Great Spirit Bluff: What’s going on and why don’t we remove the nest box?

After three young falcons jumped out of the box at GSB yesterday, some followers are asking us to remove the nest box entirely. But based on our history, removing the box would make the site even more likely to fail. Here’s an explanation of Great Spirit Bluff’s successes, failures, and why we installed the nest box to begin with.

Ledges, Raccoons, and Nest Boxes

Back in 2003, RRP founder Bob Anderson was trying to figure out why a large cliff in southern Minnesota was attracting adult falcons, but not producing young. The team roped down to explore the bluff face and discovered a nest scrape and raccoon feces on the rock ledge that fans now call ‘The Rock Ledge Diner’. Falcons were laying eggs, but the eggs and/or nestlings were being eaten by raccoons before they could fledge.

We asked the Howe family if we could shift the falcons to a safer location by mounting a nest box to the sheer rock wall above the ledge. We installed the box in 2003 and banded our first nestlings – Alice, Rachael, George, and Ryan – on June 14 of 2005. The deep overhang beneath the nest box presented an insurmountable barrier to even the hungriest raccoon and so we visited the site year after year to band nestling falcons. Between 2005 and 2012, we banded a total of 25 falcons, which works out to about three falcons per year: pretty standard for a nest box and much better than zero on the ledge.

What We Learned With a Nest Cam

Great Spirit Bluff quickly became one of Bob’s favorite sites. Following the success of the Decorah Eagle cam, we decided to install a camera with the help of John and his son Jonathan in the fall of 2012. We were looking forward to watching fledge in 2013, but instead got to watch blackflies drive three young falcons out of the nest box in about mid-June. It’s also how we discovered that parents will fly into the understory to find, feed, and defend their young until they are old enough to fledge. Since 2013, we’ve had five years where falcons left the box early and four years where they did not. Blackflies lay their eggs in running water, which means that wet years are also bad blackfly years. More about that here:

Nestling Survivability

How did nestlings do in 2013, 2014, 2017, and 2019 – the years they jumped? We don’t have data from 2013, although we think they survived based on what we saw and heard below the bluff. Here’s what we know about every other year:

Over the years, we’ve tried a number of strategies against the blackflies.

  • In 2017, we replaced the original nest box with a backless design. Would a cooler pothole-like nest box keep blackflies away? While we love the backless design, blackflies kept coming.
  • In 2018, we added a blower fan. The nestling falcons appear to enjoy having central air, but the blackflies kept coming.
  • In 2019, we treated the box. Unfortunately, our treatment volatilized pretty quickly, and the blackflies kept coming.

Blackflies were a problem before we knew about them, and they aren’t going away. While we will continue to look for a solution, falcon parents are deploying their own age-old strategy: find the young and get them to fledge, wherever they landed. Even in bad blackfly years, falcon production has been higher than zero, which is what we had before we installed a nest box back in 2003.

As of this morning, our camera operators have spotted nestlings in the thick underbrush and we’ve watched Zooey dive at a raccoon. We’ll be watching and hoping all three reappear on the cliff ten or so days from now. Watch with us here: