This time of year it is helpful to look at bill color of Yellow Warblers to assist in aging. The bill color of hatching year birds have a flesh colored lower mandible. The adult (After-hatch year) will have a bill that both mandibles are slate gray (see below with the adult on left and hatching year bird on right). **note this does not work in all species of warblers. I know that adult Prothonotary Warblers in late summer their lower mandible turns a pinkish which can make you think it may be a hatching year bird.**
Here is another yellowish bird for the summer. It is a nice comparison to its cousin the Baltimore Oriole. Both are orioles with their gray leg color and bill coloration. They are both hatching year birds with the lower mandibles not having the nice slate-gray color of the adult birds. Can you tell what sex either bird is? Unfortunately you cannot. The wing chord works for the Orchard Oriole which is the bird on the left. The bird is a male with a wing chord over 74 mm. Females are less than 74 mm. Baltimores have a sex determination using wing chord as well which says that it works “in most cases.” Hatching year males are greater than 91 mm and females are less than that. Here is the back side. Note the size differences in these species.As you can guess there would be a little overlap in wing measurements of males and females of the same species. After all, there are small and large female and male Homo sapiens.