How long is 3 generations for the Ostrich? A "3-gen or 10 yrs, whichever is
longest" rule is used by the IUCN to compare with rates of decline for
classifying threatened species. It is a measure of time, not a matter of having
grandchildren. A generation is defined as the average age of first breeding in
females of the population. It is a seriously flawed criterion because it is
extremely difficult to determine, especially in rare species.
I'm not sure if a criterion of 3-gen for establishment of a self-sustaining
population is defined in the same way. I'm not aware of any formal recognition
of this criterion for introduced poulations. In a pure sense, you can't
determine what the generation length is in an establishing population (or a
declining population!), because it is not stable. Since the 1980s I have
understood 10 years to be the rule for feral species. It seems very arbitrary
and inadequate. However, as far as I am aware, Christidis & Boles 1994 and 2008
did not use very specific criteria. The 2008 list defined that "Introduced
species accepted are those whose populations are naturally self-sustaining
without the need for additional releases or escapees to remain viable."
To point out how stupid the IUCN generation length is for threatened species,
Christmas Island Flying-fox failed to be classified as threatened by the
Australian Environment Department's Scientific Advisory Committee in 2008
primarily because they did not know how long the species' generation length is:
Rapidly declining towards extinction? Sure. Generation length? Unsure. List as
threatened? Nope!
David James,
Sydney
==============================
From: Ed Williams <>
To: ; ;
Sent: Tuesday, 6 September 2011 7:30 PM
Subject: Barham Ostriches?
Hi all,
There were certainly some immature ones there when I drove past a few months
ago - so they've clearly breeding recently.
They were right by the fence but spooked when I pulled the car over - so they
certainly didn't seem very domesticated either.
Doesn't help prove the 3 generations rule though...
Cheers,
Ed
Ed Williams
Seddon VIC
> From:
> To:
> Date: Tue, 6 Sep 2011 19:08:35 +1000
> CC:
> Subject: Re: [Birding-Aus] Barham Ostriches?
>
> Hi Joshua
>
>
>
> The information broadcast a few months ago is that this group of Ostriches
> has been known by locals in the area to be self-sustaining for at least 25
> years. So it is possible to argue that they may not have been through three
> generations (another test), but it is most likely that they have. They have
> been seen with young.
>
>
>
> Bob Cook
>
>
>
> _____
>
> From: Joshua Bergmark
> Sent: Tuesday, 6 September 2011 6:47 PM
> To:
> Subject: RE: [Birding-Aus] Barham Ostriches?
>
>
>
> Hi everyone, this is just a quick question that I've been wondering about
> since the Ostriches were found - how is it that these birds have been deemed
> "tickable", and not just escapees, which seems like the more likely option?
> Is there proof that they've been sustaining themselves for 10 years?
> Regards
> Joshua Bergmark
>
>
> > From:
> > To:
> > Date: Tue, 6 Sep 2011 18:41:42 +1000
> > CC: ; ;
> ;
> > Subject: Re: [Birding-Aus] Barham Ostriches?
> >
> > Hi all
> >
> > Successful trip today to find Ostriches near Barham, South West NSW.
> >
> > We found them very close to the published point - 35.37.15, 144.20.45.
> This
> > point is actually a little way up Lashbrook Rd.
> >
> > However, they are in a large "paddock" on the North East corner of
> > Deniliquin-Barham Rd and Lashbrook Rd. This corner is just to the West of
> > where the large powerlines cross the Deniliquin-Barham Rd (otherwise easy
> to
> > miss that road). We first saw two birds from Lashbrook Road about 3/4 km
> > from the main road. They were in a Canola crop and a long way, at least
> > 500m, from the road. We later saw 5 birds from the Deniliquin-Barham Rd,
> > exactly where the powerlines cross, but still over 100m from the road. So
> > definitely 6 and probably 7 adult birds - did not see any chicks.
> >
> > As this paddock is probably at least 1km x 2km and they were actively
> > roaming around, they are not all that easy to spot. (Others have told us
> > that they would be right by the fence...!!!)
> >
> > Also of interest seen along Lashbrook Rd were a family of Grey-crowned
> > Babblers and a lone, probably juvenile White-winged Triller.
> >
> > And I have seen more White-necked Herons on this trip (from near Bendigo)
> > and around Vic generally in the past six months than in the past 20 years!
> >
> > Bob Cook
> >
> > 0427 266 770
> >
> > -----Original Message-----
> > From: John Tongue
> > Sent: Tuesday, 6 September 2011 11:16 AM
> > To:
> > Subject: Re: [Birding-Aus] Barham Ostriches?
> >
> > Hi Bob,
> > Thanks for that, and good luck!!
> >
> > Hope you have a successful report to post tonight.
> >
> > John T,
> >
> >
> > On 06/09/2011, at 11:07 AM, Bob Cook wrote:
> >
> > > Hi John
> > >
> > > We are about to drive out to look for them today. Will post a report
> > > tonight!
> > >
> > > Bob Cook
> > >
> > >
> > > -----Original Message-----
> > > From:
> > > On Behalf Of John
> Tongue
> > > Sent: Tuesday, 6 September 2011 10:35 AM
> > > To:
> > > Subject: [Birding-Aus] Barham Ostriches?
> > >
> > > Hi All,
> > > Does anyone have any up to date info on the Ostriches around Barham?
> > >
> > > Considering whether it's worth a detour.
> > >
> > > Thanks,
> > > John Tongue
> > > Ulverstone, Tas.
> > >
> > >
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> > >
> > >
> >
> >
> >
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