Hi all
I have been asked to forward an email to the group on behalf of Dr Clive Minton
regarding some recent postings on birding aus
Cheers Adrian Boyle
Since Ian May’s latest posting on the leg flagging of waders quotes excerpts
from a telephone conversation with me, two or three years ago, I thought I
should provide some input to rebut his erroneous assertions about the
detrimental effect of flags on wader survival.
Firstly I would like to correct a misunderstanding (or a misquote). Almost all
coastal migratory waders are extremely site faithful to their non-breeding
grounds – that is, individual adults typically return to the same non-breeding
area year after year. A few individuals relocate, either permanently or
temporarily, to other non-breeding grounds, especially the Sanderling, Red Knot
and (to a lesser extent) Bar-tailed Godwit. There is also some movement of
birds in their first year as they explore for their preferred non-breeding
area, and of course birds on migration can be seen far from the non-breeding
grounds on which they were banded. Yet emerging data suggest that in many
species, even migrating birds are highly site faithful, using the same
migratory stopover sites year after year.
The reason Ian saw no flagged birds in his recent scanning of wintering waders
in the Spencer Gulf (about 500 km from the nearest sites in Vic and se SA where
shorebirds are regularly banded and flagged) is because these birds would have
all been immatures (mostly first year) which had not been exposed to flagging.
All of the flagged birds he does see in that area will have been flagged
elsewhere in south-east Australia and most would have only been temporarily
stopping in his area during migration. (Surprisingly quite a few waders make a
short move from Victorian and Tasmanian non-breeding areas to South Australia
in March/April – at the beginning of their northward migration – presumably to
reduce the transcontinental first leg.)
I would like to now present one or two specific pieces of information to refute
Ian’s claim that flags reduce birds’ survival, particularly if they are
migrating.
a) Red-necked Stint
Ken Rogers has calculated average yearly survival from previously banded birds.
The Red-necked Stint is the most suitable species for such an analysis because
it is the most widely banded and flagged wader in Australia and is one of the
smallest species, which Ian claims is one of the most adversely affected.
Period
No. birds caught
Average yearly survival
78/79-88/89
11258
75.1%
89/90-94/95
6186
78.2%
97/98-03/04
5849
78.8%
Data was analysed for three marking periods, as shown in the table above. In
the first period birds were only given metal bands. In the second period many
also had flags (flagging in Victoria commenced in 1990). In the third period
almost all carried a flag (as well, of course, as a metal band). The annual
survival rates for all three periods were similar. They showed that three out
of every four Red-necked Stints successfully returned to the banding area after
completing their migration to their Northern Hemisphere breeding grounds (a
24,000km round trip). This is the level of survival rate which would be
expected for a species of this size based on wader survival rate analyses
carried out elsewhere in the world. It strongly demonstrates that flagging
birds does not prejudice their survival and that a high proportion, even of
this small species, returns successfully from migration each year.
b) Larger Waders
Resighting rates and calculated survival rates of some of the medium and large
size migratory waders in Australia show annual survival rates in the 80-93%
range. (It is normal for larger birds to have higher survival rates).
Furthermore recaptures up to 15 to 20 years after the original marking have
been made on flagged birds of most species, including the smaller species such
as Red-necked Stint, Sanderling and Curlew Sandpiper. Such birds will have made
a migration to the Northern Hemisphere each year, with a 20-year-old bird
having flown almost 500,000km on migration alone!
c) Ruddy Turnstone
Another example of the lack of any negative effect of flagging on survival
concerns a Turnstone carrying an engraved flag – which enables it to be
identified in the field with the aid of a telescope or telephoto camera – which
has been seen on migration through Taiwan in seven of the past eight migration
seasons (four northward, three southward). And of course the Turnstone which
made two 27,000km round trip migrations from Victoria to Arctic Siberia,
through Asia and then back via the Central Pacific, was carrying a flag – and a
1g geolocator attached to a second flag! This further suggests that Ian’s views
are not supported by the facts.
I take some of the blame for Ian’s regular outbursts because I should have
communicated the Red-necked Stint survival results to him – direct or via a
posting on Birding Aus – when they became available. But I hope that now I have
set out just a little of the large amount of evidence Ian can accept the fact
that flagging waders does NOT impair their survival.
It is perhaps also worth pointing out that:
a) those persons who have volunteered so much of their time to further wader
studies are devoted to the wellbeing of these birds and are the last people who
would want to be involved in any activity which prejudiced their survival.
b) scientists take great care not to carry out studies which generate results
that are biased by, for example, marked birds behaving differently or surviving
less well than the norm, as this would compromise the scientific integrity of
the results, the reputation of the researcher, and (as Ian points out) harm the
very species the research is designed to help protect!
We would be extremely interested in seeing Ian's data, which sounds like a very
detailed and long-term time-series of local observations. As discussed above,
we believe they will most likely be readily explained by existing evidence on
migratory behavior of each species, but the only way to be sure of this is to
look at the actual observations. Please Ian, support the generation of data
which is fundamental/essential to the conservation of waders and their habitats
in our Flyway. Send in your flag sightings, rather than let them collect in
your notebook, and let them be utilised for the benefit of the waders
themselves.
Clive Minton.
8/8/2011
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