I am incredibly fortunate to be able to sit on our outdoor couch, on a weekday morning in September, and spot many migrants directly above my head (once during a small fallout, I had at least 100 warblers flitting in the trees right above me). From that, I have gained lots of knowledge of the passerine migrants that pass through the Chicago region. Autumn migration is slightly better here in Carpentersville, which is somewhat unfortunate because the migrants are much more colorful and easier to identify them in the spring. So below I will give you some tips and tricks on how to correctly identify fall passerines:
SOME OF THE FIELD MARKS MENTIONED:
Wondering how to determine whether your bird is a warbler, a vireo, or a kinglet? Simply look at the bill, thick for a vireo; medium, dagger-like for a warbler; and thin, needle-like for a kinglet. This method usually works, but be cautious and please consult other resources (field guides, etc.) on this topic.
Part 1: warblers
What to look for in a warbler?
Color, pattern, undertail coverts & tail feathers, and wingbars.
- First, start off with, what is the overall color of your bird (e.g., pale yellow, bright yellow, gray, brown, etc.)? This alone can separate many passerine species into different groups.
- Next, move on to the overall pattern (does the bird have lots of streaking and a highly contrasting head and underside or is it just plain?). This again can eliminate many passerine species.
- Look at the undertail coverts (untc) and tail feathers (tfs)(see sketch above).
- Does the bird have wingbars? This field mark will eliminate even more warblers!
Now you should be able to ID the bird through a field guide, but what about the ones that look similar?
Orange-crowned vs. Tennessee
Envision yourself at Illinois’s premier birding spot, Montrose Point and you are walking through the magic hedge in late September, and you locate a pale warbler that is an Orange-crowned or a Tennessee Warbler. You might look in a field guide and think, “how on earth am I going to be able to identify this?”. Okay, the ID is hard, but you can ID it (hopefully). Well first, let’s check out the facial pattern. Tennesse Warblers have a pale supercilium and a dark eyeline. Orange-crowned Warblers, on the other hand, have a VERY plain face. I would not call the ID with that field mark alone (unless you got a crystal clear photo of it and even then I don’t know if I would call it). Now, we can look at the undertail. Does it have pale tfs or dark and does it have a yellow untc or white? Dark tfs and yellow untc for Orange-crowned and pale tfs and white untc for Tennessee. Now, from those three field marks, we can fairly confidently identify it. Please do your own research and try to get more field marks, but hopefully, this gives you an idea of how to differentiate these very similar species and you can ID that tricky bird at Montrose!
Blackburnian vs. Bay-breasted vs. Blackpoll vs. Pine
“Now what? You’re informing me that there are four warblers that look very similar!” Yes, there are four warblers that look alike, and these can cause quite a headache for some birders including me! But there are ways to tell them apart. let’s start off with the facial pattern. Bay-breasted Warblers have white eye-arcs, a dark eyeline, and an otherwise plain face. Blackburnian Warblers have a very pronounced pale supercilium connecting to a pale collar making the dark ear coverts a diagnostic mark. Now on to the Blackpoll Warbler, which has a dark crown (most of the time) & eyeline and pale eye-arcs, ear coverts, and throat. Pine Warblers have a plain head with white eye-arcs and a faint eyeline. Okay, we know the facial pattern, but that’s just not enough (except for Blackburnian). Now we need to know if the back has streaking or not. If the back does, in fact, have streaking, then we can eliminate Pine, and if the facial pattern does not match Blackburnia, then we can rule that out too! Does your bird have streaking? If so, we can eliminate Bay-breasted, and if the bird has a rusty patch on its flanks, then we can eliminate everything except for Bay-breasted.
Finally, done with the tricky IDs!
Part 2: vireos
What to look for in a vireo?
- What is the overall color of the bird (e.g., white & yellow, yellow, white& blue, gray, etc.)?
- What is the color of the head? You might be surprised at how many birds this field mark alone can eliminate.
- Does it have “spectacles”?
Cassin’s vs. Plumbeous vs. Blue-headed
This is the only hard identification within the vireo group in North America, but it can be solved usually with the simple question, WHERE ARE YOU? If you are reading this you’re probably in Illinois, so the short answer is Blue-headed. “But I want to be certain about the ID, I don’t want to miss a vagrant” you may say, neither would I! So, we’ll start off with the head. What is the head color? Is it more of a gray or blue and does the head color blend into the back? If the head is bluer, and there is a sharp contrast between the head and back, then give up, it’s a Blue-headed:( If not, GET A PHOTO AND POST IT EVERYWHERE! Probably still a Blue-headed though. “WAIT! There were supposed to be three birds in this group, right?” Yes, but Plumbeous is easier to identify than the other two, basically, it is all gray, but in bad lighting, it can still be a challenge. So what do we do? My suggestion, if you REALLY want to make sure it is a Blue-headed and not a Plumbeous, then wait for it to come into better lighting.
Part 3: kinglets
Not sure how to identify kinglets?
We’ll start with the crown. Golden-crowned Kinglets have a golden median crown stripe (the very top of their head) & an otherwise black cap. Ruby-crowned, on the other hand, have an olive-colored crown with a usually concealed trademark ruby crown patch (again on the very top of its head). This alone can conclusively differentiate the two. We can also tell from the rest of the head. Golden-crowned have a very pronounced white supercilium, below the eye is also white, making it look like it has an olive-colored mask. Now, the Ruby-crowned version, has a plain olive-colored face. So basically, if the head looks plain, it is a Ruby-crowned, and if the head has a neat pattern, it’s a Golden-crowned.
The back of a kinglet?
“Kinglets are easy for most birders, why are you writing this?” Well, what if you could only see the back, then could you identify it?
This time we only focus back of the bird!
- Look at the wings, do they have lots of gold in them? If so, it is probably a Golden-crowned but some Ruby-crowned Kinglets do have lots of gold in their wings as well.
- Overall coloration, Ruby-crowned Kinglets are usually a brown vs. Golden-crowned a gray, but not diagnostic.
- Ruby-crowned Kinglets have almost always two wingbars and although Golden-crowned Kinglets can show two wingbars, they are usually not as prominent as a typical Ruby-crowned.
You may never be certain by just looking at the back but you can get a pretty good guess! See if you can guess what the bird below is!
Looking for more info on warblers? You should check out The Warbler Guide by Tom Stephenson and Scott Whittle (which helped me very much with this post)! Vireos and kinglets? Try the National Geographic Complete Guide to Birds of North America (which also helped me with this post)!
Lastly, if you see ANY misinformation please comment below.
The above photo is of a Ruby-crowned Kinglet