Date: 1/17/25 8:31 am From: Mike Britten <mikebritten25...> Subject: Re: [cobirds] Status of Yellow-billed Loons in Colorado
I agree there are often multiple reasons contributing to phenomena. I'll
add another possibility. Many of the large reservoirs in the Front Range
and across the west aren't that old (1900s on with some larger ones
completed more recently (Cherry Creek completed in 1950, Chatfield and Lake
Pueblo completed in 1975, for example). It is possible that yellow-billed
loons are adapting to these as migration stopovers and wintering areas.
There is a famous example (to ornithologists at
least) of European blackcaps changing their migration routes and
overwintering areas within decades published by Berthold, et. al. in a 1992
paper in Nature: "Rapid microevolution of migratory behavior in a wild
bird species." I've pasted the abstract below. Caveat, I don't know if
subsequent studies supported this paper or whether other examples have been
found and published.
I wonder whether data on common loons occurences in the Front Range show
the same pattern?
************************************************************************************************************************************************************************************************************************
"THE Blackcap, Sylvia atricapilla, a widespread Palearctic migratory bird,
rarely wintered in Britain until the 1950s. The winter population has since
increased to several thousand birds1,2. Ringing indicates that these are
not British Blackcaps forestalling migration, but birds breeding in
Continental Europe reaching Britain on a novel westerly migration route3,4.
The proportion of north-western migrants among Blackcaps ringed in parts of
Germany and Austria has increased from 0% before 1960 to currently 7-10%5-7.
We bred British wintering Blackcaps in captivity and determined the
migratory direction of their offspring. Here we report that these birds
migrate west-northwest in autumn, a direction genetically distinct from the
British breeding population and the predominantly southwestern migratory
population of west-central Europe. The novel route must have evolved within
the past 30 years with selection favouring birds wintering some 1,500 km
further north than most of their conspecifics. To our knowledge, this is
the first case in any vertebrate in which a drastic and recent evolutionary
change of behaviour has been documented and its genetic basis established."
On Thu, Jan 16, 2025 at 5:31 PM Todd Deininger <goldeneagle90a...>
wrote:
> There seems to have been a push of YBLO inland through the NW this
> fall/winter. CO, UT, WY, MT, ID, TX had sightings. Weather?
>
> On Thu, Jan 16, 2025, 5:17 PM Robert Righter <rorighter...>
> wrote:
>
>> Hi All
>>
>> In 1992 with the publication o Colorado Birds, the Yellow-billed Loon
>> was considered a casual fall migrant (5 records) and winter resident (4
>> records). According to this winter’s eBird reports there has been multiple
>> sightings, at multiple reservoirs. Something is going on with the
>> Yellow-billed Loon. Could they be having more successful breeding in the
>> arctic (if so why) thus significantly more YBLO are moving south in the
>> winter? Usually there isn’t just one reason to explain phenomenon, but
>> multiply inter-connected reasons.
>>
>> Anyone have any ideas!
>>
>> Bob Righter
>> Denver, CO
>>
>>
>>
>>
>>
>>
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