If a vertebrate animal has broken bones or lost the use of a leg, its chances of surviving for very long are usually small, and we seldom note their passage. Most die of starvation or predation. Sometimes a hardy or lucky individual manages to go on making a living for a considerable time, and there are a few scattered reports –a rabbit with a healed hind leg, or a shrew with a separated fracture in one leg, and an elk with a healing leg fracture. A couple of long-legged wading birds with misaligned leg fractures managed to survive. A few non-migratory curlews on a tropical island survived several years with broken wings and even a mallard (victim of hunting) is recorded with healed breaks in a wing. A rough-legged hawk was able to snag prey such as a rabbit even though it had only one functional leg; that leg later healed.
Much of the evidence for such exceptional individuals comes from museum specimens that became specimens long after their wounds had healed. A nice example is a lynx in Spain: an old female had lost one foot, yet she had recently produced a litter of kits. Gray squirrels in Georgia showed healed fractures in thirty-seven specimens of a sample of over ninety specimens, including seventeen with healed long-bone fractures. A study of several species of small mammals in northeastern U.S. found that thirteen to twenty-five percent of adults had healed broken bones.
These critters had survived despite serious impairments. They lived by the motto of a centenarian who (as various body systems faltered, one by one, and began to fail) said: “you just have to get on with it!” A coyote in Gustavus has been doing just that: this one has only three functional legs; one hind leg dangles uselessly. But for over a year, it had been hunting for itself, even making those wonderful leaps that pounce down on some rodent in the grass.
Photo by Katherine Hocker
Many animals are able to self-amputate a leg or a tail—the list includes some spiders, crabs, centipedes, true bugs, salamanders, and lizards (notably NOT birds or mammals). This capacity is well-documented as a means of distracting or escaping predators or, in the case of arthropods, to free a molting individual from being stuck in its old exoskeleton. A self-amputated leg is even used by certain male invertebrates as copulatory plug after he’s mated with a female, to prevent other males from inseminating her.
There is, however, another possible function for self-amputation: reducing the damages associated with a serious injury. All the animals listed above are known to break off an injured appendage upon occasion, but the adaptive value of doing this has been little studied. A study of the leaf-footed cactus bug showed that there is, in that species, an advantage to cutting off a seriously injured leg: individuals that self-amputated survived better than those that did not. However, it was not clear exactly by what means survival was improved.
Self-amputation has costs, of course: the animal has to function without that limb at least until it regenerates or do without it. There may be some loss of body fluid and a risk of infections, although self-amputation takes place at particular places where healing may occur quickly. And there is the additional metabolic cost of regenerating the lost limb, if that is possible. To be adaptive, the benefits have to outweigh such costs.
As February became March, the longer days and a streak of relatively warm days meant that folks on the trails were greeting me with “It smells like spring!” and “Spring is in the air!” Of course, we weren’t really done with snow—one day in the second week of March, I slithered and slewed, creeping through deep slushy snow on the North Douglas highway, and my driveway was thick with the same. More snow came a few days later.
Critters and plants are getting ready for spring, too. Ravens carry sticks to build a nest. Eagles are building too, bringing sticks to a growing platform that will, one day, hold some eggs in a soft cup. Mallards are seen in pairs on the wetlands; mergansers too. Juncos begin to sing, but not yet in full voice. There is a report of snow geese, the first of their kind this year.
Eagles nest-building. Photo by Jos Bakker
Plants also know what’s coming. Skunk cabbage pokes sharp green tips of folded leaves above the surface of ice-fringed ponds. Buds on elderberry and cottonwood are getting fat, preparing to send forth young leaves in a few weeks; buds on the rose bushes at the end of the dike trail are also showing promising signs. Woolly cinquefoil on a rocky outcrop above the beach shows green leaves tucked under old brown foliage.
Meanwhile, we’re still ski-ing the campground and the Montana Creek trail. The big lake and the ponds in the Valley are still covered with (softening) ice. The slate-colored form of dark-eyed juncos that visit us from the Interior are still here, coming to feeders along with the local Oregon form.
