The observation that started this thread was of beach washed Wedge-tailed
between Seal Rocks and Tea Gardens on the central coast of NSW where an
estimated minimum thousand were reported on the 11 October 2000 (Ian McAllan
and Dick Cooper). There had been none on 10 October.
Since then most of the thread has been interesting and occassionally
illuminating. It would seem that Short-tailed have been most affected,
perhaps because they arrive more knackered, having come from the north
Pacific. But clearly two species have suffered some mortality and whilst
species survival might not be an issue the life history strategy is
fascinating. And it would be interesting to tie these periodic wrecks to the
recent Tristam's Storm-petrel - a north Pacific species.
Anyway, the veterinary pathologist at Taronga, Karrie Rose, has done a few
autopsies and she has kindly offered her opinion.
Regarding the recent mortality of short-tailed shearwaters along the east
coast of Australia.
Veterinarians at Taronga Zoo have been examining many short-tailed
shearwaters and have been fielding dozens of phone calls regarding their
mortality.
In New South Wales, we tend to see quite significant short-tail shearwater
mortality each year at the end of the migration (November/December). This
year the die off seems to be about a month early and it seems that larger
numbers of birds are coming ashore.
In the past, the birds have been emaciated, dehydrated, they have had
hepatic and pancreatic atrophy, and often die with urate nephrosis. Most of
the birds have underlying, and probably incidental, renal coccidiosis,
proventricular nematodiasis (Anisakis and Contracaecum spp) and small
intestinal cestodiasis. Approximately half of the birds examined have pale
musculature, pale internal organs, and have haemorrhage into the
proventriculus and/or duodenum. It is difficult to differentiate
antemortem gastrointestinal ulceration and haemorrhage from post-mortem
diapedesis; however, I am confident that there is antemortem
gastrointestinal ulceration in at least a proportion of these birds. We
have not detected significant numbers of haemoparasites, or seen evidence of
an underlying viral infection in any of the birds examined.
Unfortunately piscivorous animals decompose quickly and we have had
difficulty getting access to freshly dead birds this year. I have examined
approximately 8 s.t. shearwaters in the past 12 days and found that each
bird has the general pattern of lesions described above. This year however,
we have also noted numerous haemorrhages at the anterior pole of the kidney
and in the serosa of the proventriculus. Histopathology is pending on two
birds with these lesions, and tissues have been frozen back for viral
culture or toxicology. Serum is being collected and frozen from both live
and dead shearwaters so that serology can be conducted to detect antibodies
to Avian Influenza and Newcastle's Disease.
We have found no evidence of external or internal contamination of the birds
with petrochemicals. The pattern of mortality is generally inconsistent with
exposure to toxins. We are seeing large numbers of emaciated, and
dehydrated birds. The hallmarks of toxicosis are large numbers of birds in
excellent body condition, usually with an intestinal tract full of ingesta.
Effectively, all of the lesions that we have been seeing in the shearwaters
are either incidental underlying parasitism, or are associated with
emaciation, dehydration and ishaemia/shock. I still have histopathology and
microbiology pending on the most recent cases, but my feeling is that it
would be useful to study the food supply of the shearwaters, and to examine
meteorological data to better understand this event.
In addition to the investigations being undertaken at Taronga Zoo,
shearwaters are being examined at the Australian Animal Health Laboratory,
the Victorian Institute of Animals Science, Melbourne Zoo, Currumbin
Sanctuary, and the University of Queensland.
Paul Andrew
Curator
Taronga Zoo
PO Box 20
Sydney 2088
tel:612-99784724
fax: 612-99784613
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