Friday, June 15, 2018

Barred Owls Eating Crayfish

A small stream tumbled and crashed through edge of Bellingham, WA. The rocky ravine it had carved over time now provides refuge for big trees, a fish hatchery, a cacophony of birds, and humans, too. Well-worn dirt paths gave testament to the popularity of this waterfall-filled neighborhood greenspace.

I was out for one last walk before packing my bags and boarding the ferry to Alaska. A great blue heron hunting above the first cascade allowed me to stalk it with my camera. Pacific wrens and towhees chattered from the bushes and wild roses bloomed along the trail.

A great blue heron allowed me to stalk it with my camera while it was hunting above a waterfall.
At one point I peeked down a side path leading toward a bridge. An older couple and their golden retriever were standing there chatting, and while I wanted to see the view, I didn’t want to disturb them. Catching my eye, though, they waved me over.

“There’s a barred owl hunting crayfish in the creek,” exclaimed one in a stage whisper. “We’ve seen him here almost every day,” added the other. As if to confirm this fact, the brown and white checkered owl swooped off its perch on the lower branch of an alder tree. After dragging its talons through the water, the owl landed among the ferns and mosses on a low rock in the edge of the creek. From this new perch it turned its back on us and stared intently into the water. For a forest bird, it was extremely well camouflaged against the dappled light of the riffle.

Then whoosh again, the owl flapped and skipped across a few feet of shallow water and came to rest on a bigger rock just downstream. Immediately it started picking at something in its talons. By zooming in on its beak with my camera, and then zooming in on the photo on my LCD screen, we were able to positively identify its meal as a crayfish.

Barred owls have a very adaptable diet that sometimes include crayfish nabbed out of a stream or lake. 
Although barred owls’ stereotypical diet of focuses on mice, they are actually very adaptable opportunists. Small mammals (including mice, but also shrews, voles, and flying squirrels) make up the bulk of their winter fare, but in summer they expand their buffet to include birds, insects and spiders, amphibians, reptiles, earthworms, fish, snails, and crayfish.

Not every individual makes all of those options are part of its diet. Like flamingos, some barred owls eat so many crayfish that their belly feathers take on a pinkish hue. (I never thought I’d compare owls to flamingos!) Barred owls in the Eastern Cascades seem (based on surveys of their pellets) to subsist mostly on beetles, with frogs and flying squirrels for dessert. One owl was observed feeding almost entirely on aquatic snails. What they eat is largely dependent on what’s available at the time in their habitat. These birds don’t migrate, so they have to muster a year-round food supply from their local territory.

Needing big, old trees to nest in, barred owls were once confined to relatively undisturbed forests in the east. The advent of fire suppression in the northwest, along with tree planting across the Great Plains during the last century, gave the owls a path for hopscotching their way into a much bigger range. Their map now encompasses the southern provinces of Canada, southeastern Alaska, British Columbia, Washington, Oregon, and northern California.

Throughout their expansion, having an adaptable palate has worked to barred owls’ advantage. By eating oddities like crayfish they can scrape by even in small fragments of forests—like this creek ravine surrounded by neighborhoods.

All of this is wonderful for the barred owl, but not for their cousins the spotted owls who are native residents of the barred owls expanded range. Spotted owls were protected under the Endangered Species Act in 1990 because habitat fragmentation due to logging had reduced their nesting habitat. Spotted owls are smaller, less aggressive, and more set on eating flying squirrels, wood rats, and mice. With the influx of barred owls, their plight is only getting worse. Not only do barred owls outcompete them for food and nesting habitat, they also hybridize with spotted owls and dilute their gene pool. The best hope for rarer owls’ continued survival is the protection and expansion of old growth forests to provide enough habitat for the two species to coexist.

I’d learned about this conflict back when I worked in the redwoods of Northern California, so my excitement at watching a barred owl hunt in broad daylight was tempered by unease over the situation. The behavior we witnessed from that bridge is exactly why barred owls are a problem for spotted owls. We could declare this a normal consequence of species expansion and competition. Surely this scenario has played out millions of times over the eons. Natural selection is all about picking winners. This feels more dubious to me, though, because humans were definitely involved in changing the parameters.

Change is constant no matter how much we humans are involved. There’s value in working to protect things as they were, but finding beauty and wonder in a changed world isn’t wrong either.

The owl caught three more crayfish while we watched. Then, in a silent flash, it swooped out of the ravine through a gap in the sun-drenched leaves.

The creek flowing through Whatcom Falls Park tumbled and crashed over several waterfalls. 
Emily is on her way to Alaska for the summer! Follow the journey in this column, and at her blog:

For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Bee Amazed!” is open.

A great blue heron allowed me to stalk it with my camera while it was hunting above a waterfall. Photo by Emily Stone.

Friday, June 8, 2018

Tide Pools!

