A bird egg gets fertilized internally when viable sperm are present in the oviduct as the developing egg passes through it.
Here's a breakdown of the process:
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Egg Development: The egg begins as a single cell in the bird's ovary, growing in size and accumulating yolk over several days.
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Passage Through the Oviduct: The developing egg then travels down the oviduct, the tube that connects the ovary. According to the reference, it is within the oviduct "where, assuming that viable sperm are present, it will be fertilised."
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Fertilization: If sperm are present in the oviduct, they will fertilize the egg as it passes through. This internal fertilization is crucial for the development of a chick.
In summary, fertilization in birds happens internally within the oviduct when the egg encounters viable sperm.
