Shorebirds

creative nesting strategies and social systems

Eleven species of shorebirds may nest in Southeast, according to Armstrong’s Guide to the Birds of Alaska. At least six of those are known to nest in the Juneau area. One additional species, the least sandpiper, was formerly relatively common near the airport dike trail and on the glacier forelands, but increased dog and human activity, plus habitat changes in those areas, have greatly reduced and perhaps eliminated this species as a local nester.

The term ‘shorebird’ reflects the fact that most people see them in winter and on migration, when these birds typically forage on shorelines. The Mendenhall wetland, for example, is recognized as a globally important stopover site for lots of migrating shorebirds. In fact, however, many shorebirds do not nest near shores. Instead, they commonly nest on tundra, in alpine zones, in forest, grassland, and muskegs.

I encounter spotted sandpipers most frequently, because they nest near rivers, lakes, or saltwater, on beaches and gravel bars. I see nesting semipalmated plovers in the tern colony near the glacier and also along marine shores. Killdeer try to nest in gravel pits, on flat rooftops, and at the edges of parking lots where the eggs are at risk of getting crushed. When I venture into muskegs in the nesting season, greater yellowlegs are hard to ignore, because they usually shriek and swoop and dive-bomb any intruder. I almost never see nesting Wilson’s snipe, but I hear them doing their aerial display high over their wet grassy or sedgy meadows—it’s called ‘winnowing’, from the sound made by air whooshing through their spread tail feathers. And nesting solitary sandpipers in their wooded wetlands I virtually never see; apparently few other folks see them either, to judge from the little research that’s been done on them.

Shorebirds are generally ground-nesters, but the solitary sandpiper is a notable exception. This species has the peculiar habit of nesting in the abandoned nests of songbirds such as robins, jays, and blackbirds. It is the only shorebird in North America to do so, and one of only two species in the world with this habit. After claiming a nest, the pair may make slight renovations to the basic structure. I wonder if they ever take over a newly built nest, driving away the owners! A pair of solitary sandpipers was known to nest this year in a flooded, shrubby area near the glacier, although we never found the nest itself.

solitary-sandpiper-by-bob-armstrong
Solitary sandpiper. Photo by Bob Armstrong

After I contemplated this strange habit for while, I realized that using an old songbird nest might be a great strategy. Predators (and bird-watchers) often find songbird nests by watching adult birds go to and fro, carrying nesting material or feeding chicks. Solitary sandpipers, however, don’t carry nesting material or feed their chicks. The chicks are precocial—hatched covered with fluffy down, eyes wide open, and able to run or swim almost immediately. So many of the usual cues for nest-finding are absent. But that leaves the question of how this nifty trick got started…

In general, our locally nesting shorebirds lay three or four eggs, but patterns of parental care vary considerably. Most of these species are socially monogamous (one female paired with one male, although copulation is not necessarily restricted to the mated pair), but some engage in degrees of extra-curricular activity, by mating with the neighbors as well. Both males and females can incubate eggs, apparently, except in Wilson’s snipe; in this species only the female sits on the eggs, and she does so for three to four weeks. During that time, the males are busily seeking extra-pair copulations. Male snipe make up for their lack of egg-tending, so to speak, by caring for some of the chicks (of which he may or may not be the father, because all his neighbors were as busy as he was). Snipe are unusual among shorebirds in that the parents actively feed their chicks for several weeks, and don’t just lead their chicks to food as the other species do.

Spotted sandpipers are exceptional to the usual arrangement of social monogamy, because they are often polyandrous: one female pairs with two to four males, either simultaneously or sequentially. Females hold large territories that include the smaller territories of her males. Males do most of the parental care, including incubation, but females may help at her first nest (until she gets another male) and at the nest of her last male of the season. Females even beat up their mates, sometimes, if the males are neglecting their incubation duties. Competition is fierce among females for males, and among females if certain females are perceived as especially desirable.

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Good finds in Gustavus

stealthy spiders, ambitious amphibians, strange ferns, and more

A summertime walk through woods and meadows is almost always good—birds are singing, flowers are blooming, and there’s always nice fresh air. But sometimes all the little pleasures form a base on which rest some observations of particular interest. Here are a few good ones from a recent trip to Gustavus.

