Boreal Chickadees on Spruce Budworm in Late Fall

A Boreal Chickadee with 1 Spruce Budworm hopped on this branch before heading to another lichen mat to get more before caching them.

One of the things I love about living here in Michigan’s Upper Peninsula is the surprises that nature can offer, bird-related or otherwise. You never know on any year or season what they might be, and my wife and I enjoy sharing these experiences.

We recently had a welcome surprise. A few days ago (11-26-2022) my wife came in after an early morning walk and let me know there were some Boreal Chickadees less than a mile from home. So we got out our photography gear and headed out to photograph them. We have never seen them before. I told her about 15 years ago that one day they should show up around here – long wait.

They would often hunt the very edge of a lichen mat after they cleaned up worms from the middle of the mat.

When we got to the location we immediately saw 3 Boreal Chickadees going to some lichen mats which had grasses and other plants growing out of them. Five of these mats were isolated in a large forest puddle at roadside, and they poked above the waterline. The Chickadees would search the mats for larval worms, eat a few, continue searching, and then fly to cache them high up in the trees when they had 2 or 3 of them. And then return, over and over. Each mat, and each with an approximate diameter less than 2 feet, may have had close to 100 worms. The only times I have witnessed something similar is when warblers feed mobile fledglings, but they never came back to the same small area – with a size around 250 square feet.

It wasn’t until I started reviewing images and blowing them up, between breaks in the action, that I said to my wife, “those look like Spruce Budworms”. But I am very familiar with Spruce Budworms, and even though the immediate area is loaded with Spruce Budworm damaged spruces, I was not sure because they looked a little different – they lacked the black head parts of spring Spruce Budworms.

Boreal Chickadee with 2 Budworms and hunting for more.

After a challenging session of trying to time the correct head angle on a bird while it hunted for worms, and returning the next morning briefly, we were sure we came up with some good images. It was difficult. They seemed to never stop moving and almost always had their heads down. But they gave us very many chances.

Soon I did some research on the internet and learned that Spruce Budworms have 6 larval stages, known as instars. They form hardened exoskeletons, which eventually shed when they grow big enough, and upon shedding they enter the next instar stage a little bigger, grow, shed their next exoskeleton, and so enter the instar stage after that, etc.

Eggs laid by the moth stage in early summer hatch as small larval worms sometime in summer. When this occurs is dependent on temperatures during the season – warm temperatures accelerate the process. During the second instar, the larval worms leave the trees and seek places where they will hibernate, and one of the places is within the lichen mats on the boreal forest floor. When they have chosen a spot to hibernate, they form a silk-like spun sac around themselves, known as a hibernaculum (plural – hibernacula), which protects them during winter. I suspect that they lose their head and mouth parts during this stage because they go into a hibernation state, without need for eating or growing, and that is why my images show no black head. Warmth in spring will wake them up and they will transform.

This mat island had unfrozen water behind it. The wind in the trees gave the shimmering effect.

I have a theory: When the larval worms were in the lichen mats, but before they formed their hibernacula, we had good rains that filled that large puddle, because I remember it as being dry during the heat of the summer. The worms may have crawled away from the water as it rose and isolated and concentrated themselves on the higher lichen mat islands, which eventually became the Boreal Chickadee’s feeding stations.

About a week before this unique photo opportunity we had 14″ of snow that melted over a period of 3-4 days of freeze/thaw conditions and partially revealed the lichen mats. That is when the Boreal Chickadees showed up. They were so busy taking advantage of the bounty that they were completely tame, and my wife and I talked as we photographed, which attracted a few Black-capped Chickadees. The Blackcaps stuck around and fed on natural seeds on the surrounding uncovered sections of forest floor and on things within the usnea encrusted dead branches of the spruces. But they never caught on to the bounty of larval Budworms in the mats or paid any attention to the Boreal Chickadees. Hunting for Spruce Budworm in lichen mats is probably not part of their survival skill set here. It seems like going to feeders and scolding people to put out seed when the feeders are empty, is.

My favorite body position of this species.

While busy hunting, the Boreal Chickadees constantly changed their head angles while peering intently into the grasses of the lichen mats and presumably knew how to identify hibernacula. I believe they pierced the hibernacula and plucked out the larval worms, in the same way a Cape May or Blackburnian warbler does where new growth occurs at the tips of spruce branches full of spun silken structures holding large Spruce Budworms in spring. That is something we look forward to capturing during the spring warbler workshops. The action happens very fast and is hidden down in the grasses so it is hard to know. But they always had a clean beak with a worm after capture, probably because the silken fibers were attached to the grasses, the same way the beak is clean after a Cape May comes up with a Budworm from a silken spun spruce tip, where the silk adheres to the tip.

The image above was taken the next morning, after a thaw during the night, and this individual’s beak is not clean. Visiting one of the lichen islands, this bird probed and came up only with silk on its beak. Maybe it tried to get a worm out of an empty hibernaculum because it already had extracted the worm before, and it grasped silk instead.

During the mostly frozen morning this individual peered under the ice to look for budworms. It actually found some this way and pecked through the thin ice to get them.

The next morning the ice was melted so they ventured off the mats a little to look for hibernacula under the water, and they did find them.

This individual briefly poked at a silken structure between its feet, within the usnea moss of a dead spruce, which could have held another Spruce Budworm.

This experience leaves me wondering if there are any other bird species that spend the winter here (or in the typically colder boreal forests of northern Canada) that feed on Spruce Budworm in lichen mats during spring thaw or a similar late fall thaw. I have found no information describing this or documenting it. Now that we know what to look for maybe one day we will get the chance to witness and possibly document similar behavior again with another species.

For a related in-depth photo-illustrated article on warblers taking advantage of Spruce Budworm in the nesting season in Michigan’s Upper Peninsula see: Spruce Budworm in Michigan’s Eastern Upper Peninsula