[Tweeters] Eurasian Collared-Dove decline

[Robert O'Brien via Tweeters]

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 at u.washington.edu> 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 at u.washington.edu> 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=-134.18099999999998&env.minY=41.418329269627435&env.maxX=-106.05599999999998&env.maxY=50.04329885125577&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=-127.14974999999998&env.minY=43.69995417791555&env.maxX=-113.08724999999998&env.maxY=48.01225544880609&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

>> _______________________________________________

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>> Tweeters at u.washington.edu

>> http://mailman11.u.washington.edu/mailman/listinfo/tweeters

>>

>

>

> --

> ​Steve Hampton​

> Port Townsend, WA  (qatáy)

>

>

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