Thursday, September 26, 2013

Fall Vireos

   Vireos are a group of birds that sometimes don't get as much attention as other groups like warblers and sparrows but they deserve more admiration. In the fall identifying some species can be tricky. I've learned this the hard way. At this time of year in my area it is possible to encounter at least 4 species of vireo at the same time. Blue-headed, Philadelphia, Warbling and Red-eyed Vireos are common migrants in Minnesota.

   Last weekend we had three of those four species end up in our nets. Easily identified by the stripe pattern on it's face is the Red-eyed Vireo.

   It shows an "oreo cookie" pattern of a light stripe bordered by dark stripes on both top and bottom. Young birds in the fall show a brown to red-brown iris. Some individuals can retain this color into the following spring. Adults have the bright red iris that gives them their name.

   The ability to separate the Warbling Vireo from the Philadelphia Vireo can be more difficult. Both were in our hands and there are a couple of things to look for that separate the two.
    This Philadelphia Vireo shows the yellow throat that clinches it's ID. The cap on the head is gray and the line through the eye seems to me to be more bold. It is a bit smaller than the Warbling Vireo and feels that way in the hand.
   This Warbling Vireo is a bit larger and shows a white throat and chest. The crown color is more olive compared to the Philadelphia. A second characteristic for separating the two is only seen with the bird in the hand. Warbling Vireos have a relatively long tenth primary (p10) on the wing while p10 on the Philadelphia Vireo is "vestigial" or completely absent.
   On this bird you can see that p10 is longer than the primary coverts of the wing. This is a quick characteristic to check when trying to decide between Warbling Vireo and Philadelphia Vireo. Having a bird in the hand allows for a whole different approach to identification versus looking at these birds up high in a tree.

   With the weather continuing to be warm and dry this weekend should be good for getting out into the field. The Warbling Vireos should just about be gone but the Philadelphias and Red-eyed will be moving through for a while yet. The next big group will be sparrows!

1 comment:

Jim Ryan said...

Thanks for the ID refresher, Roger. I so rarely see Philadelphia Vireos and I often hear but so rarely SEE Warbling Vireos!

It's nice they have a "clincher" ID mark that can be seen from below as well.