> Gidday Jill,
> I do remember the posting and it is good to see a
> positive follow up story. But I have a question, how do the Japanese
> birds relate to the Australian population and if they are the same ??
> Does this mean they have two breeding seasons??
Hi All,
This question, which came to me privately, may well be of interest to some
list members, and so I choose to respond publicly. It's a tricky little
story.
The Little Tern occurs in various parts of the world, but in our flyway, we
have Sterna albifrons of the subspecies sinensis. It has only ONE breeding
period in its annual cycle.
One population breeds in the northern hemisphere during the northern summer
(Australian winter) in places like Japan, the coast of China, Philippines,
Vietnam, and more locations. Birds from this population come to Australia
from about October until April, in the same seasonal cycle as most migratory
shorebirds. This population forms the majority of the individuals which
spend the summer on the Caloundra sandbanks, SEQ.
There are two known Australian breeding populations.
One population breeds in the Gulf of Carpentaria during our autumn/winter.
We know little about this population. We don't really know if they are
sedentary, dispersive, migratory or nomadic, but I suspect that their area
of movement is not great in migration terms. Marking of birds would give us
the knowledge we lack on this matter. One day.
The population which grabs all the headlines in Australia is the threatened
population which has its breeding stronghold along the NSW and Victorian
coastlines, with a concentration in sthn NSW and eastern Vic. This
population extends from the odd one in Tasmania to as far north as Cairns,
but at its extremities, there are very few individuals. For instance, we
only see the odd ones in Moreton Bay. This population struggles to maintain
itself in the face of human activity on beaches, where it nests just above
the high tide mark, and natural weather events. After breeding the
population leaves the breeding areas, and to date we have not found out
where it spends the Australian winter. We know from colour-flagged birds
that it spends time in Caloundra as it presumably heads north, but where it
goes. who knows? Does it go to Japan? We don't think so, because we have not
had records of flagged Australian-breeding birds mixing with the Japanese
breeding birds at their breeding grounds.
How do we know which one belongs to which population? Now we're getting into
tricky stuff. To this point we have not succeeded in separating the
populations by DNA testing, although it may occur in the future. So at this
stage we assume that they are the same subspecies. Because we have the same
subspecies breeding at different times of the year in a range of locations,
and because they change their plumage according to the season, we are able
to pick clues which tell us to which population a bird belongs. This is
relatively straightforward in summer and winter, but in autumn and spring,
when one population is moving out of breeding plumage and another is moving
into breeding plumage, it is extremely tricky. By knowing the moult strategy
of the species, you can often work it out, but you need to see the
individual bird very clearly to do so, and even with perfect viewing it can
be confounding.
I think I had better leave it at that. I could talk for hours about what I
know, but I could talk for the rest of my life about what I don't know.
Cheers,
Jill
--
Jill Dening
Sunshine Coast, Qld
26º 51' 152º 56'
Ph (07) 5494 0994
Birding-Aus is on the Web at
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