Field Note: A Great Blue Heron on Thin Ice! … and Its Neighbors – a Drama in Three Acts

It often happens that shortly after I publish a blog about a particular park, something interesting pops up there that I wish I could have included.

Text by Cam Mannino

So to solve that issue, Dr. Ben VanderWeide, Oakland Township’s Stewardship Manager and I decided that it might be fun to slip in a short piece, a “field note,” now and then about these intriguing and/or surprising discoveries. And wouldn’t you know, one cropped up last week!

A Young Blue Heron Discovers a New Challenge: Ice!

Readers may remember that in the recent Bear Creek Nature Park blog, my photographer friend Paul Birtwhistle introduced us to a voracious juvenile Great Blue Heron (Ardea herodias) who for weeks spent its mornings snapping up green frogs and fish from the drought-depleted Center Pond at Bear Creek.

Photographer Paul Birtwhistle and Stanley the Wonderdog

Well, after one frigid night last week, the pond froze with a thin sheet of ice. And of course, the Heron returned in the morning to continue its feast. But to its apparent dismay, the water had changed drastically since the day before. The heron stepped out cautiously on this oddly slick surface and looked about. In the short video below, you’ll hear that Paul was amazed at what he was filming. And the young Heron was just as surprised at finding the pond surface inaccessible after weeks of dipping into it to find a rich trove of food. [Note: Vimeo, which formats our videos, attributes everything on Ben’s Vimeo account to Ben. But this week, all of the photos and videos were generously shared with us by Paul Birtwhistle.]

“What’s this? Tap, tap, tap. The water is hard?!!! What’s this? Video by Paul Birtwhistle

This youngster didn’t give up easily! It stared at the surface repeatedly. Paul guessed that he was seeing movement under the thin ice.

I see something down there, but why is my vision so fuzzy? And how do I deal with the slick, hard barrier between me and breakfast? Photo by Paul Birtwhistle

I wonder if perhaps the juvenile thought something was wrong with its eyesight, as it tried to bend down and get closer to the ice. Or perhaps it still thought it could snag its prey if it crouched down a bit…

Hmmm…maybe I just need to get a little bit closer. That usually works. No? Drat! Photo by Paul Birtwhistle

The heron tread verrrry cautiously on the thin, icy surface but – Yikes! Suddenly its feet slipped from under it and up went those dramatic wings to help it find its balance.

Whoops! Wings up! What’s the deal with this weird pond? Photo by Paul Birtwhistle

Trying to keep its hopes up, the bird spent about a half hour stepping carefully on the slippery surface and peering down at the ice-blurred surface of the pond. The youngster appears to warm one foot by bringing it to its feathers – or maybe it’s simply scratching an itch. In any case, this young bird looks pretty frustrated at this puzzling new experience.

I just don’t get it! How annoying! Photo by Paul Birtwhistle

After more than a half hour of exploration, the young heron took flight. Let’s hope it found its way to deeper water and the society of older herons who would show this young ‘un how to fish from the icy edge of open water.

OK! I’m outta here! There must be normal water around here somewhere! Photo by Paul Birtwhistle

Paul was surprised and delighted to see a heron on ice! And so was I when I received his photos! We thought Great Blue Herons would already have migrated. But when I contacted experienced naturalist and bird bander, Allen Chartier, he explained that, in his experience, though many migrate further, some herons just keep moving south to find open water. He sees them where warm water thaws the ice near power plants, for example. He believes most of them depart by January when even large bodies of water freeze over. Cornell University’s subscription website, Birds of the World, indicates that those mighty wings carry many of them as far south as the Caribbean. So bon voyage to our young puzzled friend. Hope you found a belly-full of food before nightfall!

Meanwhile, Nearby, More Experienced Neighbors Also Coped with the Icy Pond

Muskrats (Ondatra zibethicus) have created a “push-up” or lodge on the Center Pond this year, probably because Bear Creek marsh, where they more often spend the winter, has less open water than usual. Muskrats spend the winter mostly under water. Their metabolism drops and they efficiently utilize oxygen stored in their muscles. They slowly swim about, foraging for aquatic plants, though their diet can also include frogs, snails, small fish, occasionally even small turtles – if any remained after our hungry young heron departed! Since muskrats are mammals, however, they need to come up for air. Their push-ups have a platform inside where they can enter from underwater and then eat and rest comfortably in the air. Nice arrangement, eh?

The first time Paul noticed a muskrat, it was near the heron, gnawing its way through the thin ice to keep its channels open. In the photo below, note the ice being pushed up onto the muskrat’s muzzle as it acts like an icebreaker. Its long fur helps keep it warm and it can close its ears when under water. But as you’ll hear Paul say in the video, “It looks ever so cold!”

A muskrat acting as ice-breaker. Photo by Paul Birtwhistle

The next morning two muskrats fed at the pond. The first one in the short video below seems to be eating frozen plant material pulled up from the shallow water. Watch ’til the end of the video to see the second muskrat emerge from the push-up, gnaw on some ice and then decide to make a beeline underwater toward the first one – probably its mate.

Two muskrats on an icy morning at Bear Creek’s Center Pond. Video by Paul Birtwhistle

It turns out that this affectionate pair is sharing its home with 3-4 other muskrats that Paul saw a few days later. They may be a family, though muskrats are known to hole up with unrelated muskrats in the winter. I suppose that more muskrats inside means more warmth. But the shallow water and the depleted amount of prey may turn out to be a challenge to these animals this winter. Drought like we’ve had lately can be a hazard to semi-aquatic animals. It’s much easier for predators like foxes and coyotes to reach the muskrats if the shallow water freezes solid.

Amazingly enough, a savvy potential predator did indeed show up on Paul’s next visit – an American mink (Neogale vison)! I’ve been hiking Bear Creek Nature Park for many years and never seen one there. But late one morning, this powerful, beautiful animal appeared on the north bank of the pond right behind the muskrats’ push up. Hmmm…. Various sources report that though minks eat several different small mammals, their favorite food is, you guessed it, muskrat! Well, winter’s a challenging time and the mink may have a mate to feed as well since minks breed during the winter. Everyone has to eat, right? Look at the magnificent specimen Paul saw! Its size, white chin patch and small white chest spot are good field marks for this impressive creature.

An American Mink looks with great interest at the push-up of a group of muskrats, a possible tasty treat for the mink! Photo by Paul Birtwhistle

What a drama played out at the Center Pond this November! Will the young heron learn quickly how to find food on an icy morning? Will the muskrats find enough prey in the shallow water after the heron’s weeks of feeding? Will they successfully fend off the hungry mink or will this elegant, potentially lethal predator find a meal for itself at the pond? We’ll probably never know the conclusion to this series of events. But thanks to Paul, you and I had front row seats for this adventure in three acts, each featuring a creature coping with the vicissitudes of the season.