I took the scenic route along the coast from Anacortes, Washington, up to my friends’ house in Bellingham. Even though I’d just returned to the mainland from a couple days on Orcas Island, every glimpse of ocean through the trees was thrilling. With so many deep green islands dotting the sparkling blue, the view felt strangely similar to my beloved Boundary Waters—on a much larger scale. I’d enjoyed being out on the ferry, too, weaving among the San Juan Islands in a grander version of navigating the granite knobs of Saganaga Lake.

So much of this landscape feels familiar—but with a twist. Western species of hemlocks, firs, and cedars are much bigger than their Midwestern cousins. The towhees who call among those trees have prominent white wing spots, and the Pacific wrens—only recently recognized as a separate species from winter wrens—sing such a rapid-fire steam of notes that I couldn’t pretend to tell the two apart. The Pacific starflowers who glow in the understory are rounder and pinker than their cousins who are probably blooming along my Wisconsin driveway without me.

My excitement at seeing all of these sort-of-familiar species may seem odd, but their friendly faces provide stabilizing anchors as I navigate new trails and recover from driving new freeways. Plus, when viewed from a certain angle, they are thrilling testaments to the steady march of evolution, adaptation, and the connectedness of life. It’s no accident that they look alike, and there are probably good reasons for them to be slightly different.

One scenic pullout along the Chuckanut Drive seemed especially promising, with dirt paths disappearing over the steep bank. A young man with a dog on a leash bounded up out of the woods, exuberant about the beautiful, sunny weather. “Where does this trail go?” I asked. “To the beach!” he responded, so I set out through the forest in the direction he’d come from.

Waves push an odd collection of things up on shore as the tide goes in and out. In the wrack line, scavengers of all kinds can find crabs, algae, shells, and more. 
The trail soon became a bit of a bushwhack among lush thickets of sword fern and the holly-like leaves of Oregon grape. Finally, through the cedar boughs, I spotted the ocean. From deep shade I entered bright sun on a stretch of beach intersected by toes of bedrock and strewn with giant boulders. After taking in the view of misty islands and blue waves, a sliver of bright purple shell in the wrack line caught my eye. The little ridge of debris pushed up by waves is an important resource for scavengers, and I scanned it for interesting bits, too. The bright reddish-purple shell of a shore crab contrasted brilliantly with a heap of vivid green seaweed. It wasn’t food for my belly, but nourishment for my eyes.

Waves push an odd collection of things up on shore as the tide goes in and out. In the wrack line, scavengers of all kinds can find crabs, algae, shells, and more.
Soon I saw an odd pattern of sunken circles in the sand. Puzzling for a second, a half-formed thought nudged me to look around. Anemones! Of course!  A flood of memories from teaching at an outdoor school in California washed over me. I’d stumbled on tidepools. This zone of constant flux is no day at the beach for the critters who must adapt to the see-saw of wet-dry, dark-light, warm-cold, and more or less saline conditions. Those who have adapted to this environment are amazing.

Aggregating anemones host green algae on their bodies. Pink tentacles are a threat to small critters swimming or scuttling by. 
 Aggregating anemones, for instance, grow in colonies of genetically identical clones. They can reproduce asexually through binary fission, and over time one anemone can generate a carpet of replicas. The light green skin on the soft plop of their bodies is tinted by symbiotic algae who provide sugars and oxygen in return for carbon dioxide and a safe place in the sun. The algae also create sunscreen to protect them both from excess rays. Pink tentacles waving in the center of a submerged anemone shoot deadly, harpoon-like nematocyst cells at small fish, snails or crabs.

The exposed anemones had pulled their tentacles in and covered themselves with sand and shells to help prevent desiccation. Higher up, in a bowl in one of the rocks, I found a true tidepool bustling with waving anemones and other life.

From my perch above, I watched as an entire colony of fingertip-sized acorn barnacles licked the water in unison. Not tongues, but feathery legs ducked in and out of shells to sweep the mini currents for plankton and detritus.

These acorn barnacles and snail are closed up tight against the drying sun. When the tide returns, the barnacles sweep feathery feet through the current to gather bits and pieces of food. 
In the aquatic jungle, bushes of algae rustled with the action of crabs. Small snails crept over every surface. . . but not all of them were truly snails. After watching for several minutes I couldn’t resist. Scooping gently, I captured one of the dark, twisted shells in the palm of my hand. After just a second of hesitation, the cream and tan-striped legs and black-tipped eyestalks of a tiny hermit crab emerged. He righted himself, scuttled sideways, rolled again, and got back up. With soft, twisted bodies, hermit crabs need the protection of a borrowed shell to survive.

Hermit crabs have soft, twisted bodies that require the protection of a borrowed shell. 
The tide was returning by then, creeping up over the beds of anemones and pushing the wrack line higher. I giggled at the clown in my hand before putting him back and scrambling up to the forest. This juxtaposition of semi-familiar and completely peculiar is what makes travel so fun. Next stop: ALASKA!

Emily is on her way to Alaska for the summer! Follow the journey in this column, and at her blog:

For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Bee Amazed!” is open.

