In his recent discussion of the Grarock et al. Myna paper Philip
Veerman states ?It is abundantly obvious that the Common Starling decreased as
the Common Myna increased, that is described in the GBS Report as the most
likely relevant interaction to any other species by the Myna.?
I wonder about the closeness of that interaction.
There is no doubt that the Myna would win in any direct confrontation
with a Starling, and competition would be strongest during the breeding season
for nesting sites. However, the strong decline of Starlings occurred just as
much in Myna-free areas as in those with Mynas present. For example, the more
than 80 pair breeding population at the ANU (from my earlier surveys) largely
vanished without a Myna being seen, nor were the Starling breeding sites (mainly
in buildings) occupied by other species. In 2008 I revisited the breeding birds
of Ainslie, and found Mynas and Starlings sharing the same building for nesting,
albeit using different entry holes to get under the roof space or in the wall
cavities, but both species would often sit fairly close to each other on the
roofs, and singing.
As Philip also points out in the GBS report, the Starling starts to
nest earlier than the Myna (a fact that would give it some advantage). The more
slender-built Starling would also be able to use hollows with a smaller
entrance, Mynas could not access. Outside the breeding season, one can sometimes
see both species in mixed flocks, but overall the Starling tends more frequently
to visit pasture, sports fields and the like.
To me, all this points to many factors impacting on the Starling,
with the Myna being one, but not necessarily the key factor.
And this brings me back to the Grarock et al. paper.
Factors other than the Myna with a negative impact on populations of
other species are not properly explored (see also Geoffrey Dabb?s and Mike
Braysher?s earlier comments). And it would have to be explained in which way
Mynas could impact non-cavity nesting birds such as Superb Fairy-wren, Grey
Fantail and Silvereye. The biology of those 3 species would largely exclude
direct interaction with the Myna. Yet predation (e.g. Pied Currawong, cats etc.)
may be a far bigger issue with those or the increasing footprints of buildings
at the expense of green space, drought etc.
In this context, the House Sparrow is of interest. It has declined
worldwide (with some significant exceptions, e.g. the city of Berlin with a
stable House Sparrow population). Many factors have been identified that could
explain its decline. Grarock et al. add the Myna for Canberra to that list of
negative factors. Yet there is agreement in the wide literature on House Sparrow
decline (none quoted by Gararock et al.) that no single factor satisfactorily
explains the world-wide decline.
Michael Lenz
