Cut-throat sex ratios

[GregH]

Does anyone know how birds influence not just the sex of the young they raise but the actualy sex ratio of young hatched? I have watched my cut-throats consistantly raise 4-5 young andnd to start off the M:F ratio was 1:1 but the last two nests are 4:1. They seem to breed continiously and start incubating before the first clutch have even fledged. Could this be a problem the cause of the problem and if it is how? If bird sex chromosomes are like mammalian ones then I can't see how the sex ratio can move far from 1:1.

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[Page0044]

Hi Greg, i would think that the tempeture of which the eggs were incubated would play a part in the male to female ratio.

[GregH]

Yes. Well I know that temperature determins sex in reptiles but I don't think that is the case for birds. I suppose I'd better Google it! According to a project in the Netherlands (http://www.onderzoekinformatie.nl/nl/oi ... ND1291428/). It is believed that the primary sex ratio is determined by the female. Apparently environmental conditions alter the females hormone levels and this in turn can control which sex chromosome ends up in the mature oocyte. Unforunately since it is a current project it can't tell me what environmental factor to alter to restore the balance. The same mechanism appears to operate in peafowl (http://www.pubmedcentral.nih.gov/articl ... id=1626203) and has been investigated for zebra finches (http://www.eko.uj.edu.pl/rutkowska/abs/2006_1.pdf).

I guess I'd better keep my eyes peeled while they find out how to make my birds less androgenic and menwhile I will find a market for unpaired male cut-throats.

[gomer]

I read this article once, saying that a well marked cock will produce more cocks.And a poorer one will produce hens.The theory behind it was the hen would keep the atributes of the cock if being well marked,buy producing cocks.And if he was poorly marked she would tend to pass on her own.

[GregH]

Well this is obviously a topic that lots are interseted in as it's been the subject of research projects and even the ABC want to report on it (http://www.abc.net.au/news/stories/2009 ... 521613.htm).

The gist of this article is that in gouldians the hen can adjust the sex ratio within a clutch to reduce mortality from genetic incompatibilities that associate with head color morphs. In humans this is analygous to embryo screening and selective abortion to favor one sex over the other to avoid the expression of diseases for example haemophilia or colour blindness. Female birds fortunately can actually determine which of thier sex-chromosomes are allocated to their eggs and so control the sex ratio.

In an aviary situation with basically unlimited resources, there must be an advantage in throwing more males as this is a common complaint. While most resources are unlimited, space is not so any more females in the available space would make the situation worse and if the males "fight it out" then only the strongest will father the next generation. It wouldn't be too difficult to design an experiment to proove this. If this is the case, then what it means for keepers/breeders is don't overcrowd breeding aviaries and remove the young as soon as they are independant.

[gomer]

that makes sense greg.

[Mickp]

guess I'll be looking for some ugly emblemas, just so I can get some more hens from them. a hen emblema around here costs about $40 while a pair costs $50

[Diane]

Ive got one 4 day old emblema so far out of 3 clutches with a total of 12 eggs. They had 2 babies in the last clutch but they tossed them. Fingers crossed for this little one.