Earlier this fall, our friends at Long Point Bird Observatory remarked on facebook that any Empidonax flycatcher seen in the area after October 1 deserves extra scrutiny. “A useful tip,” I thought to myself, and filed it away in the back of my mind, to be pulled out in case a late empid ever wanders through Braddock Bay.

Empidonax flycatchers can be difficult under even the best of circumstances. Here on the east coast, we have five regular empids: Yellow-bellied, Acadian, Alder, Willow, and Least. The west coast adds five more: Hammond’s, Gray, Dusky, Pacific-slope, and Cordilleran. While there are some subtle visual differences between most of these species, there are a few that look so similar they can’t really be distinguished in the hand. Willow and Alder Flycatchers are close enough in appearance that they are often referred to as “Traill’s”, and Pacific-slope and Cordilleran are often referred to as “Western.” Yellow-bellied and Acadian Flycatchers are similar in some ways, and – to make things more confusing – Yellow-bellied also look quite a lot like the “Western” complex. In the field, range, habitat, and vocalizations can be helpful in distinguishing them. In the hand, we are often stuck taking fiddly fussy measurements to tell the difference.

When I headed out to the station this morning, my plan was simple: open about half the nets, give them a few minutes to dry thoroughly, and then take them in for the winter. The plan was working well. With nets 1-6 all safely in grocery bags and the guylines wound and stowed, I turned my attention to the nets around the field.

I headed out on a net run to make sure the nets were clear before I started taking things down. Net 13 . . . clear. Net 12 . . . clear. Net 11 . . . clear. Net 10 . . . WTH??? A small yellow empid was hammocking in a short net between the field and the edge of the woods. “It looks just like a Yellow-bellied!”, I thought to myself. And, if it had been August, I would have banded it as a Yellow-bellied Flycatcher without a second thought. But Yellow-bellied Flycatchers move out early, and by mid-September they are scarce. So I unpacked the sage advice of our Long Point friends . . . beware the Empids of Winter! Whatever I had in my hand, it deserved extra scrutiny.

Once I had the bird back at the banding station, I took a few moments to gather my thoughts. I texted two friends – Jay Carlisle of the Intermountain Bird Observatory in Idaho, and Stu Mackenzie of Long Point. Since western empids aren’t in my wheelhouse, I needed advice on what species might be most likely, and how best to distinguish them from anything more familiar to me. The word came back almost instantly – “Western” Flycatcher was the complex to consider, and Jay noted that the primary projection (i.e. how far the longest primary flight feathers extend past the longest secondaries/tertials) in Western is much shorter than in Yellow-bellied. I pulled out Sibley and did some quick reading, and then I pulled out Pyle and did some not-quite-as-quick reading. Finally, I pulled out my “Empid ID” chart, updated it with stats for Western, and got to work.

Below are several pictures of the bird, a video with vocalizations, and a chart with the measurements I took along with the expected ranges for several of the look-alike empids. The measurements do a pretty convincing job of ruling out Acadian (which wasn’t really a big contender anyway), but don’t do much to clarify whether our bird is a Yellow-bellied Flycatcher or a Western Flycatcher.

Fortunately, we also took a feather sample and a fecal sample (he pooped on Pyle!), and we are hoping that a DNA analysis will reveal what species graced our nets today.

— Andrea Patterson

To see Part 2 of this tale, click here.

 Yellow-belliedAcadianWesternOur Bird
Wing60 – 7265 – 8056 – 7267
Tail46 – 5552 – 6250 – 6355
Wing – tail12 – 1912 – 216 – 1512
Bill from nares7.0 – 9.49.2 – 10.17.7 – 9.27.4
Bill width4.8 – 5.65.3 – 6.35.0 – 5.85.4
p6 emarginated?usually yesnoyesyes
Longest p – longest s10.3 – 17.513.3 – 23.58.6 – 17.112.9
Longest p – p62.2 – 6.75.2 – 9.30.2 – 4.44.4
p6 – p101.9 – 6.3-2.9 – 1.74.7 – 9.85.4
p9 – p55.8 – 11.58.6 – 14.42.9 – 9.87.8
p10 – p50.8 – 5.1 -4.4 – 0.3Almost identical
Ranges that do not match our bird are shaded in red. Note that many of these measurements are difficult to take. I was as precise and as careful as possible (in some cases, taking a measurement two or three times), but differences are often in tenths of millimeters, and even a little error might throw a measurement into one species or the other.