This exercise was prompted by the range of views expressed
– in conversations and on this forum – about what is happening in
relation to the local birds. Clearly enough, several different
things are happening at the same time, and trends are elusive. It is
particularly difficult to be sure of trends for a relatively small area -
‘the Canberra area’ – which takes in a wide range of
habitats, some classified together under one label or other although of varying
quality.
I do not need to be told about the limitations of this
exercise and will not waste time anticipating and responding to any criticism
in that regard.
26 persons contributed, offering about 80 significant or
striking ‘changes’, several of which were to the same effect.
Leaving aside waterbirds, the breakdown was as follows:
DECREASES
“Small woodland birds” and honeyeaters,
including Hooded Robin and Brown Treecreeper where mentioned specially (13);
House Sparrows (4); Starlings (3); Kestrels (2). Two responses specified
loss of species due to development of suburbs.
INCREASES
There were more of these than ‘decreases’.
Crested Pigeon (8); Common Myna (4); Superb Parrot (4); Pied Currawong (3);
King Parrot (3); Noisy Miner (2); corellas (2); Koel (2). Two responses
mentioned increase of small woodland birds in gardens. Two interesting
responses referred to nesting patterns in suburbs (one on parrots, currawong,
and raven, one on woodland/migrant species increasingly using non-native trees).
Two other interesting points by experienced observers were
as follows:
EO 1: <<Diamond
Firetail has disappeared from the above 2 areas [Cook, Gooroo], but given that
it seems to have appeared regularly in other parts of Canberra I couldn't say
that this is a population decline or increase, just a shift in location. As for
other woodland birds I don't feel there have been 'significant or
striking' changes, maybe minor fluctuations, in contrast to the doom and
gloom of the 7.30 segment.
EO
2: << One of the biggest changes to my GBS has been the
Satin Bowerbird from a winter roost nearby with up to 80 of this species, many
of which came through every day, to a time when I hardly seen one (only 1
sighting this GBS year so far). They seem to have become even scarcer
over the past couple of years compared with straight after the fires, though I
do see or hear one occasionally, often much deeper in suburbs than they used to
be.
I was going to attach my rough notes of all responses, but
the above may be enough for present purposes. Thanks to everyone who took
the trouble to think about their contribution and made the effort to put
something into words.
Having taken it this far, I add the following on our changing
bird life, a subject on which we shall hear much more, I am certain.
The following helpful sources might be mentioned –
-
The 2003 BA atlas lists changes from the previous
atlas. Among factors mentioned are changed survey methods, changed weather
conditions and ‘changed observer behaviour and knowledge’.
Examples of changes in the zone including Canberra: >20% decrease –
Brown Falcon, Jacky Winter, Crested Shrike-tit; >20% increase –
Purple Swamphen, Spotted Pardalote, Western Gerygone.
-
Steve Wilson’s Birds of the ACT: two centuries of
change (1999) comments on the status of all species recorded in the ACT
-
Birds Australia’s State of Australia’s
Birds (SOAB) series. SOAB 2008 compiled by the ANU’s Penny
Olsen has contributions from a number of experts, including a summary of
COG’s Woodland Bird Monitoring Project (also dealt with in CBN 32 (2), on
the COG website). A 10-year analysis is to be published soon. This will
be a valuable document to set against the below item.
-
The recently-publicised Victorian survey 1995-2008,
published in Diversity and Distributions (2009) 15 under the title
“Collapse of an avifauna: climate change appears to exacerbate
habitat loss and degradation”.
-
COG’s Garden Bird Survey, frequently cited on
this chatline. It has run continuously since July 1981, the results
appearing in COG’s Annual Bird Report. Philip Veerman has privately
published an analysis of the results for the first 21 years, and the present
coordinator, Martin Butterfield, produces useful updating graphs from time to
time.
The following suggested factors may influence the periodic
occurrence of birds in the Canberra area:
a)
The ‘habitat loss’ effect, caused mainly by
agriculture and development, and bearing mainly on woodland birds;
b)
The ‘drought’ effect. This, otherwise
known as a ‘prolonged severe rainfall deficiency’, has
clearly led to the degradation of some dryer woodlands in the Canberra area,
affecting some nature parks in particular. It might, as the Victorian
work suggests, have caused reduction of woodland bird numbers overall, even of
species not previously considered at risk;
c)
The ‘drought push’ effect.
There is a view, one might call it a traditional view, that this, from time to
time, sends a wave of dryer-country birds eastwards towards and even beyond
Canberra.
d)
The ‘weed-and-seed’ effect.
This continent-wide phenomenon, under one name or other such as
‘large-scale changes in agricultural practices’, is said to be
responsible for the success and spread of large and medium-sized seed-eaters eg
Crested Pigeon.
e)
The ‘Fires’ effect (self-explanatory).
f)
The ‘native revegetation’ effect.
Still being developed and assessed, although subject, one would think, to the
simultaneous effect of some other factors mentioned.
I am not sure they have been documented as such but to the
above I would add 2 considerations particularly relevant to Canberra –
g)
The ‘garden’ effect. This is
surely a dominant influence. The garden environment is expanding and
maturing. Well-watered plantings of both exotic and native species
attract birds. However, while some woodland birds will readily make use
of gardens, perhaps as winter visitors or transients, other will not .
Consider the Golden Whistler and King Parrot, on the one hand, against the
Rufous Whistler and Varied Sittella on the other. I think the GBS records
demonstrate the importance of gardens to SOME woodland birds. The
precise effect of garden maturation is an issue, and the input could do with
some sorting as some of the 3-hectare GBS sites include woodland.
Garden-type plantings to our north and east possibly account for influx of such
species as the Koel.
h)
The ‘oasis’ effect. Some patches (query
whether they all qualify as ‘woodland’) remain relatively rich
in woodland birds while numbers have collapsed in other areas. Typically
these are moist areas with deep soil that have a vigorous plant growth, often
weeds. Examples of such tracts are Campbell Park proper (before it dried
out and was weed-cleared), part of Mulligans Flat near the big dam, the Newline
Paddock, and the lower section of ‘East O’Malley’ before the
development. A typical bird of such places is the Grey Fantail, which can
be found there when it has disappeared from dryer patches. In my view the
birdiness of such places is often enhanced not only by weeds such as thistles,
Patterson’s Curse, the Wort and blackberries, but by exotic shrubs such
as briars, box-thorn and pyracanthus. The Awful Truth may be that
weed-clearing is destroying useful bird habitat – where drying is doing
the same job elsewhere..
