Hi all,
Just did a quick calculation:
Population 23,000,000
Average lifespan 15-19 years say 17
Deaths per annum 1,352,941
Deaths per day 3,706
KIlometres of coast passed 500 kms per day
Deaths per km of coast per day 7.4134
Assume 50% get washed in 3.71 per km of coast per day
Duration on the beach 7 days
Number of dead birds on the beach 25.95 per km = 1 every 40m or so
So during migration one should expect 1 dead STSW per 40m of beach.
During the breeding season around Tasmania and Bass Strait, one would expect
occasionally huge numbers to wash up together in Tasmania, Victoria or South
Australia.
Population dynamics is a numbers game.
Cheers,
Graham Buchan
On 30/11/2010, at 9:51 AM, Mark Carey wrote:
>
> Is it really that surprising that after a journey from the Bering Sea back to
> Australia that a few birds die? Wrecks of Short-tailed Shearwaters (STSW) and
> other seabirds occur regularly all over the world. In Australia, wrecks are
> common at this time of year because STSW adults returned at the end of
> September. Juvenile wrecks occur in April/May after they fledge. Some birds
> just aren't going to make it. Given the breeding population is estimated to
> be between 23 -30 MILLION I don't think the numbers that have been reported
> will have any significant impact on the population.
>
> Wrecked birds can be very useful to science. Birds can be used in a number
> of different ways such as looking for effects of plastic ingestion, heavy
> metal contamination and staple isotope studies. Numbers and timing of wrecks
> can also be used to infer migration. Don't forget, all birds should be
> checked for leg bands. STSW are the third most banded species in Australia
> (120,000 to date!).
>
> Regards,
>
> Mark
>
>> Date: Mon, 29 Nov 2010 11:17:54 +0000
>> From:
>> To:
>> Subject: [Birding-Aus] Dead Shearwaters
>>
>> Tonya's post about the dead ST Shearwaters in southern NSW, extends the
>> grim picture that had been painted by my daughter who lives beside the
>> beach at Peregian on the Sunshine Coast of Qld - by several hundred
>> kilometres.
>>
>> About the first week in November, she, and a young boy who happened to
>> be walking on the beach, moved by compasssion rather than rationality,
>> had been prompted to enter the surf to rescue a couple of floundering
>> young shearwaters and took them to the Australian Wildlife Zoo -
>> inevitably without a happy ending.
>>
>> Apparently there were many dead shearwaters along the northern Sunshine
>> Coast beaches and there had been even more a couple of weeks earlier.
>> She is not sufficiently knowlegeable to have aged the dead birds she saw
>> on the beach on those occasions, although the floundering birds were
>> juveniles.
>>
>> I join Tonya in an interest to hear explanations of the phenomena - the
>> likely causes and whether juveniles are particularly at risk.
>>
>> Angus Innes.
>>
>>
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