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Utah Winter Gulls Matrix Part 1

posted by Tim Avery at
on Thursday, February 20, 2014 

As we near the end of gulling season here in Utah, it often becomes the best time of year to find rare and uncommon gull species.  With water starting to open up and more food available, the large ocean-favoring gulls show up with more frequency, or at least become noticed more.  In a short month from now, the vast majority of these birds will be gone, and we won't seem them again till November.  There have been a few identification requests for gulls lately, so I thought I would take a second and give a crash course on the basics for helping narrow down the possibilities when you see a gull you don't recognize using a matrix.

This is only for Adult Gulls however, so I will be working on similar matrices for each other age as well.  As a disclaimer this is NOT 100% accurate in all cases.  Measurements, relative sizes, colors, eyes, bills, etc are all somewhat averages.  If you think something is drastically off or could be improved please contact me to talk about it.  I would like these to be as useful as possible.  With that said I wanted to throw some numbers around.

The best way to recognize the not so common stuff is to really know the common stuff well.  This means getting to know our State Bird--the California Gull, and its smaller relative the Ring-billed Gull very well.  I went into eBird and did some quick data compilations to show how common these two are in relation to everything else.
Between November and February there have been 711,265 total reported gulls in the database (rough estimate).  

This is not total number of actual birds, this is total number of birds reported--so multiple people may have submitted checklists for the same birds.  Of those, 14,643 were hooded gull species (Sabine's, Franklin's, Bonaparte's, and Little) so I removed them from the total to end up at 696,622 total white headed gulls reported during the gulling season into eBird (all time). 

California and Ring-billed account for about 680,000 of these individuals, or roughly 97.3% of all gulls reported in eBird in Utah between November and February.  

That means the other 8 species that you might encounter make up just 2.7% of all the gulls reported--roughly 16,600 individuals--still a pretty hefty number, but at least you know the odds are in the favor for the 2 most common birds.

So let's break it down a little more--aside from those two species, the other 8 most likely species you can encounter in Utah in the winter from most common to least:

Herring Gull -- 15,000 reported
Thayer's Gull -- 780 reported
Lesser Black-backed Gull -- 299 reported
Glaucous Gull -- 183 reported
Western Gull -- 176 reported
Mew Gull -- 96 reported
Glaucous-winged Gull -- 56 reported
Iceland Gull -- 29  reported

Using the matrix above, with a little practice, you can learn to narrow down the possibility of the species you are seeing based on the included attributes.  The colors in the matrix may not be exact but for most adult birds its a good starting point.  click on the above image or link below to download a high resolution version to your smart phone or iPad.

Check back soon for the matrices for 1st, 2nd, and 3rd winter birds, as well as another for hybrids.

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Anonymous Ann said...

wonderful wonderful wonderful!!! im excited to try this out ive been struggling with gulls all winter

February 20, 2014 at 10:02 AM  
Blogger Jeff Cooper said...

I've had the idea in my head for a couple of years to do a decision tree for identifying gulls by going through the mantle shade, bill color, etc. It's just how my brain works with problem solving. I guess it's part of my personality. However, I never completed it because I ran into so many exceptions. What you've shared here is excellent. I love that it is simple, visual, and can be easily tucked into a field guide, file for a phone, etc. Thanks, Tim!

February 20, 2014 at 10:31 AM  
Blogger Jonafriendj said...

This is great Tim!

February 20, 2014 at 11:16 AM  
Blogger Tim Avery said...

@Ann: Thank you! I hope it helps you out, please comment back once you've given it a shot and let us know if it was helpful.

@Jeff Cooper: Thanks Jeff. There are lots of different ways to go about this. When I first started I looked at a similar method to what you mentioned. The only issue for something super simple was finding a starting point--because you could start with size, mantle color, leg color, age, etc, almost anything and that would change the flow. It would be wicked useful though, as it narrows things right from the starts. I might sit down when I have some free time (ha) and try to work something out programatically for just gulls--In reality you could expand it to more species as well, it's just a matter of setting up the flow.

@Jonafriendj: Thanks dude! Read my previous comment to Jeff--perhaps we could team up on something ;)

February 20, 2014 at 11:33 AM  
Anonymous Cullen said...

Thank you, I really need this.

February 20, 2014 at 4:28 PM  
Blogger Dickson said...

This is fantastic, but my Epson printer cuts off the Glaucous Gull. Any ideas on how I can get the entire thing to print????

February 20, 2014 at 9:05 PM  
Blogger Jeff said...

Thanks, Tim. One question (from an amateur, so pardon me if it's a stupid question): does bill marking (rings, red dots, etc.) or lack thereof have any significance when it comes to adult gull identification? There seems to be some differentiation by species. Or is this not a good indicator for some reason?

March 12, 2015 at 12:52 PM  
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