Con raised a worthy point. Surely the migration of raptors is more
marked in North America than it is in Australia. The same applies to
passerines, and waterbirds and probably many others. The only local
raptor with an obvious migration locally is the Australian Hobby and
even that is not complete. There is evidence of migration of Brown
Goshawks too but this is not at all clear in Canberra. The Square-tailed
Kite is another but we have not yet been lucky enough to have any
records of this one here yet..... We will one day.
Sort of related is the question or comment put by Jerry Olsen at a COG
meeting I think last year, that we don't have many owls either.
Philip Veerman
24 Castley Circuit
Kambah ACT 2902
02 - 62314041
-----Original Message-----
From: con
Sent: Wednesday, 7 October 2009 8:03 AM
Cc: canberra birds
Subject: Australian Raptors- low density?
I suspect, but don't know, that one difference between Australia and
North America is that our raptors do not migrate in the same way that
North American raptors might (?). If true, this would mean, if food is a
limiting factor, that Australian raptor numbers are determined by when
food is at a minimum. In this area that would be when many of our
passerines have headed to the coast, overseas or downhill.
I am not sure of the impacts on raptor numbers, but there is also a
significant degree in Australian avifauna of birds wandering about
regionally in response to boom and bust conditions.
The Botanic Gardens is set in Black Mountain Nature Reserve. Most of
Black Mountain has very poor soil. A recent talk by Stuart Rae
demonstrated that this reserve has a very low density of Tawny
Frogmouths. So, while the Bot Gardens has an artificially raised number
of small birds, the surrounding areas probably have low bird densities.
Australian soils more generally are also poor compared with US soils
more generally, so that might have systemic effects on bird densities.
As always, I suppose, there is no substitute for comparative statistics,
of which I have none to hand.
regards
Con
Adam James Searcy wrote:
> Hello COG,
>
> A brief inquiry; I have been working in the National Botanic
> Gardens since mid-August, and either myself or my boss Tonya Haff are
> in the gardens (usually both of us) 6-7 days per week, for 6-8 hours
> per day. We have both noted what seems to be a much lower raptor
> density in this area than expected, when compared with similar areas
> in North America (where we both hail from) and elsewhere (areas which
> also have several different sized /Accipiter/ species, as are present
> in this area, and numerous other raptor species). There are abundant
> prey species in the gardens, and it seems that they could/should
> support at least a pair or two of Sparrowhawks, a Brown Goshawk or
> two, associated juveniles, etc. While I have observed these species
> in the gardens and elsewhere, they are definitely less conspicuous
> than I would expect, both in the gardens and elsewhere. Note that we
> are out doing observational work with small passerines, and they or
> the surrounding Honeyeaters etc. are generally vocal enough to alert
> us of any nearby aerial predators (and we are looking about for such
> things anyway...)
>
> Any comments on this situation? Also, have raptors undergone
> declines in this area and Australia in general? I'm sure the
> Australian Bird Atlas will have more broad-scale information on trends
> in raptor populations, but information from anyone with extensive
> local experience would be welcome. Anyone with comparative experience
> in both N America and here would obviously have a better grasp on the
> situation. Cheers,
>
> Adam Searcy
> Macquarie
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