Hummingbird Banding in Michigan

Determing Age and Sex

Many people will immediately recognize the bird in Figure 13 below as a male.  The reason this is simple is that it is widely known that only the male Ruby-throated Hummingbirds have the iridescent ruby throat.  More precisely, the bird below is an adult male, as young males do not have a full red "gorget" the year that they are hatched.  Young males acquire this full red gorget the year after they hatch.  Therefore, an adult bird is called an After Hatch Year bird, and these young birds are termed "Hatch Year" because they are in the same year that they are hatched.  

Figure 13.  After Hatch Year male Ruby-throated Hummingbird.

Hatch Year males can very closely resemble After Hatch Year females and Hatch Year females, so additional techniques are required to determine their age.  In 1972, Dr. Fernando Ortiz-Crespo discovered that all young hummingbirds possessed "corrugations", looking like wrinkles or grooves, on their bills.  These must be viewed with a 10 power hand lens by the bander.  Hatch Year birds have these corrugations for most of the length of their bills (Figure 14).  After Hatch Year birds typically lack them, although a bird in spring that shows up to 50% of its bill with corrugations can be called a Second Year bird fairly reliably.  Some retain corrugations on 10% or more of their bills throughout their lives (Figure 14, bottom).

Figure 14.  Bill corrugations on Hatch Year Ruby-throated Hummingbird (top), and subtle corrugations on basal 10% of an After Hatch Year Ruby-throated Hummingbird (bottom).

Determining a Ruby-throated Hummingbird's sex is most often done using the wing and bill measurements taken during the banding process.  Female Ruby-throated Hummingbirds are larger than males, and have longer bills.  There is relatively little overlap in size, but in those cases where it might be difficult to tell, there is a feature on one of the wing feathers that is consistently useful in determining their sex.  In males, this feather (the 6th primary) is rather pointed and attenuated (Figure 15), while in females it is much less so.

Figure 15.  Attenuated and notched sixth primary feather of an After Hatch Year male Ruby-throated Hummingbird.