–Dandelions had mostly gone to seed, so fields that had been golden with flowers were now white with plumes on mature seeds ready to disperse on the wind. But here and there we found a laggard flower, still yellow and conspicuous on the background of white. On one of these late bloomers there was a bumblebee, a strangely immobile bee. Looking more closely, we saw a yellow crab spider with the bee in its clutches. Crab spiders are venomous (to insects), immobilizing their prey and then sucking out the juices. Dinner was in progress and the bee would fly no more. Crab spiders are generally ambush-predators; some of them lurk on flowers in hopes that a tasty insect will alight. The color of the spider often matches the color of the flower on which it awaits a victim.

crab-spider-howard
photo by Kerry Howard

–The ponds at the gravel pits are a great place to see shorebirds, swallows, and kingfishers. There were sticklebacks swimming around and, in June, there were gravid females full of eggs. One pond held many thousands of toad tadpoles, swarming in the shallows where the water temperature was salubrious. They came in a variety of sizes—some at least six times bigger than the smallest. A female toad can lay thousands of eggs; the hordes of tadpoles that we saw undoubtedly had many mothers, which probably laid their eggs at somewhat different times, accounting for the size variation. None of them had begun to transform into toadlets; no little legs were visible. A dense pack of tadpoles clustered around a silvery object, each one trying to grab a mouthful. Looking closely, we discovered that the silvery object was a dead stickleback. Toad tadpoles commonly feed on algae and detritus, but they are also known to scavenge carrion and even the dead bodies of their comrades. Toad (and frog) populations have declined dramatically almost everywhere, and it was heartening to see this large aggregation of juveniles.

–Gustavus is noted for (among other things) its wide sandy beaches. On our way out to one of them, we heard some odd sounds, rather like the hooting of a small owl. As we listened carefully, however, it became apparent that several snipes were performing their aerial territorial display. It’s called ‘winnowing’, and it’s made by the rapid passage of air over the spread-out tail feathers, usually as the bird dives toward the ground from high in the air. Usually the male does this but sometimes females do too. I hadn’t heard this display for a long time and it was a gladsome sound.

–Out on the sandy beaches we found windrows of long, flexible tubes that were the former housing of certain marine worms. The worms were long gone, possibly starved at the end of winter when food is scarce. Then the tides presumably stripped the empty tubes from their attachment points and piled them up on the beach. This observation stimulated a lot of conjecture but no concrete answers.

–On the vegetated sand dunes there were lots of the strange little ferns called moonworts (a.k.a. grape ferns). They don’t look at all like ferns to the layman’s eyes, because the fronds are generally not very lacy or branched. We found many that appeared to be the common moonwort, but there were also a few much more robust individuals that were certainly a different species. On one of the postglacial-uplift meadows we found another kind, one that is now classified in a different genus; the fronds on this one (so-called rattlesnake fern) are somewhat more ‘fern-y’. All three of these are widespread species in North America and even beyond, but they are so odd that it is always fun to find them.

–The pilings of the public dock usually offer something even to a casual observer. Enormous white anemones, far larger than any we usually see in the rocky intertidal zone, wave their tentacles if the tide is in. Sea stars cling to the vertical surfaces too, but the largest ones have trouble hanging on when the tide goes out and leaves them above the waterline. Colorful sponges and tunicates add to the array. Sometimes there’s a giant whelk laying a coil of egg cases. Small fish sometimes gather under the docks and are visible between the pilings. And while one inspects the fauna on the dock, barn swallows are swooping overhead, gathering flies and mosquitoes for their chicks.

–We searched for lady’s slipper orchids (of which more, later). One clump of flowering stems still included a stalk with last year’s seed capsule, well dried. Someone opened the capsule to see if any seeds were left and found, instead, a tiny spider guarding her minute ball of orange eggs. We were sorry to have destroyed her safe-house!

