CSI Critter: birding forensics on a snowy owl feather

Snowy Owl: Now is the time to check out airports for wintering Snowy Owls photo by Sharon Stiteler

One of the things I’m always on the lookout for is a good bird feather or two, not just for trying to figure out the identification of the species but for whatever story they might tell. What bird did the feather come from? Did the bird drop the feather naturally by molting, shedding old feathers so new ones can grow in their place. Or was the bird killed by a predator and if so…what kind? Were the feathers plucked or were they chewed?

Big caveat here: For the record, when it comes to the feathers of birds native to North America, it is a violation of the Migratory Bird Treaty Act to keep feathers or other body parts of a bird without state and federal permits. If you see a feather outside, you legally need to leave where you found it after you have looked at it. I work as a National Parks ranger and I still need to have a permit to salvage feathers that I find outside for educational uses, and my permit does not include eagle feathers. That’s another level of permits altogether! So you can examine a feather outside, but then leave it. And don’t worry, the feather will most likely be put to use lining a bird’s nest.

Because my visitor center is located in the lobby of the Science Museum of Minnesota I can sometimes get a loan from their collection to use in the visitor center for interpretive purposes. I have a salvage permit that allows me to have some bird feathers native to North America in my possession for educational purposes. Recently, Dick Ohlenschlager, the man in charge of the museum’s bird collection loaned me some raptor wings and feathers. One exciting piece was a clump of snowy owl wing feathers. I like having a snowy to talk about since this is the time of year we often see them appear around the Minneapolis/St Paul International Airport.

As I was showing the feathers to a visitor, I noticed a split in the vanes along the shaft, it looked like the top part of a triangle. I looked at the base of the feather shaft and noticed the base was intact, as if the feathers had been plucked rather than ripped out. I got suspicious and turned the feathers over, the same imperfection in the vane was on the other side but there was also a crease. I knew what I thought this meant but needed one more clue, and I found it. Right where the top of the triangle came to a point at the shaft, it was crushed. My brain exploded with possibilities!

When a bird is killed or scavenged by an aerial predator, the feathers tend to be plucked out. A mammal will chew and rip, causing shredder like damage to the base of the feather shaft. Also the feathers will be matted with dried saliva. You don’t see that if a hawk or falcon has eaten a bird since they cleanly pluck out the feather with minimal damage to the shaft. But you will see beak marks from where the bird of prey grabbed the feather and plucked it out.

Snowy Feather Beak Bite: Note the bite mark, the crease left from a predatory bird beak and the crushed feather shaft. All point to an avian predator. photos by Sharon Stiteler

As I surveyed the damage and wondered what would kill a large snowy owl and have that size of a beak, I realized this snowy had most likely been eaten by a bald eagle. Snowy owls can fall victim to all sorts of hazards, cars being quite common. Maybe the eagle didn’t kill the snowy, but it did what eagles do well: scavenge for an easy meal of something that’s already dead.

I emailed Ohlenschlager to find out where the snowy owl parts came from, but he didn’t have a clear record of how it died. This is sometimes the nature of bird parts donated to the museum by the public. Even though we don’t know the whole story, we have some clues of the predator/prey relationship out there.

If you would like to learn more about the bird feathers you find outside, two books I really like are Bird Tracks and Sign: A Guide to North American Species and Bird Feathers: A Guide to North American Species.

 

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