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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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
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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
________________________________ Sent: Thursday, 22 September 2011 5:27 PM
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 burunglaut07@yahoo.com ==============================
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 burunglaut07@yahoo.com ==============================
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.
________________________________ Sent: Tuesday, 20 September 2011 5:53 PM
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/ ===============================
To unsubscribe from this mailing list, send the message: unsubscribe (in the body of the message, with no Subject line)
http://birding-aus.org =============================== ===============================
To unsubscribe from this mailing list, send the message: unsubscribe (in the body of the message, with no Subject line)
http://birding-aus.org ===============================