1. Incubation Period Variation: While the average incubation period for budgie eggs is around 18-21 days, there can be natural variation among individual birds. Some hens may take slightly longer to incubate their eggs, and this could be the case if your mother budgie is still sitting on the eggs after 21 days.
2. Infertile Eggs: If some or all of the eggs are infertile, the hen may continue to sit on them longer than usual, as she may not be able to instinctively recognize that they are not viable. Infertility can occur due to various factors such as age, health issues, or incompatible breeding pairs.
3. Double-Yolked Eggs: Occasionally, budgies may lay double-yolked eggs, which can take longer to hatch compared to single-yolked eggs. This could be a reason for the extended incubation period in your case.
4. External Factors: Environmental factors such as temperature, humidity, and light can also affect the incubation period. If the nesting environment is not optimal, such as being too cold or too hot, it can delay the hatching process.
5. Mother's Health: The health and well-being of the mother budgie play a critical role in successful incubation. If she is experiencing any underlying health issues or stress, it can affect her ability to properly incubate the eggs and may prolong the incubation period.
It's important to provide the mother budgie with a calm, comfortable, and stress-free environment. Ensure that her diet is balanced and nutritious, and that she has access to fresh water. If there is no sign of hatching even after a few additional days, it's advisable to consult an experienced avian veterinarian for further guidance.