Robin Diaz led the Tropical Audubon Society walk through Cape Florida on Sunday Sept 27, and they stopped by the banding station. As luck would have it, we had just captured a very unusual warbler!
We have been discussing ever since about whether this is a Mourning warbler (MOWA) or it’s western counterpart, a MacGillivray’s warbler (MGWA). We occasionally band MOWA at the station in fall, but MGWA would be a first for CFBS.
Characteristics that support MGWA are the completely gray/whitish hood and the long tail extension past the undertail coverts. This is a hatch-year bird, and young MOWA have yellowish throats. MOWA also has a shorter tail extension. The biggest strike against MGWA is the thin and almost complete eye-ring; most MGWA have thicker arcs over and under the eyes that have distinct blunt ends at the break. However, the eye ring/arcs are variable across both species, although MOWA tends to have a thin complete eye ring on young birds and females while the males have none. An important in-the-hand measurement, wing chord-tail, came out right on the boundary where MOWA and MGWA overlap.
Here is a discussion from last fall about Mourning warbler vs Connecticut warbler vs Common yellowthroat.
Any follow-up on the ID of this bird?
We sent the pictures to different people with experience with both Mourning and MacGillivray’s and came to no firm conclusion one way or another. Some of its characteristics suggest MOWA and others, especially structure of tail, suggest MACW. We submitted it as a hybrid to the Bird Banding Lab.