Thursday, June 28, 2012

Lots of Dickcissels in Wisconsin!


Dickcissel

Hey! What's going on with Dickcissels this year? Birders from Wisconsin and Minnesota are reporting extraordinarily high numbers of them compared with recent years. Some have suggested the present drought might be responsible, causing the birds search for more suitable habitat outside of their core breeding range. That's one possibility and here's a citation from Birds of North America to support that hypothesis: 
Drought in core breeding range apparently forces many Dickcissels to move outward in search of more favorable conditions for nesting, as, for example, occurred during droughts in 1964, 1973, and 1988 (Emlen and Wiens 1965, Sealy 1976, Igl 1991).


Dickcissel Range Map

Here's an eBird graph showing the anomaly for Wisconsin (2008-2012):

 

And the same time period for Minnesota:



Incredible, isn't it?

Also note how much earlier they arrived this year. From this data I assumed I should to be able to find locations within their core breeding range where Dickcissel numbers are down (because they shifted north to escape the drought). I checked states like Kansas, Oklahoma, Nebraska, Missouri, and Iowa, but numbers there appeared to be pretty normal. Perhaps these birds came from some part of their breeding range where nobody is counting them? Could these higher numbers in WI and MN be on account of just one (or few) isolated high-density breeding location(s) they abandoned this spring? That seems unlikely to me, but it's possible. However, when I looked at a national graph, it appears Dickcissel numbers have been steadily increasing for the past several years:



Additionally, June maps from 2009 to 2012 seem to indicate a steady increase:









One explanation might be that Dickcissels had a highly productive breeding season in 2011 and experienced low mortality (from persecution) on their wintering grounds. The increase we're seeing in Wisconsin this spring and summer appears to be too great an anomaly for that to be the only explanation, so maybe it's a combination of drought, a general increase in numbers, recent breeding success, and/or something else we haven't discovered yet. I confess it remains something of a mystery to me, but I'm grateful there are more of them here for us to enjoy this summer!

Dickcissel image © 2012 Mike McDowell

8 comments:

  1. Excellent post, Mike! As far as I know, Dickcissels have now been reported in most counties in both Wisconsin and Minnesota this year, including some counties in northern Minnesota that lie outside of the peripheral breeding range. Here around the Twin Cities area, they are also showing up in some unexpected spots where I don't think they've been found previously.

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  2. Great stuff! I wonder if some of that increase in Dickcissel reporting is due to an increase in use of eBird generally. Anecdotally, it seems that vagrancy of Dickcissels has also increased in the last couple of years.

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  3. Robert,

    Good point. I just ran the same maps and dates with House Sparrow. While the 2012 map shows more purple markers than 2009, it isn't nearly as extreme as what is revealed for Dickcissel.

    Thanks for the comment!

    Mike M.

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  4. Ontario is experiencing a major increase of Dickcissels this year as well. Most years there are very few, but this year people are finding them in good numbers and in more places. E-bird doesn't show this well since I guess most sightings are not getting reported, but the concensus is that is an "invasion" type year.

    Adam

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  5. Western Pennsylvania is seeing the same thing with multiple birds at several different spots.

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  6. Spraying from airplanes in Winter Grounds probably missed some big flocks last winter....

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  7. Global warming...they are moving North!

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  8. Hello, I just identified a Dickcissel on the telephone wires by my yard. I did get some pictures. I live on the Northside of Appleton Wisconsin, in Outagamie county. The bird has been in are area for several days singing non-stop from the wires. I also had a sighting of a Mockingbird by in our yard.I was able to capture the Mockingbird on video. This was the grey bird with black and whit markings.It also sang non-stop for 2 days on June 30th thru July 1st. Of each of the birds,they were alone.Not sure if you can use this info, but this was the first time I saw these birds in my area.
    My name is Sandy Pennings.

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