Shorebirds in winter

Waders large and small

On Christmas day, a little group of friends walked along the airport dike trail. Loose snow had drifted over the trail in places and low streamers of more snow were whisked over the meadow by capricious breezes. The shallow lagoon in front of the small shelter was covered with ice. On the ice I saw two killdeer, rather forlornly peering through the ice, unable to reach any bits of food below. Hungry and hopeful, they spent some minutes there, in vain.

Soon thereafter, I was told that killdeer are not uncommon over in the Fish Creek area, so of course I went over to look. In the parking lot, I met someone coming off the trail who reported seeing lots of killdeer out on the west side of the berm leading to the ‘island’. But—again, of course—by the time I got out there, they were not to be seen.

These observations made me think about what shorebirds might occur here in winter and the kinds of places they might be found. Consulting with some experienced birders, I used the Juneau checklist to learn which species are most likely to be seen and which are less likely. Occurrences vary from year to year, of course, but the list serves as a starting place.

“Shorebirds” include the sandpipers, plovers, godwits, and oystercatchers, earning their common collective name from their frequent use of shorelines outside of the breeding season, on migration and in winter. That’s when the species often overlap in their habitat use and bird watchers are mostly likely to see them. Nesting habitats are varied, including wet tundra, dry alpine tundra, bogs, marshes, grassy meadows, and the birds are then spread out over the landscape. All of them forage primarily for invertebrates. https://vimeo.com/661860407 (a mixed-species group at Tee Harbor; Bob Armstrong).

The rock sandpiper is reported to be common in Juneau in winter: It forages on gravelly and rocky beaches and headlands, but also on intertidal sand and mud flats. This species has been studied in upper Cook Inlet, where it is the northernmost wintering shorebird in North America. It feeds primarily on the small clam Macoma baltica, picked from the sandy-muddy flats. In midwinter, its daily energy requirements were estimated to be more than six times the basal metabolic rate—that’s a lot of clams! The subspecies in Cook Inlet has faster prey-handling times and higher rates of energy intake and of shell disposal than the more southerly subspecies.

Rock sandpipers. Photo by Bob Armstrong

The next four species are said to be uncommon or rare in Juneau in winter:

Dunlin: It is found chiefly on muddy estuaries on the coast in winter, but also on other wetlands. It eats invertebrates picked from sand and mud flats. Juveniles are apparently more vulnerable than adults to predation and to severe weather.

Black turnstone: In winter, it’s mostly on rocky shores and reefs, headlands, but also on deltas and mudflats; it may attend late runs of anadromous fish in streams. They feed on intertidal invertebrates in winter, including lots of small limpets.

Killdeer: In all seasons, it is found mostly in open habitats including mud flats, gravel bars, and wet grassy fields. Killdeer eat a variety of terrestrial and shallow-water invertebrates, including crustacea, worms, larval moths, and sometimes small vertebrates (e.g., dead minnows). Killdeer in some areas are reported to forage quite actively on moonlit nights, while reducing activity on the following day; this pattern reduces exposure to daytime predators such as falcons.

Killdeer. Photo by Bob Armstrong

Wilson’s snipe: Wintering habitats include marshes, swamps, wet meadows, and wet fields; I also see wintering snipe along rivulets in the forest (e.g., mountainside tributaries of Gold Creek). It often probes the substrates for prey, including larval insects and earthworms, and also eats small molluscs and crustacea. At least in some regions, male snipe put on more fat in winter than females, in preparation for their early northward migration; females migrate later, when food is more available on the journey.

Other species are thought to be occasional and incidental in Juneau in winter: greater yellowlegs, semipalmated plover, spotted sandpiper, long-billed dowitcher, ruddy turnstone, surfbird, and sanderling.

Good places to look for any of these wintering birds include Eagle Beach, Sheep Creek, Fish Creek, lower Switzer Creek, Salmon Creek and northward along Gastineau Channel,Mendenhall wetlands. Boaters might check the sea stacks and rocky reefs, which are less accessible to observers.

Many thanks to some experienced bird observers for helpful consultation!

Surf, bird food, PSP

Toxins along a stirred-up shore

Surf’s up! In early January, high winds stirred the waters of Juneau, making boating an unpleasant if not downright dangerous proposition. The waves pounded the coastlines, roiling the waters next to the shores. Even moderate wave action at the shoreline is sometimes a good thing for hungry birds—the turbulence seems to wash out small invertebrates into open water where ducks can gobble them up, one little item at a time (https://vimeo.com/662110696). It also may loosen cobbles and gravels, making hidden invertebrates accessible to gulls and shorebirds that pick and probe (https://www.naturebob.com/gulls-taking-advantage-surf). Splashes and wetting might encourage upper intertidal mussels relax their tightly closed valves a bit, making it easier for oystercatchers to insert their long, thin bill and extract the soft parts. We see the birds doing these things, but I don’t know that anyone has actually measured the effects of wave action on the inverts…Maybe the birds know more than we do.

