egg Fragility
Bird eggs are very fragile and have a delicate internal structure. The yolk and embryo must remain centered within the egg for proper development. If the egg is shaken, turned too much, or exposed to sharp impacts, it can damage the embryo or vessel networks inside.
This fragility makes it challenging for parent birds to transport the eggs without harming the chicks growing inside.
Incubation Requirements
Bird embryos require consistent incubation at proper temperatures for normal growth. The parents keep the eggs at ideal warmth by sitting on the nest. Moving the eggs would expose them to temperature drops that can retard development or even kill the chicks.
The stillness of the nest provides the physical stability needed for undisturbed incubation.
High Predation Risk
Bird eggs and hatchlings are vulnerable to predators. Having parents constantly sit on the nest deters predators. If parent birds leave the nest unattended to transport eggs, predators like snakes, raccoons, or crow may seize the opportunity to raid the nest and eat the eggs.
Keeping the eggs stationary in one secure site is safer.
Nest Site Selection
Birds invest energy in carefully selecting nest locations that meet their habitat needs. Cavity nesters search for appropriate holes, shorebirds look for safe sites with protective cover, and songbirds choose sites with preferred materials for building.
Moving eggs would undo the benefits of this selective nest site engineering. The original nest site is tailored to give eggs the best chance of survival.
Energetic Costs
Transporting eggs requires substantial effort and time for parent birds. Having to carry eggs gently in their mouths or awkwardly balance them on their backs would force birds to trade-off precious time sitting on the nest regulating egg temperature and protecting the clutch from harm.
The energy costs of moving eggs frequently would be prohibitive.
Exceptions and Unique Cases
Brood Parasitism
Brood parasitism is a fascinating reproductive strategy in which some bird species lay their eggs in the nests of other bird species. The host birds end up raising the chicks of the brood parasite, often at the expense of their own offspring.
One of the most notorious brood parasites is the brown-headed cowbird, which parasitizes over 220 host species in North America. The cowbird evolved this strategy after following nomadic bison herds, which prevented them from establishing their own nesting territory.
Other common brood parasites include cuckoos, honeyguides, and black-headed ducks.
There are a few ways that brood parasites can manipulate their host species into caring for their young. Some will remove a host egg when they lay their own or kill host nestlings. Their eggs often mimic the appearance of their host’s eggs.
newly hatched brood parasite chicks may evict host eggs from the nest or monopolize food brought by the host parents. This obligate interspecific brood parasitism allows the brood parasite species to reproduce without the energy expenditure of nest building, egg incubation, or chick feeding.
While detrimental to the host species, brood parasitism is an extremely successful evolutionary strategy. About 1% of all bird species are obligate brood parasites. The ability of some brood parasite chicks to mimic the begging calls of multiple host species may have driven the evolution of this unique reproductive technique.
Brood parasitism provides a fascinating look into the arms race between coexisting species.
Helpers at the Nest
Most bird species rely solely on the parents to provide care for their offspring. However, some species have developed cooperative breeding systems in which other adult birds help care for the nestlings.
These helpers are often previous offspring that remain with their parents instead of dispersing to breed on their own. This unique nesting strategy is found in around 9% of all bird species and is especially common in the diverse avifauna of Australia and Africa.
Helpers may assist with building the nest, incubating eggs, brooding chicks, defending the territory, or gathering food. In some cases, the helpers are more successful at provisioning chicks than the actual parents! The helpers may be motivated to assist for various reasons.
They may gain parenting experience before having their own brood or benefit from group mobbing of predators. Alternatively, they may be paying rent in return for staying on their parents’ high-quality territory.
Regardless of the exact evolutionary origin, cooperative breeding improves the quantity and quality of care provided to offspring in these species.
Some well-studied examples of helper species include the Florida scrub jay, the apostlebird of Australia, and the sociable weaver of Africa, which builds enormous communal nests housing over 100 individuals.
The presence of helpers can allow the breeding pair to lay larger clutches and fledge more chicks per nest. This unique social structure demonstrates that for some species, it really does take a village to raise a child.
Conclusion
While most birds do not actively move their eggs after laying, some species exhibit fascinating behaviors around egg relocation that aid in breeding success. Grebes carry eggs on their backs, megapodes bury eggs for external incubation, and even thieving cuckoos manipulate host nests.
Understanding the diversity of avian reproductive strategies can deepen any bird enthusiast’s appreciation of nature.
