Hi All,
The appearance of this single house crow and the discussion it has incited has
scratched the surface of an entire field of study that has become known as
‘invasive species biology’. Below is my rather lengthy contribution to this
discussion – see my concluding remarks for an explanation!
Australia, as we are all well aware of, has a large number of introduced
(invasive) species. The majority were deliberately introduced for biological
control (e.g. cane toads, common mynah), acclimitisation purposes (e.g. house
and tree sparrow, common starling, lantana, camphor laurel), or for recreation
(e.g. rabbit, fox). Typically, many individuals were released and in some cases
at multiple sites over a prolonged period of time. For example, the common
starling was introduced over a period of ~30 years in the late 1800’s in
Sydney, Melbourne, Hobart, Brisbane and Adelaide. It is noteworthy that
numerous introduction attempts in Australia failed to establish persistent
populations despite attempts with some of the same species being successful
elsewhere in the world. Examples include waterbirds, gamebirds and various
passerines from the northern hemisphere.
Invasive species that were not the result of a deliberate introduction can be
broadly considered as either ‘accidental introductions’ or
‘self-introductions’. Importantly, introductions in both categories are
facilitated through human activity. This includes promoting persistence of a
species in human-modified habitats and by providing a means of transport (e.g.
ship assisted such as we assume to be the case with the House Crow). Among
birds the only clear example of a successful introduction of this form is the
cattle egret, and even in this case deliberate introductions were also
undertaken. It is also worthy of noting that native species have been
introduced to parts of Australia outside their normal range and have
established persistent (and often growing) populations (e.g. laughing
kookaburra, rainbow lorikeet, long-billed corella). While introduced species
can spread rapidly, they can only do so once they have established a
self-sustaining population capable of growth. This initial period of
establishment can take much longer than the subsequent rapid spread might
suggest.
The economical and ecological impacts of introduced species that have
established viable populations in Australia have been well documented and are
undisputed. Consequently, it is not surprising that many people have developed
(and expressed in the present discussion) an alarmist attitude towards
non-native species. However, I believe adopting this attitude only hinders
discussion about the house crow at Dee Why. For example, comparing an
individual fox to an individual house crow is hardly valid given the greatly
disparate ecology of the two species and their potential individual impact(s)
on native biota (i.e. large voracious predator vs small predominantly
scavenging bird). While I appreciate that this example was being used to make a
point it highlights the lack of objective consideration in the present
discussion.
So far two key questions have been raised by several contributors.
1) How likely is it that this individual house crow at Dee Why will lead
to the successful establishment of a viable population in Australia?
2) How does the house crow pose a threat economically (i.e. as an
agricultural pest) and ecologically (i.e. direct and indirect effects on native
biota) to Australia? That is, should we be concerned that house crows may
become established in Australia?
It appears that the first question has been overshadowed by the alarmist
response to the second question as the answer is clearly in the affirmative
given house crows have become a serious problem where they have been introduced
elsewhere in the world. While this is somewhat understandable given the public
perception towards invasive species in Australia (e.g. foxes, rabbits, cane
toads), I believe that this question only becomes relevant after considering
this first question and some follow-on questions, including:
3) Given the establishment of a population of house crows in Australia how
effectively can it be controlled or eradicated? That is, can we ‘afford’ to
wait and see if this one house crow becomes many?
It is here that we really need more information about house crows in Australia,
which has been neglected in the discussion thus far. In my cursory research on
the subject I discovered that in addition to house crows appearing occasionally
as singles or pairs at several locations in Australia (something I think many
birders would already be aware of) at least one small population of at least 15
individuals persisted in Perth for over two decades before finally being
destroyed (along with all others that have been detected). A signifiant feature
of the ecoplogy of the species is that it usually lives in close-association
with people, both in its original range and where it has been introduced. So,
it would appear that house crows can be readily managed if a population becomes
established in Australia because they are large birds, prefer human settlement
and thus easily detected, an effective control method is available (i.e.
shooting), and the rate of population growth appears to be slow providing ample
time to implement control actions. This leads to a fourth question:
4) If there is no threat posed or the likelihood of any threat being
realised is low, and/or the ability to control or eliminate the threat is high,
what action (if any) should be taken with the Dee Why house crow? That is, we
now have a fourth question:What are the pros and cons of the options for
management of the house crow in Australia?
This is where this issue starts to get much more complicated as we delve into
issues beyond the biology of the invasive species including public perception
about wildlife management, animal ethics and resources available for monitoring
and control of invasive species. Here are just some things to consider:
- Is it acceptable/ethical to destroy the Dee Why house crow given it
may not pose a threat? It is unlikely this single individual, given the ecology
of the species, will have direct or indirect effects on native biota above and
beyond that of ecologically similar native species. (Note that disease
transmission has been suggested as a threat but in reality this is a low risk.
There are numerous native species that regularly travel between Australia and
other parts of the world that are just as likely to be carrying the same
pathogens that the Dee Why house crow may be carrying. So the chances are if
the Dee Why bird has it, native birds have previously been exposed).
- Are resources available to monitor this individual house crow in the
event that it becomes the founder of a population? This is really where the
second question of house crow impacts in Australia (i.e. the potential threat
they pose) becomes an important consideration. Is there a high likelihood that
a house crow population will become established and start to spread before
being detected and/or control/eradication measures can be implemented? Here we
must consider the balance between the risk of the Dee Why bird becoming a
threat (i.e. population established) and the risk of being unable to manage
that threat should it arise. This is what underlies the precautionary principle
advocated by the late Graham Pizzey and others.
- Should the Dee Why bird be destroyed because future costs of
eradicating a population may be considerably higher, even if it is unlikely
that a population will become established?
- Is it important that the public perceives government taking action to
control an invasive species? That is, be seen to be doing something. The
disastrous results of previous decisions to introduce organisms for biological
control and the prominent negative profile of feral animals in Australia are
important considerations when considering this question.
CONCLUDING REMARKS
It was not my intention to write such a detailed reply, but the deeper I dug
the more complex things became. In any case it was a stimulating exercise and
helped fill the time that insomnia was otherwise wasting.
I was originally prompted to write this reply because I take a great dislike
to discussions on birding-aus becoming personal in nature. I feel this is both
unnecessary and detracts from the discussion. It can also discourage people
from contributing. This present topic is a case in point. For example, one
person criticised another contributor saying "you seem to have failed to grasp
the fundamentals of the argument...". I don’t think the comment was justified
(or at least the tone of the comment wasn't) given the context of the previous
comments by the other contributor. Furthermore, I am of the opinion that it was
the critic that has demonstrated a poorer understanding of what was fundamental
to the issue being discussed.
I think birding–aus has great potential to facilitate very stimulating
discussions about anything ‘birds’ but this, in my experience, is too often
hindered by intolerance of the opinions of others, inflammatory comments, and a
tendency for people to jump to conclusions. Indeed, it is for these reasons I
now only rarely contribute to birding-aus.
_________________________________________________________________
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