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Birds sperm and eggs

Fewer than one per cent of inseminated sperm reach the egg and a new study has discovered that successful sperm have certain characteristics which are preferred by the female bird. Scientists believe that these traits help the sperm swim faster through the vagina. The bird then stores these sperm before giving them the chance to fertilise her egg. However our study shows that the specific design of sperm is more important than total length alone.
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Hot weather is bad news for bird sperm

Unlike humans, birds require multiple sperm to penetrate an egg to enable their chicks to develop normally. A new study by scientists at the University of Sheffield revealed there is a functional role for 'extra' sperm in the early stages of embryo development. This is very different to humans and other mammals where the entry of more than one sperm into an egg is lethal. Researchers also discovered female birds are able to regulate the number of sperm that make it to the egg, ensuring that sufficient sperm are available for fertilisation -- particularly when the numbers of inseminated sperm are limited.
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Bird Reproduction & Anatomy

Male birds have paired abdominal testes lying cranioventral to the first kidney lobe. Testes increase dramatically in size during the breeding season. The vas deferens emerges medially and passes caudally to the cloaca where it has a common opening with the ureter in the Urodeum.
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November 14, An unexpected discovery about fertilization from the University of Virginia School of Medicine reveals new insights on how sperm and egg fuse and could have major implications for couples battling infertility—and may lead to a future male contraceptive. The finding has the potential both to boost the success rate of in-vitro fertilization and reduce its cost.
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