spectacular gathering of corellas (not local!)

["Paul T." <>]

At 04:45 PM 19/12/2009, you wrote:
> Aha, Martin, a question of one?s
> perspectives perhaps.  I would have thought it was tempting to
> attribute extensions due to escapes and introductions to natural
> causes.
>  
> Joe Forshaw, a silent reader of this chatline, says he agrees broadly
> with my position on the Long-billed, the true correlation being with
> human settlement,  and we should look at Australian Parrots Third
> Edition 
>  

Geoffrey et al,

Excuse my amateur ignorance, but why does the tracking of the Long-billed
with human habitation mean that the inhabitants are all escapes or
introductions (which is who I think you've argued, unless I have read it
incorrectly)?  Could it not just be that we are creating artificial
food sources that are just too darn good to ignore?  Human
habitation dramatically increases the food yield with many of our crops
etc being suitable food for the Corellas.  If we plant it, will they
not come? <grin>

And no, I am not saying that I think that following human settlement is a
"natural cause", but I am still wondering why the Corellas
appearing with our settlements would necessarily mean that they were
escapees.  All it needs to start a new area is for a group of them
to be interrupted/picked up by a particular storm system and deposited
elsewhere.  In the past these small groups would not have been
sufficient to start a full colony as there would not have been enough
food to establish themselves fully in the new location.  Now that
humans have developed the land though, these accidental outliers have a
much better chance of survival and establishing a viable colony?

And just wondering...... do we really have that many Long-billed Corellas
released from captivity that can then colonise and extend the ranges so
extensively?

As I said, I'm an amateur and have no idea whether this is feasible or
not.  I hope my uninformed hypothesis is not considered unsuitable
for the list.

Thanks.

Paul T.
Higgins, ACT

> From: martin butterfield
>  
> Sent: Saturday, 19 December 2009 10:42 AM
> To: Geoffrey Dabb
> Cc: Cog line
> Subject: Re: [canberrabirds] spectacular gathering of corellas
> (not local!) - and channel-billed cuckoo in Wanniassa yesterday
>  
> Geoffrey
> It is always tempting to attribute range extensions to escapes and
> introductions.  
>
> Looking at the attached  LB Corella map from birdata (at I think10
> minute level rather than the one degree cells of the Atlasses) there
> appears to be a rather high correlation between reports of outlier LB
> Corella reports (other than Sinny metro area) and the watercourses of the
> Murray Darling system.  Possibly that is a coincidence reflecting
> the likelihood of towns being on the rivers (or birders being on the
> rivers) but it does suggest to me that the birds might have spread
> themselves up the system from Balranald(ish).
>
> Martin
>
> On Sat, Dec 19, 2009 at 10:03 AM, Geoffrey Dabb
> <>
> wrote:
> Interesting about the corellas, Sandra.  Numbers might be unusual,
> but I?d suggest they are still in their ?normal? range.  In the
> below adaptations of the atlas maps I?ve marked Deniliquin with a green
> star.  Even in 77-81 that was on the edge but within the natural
> extension.   The great spread further afield in 98-02 has been
> attributed to releases and escapes, and I think that accounts for the
> birds in Canberra.  By contrast the map for the Little Corella would
> show a continuous extension.  I think that is reinforced by the
> large numbers that turn up here periodically.  Therefore if we were
> suddenly to get a hundred Long-bills I would say the resident
> introductions had been augmented by an advance party from the
> riverina.  Another indication would be to watch carefully and see if
> they show a preference for Australian Rules, western Victoria and the
> riverina having strong traditional associations with that particular form
> of boot-ball.     
>  
>  




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