Hervey raised several points - "It raises in my mind the question of which of
two factors, instinctive
'route following' or food availability, plays the greater part in
determining migration routes."
Ursula Munro, then at the University of New England now of the Uni of
Technology, Sydney has a real interest in this subject. In her PhD,
Ursula determined that captive wild caught Yellow-faced Honeyeaters
maintained an instinctive migratory pattern of heading north-east and then
shifting orientation north-west. This coincided with the timing of
honeyeaters reaching the NSW north coast. If the birds kept moving
north-east they would end up at sea. It is interesting that this
orientation was present in captive birds that had no visual clues. It is
important to remember that this was an overall pattern. This pattern was
much stronger in some individuals than others suggesting that there is
individual variation. This work is published. A search of "Emu" should
find at least some of this work. Ursula is now working on migration
patterns of other birds such as Silvereyes.
I believe that this instinctive behaviour can be overridden by
environmental factors, especially in Regent Honeyeaters. I also believe
that resource availability can affect migration of the longer distance
migration of the smaller honeyeaters.
I have a Regent Honeyeater record sheet in front of me for the Regents
seen at Buttaba on the Central Coast last week. It records Noisy
Friarbirds, Yellow-faced Honeyeaters and White-cheeked Honeyeaters as
abundant, Red Wattlebirds, White-naped Honeyeaters, Scarlet Honeyeaters,
Musk Lorikeets and Rainbow Lorikeets as common. Little Wattlebirds, Noisy
Miners, and Eastern Spinebills were listed as scarce. This would suggest
that large numbers of the migratory honeyeaters are not stalling on the
south coast as somebody (I've forgotten who) hypothesised (although this
may have been suggested for Swift Parrots).
"Is it known how much YFHE eat during migration? Are their routes
determined by food availability or do they follow instinctive and defined
routes and feed opportunistically as they go?"
I don't think small honeyeaters could get very far without replenishing
reserves. As such their route must be determined by food availability.
However, many honeyeaters are generalists and will get by on lerp and
other resorces. We had good numbers of honeyeaters at a site near Mudgee
on the weekend where there was no flowering with the birds clearly feeding
on lerp.
"How would honeyeaters migrating along the ranges know that there are
flowering Bloodwoods along the coast?"
Now, there's the $64 000 question. How do Regent Honeyeaters know there's
a good flowering of Swamp Mahogany on the Central Coast? I can more
clearly see a possible answer for Regents than other more long distant
migrants. I think Regents routinely visit a series of known "resource
rich" sites. If Site A is not suitable they move onto Sites B, C, D etc
until they find what they are looking for. They exist by being more of a
generalist when pickings are slim. If there is a poor year generally in
their core area, as this year is in central NSW, they end at the end of
their circuit in a "resource drought refuge" - the Central Coast for the
central NSW Regent HE population. This begs the question of why don't
they go there every year. It might be as simple of why move all that way
if there is a good flowering of White Box just over the hill.
I think the answer for the smaller, long distance migratory honeyeaters
will be much more complex than this.
Confused? I am most of the time.
David Geering
Regent Honeyeater Recovery Coordinator
NSW National Parks & Wildlife Service
P.O. Box 2111
Dubbo NSW 2830
Ph: 02 6883 5335 or Freecall 1800 621 056
Fax: 02 6884 9382
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