Rigor Vitae: Life Unyielding

Tuesday, July 17, 2007

ON THE WRONG SIDE OF TOWN


Where we humans alter the face of the earth, it becomes more difficult for most other organisms to thrive. Quite a number, though, manage to exploit those changes and to benefit. These species often end up as human commensals, living in a state of dependence just a bit south of parasitism. During the second millenium CE, the Black Rat (Rattus rattus) and later, the Norway Rat (R. norvegicus) followed humans around the world, as the House Mouse (Mus musculus) did centuries earlier. A hundred years ago, lost African Cattle Egrets (Bubulcus ibis) established themselves in the Guianas, and, exploiting the newly created habitat of pastureland, began to spread from there. By 1940 they were breeding in Florida. Utah's first record came in 1963, and by 1980 it was a common breeder here. Today the species thrives throughout the Western Hemisphere. More often than not, a newly introduced species that achieves such a degree of success does so as a human commensal. Otherwise, it generally does it by out-competing established natives.

Currently, the most impressive case of tetrapod invasion is probably the Eurasian Ring-necked Dove (Streptopelia decaocto). Originally native to southeastern Europe, central Asia and Japan, its range began to expand in the 1930s, eventually stretching west to Ireland and Iceland, and north to Norway.
In the 1970s, introduced Eurasian Collared Doves established themselves in the Bahamas, and over the next decade they spread into Florida, from where they've been dispersing across the continent. At this point, little is known of their impact on native species. The general consensus is that they exploit a niche between that of the native Mourning Dove (Zenaida macroura) and the old-timer invasive Rock Dove (Columba livia). Some have suggested that it is taking over to some extent the ecological function of Passenger Pigeons (Ectopistes migratorius). Over the past three years, they've established healthy populations in several towns in Colorado, Idaho and Montana, and many of them have been recorded in my own state. I spent a good part of last week touring around eastern Utah, where I saw quite a few of them, always close to agricultural areas, in a band running from the town of Roosevelt, east nearly to the Green River. It's not surprising that these birds are expected to behave as ecological intermediates between Mourning and Rock Doves. In size they fall between those two species, and they seem more social than the Mourning, and less so than the Rock. The fact struck me, though, that I never saw those other species in any sort of proximity to Collareds, despite what appears to be a wide overlap in habitat preference. In fact, a sizable Collared colony exists on the west end of Jensen, ten miles east of Vernal. Locals informed me that the birds appeared two years ago. Native Mourning Doves have been relegated to the eastern part of town, and the two species appear to me to live in absolute segregation.
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Erasian Collared Dove photo taken by CPBvK in Jensen, Utah July 14, 2007

8 Comments:

Anonymous mary said...

We live just about 45 miles southeast of Jensen, in Rangely, and have both types of doves visiting our yard. They do not associate with each other or with the pigeons who hang out around town, from what little we have seen. They do condescend to eat rolled corn or sunflower seed from the ground, but are pretty wary of people.

Did you get to check out any of the areas around where they have released the black-footed ferrets?

6:16 PM  
Blogger Neil said...

Interesting note. I can't seem to recall ever seeing a Mourning Dove in my old neighborhood in SLO, where Collards abound. In the ag fields outside of town Mourners are everywhere and there isn't a collard to be found...

What's the secret behind the partition???

6:17 PM  
Anonymous Roger B. said...

I remember when collared doves first appeared in northern England, way back in the late 1960s. The colonisation was very rapid - with five years they had become a common breeding species.

Over here they seem to co-exist happily with the much larger woodpigeon (Columba palumbus), which is increasing in numbers as it spreads from rural to urban habitats.

One of the secrets of the collared dove's success appears to be its ability to breed at any time of year - provided food is available.

The collared dove is quite a pretty bird, but it has one of the most monotonous songs you're ever likely to hear. Believe me, it can get really irritating when one is sat outside your bedroom window at 4.00am!

1:04 AM  
Blogger cpbvk said...

Mary: It's interesting that both doves feed in your yard, even if it's not simultaneous. I haven't gone looking for Blackfoots. I imagine that observing them must be very time-intensive.
Neil: Your observations jibe more with my own extremely limited ones.
Roger: Thanks for a British perspective. The birdfeeder-owning woman I talked to in Jensen said they remain all winter--and Jensen winters are nothing to sneeze at.

2:45 PM  
Blogger Neil said...

I meant 'collared' of course, by the way. My recent post on cabbage aphids must have had me thinking about leafy greens...

I haven't seen any Collared Doves here in Davis yet, but I'll be keeping my eyes open now.

5:08 PM  
Blogger mdmnm said...

That's pretty interesting. I have relatives in Houston where collared doves have been for a number of years and I've seen collared and mourning doves sharing the same feeder, much like mourning and white-winged doves share my feeder (which is to say- they squabble).

7:40 AM  
Blogger Steve Bodio said...

Fascinating.

When I came to Magdalena (75 miles south of Albuquerque but 2000 feet above the Rio Grande, there were only mourning doves, mostly outside town-- not even rock doves except for my domestic ones. Twenty years ago whitewings invaded from the south and below-- they bred in town. Then Eurasian collared doves, less that ten years ago, and flocks of feral rock doves, both in town. (We have also added great- tailed grackles in the past five).

All appear to coexist-- mournings out in the wild lands, the others in (tiny, dirt- road) town as commensals, though there may be some competition between whitewing and collared, perhaps for nest sites.

Question (philosophical)-- are whitewings (who invaded from the south) more "natural" than collareds?

No agriculture for 30 miles (Rio G valley there)-- just high grassland, mountains (no doves, only bandtails) and town. Harsh winters, but collareds court in good weather. They seem to breed earliest too, including in my yard.

8:22 AM  
Blogger Bevan Badcott said...

Here in Oz I often stop at road kill to check the pouches of marsupials found in the road. Sometimes it means a long slow trip to wherever I'm going plus months of rearing young wombats or kangaroos until release weight.

7:34 PM  

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