Sunday, 16 July 2017

Dickcissel invasion!

The Dickcissel is a small songbird in the family Cardinalidae, a family which includes familiar species such as Northern Cardinal, Indigo Bunting and Rose-breasted Grosbeak. Dickcissels superficially resemble sparrows due to their overall size and coloring as well as their penchant for grassy habitats, but the stout beak is one feature that gives it away as a member of Cardinalidae. Dickcissels breed in weedy fields and grasslands throughout the center of North America, ranging from Texas north to North Dakota, southern Minnesota, Wisconsin, Michigan and Ohio.

Dickcissel - Hillman Marsh Conservation Area, Essex County

Dickcissels are known for temporarily colonizing areas at the periphery of their range, usually during years when drought occurs in a portion of their core range. Here in Ontario we are right at the boundary of where Dickcissels can normally be found and in a typical year there are only a few breeding locations, usually located in the extreme southwest of the province such as Essex County, Lambton County and the Municipality of Chatham-Kent. Using eBird, below is a screenshot of a typical year for Dickcissel sightings in Ontario; in this case, I used 2014 as the example. I have limited sightings to the months of June and July when Dickcissels would be breeding, to eliminate sightings of migrants/vagrants from other times of the year.

Dickcissel sightings: June and July, 2014 (source: eBird)

A closer look at southwestern Ontario:

Dickcissel sightings: June and July, 2014 (source: eBird)

2017 is shaping up to be an extreme year for Dickcissel sightings further north and east of their usual range. Sightings have been popping up all over southwestern Ontario and there is an argument to be made that this is the biggest Dickcissel invasion year ever. While this post will discuss sightings in Ontario, there are clearly numerous sightings elsewhere at the periphery of their range. For instance, the northern halves of Michigan, Wisconsin and Minnesota have also seen more sightings than normal, as have places further east such as eastern Ohio and western New York. Here is a screenshot of the eBird map for June-July 2017.

Dickcissel sightings: June and July, 2017 (source: eBird)

Zooming in on the map, the scope of the 2017 invasion in southern Ontario is quite apparent. Not pictured in the map below are some of the other extralimital sightings from the City of Kawartha Lakes, Durham Region, Rainy River District and Northumberland, Prince Edward and Bruce counties.

Dickcissel sightings: June and July, 2017 (source: eBird)

The first Dickcissels on territory this year were discovered at a typical location, the Campers Cove Road field near Wheatley, Chatham-Kent, where individuals have now been found for seven straight years. It appears to be the only location in the province that recently has hosted Dickcissels on an annual basis. On June 11 Jim Burk discovered a few Dickcissels near Rondeau Provincial Park and in the following days and weeks birds began to appear in suitable looking habitat all across southwestern Ontario. In Chatham-Kent alone, Allen Woodliffe estimated in a recent blog post that there are at least 30 known locations likely harboring over 100 birds.


Dickcissel - Fenwick, Niagara Region

Below, I've listed each of the counties that have known Dickcissels this year, along with the first date that the first bird was discovered as part of the invasion. Most of these birds likely showed up in mid-late June, though it is of course difficult to say with certainty. Note that these dates were gleaned from Ontbirds posts and publicly accessible eBird data. If there are any other counties not represented in this table, or if you know of an earlier date for one of the counties, please let me know!



While the greatest number of Dickcissels are in the extreme southwest of the province and along the Lake Huron shoreline to the Bruce Peninsula, sporadic individuals have been found as far afield as the City of Kawartha Lakes, Algoma District and Rainy River District. While most of the counties in the southwest have noted Dickcissels, some counties have yet to get on the board. The most obvious candidates include Oxford, Haldimand, Brant, Perth and Dufferin Counties - these also happen to be counties with relatively few birders. York Region, City of Toronto, Peel Region and Simcoe County could also be hosting individuals. If you are a birder in these areas, get out and look while there is still time! Fortunately Dickcissels will sing incessantly, even during the middle of the day, so slowly cruising roads passing suitable habitat with your vehicle's windows open is a good way to detect them.