We all have signs of spring that we await eagerly and greet with glee. Here is a sampling of favorite signs from a few trail-walking friends (a few of these examples have happened already!):
–Pussy-willow catkins, males presenting pollen
–the squalling of varied thrushes
The first crocuses on a sunny bank. Photo by Pam Bergeson
— the first bumblebees, coming to crocus flowers and willow catkins
–mermaids’ purses (egg cases of long-nosed skates) washed upon a particular North Douglas beach
–the rollicking song of ruby-crowned kinglets
— early yellow violets
–wren songs from the thickets
–footprints of a bear, just emerged from hibernation
–arrival of sapsuckers, their drumming and tapping and calling
–the appearance of rufous hummingbirds (in addition to Anna’s, some of which stayed all winter)
–a flight of shorebirds on their way north for the nesting season
Spring swans. Photo by Jos BakkerBlueberry flowers. Photo by Bob Armstrong
–alder catkins starting to get soft and limp, in preparation for releasing pollen
–the refreshing aroma of cottonwood buds (after some warm days and nights)
Looking for signs of spring as they develop is a big part of the pleasure in taking a walk at this time of year. Given Juneau’s assortment of microclimates, we can expect to see things happening at different times in different places. And the lookingwill only get better in the next few weeks!
A long-standing myth says that birds have no (or very little) sense of smell (olfaction). Myths usually have long lives, and this one became dogma despite many casual observations suggesting that birds can smell. Only gradually, over many decades, and facing lots of resistance, has the myth lost strength—and finally we can say with certainty that the myth is effectively dead. Birds do have a very functional sense of smell and they use it in many ways (just as mammals do).
Scientists have determined the genetic basis of the olfactory sense and birds have the requisite genes for appropriate receptors. Studies of birds’ brain activation during exposure to odors show definite responses, usually very specific to particular odors. The olfactory bulb of brains varies in size, but even the very small ones (representing a lower number of olfactory receptors) have exhibited clear functional responses. Anatomy, electrophysiology, and genetics back up interesting observations and experiments that clearly demonstrate the variety of uses for the avian sense of smell. Some examples follow:
The myth of no-sense-of-smell began to be perforated by the late 1900s; although at first, the few documented examples were just ‘exceptions’ to the dogma. The examples accumulated, and a number of birds were generally acknowledged to use olfactory cues for foraging. For instance, kiwis of New Zealand have a long bill with nostrils at the tip, and they use that long sniffer to grub for earthworms in the soil. Woodcocks in the northern hemisphere do that also. Carrion-eating turkey vultures can detect the aroma of freshly decaying meat (not rotten) far downwind of a carcass (sometimes misled by the same odor coming from leaking natural gas pipelines). Seabirds such as albatrosses and petrels can follow the odor plume of an aggregation of krill for miles, until they reach a concentration of that favorite planktonic crustacean. In Europe, storks can trace the smell of newly mown grass to find meadows for hunting bugs and rodents. European great tits and blue tits track down the volatile chemical aromas emitted by pine trees that are assaulted by insects, and there they find lots of prey.
More myth-perforating information appeared from studies of navigation. For example: Homing pigeons exhibit an ability to locate their home lofts by smell, especially in conjunction with using visual, landmark cues. European starlings can return to their nest sites after being experimentally displaced for long distances, if their sense of smell has not been blocked. Shearwaters can navigate over the open ocean, back to their nesting colonies, using their noses.
Furthermore, several kinds of song birds, including European starling and blue tit, can detect the presence of predators such as weasels; parent birds spent less time visiting their chicks if the nest cavity was decorated with the scent of weasels. Hummingbirds often forage on flowers, but they are deterred by ants—not just the presence of ants but even the aroma of the ants’ formic acid (which they can spray to deter their own attackers). Several kinds of birds (e.g., starlings and blue tits in Europe, russet sparrows in China) add aromatic herbage, such as yarrow, milfoil, and wormwood, to their nests. The effects of the greenery seem to differ among the species, often leading to better chick growth–in some cases reducing parasites (ticks, bacteria), or reducing mosquito bites at night, or somehow improving the parents’ incubation patterns, and even affecting mate choice.
