Date: 5/26/19 11:00 am
From: Nathan Pieplow <npieplow...>
Subject: Re: [cobirds] Request for help: Ravens in Prowers County

You raise excellent questions about the range of ravens in SE Colorado. I
haven't spotted many ravens in Prowers County, but I've spent some time
carefully studying a few in Kiowa, Bent, and Lincoln Counties in the past
two years, and in other SE counties before that. In general I think your ID
article in Colorado Birds is spot on. Identifying the ravens in the field
is extremely difficult. After my careful studies I usually end up entering
them into eBird as "raven sp.".

I tend to be a Chihuahuan Raven skeptic. Whenever I encounter a raven in
Colorado, including on the SE plains, I need to be convinced that it is a
Chihuahuan. In my experience, Common is the expected raven species in the
canyons south of the Arkansas river, and I have come to expect it at John
Martin Dam, which is at least a potential nesting site. This may represent
a fairly recent range expansion for Common Raven.

Fifty years ago, Bailey and Niedrach wrote that "White-necked [i.e.
Chihuahuan] Ravens once occurred on the Colorado plains in thousands, but
they have disappeared from all except a small area, with nesting now
localized from Cheyenne, Kiowa, Kit Carson, and Lincoln Counties to the
eastern border of the state. [...] All of our observations of the species
have been in the four counties mentioned above, especially south of Kit
Carson. In this area in the 1920s and 1930s there was a nest on almost
every windmill, and each of the dwarfed trees had one or more. [...] During
the past twenty years we have seen a few ravens on practically every trip
through that region, but the birds have gradually decreased, until now, in
1964, they are no longer common."

Bailey and Niedrach gave zero information about either raven species east
of the mountains and south of the Arkansas River. They say of Common Raven,
"a fairly common bird of the mountains and western areas of the state,
[...] reported from all counties west of the prairies." It seems that fifty
years ago, there were few ravens of either species south of the Arkansas.
The area was surely undersampled, but Niedrach mentions several trips to
Baca County and Bradbury led museum field trips to Baca County in 1921-22,
so it seems clear that ravens must have been much less common there then
than they are now.

A couple years ago, Andrew Spencer and I decided to start measuring the
nasal bristles of the Common and Chihuahan Ravens in museum collections,
because it turned out nobody had ever done a quantitative study of nasal
bristle length, which is often touted as a key field mark to separate the
two species. I'll be presenting the results of our study at this year's CFO
convention in Montrose. For now, I'll say that identifying raven specimens
on a table in a museum is straightforward. The size distance is striking
when the birds are dead and in hand, and the color difference in the
feather bases is pretty easy to see when you part the neck feathers. But a
live bird in the field is a totally different matter.

Personally, I'd recommend the conservative approach, asking all birders to
supply comments and media on all ravens they encounter in SE Colorado, with
"raven sp." the default unless the bird is carefully studied.

Nathan Pieplow

On Sun, May 26, 2019 at 10:37 AM coloradodipper via Colorado Birds <
<cobirds...> wrote:

> All:
> I write to request help with discerning the occurrence pattern of Common
> Raven in Prowers County. In my experience, the only ravens that I’ve
> seen/heard in Prowers (away from the very southernmost bit by Two Buttes
> SWA) that I was convinced were Commons -- and not the expected Chihuahuan
> Raven -- were all in the fall/winter period, a period in which Commons seem
> to spread out/wander. Additionally, all of my very few definite Common
> Raven records in the county are from my previous sojourn in the state, so
> the subsequent 11+ years might have seen a change in the species'
> occurrence pattern.
> Because Prowers and Bent Counties are currently covered by the same eBird
> filter, and because Common Raven is an expected breeding species in, at
> least, southern Bent, the filter allows Commons all year in the filter
> region, thus in Prowers County. As I did not record Common Raven in Prowers
> in summer in my previous occurrence in the state and I have yet to record
> it at all in my current sojourn here, I am confused by the eBird record for
> the species in the county:
> Relevant to the discussion is my essay on raven ID in the In The Scope
> column in *Colorado Birds:*
> So, I’d appreciate the thoughts of those that have spent time in the
> county AND paid careful attention to ravens there. I could use other
> opinions, because I am in the process of splitting Prowers Co. out of the
> current filter, and I need to figure out what to do with Common Raven.
> Thanks,
> Tony
> Tony Leukering
> Wiley, CO
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