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Question about bird egg fertilization (1 Viewer)

T

Terry O'Nolley

Cow-headed Jaybird
I just finished watching Sir David Attenborough's marvellous The Life of Birds and heard him say something multiple times that struck me as odd.

What he said boiled down to female birds could be mated with one day and lay a fertilized egg the next day.

I am asking how this is possible. Please understand that I am not discounting anything he said. I am only saying that my long held assumptions run counter to this.

I thought it took several days for a female bird to develop and lay an egg. I also thought that a fully formed egg couldn't be fertilized through its shell after it was already full-sized.

Can anyone clarify this for me?
 
The shell is not formed until a few hours before the egg is laid, so the egg is fertilised before that. Small birds lay one day per day, so while it may take a few days for the ovum to 'ripen', it only takes a day to make an egg. Birds can also lay unfertilised eggs, as any domestic chicken will show you, so they do not need to be fertilised to develop. Small birds also have a fast metabolism, so things happen much quicker. Having said that, birds can lay mixed-paternity clutches, but it was always my understanding that there was a fertile period several days before laying the actual egg that had been fertilised. Mixed paternity shows that not all eggs are fertilised at once, but I'm not exactly how far in advance of laying they are fertilised. But Attenborough is briefed by researchers who get the info from people working in the field, so he's probably not fibbing.
 
Also just to add that once a cockerel has been mated with a hen they lay eggs that are fertile for some time - weeks afterwards, sorry only know about chickens! Amazing really.
 
In addition to what Poecile has said, the shell, once "applied" to the egg is only marked with its colours/patterns virtually as it is being laid.
 
halftwo said:
In addition to what Poecile has said, the shell, once "applied" to the egg is only marked with its colours/patterns virtually as it is being laid.
Click to expand...

I'm not sure about 'virtually'. It's more like an hour or so before. Pigment cells stain the shell, and in some birds the egg rotates over the cells as this happens, giving a scribbly pattern as in Yellowhammer.
 
Hi All,
I can add a little more to this - and it makes the story even more remarkable.

Most birds lay one egg a day (there a just a few exceptions). One egg (ovum) is ovulated a day from the ovary during the laying period and fertilisation has to take place at the upper end of the oviduct before the shell, shell-membranes or white (albumen) have been added.

In the domestic fowl (and assumed the same in most birds) after a single mating, fertile eggs can be laid for 2 weeks. In the hen's vagina there are sperm host "glands" which seem to store sperm although this is probably not the only site of storage. Sperm appear at the site of fertilisation (top of the oviduct) within minutes of mating, then new batches of sperm appear at each ovulation. Just where they have come from (sperm host glands or somewhere along the oviduct) and what triggers their release is not known.... but just think of the difficulties as a batch of sperm are moving up the oviduct, meeting an egg on its way down. Its surprsing that we have any birds at all!
Probably more info than you wanted but I teach this stuff to the vets.
Pete
 
Hi Quercus
Yes, because the development of the embryo starts with incubation and generally (and again there are exceptions) incubation only starts after the laying of the last egg (or the penultimate egg) so that all eggs get approximately the same incubation and hatch at the same time.
Pete
 
not at exactly the same time, they usually hatch over 24-36 hrs or so. Even though incubation doesn't begin until the penultimate egg, the ones laid first do hatch first, so the embryo does develop a little before incubation. This may be during the night when the female is roosting in there but not incubating. Even pheasant etc can leave eggs beind that haven't hatched in time, even though they usually hang about for a day or so to wait.

There is also evidence that females can skew the sex ratio and paternity of their offspring, so not only do they store sperm, they also sort and rank it.
 
Poecile said:
There is also evidence that females can skew the sex ratio and paternity of their offspring, .
Click to expand...

Absolutely fascinating! How can the female skew the sex ratio? Something to do with temperature, maybe?

I used to keep chickens...(free range, just for our use) and we had many broody hens over the years....always more cockerel then hen chicks which were of course the ones we wanted to keep. I just thought they were naturally cockerel heavy.
 
It's not all clear yet, there's still competing theories, but:

Sex ratios:

this is what they definately can do:
http://calvin.st-andrews.ac.uk/external_relations/fp_news_article.cfm?reference=613

and this is one way they can do it
: http://www.news.cornell.edu/stories/May05/birds.gender.ssl.html

Megapodes have also been shown to use temperature, like in reptiles, but they're weird.

Sperm competition is common in birds, and females control when copulation occurs, so they can store sperm and time copulations with various males to skew the chances of fertilisation being by a particular male. That's one mechanism: http://ror.reproduction-online.org/cgi/reprint/3/2/123.pdf

and here's a variation, that the sperm compete amongst themselves: http://www.springerlink.com/content/tx88773347h00r76/

but there is also a theory that females can affect this somehow, through stratification or dumping, although that last paper doesn't think so.
 
The Cornell article ends by saying that this has no practical applications to the poultry industry, but as Joanne points out, egg producers wants more females than males.

Has this not got implications for captive breeding projects? A higher female to male ratio could lead to a more rapid build up of a population.
 
Quercus said:
Has this not got implications for captive breeding projects? A higher female to male ratio could lead to a more rapid build up of a population.
Click to expand...

and also declining wild populations. where birds are under stress, the ratio gets skewed towards males and you end up with not enough females. In my tit population this year, the number of pairs has halved due to a lack of females, possibly due to the bad spring last year skewing the sex ratio. There's lots of unpaired males. A few years of that, and you can see how local extinctions can happen.
 
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