Since our last blog post 6 days ago we’ve seen some ups and downs in the daily capture rate, but things are picking up as more and more Myrtle Warblers move through. Our biggest day of the season thus far was last Friday (Sept. 21), when we processed 78 new birds, 57 of which were Myrtles! This is a widespread and abundant warbler that breeds in coniferous forests and winters as far north as Massachusetts.
Part of what enables this species to winter at such high latitudes is their ability to digest bayberry and other waxy fruits, though they still enjoy a tasty and nutritious invertebrate when available.
We’ve also seen a moderate swell in vireo numbers over the last few days, with a nice mix of both Red-eyed and Blue-headed Vireo (below) flocking-up with other migrants. Vireos are closely related to Shrikes, and one of the characteristics they both share is a somewhat menacing hooked bill, which aids them when feeding on fruits, invertebrates or (in the case of shrikes), small vertebrates.
And we finally had our first Baltimore Orioles pass through this week…pictured below is a hatch-year female.
Many passerines show similar patterns of molt, and as with the hatch-year Black-throated Blue Warbler discussed in our September 5 post, this female had a good degree of contrast between older juvenal feathers and newer, recently replaced ones. More often than not, this indicates a young bird, as the adults undergo a complete molt and do not show marked differences in feather aspect. Below is a closer look at the wingspread of this young female oriole.
Known as ‘molt-limits’, these differences in feathers allow bird banders to accurately assign individuals to age-classes, and one of the leading figures in understanding this phenomena is Bob Mulvihill (below, with a ‘Yellow’ Palm Warbler). Bob’s yeoman work on molt, as well as a devotion standards rarely matched has equipped a generation of North American banders with the tools necessary to collect accurate, robust data. It goes without saying that we were honored and delighted to have been visited by he and his wife Pam on Saturday (Sept. 22).