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
