The squirrel that cried hawk
Small mammal banter, flammable trees, and plant of the week
Looking for early spring birds during last weekend’s thaw, I mostly found chipmunks scrabbling around brush piles and seeking food before the next freeze.
The small mammal activity attracted a red-tailed hawk. Turning a corner, I spooked the hawk off the ground. There was a dark shape in its talons—probably a squirrel or chipmunk. I had interrupted lunch.
I swung around a spur of the trail that leads to a salt marsh, found few birds, and returned to the trees. I heard an odd noise from above. At first I thought of a blue jay imitating a red-tailed hawk scream—feeeeeaaarrr. It’s something jays do to scare off other songbirds or make them drop their food so the jays can steal it. But the voice wasn’t quite right for a blue jay—too squeaky. Squirrely, you might say. After a minute or so I traced the sound to the right tree:
It was a gray squirrel making the sound, to my surprise. I wondered if it was imitating a hawk on purpose, like a jay—something I wouldn’t expect of a squirrel. (Maybe I underestimate them a bit.)
It turns out that gray squirrels use different alarm calls depending on the threat, somewhat like certain bird species such as chickadees. Their general alarm noises are “kuks”—miniature dog-barks—and “quaas”—a longer bark. There’s also a “moan” alarm that sounds more like a whistle. This recording of a squirrel moan from researchers studying squirrel alarm calls is pretty close to what’s in my video.
Scientists have sought to decipher what a squirrel moan means. Experiments using simulated attacks from terrestrial predators (a fake cat riding a remote-control car) and aerial threats (a glider decorated to look like a hawk) indicated that squirrels tend to moan when there’s an attack from the sky. The squirrels usually gave out rapid kuks or quaas and flagged their tails when RoboCat approached.
However, it’s hard to test whether other nearby squirrels hear a moan and interpret it to mean there’s a nearby hawk. That’s partly because squirrel alarms aren’t as neatly specific to predator type as they are for chickadees. Another benefit could be letting a predator know that the squirrels have seen it. This works better on a cat quietly stalking and hoping to ambush. A bunch of squirrels barking at it could discourage further hunting. That approach might not succeed with a hawk that’s cruising around for a clear target and isn’t easily persuaded to stop.
That’s why the researchers suggest that the narrow frequency band of the moan might help a squirrel express its fear while also concealing its location. In general, a narrow-band whistle is harder to pin down than a broad-band bark. It did take me a little while to figure out where the moaning squirrel was, after all.
It’s probably just a charming coincidence that the moan I heard sounds a little like a red-tailed hawk call. Based on the available research, gray squirrels would likely use the same alarm for a Cooper’s hawk, which has completely different vocalizations.
Regardless, I can at least say that I have a greater appreciation for the skills of the humble squirrel after this week.
For more on squirrel alarm calls, here’s a fairly comprehensive scholarly review on the subject. The internet—what a place.
Another thing about eucalyptus: they burn like matchsticks
Last week, I talked about the flaky bark of blue gum eucalyptus trees and how they wound up in California by way of Australia. Writer and wilderness firefighter Robert Langellier wrote in to note that the introduced tree’s bark is notorious for its flammability:
“Eucalyptus trees are well-known in the western firefighting world for their mile-long arcs of their bark cannons. They can cause absolute chaos in western California fires.”
In a fire, eucalyptus bark can fly off the tree and carry an ember up to several kilometers away, a phenomenon called “fire-spotting.” This has led some researchers working in Australia to speculate that eucalyptus bark is designed to burn. If the tree causes a small fire on the ground to travel up its trunk and into the canopy, leading to a forest-clearing crown fire, perhaps the fire-adapted (pyrophytic) eucalyptus can recover and thrive in the wreckage of the burned out forest—the so-called “kill your neighbor” hypothesis.
Robert also raised some interesting questions about the lifestyle of a living matchstick:
“I’ve never looked deep into eucalyptus, but I’ve always assumed they were pyrophytic, otherwise how on earth could they have survived through history as one of the known world’s most flammable trees? They have odd fruits, and I’d be surprised if fire opened them. Maybe they have seeds with really long viability. I wonder how their seeds germinate. Of course some pines only release seeds in fires, plus some species’ seeds have to be scratched in flash floods, some seed walls must be broken down by digestive animal enzymes. Maybe I’ll write a book someday on germination tactics.”
We can only hope so! In the meantime, check out Robert’s story for Esquire on 24 hours contending with California’s worst wildfire season to date.
Did you know that there are fire-resistant Nomex face masks available for firefighters? Stopping two kinds of spread at once.
Plant of the week: Spotted wintergreen
Every year, there’s one walk I take that stands out as the last one in true winter, just on the edge of spring. That happened on Tuesday for me. Along a small pond bank beside pine tree roots, I found spotted wintergreen (Chimaphila maculata). While it’s an evergreen plant that sports the handsome dark green and red colors I associate with winter plants, it seemed like it was perking up in the March sun. Maybe that was wishful thinking.
The stripe down the center of the leaf helps distinguish it from other low-growing wintergreens. Unlike teaberry/American wintergreen (Gaultheria procumbens), deer don’t like spotted wintergreen berries. Among the Cherokee and other Native Americans, the plant has many uses in traditional medicine, including for ulcers, rheumatism, pain relief, and urinary problems.
The blog The Natural Web has a lovely post about spotted wintergreen as an emblem of winter’s charms. Maybe you’ll agree with me that the charms of winter are sometimes best appreciated when you know the season is on its way out. The hunt for the first skunk cabbage is on.
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Possum Notes is a weekly newsletter about wildlife and landscapes around where I live. It’s produced on occupied Massachusett and Wampanoag land.