It’s a thoroughly human practice to classify things, to put them in neat compartments that make sense to us. We often do it with people. We give them labels: they’re shy or they’re outgoing; cautious or reckless; an optimist or a pessimist.

We classify plants and animals, too, grouping them based on their appearance, their behaviors or their genetic similarities or differences. We develop expectations about where we’ll find them, what they will look like and—for members of the animal kingdom, especially—their behaviors.

Sometimes, though, a critter doesn’t quite follow the rules as we’ve come to understand them. It’s a reminder that the only thing that matters in Nature is survival, by whatever means are necessary. It’s definitely not about a wild lifestyle that conforms to what humans expect.

I’ve seen this in the wildlife I watch, and sometimes photograph, in my travels between home and other destinations. Within just the last few days I’ve had it demonstrated by two wild creatures that I thought I knew pretty well. So much so, that when I found them in roles that seemed unexpected, I mistook each for the other.

Two of the more interesting birds in my neighborhood from spring through fall are sandhill cranes and great blue herons. My late mother-in-law, Betty—and no doubt others—routinely called the herons she saw winging over the lake beyond her cabin window “cranes.” But science-minded people like me—who sometimes know too much for our own good—would point out that the two aren’t even in the same family of birds, despite their similar size, coloration, stilt-like legs and long sharp beaks.

Sandhill cranes are a relatively recent addition to the birdlife of the fields, forest, lakes and wetlands in the rural area where I live. Only within the last dozen years or so have they become a common sight feeding, or engaged in their leaping, pivoting, wing-flapping mating ritual or having their rattle-like calls in several variations heard regularly.

I’ve almost always seen them in a crop field or pasture, striding on long, bone-skinny, stilt-like legs in search of whatever insect, reptile, amphibian or hapless small mammal prey might be found there. The few times I had seen them near water they were skulking through cattails at the margin of a large, shallow pond, whose water ultimately drains into the lake where the family cabin stands. I assumed they were there for a drink of water, important for any creature that can’t get enough from dew on vegetation, puddles of standing water or in what it eats.

Recently, workplace-bound in the early morning, I was passing this pond as I usually do: camera on the front passenger seat, window down, driving at a pace slow enough to irritate anyone following close behind. It’s a place where I’ve photographed loons, swans, ducks and geese, so I try to be prepared for any opportunity it presents.

Nearly past the pond, I spotted a pair of large, gray-blue birds well out from shore, beyond the edge of a thin stand of bulrushes. This is a place where you’d expect—where I’ve seen and photographed—great blue herons stalking fish, frogs or other victims of opportunity that are likely to be found there.

Despite the similarity in plumage tones, these were not great blue herons. They were sandhill cranes, identifiable—even at a distance—by the bright red patch of bare skin on their heads. This telltale feature begins at the base of their upper bill and extends back over the forehead to the crown of their skull. I had overshot them, but made a U-turn at a driveway beyond the pond, returning with window down and camera at the ready. The photo images I got may not make the cover of National Wildlife Magazine. But they had revealed an aquatic side of sandhill cranes that I had not seen.

Great blue herons can play the double-agent game, too. Along this same county road, but in the opposite direction, are several fields of small grains, planted by a farmer whose well-maintained barn on a hill above the shore is a welcome anachronism as today’s lakeside properties go. One of his fields—rye or barley, I’m not sure which—follows the broad curve of this road.

A day or so after the sandhill crane incident I was returning from a visit to a local produce stand. Rounding this curve, my attention was caught by a tall gray bird standing still as a statue. It was in a narrow strip between the field of waving grain and the road ditch, a strip where it appeared the farmer’s crop was stunted and short. It was a great blue heron, not the sandhill crane I would have expected; far from any pond, wetland or the margins of the lake. What was it doing here?

As the car slowed and I angled onto the road shoulder, I lowered the passenger-side window and raised the camera with its long telephoto lens. In my experience, herons are one of the birds least tolerant of human disturbance, and this one was no exception. As I struggled to frame the bird in the camera viewfinder, it wasted little time taking flight. Instead of a photo of a statuesque heron, I got a freeze-frame shot of its wings raised above its head, just before their downstroke launched the heron into the air, and escape.

With the heron gone, I looked closer at where it had been standing. There, from that narrow strip where the grain was stunted, came a reflection of sunlight off a film of standing water. It was likely left by recent rain in this poorly-drained corner of the field. Just enough to suggest to a heron the possibility of frogs, or another menu item it might find appealing.

As if to underscore the unpredictability of such bird world juxtapositions, the next day I drove past the same field, and—instead of a heron—a pair of sandhill cranes were ambling along the edge of the small grains, intent on finding their next meal. Just as one would have expected!