Black oystercatcher eating blue mussels. Photo by Bob Armstrong

The oystercatcher feeding on open mussels in the video was filmed in Tee Harbor in spring of 2019, at a time when the level of PSP in the mussels was already high and getting higher. Paralytic Shellfish Poisoning is caused by neurotoxins produced by microscopic algae that feeding molluscs filter from the sea water; certain algal species are especially known for their neurotoxins. The term is earned for the unpleasant and sometimes devastating effects on humans that ingest clams and mussels containing the toxins (and other animals that ate such molluscs). Also, I’ve read that heavy surf can break up the bodies of small planktonic and shoreline organisms, allowing the wind to carry body fragments and neurotoxins as aerosols. By impeding the transmission of nerve impulses, these toxins affect respiration, muscle contraction, and other essential functions. Micro-algae also produce other toxins, which affect digestive systems, memory, and other aspects of consumers.

What about non-human consumers, including the molluscs themselves? Some molluscs just stop feeding when exposed to toxic algae; others are sensitive to the toxins and suffer some negative physiological effects. But some develop resistance to the toxic effects when they are repeatedly exposed to the toxinsand accumulate them in their bodies, in some cases retaining the toxins for many months, passing them on to other consumers. When crabs eat molluscs, they can build up toxins in parts of their bodies too. So sea otters, which eat both molluscs and crabs, may suffer some of the negative consequences; but they can learn to reject prey with high levels of the toxins. Predatory snails (whelks) that feed on mussels and clams ingest the toxins too. And when small fishes (anchovies, sand lance, young salmonids, etc.) and crustaceans feed on the toxic algae in the plankton, and then become prey to other predators, the toxins can pass up the food chain, becoming more concentrated at each step. All around the world, massive die-offs of marine fish (e.g., sardines), mammals (e.g., whales, dolphins, sea lions, seals), and birds (e.g., cormorants, pelicans) have been attributed at least in part to PSP, wreaking havoc in marine communities. 

All those reactions and interactions begin with the neurotoxins in the algae. The toxins are produced all the time by the algae, but the reactions we notice happen more often when there are ‘blooms’ of algae; the blooms result from strong inputs of nutrients (such as nitrogen, iron, and phosphorous) stemming from spring run-off, outflow from melting glaciers, and drifting volcanic ash, which carry minerals dissolved and eroded from rocks and fields. Tides and ocean currents redistribute the nutrients along the coast. Those nutrients allow the algae to reproduce prodigiously, so they are then a super-abundant food source, readily available to consumers.

And that leaves the question of why the algae make those (and several other types of toxins) in the first place. How and why did all those varied compounds arise? So far, I have not found agood answer to that. However, I thought of three kinds of answers: 1) perhaps the compounds contribute to some essential metabolic process or they are produced just as a byproduct in the course of some metabolic, physiological processes that have some effect on growth or reproduction—the toxicity to other organisms is just incidental (from the point of view of the algae).In other words, their function is simply related to the internal workings of the algae. 2) The toxic compounds serve as a defense again would-be consumers, presumably small, planktonic critters (such as copepods) that would feel the direct effects of the toxins and be deterred from eating the algae. There is experimental evidence for this in some cases. In general, the advantage of deterrent or protective effects would be expected in the first level of consumers (the primary consumers); any indirect effects and consequences for secondary consumers higher in the food chain would probably be ‘collateral damage’–irrelevant to algal fitness and the evolution of the compounds. 3) Both #1 and #2 could happen. In other systems, researchers have found that something that arose for one function eventually evolved another function. Given the wide array of micro-algae involved and the variety of compounds that are toxic to many animals, it would not be surprising if all three kinds of answers turn out to be valid. Scientists have a big job ahead of them, to sort out all of this.

A hearty thanks to four fine folks at the NOAA lab who responded so promptly and helpfully to my queries.

Autumn is here in earnest

the subtle fruits of a somber season

We pass the autumn equinox, and the days get ever shorter. They’ve been getting shorter ever since late June, but now we really begin to feel it. The fall rains are here, and when we look out our windows, we see gray gray gray. It’s seldom as bad as it might look, however, so it pays to get out and about.

