The primary purpose in banding birds is to mark them in order to build a data set which describes the breeding range, wintering range, and migration paths of the species being studied.
After capture, birds are held in storage tubes until they are banded - during heavy flights, it is common to capture two or three, and at times up to six, hawks nearly simultaneously.
After banding the bird, the processor takes a series of morphological measurements. These measurements give us some idea of the range of variation in the morphology of various hawk species in our area, and may possibly allow us to correlate these variations with specific populations as our data base of band returns increases in size.
After being banded and measured, the hawk is released unharmed to the wild.
Storage tubes are made of food cans, carefully taped together from the outside so
that the hawk's feathers do not come into contact with the adhesive. Air holes
are punched in the closed end, and the birds are stored horizontally, in the
shade.
While this may look bizarre to the outsider, hawks are very visual creatures and become still and calm when in a dark space, such as in a storage tube. The same principal is used by falconers, who use hoods to calm their birds. We use tubes because the birds we capture, being wild, have not been trained to sit on a perch while being hooded. The can is loose enough for the hawk to breath, while being snug enough to prevent the hawk from hurting itself with its own talons.
The storage tube also helps calm the bird while it is being weighed, banded, and measured. By keeping the hawk's head in the darkened can, stress levels are kept low while foot and tail measurements are taken.
Can sizes range from orange-juice size (American kestrals) to #10 size (red-tailed hawks
and some northern goshawk). We have no cans large enough for eagles and band and release
the handful we catch each year immediately.
Hawk species vary tremendously in size, so of course we must use different sized bands
for them. This photograph demonstrates the use of a band sizing tool. The vast majority
of individuals of the same sex and species take the same sized band, except for more
variable species such as the buteos. The birding being banded in this series of photographs
is a male sharp-shinned hawk, which takes the smallest band size we use, a #2. Eagles,
of course, take the largest band size in our inventory, and because of their strength
their bands are held closed by a pop-rivet.
Bands are shipped by the US Fish and Wildlife Service (USF&W) in sets of a hundred bands, consecutively numbered. The numbers come in two parts, a series-prefix of three or four numbers which, among other things, encodes the band size, and a five-digit number which uniquely identifies the band within the series.
The USF&W Service requires data be recorded for each bird banded, and submitted to them at the end of each banding season. The data must be segregated by species, sex (when determinable), and in order, so great care is taken by the bander to correctly record all pertinent information.
The bands for larger birds are easy to open and squeeze shut by hand, and come with locking tabs which are closed with a regular pair of pliers.
Many of our measurements are taken with calipers, including measuring tarsus width,
as in the photo to the left. The metatarsus is the lower "leg" of a bird, though
it is really what is left of the tarsus bones in the foot of a reptile or mammal.
We also measure tarsus length, halux length, and the culmen length - that part of
the bill which is not covered by a raptor's fleshy cere.
In the photo to the left, you can see the length of our male sharp-shinned hawk's tail
being measured. We measure from the base of the preening gland to the end of the longest
tail feather. We also use rulers to measure wing chord, perhaps the most important
measurement taken because this single measurement can be used to determine the sex
of accipters, the sexes of which look alike.
When banders have gained experience and confidence banding smaller hawks, we slowly let them band larger species. The largest species we deal with is the golden eagle. Our trapping setup is optimized for the capture of accipters ("bird hawks"), so we only capture and band a few eagles a year. As you can see by comparing this photo of a golden eagle's halux (rear talon) being measured with the earlier photo of a male sharp-shinned's foot, raptors vary greatly in size and strength.