–Sweetgrass grows in many Gustavian meadows and some of us stopped to braid some stems. Braided sweetgrass is used, especially by Native Americans, to construct baskets and decorative items, and we had to try just a simple braid. As we concentrated on our task, we heard thundering hoofbeats, getting rapidly closer. Turning around, we saw a fast-trotting female moose, followed by a young calf. They were so intent on getting away from whatever startled them that they ignored us and passed by, barely thirty feet away, and off they went, full tilt.

Visiting Gustavus

observations on geese, raptors, otters, and the effects of moose browse

One of the first things I noticed was a roadside muskeg in which the shore pines were in sorry shape, with many brown needles. Upon inquiry, I was told that these pines are infected by a fungus that causes needle blight. The fungus kills off mostly the older needles, so an affected pine has only small tufts of newer needles near the branch ends. A serious level of infection can kill the tree. Cool, wet weather favors the production of spores, which are spread by wind or rain-splash, and the spread of this disease. And that’s the sort of weather that has prevailed this spring, it seems.

A flock of several hundred white-fronted geese loafed peacefully in someone’s back yard, while an off-shoot group foraged nervously in a nearby field. These birds were on their way to the nesting ground on the tundra up north. They were enjoying an important way-station on their journey, where they can feed and rest.

A pair of Canada geese seemed to own a piece of pasture, apparently unruffled by grazing horses. But they reacted sharply when a little flock of other geese came in to graze. The small group of new arrivals was a mixed lot—mostly white-fronts, a couple of Canadas, and a sole snow goose. The residents paced back and forth, talking at the unwelcome visitors, who went right on grazing but did not venture much farther into the pasture.

The great outwash plain created by melting glaciers supports numerous stands of willows, most of which have been severely browsed by moose, such that they seldom exceed three or four feet in height. ADF&G has a long-term study of moose ecology and the effects of moose browsing, focused on a set of exclosures that prevent moose access. The willows inside the exclosures look markedly different from those outside: the inside willows are much taller and produce more catkins. The paucity of catkins on the heavily browsed willows may have extended effects, well beyond the diminished reproductive capacity of the willows themselves. Willow catkins are an important source of food (pollen, nectar) for queen bumblebees, which mate in the fall and overwinter in small burrows. In spring, they need to feed so they can produce broods of workers. Bumblebees are important pollinators of blueberries, beach pea, lupine, and many other flowers. So the obvious question is: Does moose browsing significantly reduce the spring food of queen bees, thus reducing their ability to produce healthy broods, and thus impairing the pollination success of various flowers?

bull-moose-young-browsing-on-willows
Photo by Bob Armstrong

There may be other ripple effects of moose browsing. For example: Browsed willows produce fewer leaves and therefore less leaf litter below the shrubs. So we can ask if the reduced leaf litter affects the mosses, lichens, grasses, and herbs that constitute the ground cover. A lower number of leaves on the browsed shrubs should reduce their growth rates, because fewer leaves mean a reduced capacity to synthesize carbohydrates that provide energy. And one has to wonder if the cropped-off willows offer fewer nest sites and foraging surfaces for birds, leading to a lower density of birds than would occur in unbrowsed stands.

A male harrier coursed up and down the deeply incised channel of a tidally-influenced river that runs across the outwash plain; he was probably hoping to snag a shorebird or two. I heard snipe, high in the air, doing their flight display: as they swoop around, the rush of air over the spread-out tail feathers is modulated by the beating of the wings, producing a characteristic sound known as ‘winnowing’. Snipe winnow both on migration and on the nesting grounds, and most of these were probably still in migratory mode. I also think I heard a pygmy owl, tu-tu-tu-ing in the trees. A male robin carried a beakful of worms to his chicks, proving that the robins thought it was spring despite the raw, cold weather.

Another treat was the opportunity to watch three river otters exploring one of the inland ponds near Bartlett Cove. I suspect this was a family of a female with two of last year’s offspring, although there was not much difference in size. Otter families often stay together over a winter and into the next spring. These otters were well aware of our presence and kept bobbing up to peer at us. I was told that river otters are often seen as they travel considerable overland distances in Gustavus, visiting inland ponds (are there fish to be caught??) and returning to the ocean shores.