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Ok,
time to quickly dump some ideas...
I
reckon breeding success this year is the same or similar to the past several
years. From my observations I would say that family groups of 4-6 birds (2-4
juveniles) are typical. A few years back when Nicki Taws was surveying
Superbs around Murrumbateman for NPWS we saw a flock of about 100+ birds, with
adult males accounting for perhaps 20% of the individuals. Made for a great
photo! Nicki could perhaps share some data with us if she has it
handy.
My
theory is that we don't have a greater number of birds due to higher
survivorship or breeding success. I think that the influx is
food related and we are observing different feeding
strategies. I think that a
regular food resource in the Wallaroo Rd/Captain Hill area is poorer this year
and has forced birds further afield. I'm no expert, but maybe the recent dry
spell has impacted on seed setting in some grasses normaly used as a food
resource by Superbs. Certainly the recent dry spell has brought about the boom
in grasshopper numbers.
We know that
groups of 30-40 birds appear in Flynn/Fraser every December and January. Is
it possible that one or two individuals seen in southern Belconnen
over the past couple of years have brought along their families and friends to
see what they can find? Research has shown that birds, particularly communal
roosting species, can flock to a new food source in a matter of days. I remember
from my Common Myna research that, with food provided, a couple of birds turned
up on day one, about six birds the next day and 20+ the third day.
Somebody more familiar with the behaviour literature might be able to
help with some examples here.
I
believe Chris' assumptions about Superbs having high breeding site fidelity
are correct. However, I have always wondered about survivorship and site
fidelity by young birds. Every year at Captain Hill there are something like
20-25 breeding pairs (can't remember the data from Warren Martin's paper). So
where did the three young per pair from last year go? Did they stop at Boorowa
on the way back south? Did they all perish? Are the birds present every year
actually very old adults? Or are the birds that come back the young from
last year replacing adults that have perished?
Post-breeding feeding habits probably vary greatly. However
one thing we do know, as Chris explained, is that birds from
this region disappear north at the end of January. In autumn/winter
Superbs can wander far and wide taking advantage of particular food
resoucres. I remember in 1999 near the Weddin Mountains Superbs were
everywhere feeding on White Box nectar. The following year there was little
flowering and very few Superbs. A couple of years ago birds were
seen as far north as the Queensland border, which is unusual, and probably
drought related.
I
better go do some work now. Please feel free to support or pick holes in the
above.
Cheers
Anthony
From the amount of chat-line mail
there has obviously been a most interesting influx of Superb parrots into the
ACT this year. I cannot help but wonder what is going
on.
It would seem to me that there are
possibly two reasons for this (or maybe three!). There has either been a
large increase in the number of adults moving into the area to breed this year
and the breeding success has been average or there has been the normal number of
adults returning to the area and the breeding success has been much higher than
usual (or a combination).
The only thing we know for sure
about Superb parrots in our area is that they move away from the area in late
summer to return in the early spring and that birds return to the same locations
to breed. Given this, if the reason for the large numbers is due to a
greater number of adults returning to the area then this must be because there
was a very good breeding season last year, there are areas that the adult
population have not returned to and have come to the local area instead or the
winter survival was much higher than usual. I am prepared to stick my neck
out here and say that migratory species that return to the same area each year
are unlikely to go to another area if conditions are not right. They are
much more likely to return to their usual haunts and not breed. I am also
prepared to say that the young return to the area that they were raised
in. These assumptions are based on what is generally known about other
migratory species.
Therefore, if the increase is due to
a larger number of adults returning to the area then it must be because of a
highly productive breeding season last year or because of a better than usual
over-wintering success. Both are possible and we would have no information
either way.
On the other hand the increase in
number that we have seen in the ACT could be because of the usual number of
adults returning to the local area but the breeding success has been
exceptional. From my readings on the chat-line there have been some most
interesting observations of the large number of birds seen at Macquarie
Oval. From my observations at the start of the breeding season, when the
birds return to the district, there are a similar proportion of adult males to
females. On 12 January 2005 it was
reported that there were 84 Super parrots on the Macquarie Oval, of which 15-20
were males. Given no major sex biased mortality since their arrival this
would suggest that there were approximately the same number of females to
males. The next day there was a report of half the number of birds (40)
but the same proportion of males (approximately 20%). This suggests that
approximately 20% of the birds seen were male, 20% female and therefore 60% were
juveniles. This would agree with Michael Lenz posting of 15 January that
he thought that there were more juveniles in the group than had been reported on
the chat-line. It would appear therefore that for every pair there are
three juveniles. HANZAB Volume 4 states that on average there are 4-6 eggs
laid in a clutch. Most parrot species do not lay a second clutch so this
suggests that a high breeding success is the reason for the very large number of
Superb parrots seen within the district during the summer of 2005. Whilst
I was surveying the local area for Superb parrots from 1993 to 1996, although my
observations were biased to road-sides, at that time I would have easily been
able to account for 15-20 pairs so I do not think the number of adults about is
unusual.
The important question though, which
I am afraid must at this stage remained unanswered, is why has this breeding
season been so successful? As Geoffrey Dabb and Benji Whitworth (posting
15 January) suggests it is surly somehow associated with food resources.
A point to remember is how much more
interesting it is to report on more than just the number of individuals
seen. As soon as there are data available on the ratio of males, females
and juveniles we are in a much better position to speculate on what is going
on.
Chris Davey
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