Date: 11/11/24 7:29 am From: Steve Hampton via Tweeters <tweeters...> Subject: Re: [Tweeters] Eurasian Collared-Dove decline
Yes, I looked at the eBird Trends map for Eurasian Collared-Dove. And, yes,
I think the time period of the map, 2011-2021, could easily mask an
inverted U with a peak in the middle.
On Sun, Nov 10, 2024 at 10:20 PM Robert O'Brien <baro...> wrote:
> Well, it seems the Eurasian Collared Dove abundance is not as simple as
> one would assume. eBird has a trend analysis page:
>
> https://science.ebird.org/en/status-and-trends/species/eucdov/trends-map?regionCode=USA&showAllTrends=true > and I hope this url works. It's possible one would have to log into their
> eBird Account to see it.
> If it does work, then simply click the +sign to enlarge and use the mouse
> to scroll around the continent. The data in the Seattle area is mixed but
> overall
> seems to show small increases over the last 10 years, with more consistent
> small increases moving south into the Portland area.
> Now if the trends were to go back further into the past than 10 years,
> such as 2001 to 2011 perhaps there would be a consistent decrease formerly
> followed by the leveling off over the recent decade. If you wish to look
> for other bird species' trends simply click on the Collared Dove Entry and
> replace it with another bird.
> Such 'expected' decreasing trends as have been discussed here for Collared
> Dove have been interesting for other 'invaders.
> 1. Cattle Egret A startling appearance in Florida followed by a truly
> amazing expansion continent-wide with numbers showing up, for instance,
> pretty regularly on Sauvie Island in the later last century. In the last
> decade they seem to have 'already' decreased down into the
> central/upper Gull of Mexico coast where they continue their decline.
> (Replace Collared Dove in the original url with Cattle Egret).
> 2. Crested Mynah. Introduced into Vancouver BC in the 1890's they also
> expanded over the next fifty years all around SW BC and there were casual
> reports a scattered few even made it into the Portland Area. They then
> declined towards the end of the 1900's and the last eBird report was for
> 2014.
> 3. As for native birds, sadly, enter Rufous Hummingbird. You will not
> like what you see. But it is completely consistent with what I have seen
> at my rural place 20 mi SE of Portland. 50 years ago,Rufous (only) were a
> common breeder and present at my feeders seasonally as is well known. Then
> Anna's finally made it here say 40 years ago and both were common for the
> mid 20-30 years. But in the last 5 years Rufous have been virtually
> absent. here.
> 4. Anna's Hummingbird. No surprises there. Huge, continuing increases
> throughout Oregon/Washington
> Could this have been displacement? No way to tell from simple trend
> analysis without further information I would guess.
>
> Bob OBrien Carver OR
>
> P.S. Please let me know if the urls above do not work and I will post the
> maps to my Flickr Account. (And I can't control my continual whining that
> it would really be GREAT if Tweeters could somehow allow photos to be
> appended to posts, as has been the case here in Oregon's OBOL for decades
> now.
>
>
>
>
> On Sun, Nov 10, 2024 at 6:34 AM Steve Hampton via Tweeters <
> <tweeters...> wrote:
>
>> Likewise, Christmas Bird Count data, especially aggregated across large
>> areas (e.g. a state) for common species, can tell a story.
>> I haven't looked at the statewide data for WA, but there has been some
>> analysis in the Central Valley of California.
>>
>> I explored the nationwide trends and plotted the Central Valley records
>> when there were still only 24 records.
>>
>> Hampton, S. (2006). The expansion of the Eurasian Collared-Dove into the
>> Central Valley of California.
>> <https://www.cvbirds.org/wp-content/themes/cvbirds/files/V.9no.1/V.9no.1pp7-14..pdf> >>
>> Then Ed Pandolfino used CBC and BBS data to show they had peaked in 2017.
>>
>> Pandolfino, E. (2020). The Eurasian Collared-Dove invasion in California:
>> Has it peaked?
>> <https://www.cvbirds.org/wp-content/uploads/2022/03/1-Pandolfino-The-Eurasian-vol23-no3.pdf> >>
>> I expect WA is somewhere along a similar path.
>>
>>
>>
>>
>>
>> On Sat, Nov 9, 2024 at 2:08 PM Bill Tweit via Tweeters <
>> <tweeters...> wrote:
>>
>>> A couple of days ago, Hans Feddern noted on Tweeters that he had
>>> observed a decline of Eurasian Collared-Doves in areas he has birded, and
>>> asked about other evidence of a decline.
