birding-aus
Dear Francis,
Thanks for your fascinating notes on Latham's Snipes. I hadn't realised how
useful dogs could be in snipe censussing, and the information on their
status on the Atherton Tablelands was new to me too.
I certainly can't disprove the idea that the snipes hop up the coast slowly,
maintaining weight until a big flight from New Guinea. Figuring out what
they do from existing distribution records is not at all easy - all sorts of
guesses have to be made, about whether you've seen a good proportion of the
number of distribution records in existence, and about how many snipe
records would be expected from an area that they stage in, given that they
are sneaky birds and that ornithological coverage is sparse and patchy. I
imagine that if Latham's Snipes usually staged in the Philippines quite a
few would have ended up in museum collections; this does not seem to be the
case, but...
Three other lines of reasoning (none of them conclusive) make me suspect
that Latham's Snipes must stop over somwehere on northwards migration to
undergo a good deal of pre-migratory mass-gain:
1. Swedish migration theory says that by and large, it is not in the
interests of a migratory bird to accumulate more weight than it needs to get
to the next point on its migration route, because flight costs are much
higher for birds carrying a lot of weight. This prediction seems to work
quite well with most waders - most that migrate by 'hopping' don't put on
huge amounts of fat. Applying it to Japanese Snipes, I would speculate that
fat coastal NSW birds would make one flight to northern Aust. or New Guinea,
arriving in quite skinny condition and then tanking up for the next flight,
rather than making lots of short flights up the coast while carrying a lot
of weight.
2. Latham's Snipes leave south-eastern Australia (well, at least Vic. and
southern NSW) with quite worn body plumage. The few photos and specimens I
have seen of recently arrived birds in Japan show very fetching fresh body
plumage, strongly suggesting that there is a partial pre-breeding body moult
between the time that they leave south-eastern Australia and the time they
get to the breeding areas. All other waders I know of suspend body moult
while migrating, performing the actual feather growth while staging. It
makes me think that the snipes must spend sufficient time staging somewhere
to moult quite a lot of body feathers.
3. (Getting much more s
eculative) Young Latham's Snipes perform a complete
flight feather moult during their first summer (the timing is almost
identical to that of adults), and they almost certainly migrate north with
the adults when c.9-11 months old (there are hardly any June/July records
from Australia). This is quite an unusual for an Australian migratory wader
- in most species young birds remain down here for at least their first
austral winter, the exceptions (e.g Sharp-tailed Sandpiper, Oriental Plover,
Oriental Pratincole) tending to be species which are thought to migrate in
relatively short hops and go through less pre-migratory mass-gain than
migrants like Red and Great Knots which migrate in very long jumps.
In general young waders tend to be less efficient foragers than adults (this
is certainly true of the Red and Great Knots I study in Broome) and I
suspect that one of the reasons that they stay in in our region for their
first austral winter is that they cannot gain mass fast enough to perform a
northwards migration on schedule in their first year. If young Latham's
snipes can counter this trend and return north in a long flight in their
first year, I'd guess that they must have access to a pretty sensational
feeding area to stage in. I would have thought there would be more strategic
possibilities in the vast areas of northern Australia and New Guinea which
are damp and insect-filled at the end of the wet season, than in the
Philippines where I understand the rainy season to be from about July to
December.
Danny Rogers
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