Birds invest significant energy into building nests and incubating their eggs. While this dedication fosters new life, some eggs may not hatch. The duration a parent bird continues to sit on unviable eggs varies based on several factors.
Normal Incubation Timelines
The time it takes for bird eggs to hatch varies widely across species. Small songbirds, for instance, typically incubate their eggs for 10 to 14 days (e.g., yellow warbler 11 days, robin 13 days). Larger birds generally have longer incubation times: woodpeckers and pigeons (12-18 days), ducks and chickens (21-28 days), and raptors (30-50 days). Some of the longest periods belong to large seabirds, like the wandering albatross (up to 80 days) and emperor penguin (64-67 days). Many bird species begin incubation only after all eggs in a clutch have been laid, which helps ensure that all chicks hatch at roughly the same time.
Why Eggs May Not Hatch
Bird eggs may fail to hatch for various reasons. One primary reason is infertility, which can stem from a lack of sperm or defective sperm. Even if fertilized, an embryo might not develop, leading to embryo mortality. This can be influenced by factors such as the maternal condition or genetic issues.
Environmental conditions affect hatching success. Extreme temperatures, whether too hot or too cold, or even freezing if not consistently incubated, can compromise egg viability. Physical damage to the eggshell or exposure to certain chemicals can prevent hatching. Disturbances to the nest, including predation or human interference, can cause eggs to fail. Hatching failure is a common occurrence in bird populations, with approximately 10% of eggs in common species not hatching.
Factors Influencing a Bird’s Decision to Continue Incubation
A bird’s decision to continue incubating eggs depends on biological and environmental cues. Species-specific behaviors vary, with some birds exhibiting greater persistence. Birds often possess an innate understanding of the typical incubation period for their clutch.
When eggs do not hatch within the expected timeframe, the parent bird may continue to incubate for an additional period. This extended incubation can range from a few extra days to over a week, allowing for natural variations or slight delays in development. Continued incubation is energetically demanding, and a bird’s physical condition can influence how long it can sustain this effort, particularly if the eggs are not developing.
Environmental cues, such as changes in weather patterns, fluctuations in food availability, or the presence of perceived threats, can also prompt a bird to abandon a nest with unhatched eggs. If some eggs in a clutch have hatched, the parent bird will typically prioritize caring for the hatched chicks, and the unhatched eggs may be left behind. When an entire clutch fails to hatch, abandonment is a more common outcome. Birds can often discern if eggs are unviable, and may abandon a nest if they instinctively sense issues with the developing chicks or if conditions are no longer suitable for raising young, with abandonment occurring more frequently during the early stages of incubation if problems arise.
Life After Unhatched Eggs
Once a bird determines that its eggs will not hatch, it typically abandons the nest. This is a practical decision, allowing the bird to conserve energy and potentially attempt another reproductive effort. Many bird species are capable of re-nesting if conditions remain favorable. This subsequent breeding attempt can occur relatively quickly, sometimes within a few days to a couple of weeks after the loss of the initial clutch. Re-nesting is a natural strategy that allows birds to compensate for early reproductive failures and maximize their chances of successfully raising young within a breeding season.
Unhatched eggs may remain in the nest, where their contents will naturally decompose over time, or they might be removed by the parent birds. Some species actively discard non-viable eggs from the nest, while others may push them aside or bury them under new nesting material as they maintain or rebuild the nest.