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<\/p>\nAnd if you think you know why, don’t be too sure about it.<\/p>\n
Most adult female\u00a0birds have only a single ovary and oviduct, the left ones. That’s in contrast to other vertebrates that have two of them, including humans of course. The\u00a0loss of the\u00a0ovary was long-presumed to be a weight saving device that enabled more efficient flight and some sources still claim that as fact.<\/p>\n
The direct dinosaur ancestors of birds had two ovaries but the earliest birds had only one.\u00a0We have compelling evidence that both statements are true\u00a0from recent discoveries of their fossilized soft tissues, including parts of their reproductive systems – further circumstantial evidence suggesting that the loss of the right ovary\u00a0might be\u00a0related to weight loss and its advantage for\u00a0flight.<\/p>\n
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This is a Long-billed Curlew egg, produced by the left ovary of course,\u00a0that\u00a0was presumably\u00a0scavenged by predators on Antelope Island. The development of the\u00a0shelled egg like this one, as opposed to eggs without shells like those of amphibians,\u00a0was possibly the most significant\u00a0development of land\u00a0vertebrate evolution. Because the shelled egg doesn’t dry out it allowed vertebrates to invade the land much more efficiently instead of being restricted to water for their reproduction. But I digress, though only\u00a0a little\u00a0– the evolution of the land egg is a subject I used to love to cover in my zoology classes.<\/p>\n
But let’s see if all<\/em> the evidence supports the theory that adult birds lose their right ovaries as a weight saving device.<\/p>\n Adult male birds fly\u00a0but they have testes on both sides. And the single ovary is of comparable size to\u00a0the testes \u2013 even during the breeding season when the testes increase considerably in mass. So why don’t male birds lose one of their testes? They have to fly too and\u00a0a single testis could certainly get the job done.<\/p>\n An alternative theory presented by some suggests that the fragility of the eggshell\u00a0might be\u00a0the key as to why the ovary\u00a0is lost. If the female has two adjacent\u00a0oviducts and both have eggs passing through them as they mature would the eggs be “clanging against each other” during flight and other strenuous activities, possibly breaking or damaging\u00a0one or more of them?<\/p>\n Perhaps the real reason the ovary is lost\u00a0is influenced by both – loss of weight for flight\u00a0and to prevent egg damage. Or\u00a0maybe it’s something we haven’t even thought of.<\/p>\n On a related\u00a0note here’s something else bird gurus wonder about. Why is it always the right ovary that is lost and never the left? After all, when female\u00a0birds are hatched (birds are hatched, not born – at least not in the biological sense) they have both rudimentary ovaries but only the left one develops. Why is it never the right instead?<\/p>\n There’s so many things about birds that we simply don’t know or understand\u00a0but I sure do\u00a0think they’re fun to\u00a0chew\u00a0on.<\/p>\n Ron<\/p>\n <\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" And if you think you know why, don’t be too sure about it.<\/p>\n