25 Years of Mountaintop Eagles

Yesterday, 323 Golden Eagles flew north over Mount Lorette, in Kananaskis Country, southeast of Banff.

If that strikes you as a very specific number, it is. And that's because for exactly twenty five years, dozens of keen volunteer bird watchers have been counting the Golden Eagles that migrate along the backbone of the Canadian Rockies every spring and fall.

On March 20, 1992, Des Allen and Peter Sherrington were doing a general bird survey in the Kananaskis Valley when they first noticed Golden Eagles flying high along the ridgetops. They saw over a hundred that day, but when they looked for other records of large numbers of eagles, they could find nothing even close.

They started watching, and they got others to watch too.  We remember that spring, because we heeded the call to volunteer. It was our very first summer in Lake Louise, and we spent a day in lawn chairs beside Banff's Lake Minnewanka, peering through binoculars to look for the mysterious eagles. And that's when we learned why nobody had noticed what Des and Peter had found that spring: you couldn't see these gigantic birds with your naked eyes! It seems impossible -- they can have 7-foot wingspans -- but they were flying so high that you needed to pick them out with scopes or binoculars.

The golden eagle migration down the spine of the Rockies.
Courtesy of the Rocky Mountain Eagle Research Foundation.

Since 1992, observers have spent over 4500 days in the field, and they've counted more than 180,000 Golden Eagles in total.  The birds are believed to nest in the Yukon and Alaska, and their wintering grounds stretch from Montana to Mexico.

On this, the first full day of spring, let's celebrate nature's splendour, and tip a hat to Peter and Des for their epic discovery.

If this blog post has made you curious about birds, we offer private birdwatching trips in June and early July every year. Come join us!

What's with all the Snow Mushrooms on the Fenceposts?

If you've driven between Banff and Lake Louise this winter, you've probably noticed the big globes of snow on top of the wildlife fencing posts. Or, if you've been snowshoeing with us, you've seen even bigger piles of snow on stumps or broken tree tops

How do these "snow mushrooms" form? Especially when the surface they're sitting on can be as small as a dessert plate.

To answer, we need to welcome you to the wonderful world of snow science, and specifically the process of equi-temperature or destructive metamorphism. We hope you're ready for a bit of physics!

When new snow falls in the Canadian Rockies through the winter, the cold temperatures almost always guarantee that it will fall as light, low density "champagne powder." But it doesn't stay that way.  If snow lands on something above the ground, like a log suspended in the air, or a stump, it will start to change. The newest snow will always be light and fluffy, but snow that's been on the log or the stump for a few weeks or months will feel like really high density styrofoam. You are hard pressed to push a ski pole into it more than a few inches, and the snow crystals stick to each other tenaciously, even though new snow in the Rockies can't even be formed into a snowball.

Here's what's going on: since the temperature around the suspended snow is the same at any given time (hence "equi-temperature"), the snowflakes start to break down in a surprising way: water in the spiky ends of the flakes sublimates (meaning it evaporates directly from ice into water vapour). The water vapour that is produced through this sublimation moves from the higher vapour pressure at the edges of the snowflakes toward the lower vapour pressure around the interiors of the snow crystals.

Still with us? This small scale water migration means that airy, fluffy snowflakes become denser over time, and closer together. This promotes the stickiness of the snow, meaning it can occupy a bit more space than the surface area of the stump or fencepost. With each subsequent snowfall the surface area for collecting new snow increases, until a giant blob of snow can sit on the tiniest of surfaces.  Big snow mushrooms can measure more than 3 metres across.

photo by Vaughan Cornish, public domain

We are not the first to notice these snow mushrooms.  In 1900, English geographer Vaughan Cornish took a winter trip on the CPR through western Canada.  He photographed giant snow mushrooms in Glacier National Park. Here's one of his archival photos, plus a few more from us.