Dean
With due respect to your research, I feel the point is, nip the
potential problem in the bud now by getting rid of the crow. It appears
to be ship assisted as it has shown up at a major port city. If it is a
natural self introduction there will be more, most likely on the north
Australian coast somewhere, and we could not hold them back even if we
wanted to.
Greg Little
Greg Little - Principal Consultant
General Flora and Fauna
PO Box 526
Wallsend, NSW, 2287, Australia
Ph 02 49 556609
Fx 02 49 556671
www.gff.com.au
-----Original Message-----
From:
On Behalf Of Dean Portelli
Sent: Wednesday, 19 March 2008 5:25 AM
To: Birding-Aus Mailing List
Subject: House Crow
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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