Such observations and experiments completely shredded the myth and demolished the dogma. But there was still skepticism about the use of smell in social relationships among birds— Canbirds identify kin, sex, and the identity of individuals? Can theyuse olfaction in avoiding conflict or in courtship and mate choice? Oh yes! Many studies now have shown that the avian sense of smell is sufficiently finely tuned to be used in these ways too. Here are some examples:
Some birds can self-identify: kiwis can discriminate between the odor of their own feces and that of other individuals, and are said to show territorial aggression when another individual has been detected nearby. Some petrels and prions can identify their own nest burrows by scent alone, avoiding conflict that would occur if they mistakenly entered someone else’s nest burrow. Blue petrels can identify their own eggs and avoid those of other conspecifics.
House finch males can assess the quality and social rank of other males. Spotless starlings can tell the sex of other individuals by their odor, and male mallards get really revved up by the smell of females in the courtship season. Kin recognition by smell can be accomplished by some species (e.g., storm petrels, house sparrows, zebra finches), in some cases avoiding mating with kin, in other cases preferring to associate with kin. Antarctic prions can recognize their mates by smell. Young zebra finches can recognize the odor of their siblings and the natal nest.
How do the birds make such particular identifications? It’s likely that genes involved with the immune system are involved (as they are in mammals, including humans). These genes vary a lot among individuals and are known to affect odor (somehow).They may be dispersed over the birds’ bodies when oils in the preen gland at the base of the tail are spread over feathers as the birds preen to keep feathers in good condition. These genes have been associated with mate choice in house sparrows and petrels. House sparrows make mate choices in part on the immune system, avoiding individuals with too few immune-system genes, preferring those with a good diversity of those genes.Blue petrels prefer mates with immune systems differing from their own, although that was not the case for Magellanic penguins.
An intriguing example comes from crested auklets, a colonial nester on sea cliffs around the Bering Sea. In the courtship season, they engage in the endearing behavior of ‘ruff-sniffing’—nuzzling each other’s feathers at the nape of the neck. The feathers there are specialized, emitting a citrus-y aroma, which comes from certain volatile lipids called aldehydes. These compounds can deter ectoparasites such as lice, and one of them seems to indicate that the owner has good metabolic stress responses (perhaps indicating status and making it a good potential partner). Auklets are attracted to the scent, and sometimes the ruff-sniffing involves several individuals. Birds emitting lots of this aroma can transfer more parasite deterrent and they are more attractive; they are likely to be favored as mates. If the possible status-indicator is transferred, the recipient might then falsely advertise its (unearned) status. These parts of the story needs more study.
Crested auklets. Photo by Gary S. Drew
We can expect to see more and more research revealing that birds can use their olfactory sense in many different social ways.
For more on auklets’ ruff-sniffing, see this article.
In early February, on a damp and drizzly day, a friend and I went out the Boy Scout trail to the beach. The lichens were fresh-looking and happy in the humidity, but nothing much seemed to be happening in the bird world. Then suddenly a flock of small birds came fluttering in from somewhere and settled in the grasses of the bid meadow. They were redpolls, dozens of them. They fossicked about in the bent-over grasses, searching for seeds and probably anything else that might be edible. I watched one demolish a dark, flat seed-head (probably yarrow) completely, seed by seed. A report from Gustavus noted that redpolls were eating lots of yarrow seeds, sometimes riding the seed stalk to the ground, and lying on their sides on the snow to consume the seeds.
A little later, we perched on a low ridge with the trees as a windbreak and watched another group of redpolls work the grassy berm above the beach, occasionally dropping down to the beach itself. I don’t think of redpolls as ‘beach birds’, but on a different day a friendly birdwatcher reported them foraging in the tidal wrack at Auke Rec. They are versatile foragers, often swarming over alder trees, probing the cones and sending down a scattering of fallen seeds onto the snow.
Common redpoll. Photo by Bob Armstrong
Redpolls eat many kinds of seeds and must snatch up bugs opportunistically. They breed in the far north, but irrupt in large numbers every two years or so, when the seed crops fail up north. Then they appear in more southern regions. Redpolls are well equipped to deal with cold weather: their plumage is heavier in winter, they can store seeds overnight in an esophageal sac, and at times they tunnel under the snow and roost for the night under the white blanket.
