Why do birds congregate on ephemeral wetlands?
This is a topic which has given me a lot of thought.
I believe that when a dry waterhole, billabong or creekbed - or just
a depression in a paddock - is re-charged, either by floodwater spilling
in from adjacent water-courses or by heavy rain, there must be a huge
hatching of microscopic life such as waterfleas (Daphnia) and
micro-plants from spores and eggs present in the dry mud and a
consequent rapid increase in anything that feeds on them. Yabbies come
up from the mud. Plus the fact that flood-waters often wash in fish-fry
and eggs, and much other water-life, which develop rapidly in the still
shallow water which is warmed by sunlight. Not to mention adult fish
which are marooned when the water goes down - alas, often Carp these days.
Back in 1977, I observed floodwater spreading across the Ivanhoe
Golfcourse (Vc.)and adjacent public park at Chelsworth Park and Wilson
Reserve. Black Ducks and Dusky Moorhens were running with the advancing
water and each time a tussock of grass was flooded, they rushed to take
advantage of the large numbers of insects and grass-seeds which were
washed out of it. A Great Egret and White-faced Herons were fishing in
the floodwaters.
In summer 1975-76 (not quite sure of date) the lakes in Wyperfeld
National Park were filled by floods from the Grampians coming down the
Wimmera River. I heard a BOC member give an account of this at a
meeting (unfortunately not noted in club journal). He observed the
water as it arrived in the park and told us that it was accompanied by
Swamphens and Moorhens which were running with the water and feeding in
what they found washed out of leaf-litter and debris in the creek-bed.
The water was moving at human walking pace. The distinctive calls of the
birds alerted him to go and see what was happening - at the time there
had been no waterbirds in the park at all.
Anthea Fleming
On 16/05/2012 12:54 AM, Chris Shaw wrote:
I've long been fascinated why birds congregate in such large numbers on
ephemeral ponds. On a recent bit of a ramble through northern Victoria I came
across another couple of places where this occurs. That and a few other
rumblings are on my blog:
http://topbirdsandeveryfing.typepad.com/top-birds-everyfing/
Chris Shaw
Mobile: 0409 675912
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