Yes but this is more than a simple abundance measure. It is based on continuous
data over a 21 year period, from 53244 observer weeks, over a cumulative total
of 1316 observer years, at a cumulative total of 294 survey sites (from 43 to
90 sites per year, whether you call Canberra and surrounds “a location” is a
moot point). And that is only for the first 21 years of the survey. The
information on the 14 years since then is not consistently compiled in any
available format to address this question. The constancy of the Blackbird
abundance is extreme. Out of over 200 species recorded in our GBS (of which
about 100 are recorded enough to offer useful comment about annual patterns).
There are only 3 species that show the same high level of yearly constancy:
Australian Raven, Australian Magpie & Common Blackbird. Even the Magpie–lark
shows more annual abundance variation than those 3. So here, which may be
different from Tylden, where so many species are migrants, this is not one. As
for movement through the area allowing numbers still to be stable, that is
fairly unlikely. It is statistically unlikely and there are not many Blackbirds
in the surrounding areas to provide a steady flow.
Philip
From: Lawrie Conole
Sent: Saturday, 22 April, 2017 10:15 PM
To: Philip Veerman
Cc:
Subject: Blackbird migratory behaviour in Australia?
Thanks Philip.
That's where simple abundance measures from a location don't really tell the
whole story. The relative abundance of resident blackbirds in Tylden is the
same today as it was yesterday - except that a significant number of non local
birds moved through and out. If I hadn't been out walking the dog I'd be none
the wiser!
There are various locations around here that are 100-300m higher in altitude
(so up towards 1000m). I surmise that any blackbirds that are on the move have
come from altitude.
Regards
Lawrie
On Sat, 22 Apr 2017 at 21:45, Philip Veerman <> wrote:
Abundance of the Common Blackbird is almost constant in Canberra. Minimal
change through the year (as from the results of 21 years of our Garden Birds
Survey, as in my book). And that variation is entirely explainable by
changes in levels of conspicuousness. No suggestion of any regular movements
in or out of our region. Similar results from the ACT Bird Atlas. In marked
contrast to the many native species that show very strong seasonal or
monthly changes in abundance due to migrations.
Philip
-----Original Message-----
From: Birding-Aus On Behalf Of
Lawrie Conole
Sent: Saturday, 22 April, 2017 1:22 PM
To:
Subject: Blackbird migratory behaviour in Australia?
Hi birders
Back in 2004 on Birding-Aus I wrote this:
"... /Some musing on that feral pest the Common Blackbird (Turdus
merula) in Victoria, Australia ..../
/A couple of observations this Autumn have me wondering whether some
proportion of the Victorian Blackbird population might be migratory -
even if its just the kind of altitudinal migration seen in various
indigenous birds here. Let me elaborate .../
/At two sites I've visited in the last fortnight, I've come across
groups of Blackbirds (about 10 birds in each case) roosting/resting in
isolated patches of vegetation in farmland during the day. In one case
the patch was a cluster of pines in a vast dry grassy paddock, no
understorey - very un-Blackbird-like habitat (Craigieburn, northern
Melbourne). The others were laid up in a mess of Spanish Heath (Erica
lusitanica) underneath remnant Swamp Gums (Eucalyptus ovata) in farmland
(south of Colac, northern Otway Ranges foothills). Both sites were at
about 200m above sea level, and perhaps less than 50km from more upland
forest (>500m ASL). In both cases they flushed in groups, and didn't
give the characteristic Blackbird cackle that usually accompanies such
disturbance./
/This seems vaguely like migrant behaviour to me. Thrushes like these
often migrate at night in their natural range, and lay up in various
copses of vegetation during the day. In the Craigieburn example, several
migrant Grey Fantails were noted in an adjacent patch in the paddock./
/I'd be interested in any comments on this matter. Does anyone live in
an upland kind of place with fluctuating Blackbird numbers which might
suggest regular short - medium distance movements? Any other similar
observations? The 'big picture' data presented in the New Atlas
publication are not finely resolved enough to address this question -
particularly if only some Blackbirds are migrating/moving/ ...".
There wasn't much of a response, and nothing to corroborate my musings.
So until today I hadn't thought about it much since. This morning
pre-dawn when I went outside briefly (Tylden, central Victoria, ~600m
above sea level) there was an unusual amount of Blackbird noise - more
than I'd expect from our apparently resident pair. Out walking with the
dog a few hours later, around 10am, I saw what could only be Blackbirds
migrating. Over a period of about 5 minutes, I estimated about 40
Blackbirds passed through in a loose stream, going N/NNE (and therefore
down in altitude) - much as you see with Yellow-faced and White-naped
Honeyeaters when they're migrating - moving from one copse of trees to
another, stopping briefly before heading on. In this case both males and
females.
So why does it matter? Just a feral pest. It has been frequently stated
in the literature that Australian introduced populations of Blackbirds
are all sedentary. In their native range some populations are migratory.
Does that reflect here then that the source populations are from
different populations in Europe with respect to migration, or are local
environmental conditions just triggering latent migratory behaviour? I
can't help but be interested ...
If anyone else sees anything similar this autumn, I'd love to hear from you.
regards
--
address.html
<#*dr.-lawrie-conole*>/Dr. Lawrie Conole/
Tylden 3444, Victoria
Australia
lconole[at]gmail.com
--
Dr. Lawrie Conole
Tylden 3444 Australia
lconole |at| gmail.com
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