They sometimes come to bird feeders too, but they may have to share the bounty. Pine siskins, which sometimes follow a two-year cycle but often irrupt irregularly, eat many kinds of seeds, as well as bugs. A Gustavian friend recently reported huge siskin flocks at a feeder, not much disturbed by the human nearby.When they weren’t busy gobbling up sunflower seeds, they bullied any other birds that came to the feeder, driving them off. Siskins are known to be feisty and aggressive, even challenging larger birds.
Pine siskins. Photo by Bob Armstrong
Out of curiosity, this friend reached a finger out toward one siskin that was perched on the feeder, driving others away and methodically dragging seeds out. It didn’t leave, even when its tail was touched; it kept grabbing seeds. The friend then stroked its back and touched its feet. But this siskin could not be interrupted in its seed-gobbling. Then it stepped up on my friend’s finger and still kept grabbing seeds. We call them little piggies…and I have another name for their feistiness that rhymes with their acronym PISI.
Fallen sunflower seeds accumulate below seed-feeders, and the bird feed on them there too. Enter another actor: a red squirrel. My Gustavian friend watched a squirrel dash out to a crowd of siskins busily eating seeds on the snow, scattering the birds in all directions. The siskins came back quickly, only to have the squirrel spook them off again. And again, and again. The squirrel didn’t seem interested in the seeds; it was apparently more interested in mischief!
Siskins and redpolls don’t really look very much alike, seen close-up, although they are similar in size. Siskins show flashes of yellow feathers in wing and tail and have heavy brown streaks on the chest. Redpolls have fewer brown streaks in front, a black chin bib, and the reddish crown that gives them their name; males usually show a wash of reddish on the chest. Despite these differences, and being classified in different genera, redpolls and siskins occasionally hybridize!
After some big winds, there were lots of downed trees over the trails. Trail crews soon cleared the ways, leaving the cut ends of tree trunks where we could count the growth rings, if we chose to do so. Seeing those exposed rings, plus thinking about the twisted trunks of some pines, made me contemplate wood a bit—wood as a biological entity, not as a commodity to be sold or a nuisance to be removed.
Growth rings are the cross-sections of xylem tissue (as botanists call it, from the Greek work for wood), constituting what we call wood. In temperate zones, rings are produced annually by living trees. Underneath the bark is a special tissue called cambium, which lays down xylem cells toward the center of the tree and other tissues, called phloem, on the bark side. Phloem carries carbohydrates synthesized by the leaves down to other parts of the tree; special horizontally oriented ray cells bring those carbos from the phloem to the xylem. The xylem tissues provide water and mineral transport from the roots to the leaves, support, and water storage. There is thought to be a limit (set by gravity and other factors) to how high a tree can lift a column of water (between 400 and 426 feet), and some redwoods come close.
In general, wide growth rings indicate good years for growth and narrow ones indicate poor years. The first wood laid down in spring has larger, thinner-walled cells, so it is less dense and light in color, while darker, denser wood is added later in the season. This color contrast is what makes it relatively easy to count the rings. Sometimes the rings are not symmetrical—wider on one side of the tree than the other. A tree that leans(e.g., if exposed to regular strong wind pressure or a fallen one presses against it) can develop more wood on the side away from the pressure, helping to make the tree grow upright.
Photo by Mary Willson
Each layer of xylem contains a variety of cell types, including starch storage cells and others. But here I want to focus on the cells that comprise the hydraulic, water-conducting system. The passage of water in this pipeline is controlled partly by the amount of water taken in by the roots, partly by conditions along the pipeline, and mainly by evaporation from leaves at the upper end (called transpiration by botanists). Water molecules are polar (with a positive and a negative side), so they tend to cling together, and the entire column of water is pulled up when these molecules move from the leaves to the air. The pipeline is very narrow, and capillary action with the sides of the pipe makes water movement relatively easy. Leaves have openings called stomata that can open to keep water moving or close to conserve water. This system can run into trouble if the tree is subjected to freeze-thaw cycles when frozen fluid pushes out air bubbles that tend to break the water column and stop the flow (an embolism, as sometimes form in animals’ blood vessels). The problem can be exacerbated if the water supply is low, as during a drought.