In fact, I think that getting outdoors is an important part of living with short days and gray skies. Some folks flee the fall and winter by going south, but I have found several ways to enjoy staying here during those seasons. I try to get outdoors every day, talking a walk on one of our trails; maybe not a long walk, but I’m out in the fresh air, seeing something besides four walls. I sometimes play a game with myself: the challenge is to find at least one thing (preferably three things!) of esthetic or natural-history interest. Sometimes these things are connected: I like to recall the visiting musician who took a walk in the forest and found that the rich variety of green tones in the mosses and ferns reminded him of a piece he had just played; now every time he plays that piece, he’ll see the rainforest. I greatly enjoy the rich cultural life in town, especially the music; the visual and thespian arts are also alive and well, and various lecture series can be both instructive and entertaining. Also, I do best when I have a project or two to work on; it doesn’t much matter if it is writing or building bird houses—a project that engages what’s left of my aging mind.

When I’m out, there are actually several autumn things to look forward to. Great rafts of scoters gather in the coves and channels. It is fun to watch them do what I call ‘chain diving’—a whole line of scoters dives, one after the other, in the same spot; then they all come up, one at a time, a little farther away. I have not yet found anyone who can tell me exactly what they are doing or what food they might be finding or why they do it in that way.

Out on sandy, gravelly bars, there might be small flocks of shorebirds that spend the winter with us. Rock sandpipers and dunlins often hang out together. Adults in breeding plumage of both species have black belly patches, and some show the black blotches as winter goes on, so look closely to distinguish them. These shorebirds breed on the Arctic tundra of western and northern Alaska. Sometimes there are surfbirds on rocky reefs and points; they nest in alpine tundra of Alaska and the Yukon. I occasionally flush a solitary snipe, not only in the marshes and swamps where they might have nested but even along streams in the forest.

I look forward to spotting the first slate-colored juncos that arrive at the bird feeders; they come from the Interior to spend the winter with us. Oregon juncos live here all year but mix with the slatey ones in winter. At present, both kinds of juncos are classified as the same species but different subspecies or races.

Thinking about Oregon juncos reminds me to ask a question: these birds are distinguished from slate-colored juncos in part by a chestnut-brown back. Likewise, our chickadees have chestnut-backs that are lacking in the other North American chickadees. Is there a particular reason why chestnut backs are popular here? Is there something about rain forests that favors that plumage pigmentation?

Of course, the black-billed magpies come to us in the fall too. They temporarily monopolize bird feeders, tease the eagles, and sample leftover salmon carcasses. On a rare sunny day, the iridescence of their black feathers makes them quite spectacular.

Flowering season is over in fall, but you might spot a few late purple asters alongside the trail. Behind the Visitor Center at the glacier, there has been a very late blooming Romanzoffia sitchensis (the common name is Sitka mist-maiden). In the muskegs, look for tiny yellowish cups that might be mistaken for flowers. These are the seed heads of the swamp gentian. Each two-parted cup holds a little cluster of seeds; when a rain drop hits the cup, the seeds get splashed out and so dispersed. This ‘splash-cup’ dispersal is not common, but it is shared by the bird’s nest fungus.

Sept-11-Dan-Moller-11-Gentian-seed-pods-resize
Gentian seed pods

One of my favorite things to do is watch the coho arrive in local creeks. When they do, the bears—which have been waiting for them, ever since the sockeye run ended—get busy again in the streams, and that makes for great bear-watching. I think that many of our local bears really depend on coho to ‘top-up’ their fat deposits in preparation for hibernation. The amount of fat laid down in fall is important in determining how many cubs a female bear can feed while they are in the winter den and it is probably important for winter survival of juvenile, subordinate bears that are not yet expert foragers.

I don’t know all the factors that regulate the size of coho runs, but there is evidence that juvenile rearing habitat is one important factor that helps determine the size of a local coho population. Incoming adult salmon are commonly able to slither over or jump over most beaver dams, so dams seldom limit the spawners. However, juvenile coho rear in pools in streams and in beaver ponds, and research has shown that they grow really well in beaver ponds. Down in the Pacific Northwest, biologists have even re-introduced beavers to certain stream systems, so that their ponds will increase the available rearing habitat for salmon and help restore the diminished populations. Because salmon typically return to their natal stream when it is time to spawn, juvenile rearing success helps determine the size of the spawning run. Thus, when beaver dams are removed from streams where coho spawn (so that their ponds are drained), or when beavers are trapped out of a system and their dams (and ponds) are no longer maintained, and rearing habitat is thus reduced, there is reason to expect that the coho population of that stream will decrease. And that leads to the expectation that the bears living in the area would lay down less fat, possibly survive less well, and produce smaller litters of cubs.