Storm,
I'd be interested to know more about what background information there is.
Whilst I would normally whole-heartedly agree, the theory may not apply to OBP
at present. As I understand it, the species has in the past, been quite fecund.
It was not unusual to have 4-5 chicks fledge per adult but the population
either remained the same / declined year to year. So for many many years, it
has been clear that habitat change at the wintering grounds is the driving
factor behind loss of the population.
So if we now have a situation where the birds are barely laying, will this mean
lowered fecundity in any future year? If over-winter mortality remains
consistent, then this would mean a reduction in the population - there being
less redundancy in the number of young. As you say and as Peter Menkhorst
rightly pointed out, the viability of wild populations depends more on adult
survivorship. However, this is only a 'model-based' assumption and is only
correct when the population is large or it is extrapolated out over long
periods of time. Population viability models / theory doesn't apply very well
to small populations or short-term scenarios because this makes populations
very prone to short-term or unexpected stochastic variation. Read the
assumptions behind any PVA and always the same warnings appear.
So whilst I agree with the theory, I don't agree that we can assume that
removal of young is not going to have an impact. It's a great point you raise
though and it would be brilliant to get some further insights.
Regards,
Simon.
> From:
> To: ; ; ;
>
> Subject: RE: [Birding-Aus] the walk of shame for Orange-bellied Parrots
> Date: Sun, 25 Jul 2010 00:43:57 +1000
>
> hey all
>
> A small point on the removal of chicks as a strategy for improving the
> survival of the species. I don't know but I suspect that pulling
> chicks from a nest will have no impact on the eventual total wild
> numbers.
>
> This is because animals are being removed from the population when
> they are at their most vulnerable and dispensable (to the population).
> Based on other species, I'm guessing that if more than a third of OBP
> that hatch successfully reproduce themselves that would be an
> extraordinary thing.
>
> In most species the population looks something like a triangle, with
> animal that start dying at an alarming rate once they reach
> independence. I imagine, although I don't know, that the OBP is no
> different. Taking animals that would have almost certainly died anyway
> isn't likely to be a huge loss for the population.
>
> It's just a shame that while pulling chicks may reduce food completion
> in the nest, it won't also remove the dangers of habitat destruction,
> cars, raptors (who have to eat) and the various other dangers that
> will take care of most of the rest of that age cohort.
>
> I'm guessing that although the numbers look and sound large, the
> impact to the wild population will be irrelevant while the impact to
> the captive population will be priceless.
>
> cheers
> storm
>
>
>
>
_________________________________________________________________
http://clk.atdmt.com/UKM/go/197222280/direct/01/
We want to hear all your funny, exciting and crazy Hotmail stories. Tell us
now==============================
To unsubscribe from this mailing list,
send the message:
unsubscribe
(in the body of the message, with no Subject line)
to:
http://birding-aus.org
=============================
|