>>>
>>> This is exactly the sort of question that eBird data are quite useful
>>> for answering. But before I point to some eBird data sources, I'll just
>>> note that it would be highly surprising if they were NOT declining at this
>>> point. The basic ecological dynamic that is operative here is that newly
>>> established species often show very rapid population growth until natural
>>> checks, such as predation, disease and competition, begin to function
>>> effectively. Typically, the development of population controls lags
>>> population growth, which leads to population declines as the newly arrived
>>> species begins to transition from a growth phase to an equilibrium phase.
>>>
>>> In this particular case, the growth phase of Eurasian Collared-Dove
>>> expansion into western North America was explosive, and may well be one of
>>> the most impressive vertebrate range expansions in our experience. One
>>> would expect that explosive growth would then result in noticeable
>>> declines, simply because the population grew so rapidly that it noticeably
>>> outstripped its 'equilibrium' population size when the inevitable
>>> population checks are fully operative. How explosive? Look at the eBird
>>> species map for collared-dove in Washington in 2005 (
>>> https://ebird.org/map/eucdov?neg=true&<env.minX...>&<env.minY...>&<env.maxX...>&<env.maxY...>&zh=true&gp=false&ev=Z&excludeExX=false&excludeExAll=false&mr=1-12&bmo=1&emo=12&yr=range&byr=2005&eyr=2005)
>>> with the 2015 map (
>>> https://ebird.org/map/eucdov?neg=true&<env.minX...>&<env.minY...>&<env.maxX...>&<env.maxY...>&zh=true&gp=false&ev=Z&excludeExX=false&excludeExAll=false&mr=1-12&bmo=1&emo=12&yr=range&byr=2015&eyr=2015).
>>> In a mere decade, their distribution in the state transitions from a few
>>> scattered areas to uniformly present in all of the non-mountainous areas or
>>> heavily forested areas. Another data source for looking at the increase
>>> is the Washington Bird Record Committee records: the first year with
>>> multiple reports was 2005, and three years later the WBRC removed it from
>>> the review list as it exceeded the criteria for inclusion in the review
>>> list. In three years! Obviously, WBRC records don't provide any
>>> information on subsequent population fluctuations.
>>>
>>> Turning to eBird for evidence of decline. My data analysis skills are
>>> surface level, so there is plenty of room for more detailed dives into
>>> eBird data. But, take a look at the annual line chart of the eBird
>>> statistic for frequency of collared-dove statewide for the five years
>>> 2017-2021 (
>>> https://ebird.org/barchart?byr=2017&eyr=2021&bmo=1&emo=12&r=US&spp=eucdov&separateYears=true).
>>> It very clearly shows declines each year from the 2017 to 2021, in fact the
>>> 2021 line never reaches the 2017 line at any point in the year. The eBird
>>> statistic for abundance shows a very similar pattern. These charts can
>>> only show five consecutive years, a quick look at the 2019-2023 chart shows
>>> some continued decline but a lot more overlap between years, so the
>>> population levels now are more similar to the 2021 levels, and remain well
>>> below the high point of around a decade ago. eBird provides data that
>>> allow us to understand how the expected decline has actually unfolded.
>>>
>>> It would be interesting to look at Cooper's Hawk numbers over the same
>>> time period, which I have not done yet, as they are clearly one of the
>>> primary predators of collared-dove. For instance, the first recorded
>>> breeding of Cooper's Hawks in the Salton Sea basin in southern California
>>> was coincident with the dramatic increase of collared-doves in that region,
>>> and they remain regular breeders at several locations in the region. I
>>> expect that eBird would show some amount of increase, maybe not as obvious
>>> as the population dynamics of the collared-dove.
>>>
>>> Bottom line is that birders do not have to rely on anecdotal information
>>> for answering questions such as the one Hans posed. eBird is available to
>>> anyone, and is easy to access.
>>>
>>> Bill Tweit
>>> _______________________________________________
>>> Tweeters mailing list
>>> <Tweeters...>
>>> http://mailman11.u.washington.edu/mailman/listinfo/tweeters >>>
>>
>>
>> --
>> Steve Hampton
>> Port Townsend, WA (qatáy)
>>
>>
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>
