On Oct 16, 2009, at 3:07 PM, Eugene and Nancy Hunn wrote:

> Stewart et al.,
>
> I was recently in Europe and Eurasian Collared Doves have recently
> colonized
> a great deal of European and North African territory, without the
> benefit of
> any direct human assistance. I suspect it is quite possible they
> colonized
> the Bahamas and then Florida and the rest of North America likewise
> without
> direct assistance, despite the general consensus that they were first
> established in the Bahamas as a result of human introduction. If
> they got
> there on their own they are an invader comparable to the Cattle
> Egret and
> perhaps other species with proven powers of over water dispersal.

It's well documented that 50 Eurasian Collared-Doves escaped into the
Bahamas in December 1974.

> What should our attitude be towards species that are invasive
> independent of
> any human intention? The Barred Owl is another case in point.

This is an very interesting point.

One would add the House Finch, Anna's Hummingbird (overwintering in
the PNW) and even American Crow and probably others those that you see
in urban and particularly suburban birds).

One thing that one might speculate is these are synanthopic species
except for the Barred Owl? Or maybe that is just more synanthropic
than the reclusive Spotted Owl?

What about the Western Scrub Jay with it's current northwards range
expansion? Is that synanthropic or is it synanthopic by one remove
with them eating the chicks of synanthopic Rock Doves, Crows and the
other suburban birds) like the with urban, overwintering Cooper's Hawks.

Are these "evil" invasive birds or merely successful birds? Does the
evilness in the humans mind go only with the non-nativeness of the
birds? Or just with the displacement of other species?

Rob raises the other issue that seems to surround the Eurasian Collard-
Dove. It seems to extend its range without displacing other similar
species.

On Oct 16, 2009, at 10:04 PM, Rob Parsons wrote:

> Paul Conover, a birder & ornithologist in Louisiana looked for
> correlations in CBC data between Eurasian Collared-Dove & Mourning
> Dove numbers, as the former began its impressive expansion through
> the state. He found no decline in Mourning Dove numbers during the
> time period. As far as I'm aware, nobody else has found any hard
> evidence that collared-doves negatively impact MODOs in any way
> whatsoever, either. The two seem to coexist because their
> ecological requirements aren't identical.
>
> Similarly birders in Texas feared the arrival of collared-doves
> in their state would impact on the White-winged Dove, which was
> undergoing an expansion as the collared-doves arrived. Again, no
> negative impact was ever found. Both species are continuing their
> expansions in numbers. This is not to say their arrival doesn't
> impact some species and that we shouldn't be concerned.


This is true also in Europe where it steadily spread across the
continent from Turkey through the 20th Century.

If you are curious about this (and some measured parameters of the
Eurasian Collard-Dove like how does a supposedly sedentary bird
colonize places so rapidly? A small fraction of the population seems
to like to move long distances) I'd recommend this paper that was
written by a Dutch researcher to encourage research on the spread
Eurasian Collared Doves in the USA. It's an easy read too.

http://elibrary.unm.edu/sora/JFO/v064n04/p0477-p0489.pdf

The timing is interesting too. Why the 20th century? Was it increasing
(sub)urbanism in south-east Europe the encouraged them to spread? But
they spread into rural "USSR" too but didn't succeed in colonizing
most of Portugal and Spain or most of Italy south of Rome. In Europe
they are now predominately a bird of the suburbs and some populated
rural areas (mostly alongside people).

Perhaps it's the assumption of a closed ecosystem is wrong here. Maybe
the current suburban ecosystem is actually open with not all niches
being occupied so it can accept another species with displacing
another? Perhaps that's a consequence of human change in the original
ecosystem that aided them to find their niche?

Or perhaps it's their "lifestyle". Maybe they live in a different
manner so they affect other similar species less than one might
expect. For example, they're colonial nesters so one might speculate
that although they like to nest where other Doves nest a large number
of them nest in a very small areas (little "towns" of Collared Doves)
that doesn't displace the lower density non-colonial Doves (in the
same way the Rock Dove hasn't displaced them?). They also eat in a
different manner to other Doves filling their crops, drinking a lot of
water and roosting to digest the huge load of food. Is food perhaps
superabundant in suburban areas for these birds?

I wouldn't be complacent about any non-native species arriving in a
ecosytem but those that claim that this (or any) particular species is
displacing other birds really have to provide the evidence to show
that is actually happening. They seem to have been in the US for more
than 30 years now and I haven't seen any evidence for the supposed
harm they're to be causing. I'd love to see some citations for that. I
seen some comments about worries about they spreading disease too but
again I don't know what evidence there is for that.

The bottom line though is (as they might say on Capitol Hill,
Seattle): "They're here. They're Collared. Get used to it".

The Brits have. A slowly repeated "CuCoooo Coo" is now the sound of
summer across the UK. As heard on many British drama soundtracks to
make a suburban summer afternoon outside sound really authentic. Even
if they do add it to dramas taking place before they arrived the
1960s :-).

The other point to make here is there are plenty of opportunities for
"citizen science" in looking at the spread and impact of the Eurasian
Collared Dove in the PNW.
--
Kevin Purcell
kevinpurcell at pobox.com
twitter: at kevinpurcell