Friday, June 1, 2018

Brown Headed Cow Birds and Bison

My hike on the Centennial Trail in Wind Cave National Park in western South Dakota had been wonderful. I felt like Laura Ingalls Wilder as I strolled over the rolling prairie hills, dodged buffalo chips on the trail, and photographed wildflowers taking advantage of spring. Thankfully, the hot sun was offset by a cooling breeze.

Twice the trail ran right through the center of prairie dog towns. Their alarm calls were incessant and pushed before me in a wave, with the closest little rodents chattering from out of sight inside the entrance to their burrow. The bell-like tones of meadowlark calls rang out across the prairie, and repeatedly I searched for the vocalists who sounded much closer than their actual perch. The volume of their songs was impressive.

Prairie dogs shouted their alarm calls at me across the windswept prairie.

The prairie’s wide open horizon seems to encourage restlessness. Back at my car, I quickly settled in for an afternoon of driving west. Pa Ingalls would have understood the feeling.

I didn’t get very far, though. Where the park road met the highway, a pair of bison grazed on the shoulder. If it was just those two great, shaggy beasts, I might not have stopped, but around their heads fluttered personal flocks of brown-headed cowbirds. The shiny black birds with namesake brown heads pecked at the ground right in front of the bisons’ giant heads, played leapfrog over their humped backs, and generally acted just like brown-headed cowbirds are supposed to act. Glad that no one was with me to roll their eyes at my excitement, I swung onto the shoulder, rolled down a window, and picked up my camera from the passenger seat.

Now, brown-headed cowbirds are not my favorite animals. My parents and naturalist friends have always given them the evil eye. Arthur Cleveland Bent (an acclaimed ornithologist of the early 1900s) called the cowbird a “shiftless vagabond and imposter.” Its scientific name, Moluthrus ater, means “dark greedy beggar.” While they are native to the Great Plains, they have a bad reputation as lazy villains who parasitize the nests of more praise-worthy songbirds.

Female brown-headed cowbirds lay their eggs in the nests of smaller birds and let other parents do the hard work of feeding their hungry chicks. Cowbird eggs hatch first, and their chicks grow faster than the others. By virtue of being the tallest mouth in the nest, the cowbird babies get more food. Their gain is another’s loss, and their success comes at the expense of one or more of the host mother’s own young.

While most birds don’t seem to recognize the cowbird eggs or chicks as alien invaders, some do. House wrens puncture cowbird eggs. Yellow build a new nest right on top of the invaded one—smothering their own eggs as well. Robins, catbirds, and a few other birds with big beaks toss out the strange eggs. I feel like giving them all a high-five for not being duped.

But on a birding walk last spring with Laura Erickson—a wonderful Duluth-based birder, author, educator and scientist—I gained a whole new perspective on the cowbirds’ predicament.

These maligned birds once depended on the bison’s feeding to flush tasty insects and their heavy hooves to break up tough prairie sod, which made seeds available despite the birds’ scrawny feet. The problem was that bison herds moved regularly, and the birds had to follow. That transient lifestyle wasn’t conducive to settling down and raising a family. The cowbirds’ only option was to deposit their eggs in the nests of birds who could find food even without the bison, and hope for the best.

Brown-headed cowbirds feed on insects that bison stir up as they graze, as well as seeds turned up by the bisons' heavy hooves.

Hope isn’t their only strategy. A female cowbird lays about one thick-shelled egg each morning, and can lay forty or even sixty eggs in a season. Using radio-tagged birds, scientists discovered that females will spend the morning in nest-rich habitats like forests and edges. They may silently observe potential hosts in preparation for a “mission impossible”-style egg laying operation; walk around in dense ground cover looking for nests; or fly noisily through the shrubs hoping to flush a mother and home in on a target. They spend their afternoons foraging in more open habitats. Sometimes they’ll even return to a parasitized nest to check on and feed their own young. Once fledged, the young cowbirds instinctively seek flocks of their own kind.

This worked out pretty well when there were still plenty of bison moving freely across the plains. Nomadic cowbirds rarely parasitized the same nest repeatedly, so their songbird hosts recovered easily from the reproductive setback. The problems came when pioneers settled the plains and replaced nomadic bison with fenced cattle, tilled farmland, and backyard feeders. The birds adapted well to the new scheme, which allowed them to spread east into new territory, where songbirds weren’t used to their skullduggery—which could now be concentrated instead of scattered. Their success came at the expense of their reputation, though, and cowbirds are now an unwelcome visitor in backyards from California to Maine.

Is it really their fault? Like so many animals, they evolved to live in a world that we have changed almost beyond recognition. But there, on the side of the road surrounded by vast prairies and restored herds, they were behaving exactly like they should. They still aren’t my favorite birds, but for just a moment I could really appreciate the cowbirds’ place in the world.

Then—restless as ever—the two bison moved on. I put down my camera, rolled up the window, and continued west.

Emily is on her way to Alaska for the summer! Follow the journey in this column, and at her blog:

For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Bee Amazed!” is open.