As a tree grows and ages, the older xylem stops conducting water and becomes darker; it retains its support and storage functions (we call it ‘heartwood’). The younger wood (‘sapwood’) has the water-conducting function but is also important structural support.
Although wood density may be mostly genetically controlled, growing conditions (shadiness, soil fertility and moisture, etc.) can also influence characteristics of the hydraulic system, including the amount of leaf surface and stomata that releasewater and the water-conducting cells themselves. Most tree populations exhibit considerable genetic and environmentally plastic variation.
The water-conducting pipelines of conifers and flowering plants (called angiosperms—woody species include maples, alders, oaks, etc.) are different. Conifer pipelines are composed of ‘tracheids’, spindle-shaped cells, tapered at both ends, with lots of pits along the sides. Adjacent tracheids are offset from each other but their pits are matched up, so water can zigzag from one to another. In a tall tree, water may pass through many thousands of tracheids and matched pits on its way up to the leaves. These pits have an intricate, specialized valve thatcontrols flow from one cell to the next, contributing to a tracheid’s ability to recover from an embolism and reducing the risk of an embolism passing from one tracheid to another.Conifer water-transport systems are relatively narrow andresistant to freeze-thaw cycles. Most of the structural support in conifer xylem comes from the tracheids. These cells die as they age but can maintain their conducting function for years.
Illustration by Katherine Hocker
The woody angiosperms have some tracheids too, but structural fibers do most of the support and (in most species) their principal water-conducting pipeline is made of cells called ‘vessels’. More columnar and wider than tracheids, these cellshave sizable openings at each end, guarded by valve-like control devices. They line up one above another, and water can move straight up the pipe. This arrangement is thought to give these plants greater capacity for water movement, but they seem to be more vulnerable to freeze-thaw cycles than conifers. In one study, comparisons of many angiosperm species found that those with greater transport efficiency had less embolism resistance, and these differences were associated with water availability in the species’ habitats. More comparative studies will surely discover more variations that are related to environmental circumstances.
Details of these hydraulic systems and their functioning are the domain of hydraulic engineers!
Strolling on snowshoes around the Lower Loop at Eaglecrest one gray, damp day, we found, as expected, that conditions forreading animal tracks were bad on the rain-packed snow. So we counted trees instead: we had noticed previously that some of the dead or dying pines in the meadows had very twisted trunks, mostly with an upward twist to the right. So this time, we counted the pines with right or left twists and also checked whatever dead hemlocks or spruces we encountered. This informal, unscientific survey produced a series of questions, largely unanswered.
As a curious naturalist, I find it great fun to generate focused questions, even if I can’t answer them. This essay is an example of how the process goes.
–Is there something particularly about pines that produces the markedly twisted trunks? The other conifers in the Juneau areaoccasionally show such marked twists (but seemingly fewer in proportion to the total population of those species) and we have the impression from other observations elsewhere that deciduous tree trunks don’t generally twist like these pines do.
–If the twists occur predominantly in pines (that casual observation should be verified, of course), perhaps there are intrinsic factors, such as differences in the cells that make the wood, that predispose pines to twist. The principal wood cells of conifers do differ from those of deciduous trees, but do pinesdiffer from other conifers? Or perhaps there are environmental factors, such as exposure to wind and snow, that contribute to twisting? We would need to find a good sample of pines that grew in more protected circumstances to examine that possibility.
–We noted that most of the twisted pines have right-twists. Along one section of the Lower Loop, Righties outnumbered Lefties more than fifty to one. However, a casual check along the CBJ Crow Hill trail found very few twisted pines and there were proportionately more Lefties there.
So now the questions can be asked: Is the predominance of Righties due to some factor of genetics (or very early development)? Is there some environmental difference between the two locations that contributes to the very different frequencies of different twists? Or is it an accident of genetics and who happened to colonize Crow Hill vs the Lower Loop?
–As luck would have it, on the return loop, we spotted a long-dead tree, probably a pine, that had broken off near the base,exposing a central core of straight-grained wood surrounded by many layers of twisted wood. Something apparently had changed as the tree grew—the older growth rings made straight wood but the later growth rings made twist. But what?