Dickcissel - Hillman Marsh Conservation Area, Essex County

I have been trying to take advantage of this year's invasion and spending quality time with Dickcissels in numerous locations. So far I have encountered them in 13 counties this year. Most of the Dickcissels I have seen have been during the late morning or early afternoon after finishing that morning's bird surveys for work; as such, the lighting has rarely been suitable for good photography and very few of the birds I have photographed. Below are a couple of photos of this year's Dickcissels. Clearly I need to spend some more time photographing them as my collection from this year is rather sparse!


Dickcissel - Fowler's Corners, City of Kawartha Lakes

Within a matter of days, if it hasn't happened already, young Dickcissels will be appearing in many of these fields. Over the past two weeks most female Dickcissels I have seen were carrying food, confirming that they have young inside a hidden nest somewhere in the grasses.


Dickcissel - Fenwick, Niagara Region



Dickcissel - Fenwick, Niagara Region

Naturally, the first question most ecologically-minded people would have is, "Why?". Generally the prevailing thought has been that Dickcissel irruptions coincide with drought conditions in the core parts of its range. Is that the case this year? Below is a gif I created using screenshots taken from the U.S. Drought Monitor (http://droughtmonitor.unl.edu/). The first frame is from May 30; each subsequent frame is from a week later. The final frame is from July 11.

US Drought Conditions: May 30 - July 11, 2017 (source: http://droughtmonitor.unl.edu/)

Clearly drought conditions have developed in the far north of the range of Dickcissels, such as both of the Dakotas. Much of the Midwest has experienced low-moderate drought conditions as well, though the Dakotas and eastern Montana appear to have been hit the hardest.

To be honest I am not 100% convinced that "severe drought conditions" are the cause of this year's Dickcissel irruption. Looking at previous years, this year has relatively light drought conditions. For instance, here is a screenshot of the drought conditions from June 17, 2014 - a year with typical Dickcissel sightings in southern Ontario (the same year that I provided screenshots from the eBird map, above). Without any other knowledge of the situation, if I had to guess I would say that the 2014 conditions looked better for Dickcissel sightings far to the north and east, but that was clearly not the case. This is not just a one-year aberration either - the drought conditions were moderate/severe in much of the Midwest in 2013 as well, another year that was typical in the sense that very few Dickcissels appeared in southern Ontario.

US Drought Conditions: June 17, 2014 (source: http://droughtmonitor.unl.edu/)

Perhaps the drougtht conditions in 2014 were located too far south for these birds to infiltrate Ontario? Maybe this year's Dickcissels all have their origins from the Dakotas? Anecdotally it seems strange that Dickcissels arriving on their breeding grounds in the Dakotas, noticing drought conditions, would decide to fly due east, eventually ending up in Ontario, New York, Pennsylvania, etc. I would not be surprised if this year's irruption was due to some other cause. What might that be? I have no idea! If anyone has any insight into the causes of Dickcissel irruptions, please let me know!

9 comments:

  1. It could be political ...

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  2. Great post Josh. I was wondering too why some counties appear to have been left out of the invasion. I was hoping something would show up here in Perth county. Definitely want to keep my eyes and ears open.

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    1. Good luck Jonathan - there are undoubtedly more out there to be found.

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  3. Earliest for Waterloo was June 19. Great post!

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  4. An excellent summary, Josh. I checked some of the ebird data from southern Missouri, for example, where I have seen them on several occasions while exploring the fabulous prairies there in the springs of 2007-09. While they appeared to be present in the usual numbers in the period from late April to late May 2017, for some reason by early to mid June the numbers started dwindling, which corresponds to the time when numbers in the northern parts of their traditional range as well as extra-limital records started to increase. I'm not convinced drought is a factor either. I have sent a request to a couple of my contacts in Missouri who specialize in tallgrass prairie to see if they have any insight, but at this point I have not received a response.

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  5. Interesting, Allen! Hopefully your contacts can provide some insight.

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  6. The dates for most observations, particularly in Essex also corresponded to a really low pressure system that had, to-date, the warmest temps we've recorded in Ontario this year so far...also good strong SW winds with this system...

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