I'm afraid I don't know either; just one anecdote and more unfounded
speculation.
About 3 years ago, doing a Waterbird Survey of Lake Bathurst, nr Canberra,
we noted that all the Grey Teal (previously the commonest duck), had
vanished. A couple of days later I saw on birding-aus someone reporting a
massive influx of Grey Teal to the Top End to take advantage of good rains!
The phenomenon of waterbirds 'knowing' that bodies of water have appeared
inland in good seasons, is very puzzling, because it doesn't (unlike the
onset of the northern hemisphere winter) happen every year. Undoubtedly it
must have something to do with atmospheric pressure?birds knowing that a
certain set of conditions at a certain time of year where they are are
likely to mean that there are bodies of water inland.
As to the birds then travelling to where the lakes are, it is well-known
how ducks are adapted to fly long distances very fast, and Pelicans can use
their size to save energy by gliding. Both these adaptations means that it
shouldn't be impossible for either ducks or Pelicans to go and have a look,
to scout out, and if there is no water, or insufficient water, to return
immediately. Are there any records of numbers of waterfowl or Pelicans
suddenly leaving a coastal area in a good year, and then returning a few
days later? Our regard for birds amazing adaptations shouldn't blind us to
the possibility that they may use trial and error tactics on occasions too.
John Leonard
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