Auxiliary markers, bird bands, and Bird Band Bonanza

Is there a wild bird that you regularly see in your daily life? Maybe you watch a pair of hawks that nest at your favorite park each summer, or maybe there’s always a group of crows that visit your lunch break spot at work. You might think that these are the same birds day after day or year after year. But do you really know for sure? 

People have been marking birds for hundreds of years so that they can know for sure who’s who. Some of the earliest examples are marking birds as property, such as in falconry. Nowadays, scientists throughout the world use metal bands to aid in bird research. Here in North America, the USGS Bird Banding Lab and the Canadian Bird Banding Office issue these bands.

On the left, a USGS band and blue color band suited for a Red-tailed Hawk and on the right a yellow color band and USGS band that would be appropriate for an American Kestrel. For context, the smaller USGS band is 6.5mm tall and the larger USGS band is 13.7mm tall. © Kate Sweet

The USGS metal band is like a bracelet that comes in various sizes depending on the species it’s placed on and has nine numbers engraved on it. This number is like a bird’s social security or VIN number—unique to each individual and never reused. Although metal bands are useful for identification if you happen to recapture the banded bird or find it dead, imagine trying to read all of the numbers on a small 6.5 mm-sized band on a live bird—even with the biggest camera lens it’s probably not going to happen! So, to make birds identifiable at a distance, scientists use “auxiliary markers.” 

Auxiliary markers are a second marker in addition to the metal USGS band and come in many shapes and sizes. While some auxiliary markers collect data, like GPS or cellular tags, many of these markers identify individuals in a population. For example, Turkey Vultures and California Condors wear patagial tags on their wings, which are visible when they are soaring, while many other species of birds are color-banded on their legs. Small songbirds often have a unique combination of multiple plastic color bands stacked on top of one another, and some birds, like geese, can wear bands or collars on their necks. Raptors often sport color bands on their lower legs with an alphanumeric code. 

Two California Condors wear their patagial tags. Patagial tags are attached to the bird’s patagium, a membrane of skin on the leading edge of the bird’s wing. © Kate Sweet

Color bands are a useful and relatively non-invasive way to track individuals and learn more about populations as a whole. We employ this powerful tool in multiple research programs at HawkWatch International (HWI), including the Cavity Adopting Raptor Ecology Studies (CARES) program where we use color bands to better understand potential reasons behind American Kestrel declines. Our CARES color-banding program has grown significantly over the years—with over 3,000 American Kestrels color-banded so far!  Although 3,000 may sound like a big number, the value of these huge efforts can really only be realized if and when we see that marked bird again. Although our team always has their eyes peeled for who’s who, we need help, and that’s where you come in!

We color-band as many nestling American Kestrels in the Salt Lake Valley CARES study area as we can. This is a female nestling American Kestrel sporting her new color band, Yellow BMB on the left leg. She hasn’t been spotted since we banded her. Maybe you’ll be the first?

This week and next (January 27th – February 10th, 2025), HWI is hosting the Bird Band Bonanza, a celebration of raptor color band resightings! We’re encouraging you and anyone you know to grab a scope, binoculars, or a camera and head outside to look for color-banded raptors. In addition to American Kestrels banded in the CARES program, HWI also color-bands Golden Eagles, Burrowing Owls, and other urban raptors like Red-tailed and Cooper’s Hawks. In addition to birds banded by HWI, resights of any color-banded birds across the Americas is still helpful and valuable data. If you happen to find a color-banded bird, submit the information here. We’ll even give out prizes for select categories! 

This color-banded Red-tailed Hawk was photographed by Doug Hawkes in October 2022. This band resight was particularly interesting because the bird’s eye was missing when it was initially captured earlier in May of that year. This tells us that this bird was seemingly alive and well for months following a serious injury.

We think that looking for color-banded birds is one of the most enjoyable real-life scavenger hunts out there! Spending an afternoon birding with the reward of helping conservation efforts— what could be more fun? Some of the fun is that pretty much no matter where you live, it’s possible you might see an HWI banded bird!  In fact, our furthest band encounter was a kestrel banded in the Salt Lake area that was spotted in Mexico by a biologist, Luis Cayo, who was able to snap the photo shown on this post. 

Biologist Luis Cayo photographed this male American Kestrel in 2024 outside of Guadalajara, Mexico. The bird was originally banded as a nestling in the Salt Lake City area in 2022.

When you submit your color-banded raptor sighting to us, we’ll use that data to answer big questions about raptor survival, reproductive success, and dispersal. But in addition to supporting conservation efforts, you also get to learn the stories of individual birds! When I’m out in the field looking for color-banded birds, I’m always so curious to know who they are. How old might they be? Were they just a nestling when they were banded, or were they breeding adults? Did they end up far away from where they were banded? Have they stayed with the same mate year after year? Although I certainly appreciate the value of the data in the big picture, I think figuring out each individual’s particular story is a fascinating treat!

So, to further share in the fun, if you happen to see a bird that our team at HWI has banded, we’ll do our best to share that bird’s story with you. And remember although the celebration is through next week, band resights are always important and useful throughout the year.  Best of luck in Bird Band Bonanza!


This blog was written by Kate Sweet, one of HWI’s Field Biologists. You can learn more about Kate here.

Scroll to Top