It can be frustrating to generate lots of questions for which we have no ready answers, but it is good fun to think about the complexities! Attentiveness to things around us as we walk andthinking about the things we observe adds richness to our strolls.
An unusual bird, an unusual mammal, and midwinter construction
Regular bird-watchers spotted an unusual bird in Auke Bay this winter—an American coot. Although range maps show occasional migrants in southern Yukon, at the present time the Auke Bay record is the most northern, according to ebird. Coots are members of the rail family, which includes the sora that is often found in the Pioneer Marsh in summer. Most coots breed farther south of here, but there are isolated breeding populations in east-central Alaska and southern Yukon; this individual is presumably doing its winter things and may migrate north later.
American coot (cleaning up the harbor?) Photo by Kerry Howard
Although they sometimes use salt or brackish water on migration, coots typically nest in freshwater marshes with fairly deep water and lots of tall vegetation. They eat mostly aquatic vegetation, but also take small animals, both invertebrates and vertebrates, at times. Food is gathered by dipping the head underwater or by diving, and usually brought to the surface for swallowing. They sometimes feed on carrion, or steal from ducks, or even snatch flies out of the air. They are strong swimmers; they don’t have fully webbed feet but they have toes with lobes on the sides that increase the size of the foot paddle.
Coots are strongly territorial, vigorously defending a nesting territory again other coots, as well as ducks, grebes, and sometimes other birds. They are socially monogamous, but in some populations there seem to be floater females that lack a mate and a territory and these females sometimes dump their eggs in the nest of a mated pair. Nests are placed on floating platforms of vegetation, often anchored on the sides by tall cattails and reeds. Multiple platforms are built by each pair and used for courtship, and one is used for the nest. The nest itself is made of small bits of vegetation, making a smooth basket big enough to hold the eggs, although this tends to get trampled flat by the time chicks are present. The floating platform tends to sink, so the parents have to continually repair and augment the structure.
A normal clutch size is about eight to twelve eggs per nest; larger clutches are probably due to the activities of egg-dumpers.However, most of the dumped eggs do not produce chicks, because the nest-owners usually reject the excess eggs. Both parents incubate the eggs, the males mostly at night. Incubation takes a little over three weeks, and the eggs hatch over a span of about three days. Chicks can hop out of the nest and swim around just a few hours after hatching, calling loudly for food to be delivered. Long ago, when I was doing my thesis research in the marshes of eastern Washington, I was fascinated by the goofy appearance of those little chicks, as they swam around after the parents. They have thick black down feathers with stiff, curly, orange tips, a nearly bald head, with some bluish patchesabove the eyes, that’s fringed with red or orange frizzy feathers, and a mostly red bill. It turns out that the oddball coloring is important in stimulating the parents to deliver food. Young birds are chased out of the parent’s territory after about three months, to live on their own and mature at age one year.
Also appearing this winter is another critter that is rare around here: Fishers live in northern forests across North America, but only recently (since the mid 1990s) have they been recorded in Alaska and southern Yukon. These pioneers are thought to arrive via the Taku River valley. Fishers belong to the weasel family (Mustelidae), smaller than wolverines but larger than marten. They climb well, because (like squirrels) they can rotate their hind feet so the toes point back; they are active year-round. Like other members of this family, they are fierce predators, capturing mostly rodents, hares, and grouse, but also eating carrion, insects, and fruit—but not usually fish, despite their name. Fishers are very good at killing porcupines, biting the face and then flipping them over to rip open the belly. They also sometimes prey on marten and weasels, and research has shown that these smaller mustelids tend to avoid times of peak foraging by fishers.
Fisher. Trailcam photo courtesy Riley Woodford
Although males and females mature at age one year, most successful breeding starts at age two. Dens for mothers and kits are usually in cavities in big logs and trees. Kits are generally born in early spring, and females come into estrus and mate a few days later. Sperm meets eggs and a fertilized zygote is formed, but it does not develop very much right away; instead, it just rests in the uterus until late winter, when it is implanted in the uterine wall and active development begins. Litter size is commonly two or three kits, weighing less than two ounces each, which depend on mother’s milk for at least three months and may be weaned at four months. By early fall, they are about full grown; males usually weigh about twice as much as females.
