If pigeon eggs are left unattended by the mother for an extended period, several potential outcomes may occur depending on various factors such as environmental conditions, the stage of egg development, and the duration of abandonment. Here are some possible scenarios:

1. **Cooling and Chilling**: Pigeon eggs require consistent warmth for successful incubation and development. If the mother pigeon leaves the eggs unattended for an extended period, they may become exposed to cooler temperatures, leading to a decrease in egg temperature and potentially affecting embryo viability. Prolonged chilling can slow down embryonic development or even cause embryo death if temperatures drop too low for an extended period.

2. **Desertion**: In some cases, if the mother pigeon abandons the nest or fails to return to incubate the eggs, they may be left unattended for an extended period. Desertion may occur due to various reasons such as disturbance, predation, illness, or the death of the parent bird. Without proper incubation and care, the eggs may become non-viable and fail to hatch.

3. **Predation**: Unattended pigeon eggs are vulnerable to predation by opportunistic predators such as rats, mice, squirrels, crows, or other birds. If the eggs are left unguarded and exposed, predators may detect and consume them, resulting in the loss of the eggs and potential harm to the developing embryos.

4. **Deterioration**: Over time, unattended pigeon eggs may deteriorate or spoil due to exposure to environmental factors such as moisture, humidity, and microbial growth. Without the mother pigeon's regular incubation and turning of the eggs, they may become contaminated or develop fungal or bacterial infections, leading to egg spoilage and embryo death.

5. **Hatching Failure**: If pigeon eggs are left unattended for an extended period, the embryos may fail to develop properly, resulting in hatching failure or the birth of weak, non-viable chicks. Without adequate incubation and care, the embryos may perish or undergo developmental abnormalities, reducing the likelihood of successful hatching and chick survival.

In summary, if mother pigeon eggs are left unattended for a long time, various negative outcomes may occur, including cooling and chilling, desertion, predation, deterioration, and hatching failure. It is essential for parent pigeons to provide consistent incubation and care for their eggs to ensure optimal conditions for embryo development and successful hatching. If eggs are left unattended for an extended period, it is less likely that they will hatch and produce viable offspring without intervention or assistance from the parent birds or human caregivers.