[Tweeters] Eurasian Collared-Dove decline

[Steve Hampton via Tweeters]

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 at pdx.edu> 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 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

>>> _______________________________________________

>>> Tweeters mailing list

>>> Tweeters at u.washington.edu

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

>>>

>>

>>

>> --

>> ​Steve Hampton​

>> Port Townsend, WA  (qatáy)

>>

>>

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>>

>


-- 
​Steve Hampton​
Port Townsend, WA  (qatáy)
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