Trailcam photo courtesy Jos Bakker
One more little surprise: a trail cam in the Dredge Lakes area has recorded significant beaver activity in the middle of winter, despite heaps of snow and some very low temperatures. Small trees have been chopped down and hauled away, presumably for food. We seldom see winter activity like this around here. Adult beavers typically live on stored fat reserves while remaining in the lodge in winter. However, kits keep growing through the winter months, and they need to eat. They usually feed on a cache of sticks in front of the lodge, but maybe this family didn’t make a big enough cache.
Thousands of insect species have chemical protection against predators or parasites. These chemical compounds are often derived from plants (which made them for their own defense); for instance, herbivorous larvae sequester these compounds, so they and the ensuing adults are protected. Enemies may be deterred from attack by the smell or learn from experience to avoid insects that produce nausea or other unpleasant effects. Chemical protection provides clear advantages to survival and reproduction. A well-known example is provided by monarch butterflies: The larvae eat milkweed plants, taking in toxic cardiac glycosides; birds that try to eat the larvae (or the later adults) get sick and quickly learn to avoid such prey.
A less well-known and fascinating example is the colorful bella or rattlebox moth, whose larvae feed on poisonous seeds of a legume, storing the toxic alkaloids in their bodies. Predatory orb-weaving spiders and wolf spiders reject toxin-laden larvae and adults. Female moths transmit the toxins to their eggs. Male moths transmit the toxins along with sperm during copulation, and females mate many times, building up their supplies of the toxins. Thus, the females and their offspring gain better defenses. Males advertise their supply of the toxins (with an airborne pheromone) and females favor males with bigger protective chemical gifts to offer, somehow even giving precedence to their sperm over those of others.
In contrast to the insects, very few birds are known to be toxic (at least to humans or other mammals). The European common quail (a subspecies of a widespread species) sometimes makes some human consumers ill, but only in fall when the birds are migrating south, possibly because of some seasonal food in the diet; other subspecies living in other regions are not usually considered to be toxic.
Bronze-wing pigeons in Australia attracted notice when introduced mammals (cats, foxes) died after eating them. The pigeons eat seeds, including those of a particular legume that contains toxins. I found no reports, however, of effects of pigeon-eating on native Australian animals (did they not eat pigeons, or were there no observations, or did they tolerate the toxins?).
The largely herbivorous spur-wing goose of Africa sometimes has poison in its body, perhaps from eating blister beetles, which contain the potent toxins cantharidin. These birds could be self-medicating by occasional beetle-eating, perhaps reducing intestinal worms and microbes. A contrast is seen with the great bustard of Eurasia, which is thought to self-medicate in this way, at least in some populations, although this bird is not reported to have toxic effects. As an interesting aside: In the mating season, male bustards eat more beetles than females, perhaps cleaning out their guts to demonstrate to females (which inspect the males’ rear ends) no diarrhea and a clean bill of health.
North American ruffed grouse sometimes made human consumers sick, but effects varied among individuals and were chiefly restricted to later winter and the eastern part of the North America in the 1800s and 1900s. These effects may have been due to winter diets that included mountain laurel, a species known to be toxic to sheep and whose honey is toxic to many consumers, even bees.
A small songbird called the red warbler, living in parts of Mexico, was long-ago reported to be unpalatable to humans; more recently certain toxic alkaloids have been identified from the feathers.
In all of these cases, the toxic effects are regional, seasonal, orvariable among consumers. It seems unlikely that the responsible compounds evolved because of their occasional effects on the particular consumers/predators; they might have some metabolic function, for example. In short, these toxic effects maybe incidental, from the point of view of the bird–they may not have evolved because of a protective function, in contrast to insects, and they may have some other function that provided an advantage that led to their evolution.
There are, however, a few known instances of direct deterrence or protection by avian toxins. Hoopoes in the Old World produce very smelly material from the uropygial (‘preen’) gland near the tail. Females spread this stuff over their feathers and their chicks, and the chicks produce it too. It is said to contain certain bacteria that destroy other bacteria that would damage the feathers.
