Geoffrey
is correct, the change in bird fauna cannot be attributed to Indian Mynahs based
on the study and the data in the paper. At best all that can be said is that
there is a correlation between the observed changes in avifauna and the
distribution and abundance of mynahs. A well designed replicated experiment
comparing treatment (areas with mynahs with areas without mynahs, would be
required) - or a comparison of changes in avifauna at sites where mynahs
were greatly reduced in density to areas where there was no reduction. There
have been many changes in Canberra's avifauna since I arrived in 1974, 6 years
after the first mynahs were released. Since then mynah numbers increased but
there were many other changes,. In 1974 currawongs were winter migrants - few
bred in the city; galahs were rare, as were crested pigeons and corellas, while
starlings and sparrows were very common with large flocks roosting during winter
in Civic and Manuka as well as being common in the Jerrabomberra Wetlands and
Tidbinbilla. There has been a massive change in the abundance of these species
since then, changes that have coincided with the increase in mynahs. However,
while these events are correlated, I doubt that anyone would attribute the
changes in these natives to the increase in Indian Mynahs. I recall some work
that David Purchase undertook in around his suburb of Macgregor from the 1960's
(for those that do not know David, he was the Director of the national Bat and
Bird Banding Scheme). David recorded a steady increase in the variety and
density of many native birds after the suburbs were first settled. He postulated
(correctly I believe) that as the suburbs aged there was a major increase in the
quality of habitat and the availability of food for native birds (both
from exotic and native plantings). This is not all that surprising as many
new suburbs were built on old grazing land. I suspect that currawongs now breed
in Canberra because of the availability of nestlings for their chicks (both
native and exotic such as mynahs) although a replicated experiment would
be needed to test this. Hence summer breeding of currawongs in Canberra could be
interpreted as a sign of a healthy avifauna that can now support the breeding of
these birds.
Nevertheless,
I believe that the basic conclusion of the paper is correct, that there is
little evidence that Indian mynahs are as damaging to native avifauna as was
previously believed. Even the conclusion that mynahs have slowed the rate of
increase of species such as sulphur cresteds and crimsons is dubious. Both are
common and cannot keep on increasing at the rate they have been as they will
eventually start to run out of resources causing the populations to slow and
possibly decrease - even if mynahs were having an
influence.
The
crucial issue with managing invasive species is to focus on the desired outcome
from management not on pest reduction per se. The question needs to asked, what
are the social, production and/conservation outcomes that need to be addressed
through management - decline in certain native species, reduced production from
orchards or social amenity? Then we should ask what are the factors influencing
these desired outcomes from management, invasive species (weeds and pest
animals) are likely to be one factor but invariably there will be other factors
such as loss of the quality of habitat due to clearing, over grazing (by natives
and exotics), impact of global warming and reduced rainfall, or changes due to
increased firing of habitat for hazard reduction. Too often in the past we have
take\n the easy route and quickly blamed exotic species for all the ills without
stepping back and taking a broader perspective. Sure many invasives cause damage
and I wish that they were not here, but if we put all our eggs in one basket and
focus only on exotics, then we may still lose native species due to other
factors. To illustrate this, David Pridell showed that a small percentage of
mature foxes knew when mallee fowl chicks were about to hatch and they predated
heavily on them. Following intensive fox poisoning there were more chicks
hatched but most did not reach maturity. Further investigation showed that the
seeds of native grasses that the chicks fed on were rare due to past grazing. If
he had stopped at intensive fox management, then there would still have been no
recovery in mallee fowl. There are many other similar
examples.
For
more information on how best to manage the damage due to invasive species,
members might like to download and read the recently released ACT Pest Animal
Strategy 2012 - 2020: http://www.environment.act.gov.au/environment2.
Mike
Braysher
From: Geoffrey Dabb [
Sent: Friday,
10 August 2012 2:43 PM
To:
Subject: FW: [canberrabirds] The
Common Myna: 'Is It Benign or Is It a Pariah?'
I
have read this article 3 times and I am unable to see how it shows the Common
Myna is responsible for a decline in small birds. Small birds may have
declined over the period but where in the opaque maths is it shown that the myna
must be the reason? Below is a random cut/paste of articles on overall
bush-bird decline, including one suggesting the NOISY MINER (expanding in
Canberra) is a reason. [In fact, as I read the piece, it suggests that
small birds are INCREASING LESS RAPIDLY in Canberra gardens because of the
myna]
THREATENED
AND DECLINING WOODLAND BIRDS IN THE
NEW... 
www.lrwg.com.au/downloads/.../WEDecliningBirdReport99Reid.pdf
File
Format: PDF/Adobe
Acrobat - Quick
View
by JRW
Reid - 1999 - Cited by
110 - Related
articles
standout Declining bird species in the
SWB. All but two of the 20 Declining species are
passerines or 'typical bush' birds. This contrasts with
the 38 Threatened ...
1.
Native bird populations declining rapidly
- The 7.30 Report - ABC
www.abc.net.au/7.30/content/2009/s2720637.htm
21 Oct 2009
– It
is well documented bird populations are
in serious decline across
the ...LISA WHITEHEAD, REPORTER: The Australian bush without the
call ...
2. [PDF]
The effect of Noisy Miners on small bush
birds: an unofficial cull and ...
www.une.edu.au/ers/staff-profile-doc-folders/.../debus-n-miner.pdf
File
Format: PDF/Adobe
Acrobat - Quick
View
by SJS
DEBUS - Cited by
3 - Related
articles
... in each time period. Totals for small
(<120 g) bush
birds,
mostly ... are a major contributor to the
local decline of many
woodland birds. The results also
affirm ...
3.
Bush Birds
www.sopa.nsw.gov.au/our_park/environment/.../birds/bush_birds
Although none of
the bush
bird species at
Sydney Olympic Park are listed under threatened species legislation,
many bush
birds are in
severe decline across ...
4. [PDF]
facing
www.cse.csiro.au/research/documents/ecosbirdsextinction.pdf
File
Format: PDF/Adobe
Acrobat
Australia's bush birds are in trouble.
Only one ... regions are in decline, and more species
will vanish if ... causes and extent of bird declines across the
southern ...
5.
No birds in
the bush
www.birdlife.org › BirdLife
News › News Archive
Search
01-06-2010.
Australia's woodland birds, including many
species generally regarded as common and widespread, are declining at an alarming
rate according to ...
6. [PDF]
AUSTRAL
