Discovering a bird egg often leads to questions about its viability. Approaching such discoveries with respect for wildlife is important, as wild birds and their nests are often protected. Understanding how to assess an egg’s condition helps determine the appropriate course of action, prioritizing the bird’s well-being and adherence to wildlife regulations.
Practical Assessment Techniques
Two primary methods offer insights into an egg’s viability: candling and the float test. Candling involves shining a bright light through the eggshell in a darkened room to observe its internal contents. A strong LED flashlight or a dedicated egg candler works well. Gently hold the egg with the larger end against the light source.
When candling, look for indicators of life. Early in development, a network of fine, red blood vessels from a central dark spot (the embryo) suggests active growth. As the embryo matures, it will appear as a larger, darker mass, and you might even observe subtle movements within the egg. If the egg appears clear with no visible veins or embryo, or if you see a distinct blood ring, it indicates the egg is infertile or the embryo has ceased development.
The float test assesses an egg’s buoyancy, which changes as an embryo develops. Gently place the egg in a bowl of warm water, around 100 degrees Fahrenheit. A fresh, undeveloped egg will sink and lie on its side. As the embryo grows, it consumes nutrients and produces gases, expanding the internal air sac, increasing buoyancy.
An egg containing a developing embryo might float at an angle or stand upright with the larger end pointing upwards. If the egg floats entirely on the surface, it indicates a non-viable egg, often due to decomposition and gas buildup. Handle eggs gently during this test and return them quickly to their original environment or incubation if viable, as prolonged water exposure can be harmful.
Observing for Other Indicators
Beyond direct testing, several other indicators suggest an egg’s condition. A visual inspection of the eggshell reveals issues; cracks, holes, or mold point to a non-viable egg, as bacteria and fungi can enter and compromise development. A strong, foul odor from an egg indicates spoiled contents and a non-viable embryo.
The presence or absence of parent birds around a nest offers clues, though not a definitive measure of viability. Birds may abandon eggs that are infertile or ceased developing, or they might leave the nest for short periods to forage. If eggs in a nest feel cold to the touch, it suggests a prolonged absence of the incubating parent, indicating abandonment or lack of incubation.
Responsible Handling and What to Do Next
Once an egg’s status is assessed, responsible action is crucial. If an egg appears viable, especially if found in a wild nest, leave it undisturbed in its original location. Interfering with wild birds, their nests, or their eggs is often illegal under federal and local wildlife protection laws, such as the Migratory Bird Treaty Act in the U.S.. Human intervention, even with good intentions, can cause more harm than good, potentially leading to nest abandonment or reduced chances of survival for the chick.
If an egg appears abandoned or in danger, or if you are concerned about its welfare, contact a local wildlife rehabilitation center rather than attempting to incubate or care for it yourself. These professionals are equipped with the specialized knowledge and permits to handle wild bird eggs and chicks appropriately. They can assess the situation and provide the best course of action, which might include rescue or allowing nature to take its course. If an egg is definitively determined to be non-viable, such as one found on the ground or confirmed through testing, it should be disposed of respectfully, perhaps by burying it, to prevent attracting predators or spreading disease.