As I recall from a zoology lecture last year, many animals are more likely
to have male babies when they're in good condition and females when they are
in worse condition. Apparently the kakapo breeding program in NZ was almost
entirely getting males until they realised this and found that if they fed
the birds less, especially in the lead up to mating, they would get more
females.
The general explanation is that for animals where one male fathers children
with many females, only the best males become fathers, so it's best to have
male babies when you're in the best condition, so that they'll be in the
best condition too. On the other hand females usually mate regardless of
their condition, so if you're not in the best condition, it's better to have
females. Of course this is just a trend, not a rule.
I also recall that the kakapo has a fairly unique breeding system, and I
don't know if OBPs have a dominate male kind of system. It wouldn't
surprise me if the remaining birds do get a lot of food when they breed in
Tassie though, since there is a feeding station and not much interspecies
food competition. Perhaps it is an area that needs research.
Jeremy O'Wheel
On Sat, Sep 24, 2011 at 1:00 PM, Glenn Ehmke <>wrote:
> Thanks David, I’ll read up on the Mauritius Kestrel, sounds very
> interesting.
>
> The genetic explanation certainly sounds feasible given how few birds there
> are left now.
>
> Some NZ friends also pointed out to me that gender bias can have a purely
> ecological cause - e.g. Kaka which apparently have a male skewed ratio in
> many areas because females are much more exposed to predation at nests. In
> that case the bias is "the cause" of the population crash rather than a
> symptom of it, which is why I wondered how long the gender bias has been
> apparent in OBPs...
>
> Glenn
>
>
> ________________________________
> From: David James <>
> To: Debbie Lustig <>; birding-aus <
> >; Glenn Ehmke <>
> Sent: Thursday, 22 September 2011 5:27 PM
> Subject: Re: [Birding-Aus] OBP article
>
>
> Extreme gender bias appears to be a frequent symptom of inbreeding
> depression when inbreeding becomes acute due to a large population crashing
> rapidly to a small population. Such a sudden bottleneck can lead to a high
> percentage of deleterious recessive genes normally not expressed suddenly
> becoming homozygous and being expressed. Gender bias toward males almost
> claimed the last of the Mauritius Kestrel some years ago, though determined
> intervention by Carl Jones saved the thing. I'm sure there are mosre cases
> in birds. A few in mammals too.
>
> David James,
> Sydney
>
> ==============================
>
> --- On Thu, 22/9/11, Glenn Ehmke <> wrote:
>
>
> >From: Glenn Ehmke <>
> >Subject: Re: [Birding-Aus] OBP article
> >To: "Debbie Lustig" <>, "birding-aus" <
> >
> >Received: Thursday, 22 September, 2011, 4:03 PM
> >
> >
> >Good article Debbie.
> >As you point out the 100% breeding participation government agencies have
> been so keen to publicise this year is tempered by the fact only 8 pairs
> bred. Of course that obviously means there were only 8 females in the wild
> last year, and a bit of simple maths tells you that (assuming there are
> actually 35 birds left) there is a 400% male gender bias!
> >I’m not sure I’ve ever heard of such a bias in any wild bird population,
> certainly not one that’s manifested “overnight”!… anyone?
> >You are lucky indeed to have seen OBPs in the wild this year.
> >
> >________________________________
> >From: Debbie Lustig <>
> >To: birding-aus <>
> >Sent: Tuesday, 20 September 2011 5:53 PM
> >Subject: [Birding-Aus] OBP article
> >
> >
> >Article written, immodestly enough, by me.Feedback?
> >
> http://blogs.crikey.com.au/rooted/2011/09/19/on-the-hunt-for-the-mysterious-orange-bellied-parrot-australias-most-endangered-bird/
> >===============================
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