The best-known cases of toxic birds are some species of pitohui and the ifrita of New Guinea. Touching these birds’ feathers and skin leads to tingling and numbing in humans (a fact well-known to the local natives), so eventually researchers discovered that the feathers are coated with material that contains alkaloids called batrachotoxins—highly potent poisons similar to those of the famous poison-arrow frogs. These birds may get the toxins from eating certain beetles, probably storing them in the skin and spreading them while preening the feathers; the toxins are also found in muscle tissues. There is evidence that the toxins reduce populations of ectoparasites such as lice and ticks, as well as various predators such as snakes, raptors, arboreal marsupial mammals, and humans. Levels of the toxins vary among species and among regions.
The subject of avian toxins is little-studied, so far. Many other birds are reported to be unpalatable or noxious in one way or another, and it seems likely that careful research may turn up more cases of both incidental and evolved chemical protection.
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.
The deep snows this winter are too much for these little snowshoes we usually use here—one just postholes, and the enlarged feet have a hard time pulling up out of the hole. The old North Woods style of ‘shoe would be more suitable. But the little ‘shoes are what we have, so we tend to stick to the groomed trails, walking on the side of the trail as much as possible and avoiding disturbance of the classic tracks set by the groomer.
One day in late December, a friend and I strolled up Montana Creek, looking for signs of wildlife activity. But nary a track could be seen. Strange. Some distance up the trail, a bit of open water appeared, just a very narrow, intermittent channel. Friend wished for a dipper—and just on cue, one came around a curve, flitting downstream. It stopped briefly in each small opening in the ice but didn’t seem to find much to eat and eventually went farther downstream. But there wouldn’t be any open water there until it reached the Mendenhall River, so its explorations would have to continue. When streams are frozen, dippers often forage in intertidal zones.
The next week, we rambled around the Lower Loop at Eaglecrest, where critter-tracking is often rewarding. This day was no exception: there were weasel and porcupine trackways ranging widely; voles and shrews had scampered in and out of sheltered spots. Snowshoe hares had explored many places, usually under brush or low-hanging conifer branches, where the snow was not so deep.
There was not much sign of squirrel activity, just a few tramplings near some trees. I wonder if they were using tunnel systems under the deep snow—the squirrel that lives near my house seems to have long, well-used tunnels, which it often uses instead of traveling on the surface, popping up near what used to be a garden. I know that voles and shrews often scurry about below the snow, but they had appeared on the surface fairly commonly. So why not the squirrels– perhaps they weresnacking on things in their snow-buried middens??
Ptarmigan or grouse left their bipedal trackways, often in and around brushy thickets; they may have nibbled blueberry buds as they walked. One of these birds came up to a steep little bank on the edge of the trail and slid on its bum down the loose snow, to find its feet again at the bottom of the short slope.
I spent quite a lot of time in a spot where tracks were overlapping and complicated to sort out. Some were from hares, some from ptarmigan/grouse, but there were others also. Only a few of these others were clear enough to allow possible ID: maybe about an inch and a half wide, with five toes, one of them set back a little from the others. Hmmm, quite possibly a marten! There was, however, no evidence of predation, so I can’t finish the story.
One critter that commonly leaves tracks near the Loop was missing from the records in the snow on this day: Deer tracks were conspicuous for their absence.
I was interested to see that the lower-most extension of the Loop, near the opening of the Treadwell Ditch trail, showed almost no sign of wildlife activity (just one vole track). I’d noticed this lack on other excursions up there. I have to wonder why so little activity is recorded there—the habitat is the same (to human eyes), so why is this part of the Loop apparently so un-used?
In early January, we walked up the Dan Moller trail, using the convenient snow-machine route, which was packed enough to walk without ‘shoes. Up through the meadows, looking for critter signs, but with little luck. The deep snow transformed the once-familiar landscape into unrecognizable terrain. A little imagination added to the fun; the heavy snows had laden the trees and stumps into wonderful shapes. One that caught my eye immediately was clearly an old woman, draped in her shawl, stooped over while mourning a dead companion at her feet. Another was a small spruce whose top bore such a load of well-packed snow that it was bent into a full-curl ram’s horn.
There’s no end to what you might find, if you go stravaiging around on our trails!
On the Trails in Juneau 