Tim Krohn: Ask Us: Bald eagles, turkey vultures battle for carrion

Dec. 26—Q: Your recent column on road kill got me thinking about turkey vultures, nature's roadkill cleaner-uppers. Over the past 20 years or more, we would always see a lot of turkey vultures circling and roosting around Sibley Park and the surrounding area. It seemed that the last few summers there have been a lot fewer of them. I was wondering if the increase in bald eagles, which are also big scavengers, have maybe chased some vultures out?

A: Stand-in Ask Us Guy turned to Lisa Gelvin-Innvaer, nongame wildlife specialist with the Department of Natural Resources in New Ulm.

She isn't sure if vulture numbers are down around Mankato-North Mankato but says there are different reasons people may not see as many in any given area.

One thing she does know is turkey vultures, overall, are doing quite well. The 2013 Minnesota Breeding Bird Atlas says the species is well distributed across North America and their numbers have increased.

"As far as competition between eagles and turkey vultures, there can certainly be competition. Eagles are also scavengers and they are big. A place where I've recreated for 20 years, there were active eagle nests and the eagles would be right next to turkey vultures. I've seen them scrabble over the same dead fish, but it kind of varied over who won out."

She said the literature notes that eagles compete heavily with osprey and great blue herons. In most cases, things don't go well for the herons and osprey, according to wildlife.org. Eagles attack the other birds' nests and steal their catches, sometimes attacking an osprey in air, forcing it to drop the fresh fish it just worked to catch, with the eagle then swooping down and catching the fish mid-air.

Turkey vultures have a bit of a size advantage compared to heron and osprey. At about 3 pounds, they are one-third the weight of an eagle. But vultures have a 6-foot wingspan, nearly as wide as an eagle's. But numerous videos and accounts online show that when a bald eagle does decide to have it out with a vulture, it's the vulture that is usually wounded or killed.

Gelvin-Innvaer said a sudden exodus of vultures in any given area is often due to a loss of roosting areas they were accustomed to using.

"Turkey vultures come back to the same roosts each year, either big trees or old buildings." She said if development removes trees or old buildings the vultures hang out in, they may head elsewhere to find new roosts.

"People sometimes call and said they have turkey vultures roosting on their house, and it's often because there was a large development nearby and the woods was taken out."

This time of year the stately eagle doesn't have to worry about any vulture competition. The vultures are enjoying the sun of Mexico and Central and South America, while the eagles stick it out in our cold winter, often congregated around open river water.

So we'll have to wait until spring and be alert to whether the turkey vultures remain plentiful here or are truly in shorter supply.

Stand-in Ask Us Guy is Tim Krohn. Contact Ask Us at The Free Press, 418 S. Second St., Mankato, MN 56001. Call Mark Fischenich at 344-6321 or email your question to mfischenich@mankatofreepress.com; put Ask Us in the subject line.