wild neighbors, rarely seen

Mid-February, and Parks and Rec hikers are headed up from Crow Hill Road to Lawson Meadows. The skiers soon disappeared, leaving the snowshoe-ers to plod our way up. The lead hikers got lucky—a snowshoe hare dashed across the trail right in front of them. We almost never see the critters themselves, just lots of tracks and occasional pellets. They are nocturnal, and often active in the twilight hours of dawn and dusk. I was not one of the lucky ones, sadly. I think the only hare I’ve actually seen was a young one (called a leveret) that was clamped in the jaws of a cat.

Hares are distinguished from rabbits in several ways, one of which is the condition of the young at birth. Female hares make a simple nest, just a shallow depression. The leverets are born with their eyes soon open, ready to hop about in a couple of days, while little bunnies are born furless, blind, and helpless, restricted for several weeks to a nest, often in a burrow. In general, hares are larger than rabbits, with bigger ears and feet. Just to confuse the issue, jackrabbits are really hares!

Two species of hare live in Alaska. The Alaskan hare is found primarily in tundra habitats in western Alaska, with scattered occurrences along the north coast. It is much larger than the snowshoe hare (well over six pounds vs three or four pounds), which is the smallest hare in the world.

Snowshoe hares are widespread across northern North America and in the mountain chains that extend southward. They live in forested and shrubby habitats where they eat a variety of woody and herbaceous plants. Winter diets include lots of twigs and bark, but sometimes the hares dig down through deep snow to reach buried herbaceous plants. They may even feed, very occasionally, on carcasses. As is common among hares and their relatives (and some rodents also), two kinds of fecal pellets are produced. A soft form is re-ingested (this is called coprophagy), allowing further extraction of nutrients. Then the more fully digested result emerges as a hard, round pellet. In hard times, hares may even re-ingest hard pellets for a third trip through the digestive tract. Pellets are usually deposited singly, so a pile of pellets means that the animal spent some time in that place.

Snowshoe hare. Photo by Bob Armstrong

Northern populations of snowshoe hares are famous for extreme variations in abundance, with around ten years between population peaks, usually. Reasons for these cycles have been much debated. Hares have many predators and mortality, especially of leverets, is high. The Canada lynx preys heavily on hares, and its abundance closely tracks the abundance of hares, peaking with the same cyclic pattern.

Snowshoe hares are solitary creatures, except of course in mating season. They are territorial, defending their home ranges vs. others of the same gender. A reputable Canadian source says that the trampled runways that we see are made deliberately by territory owners. Each runway is trimmed of intruding twigs and herbs and packed firm by hopping up and down, leaving clear escape routes through the territory.

Female hares can produce several litters a year. They can mate right after producing a litter and gestate the next litter while nursing the first. Considering the high energetic cost of lactation, this is noteworthy. A single litter often has more than one father. Birthing a typical litter of four takes just a couple of minutes, after which the female leaves the nest, coming back once a day to nurse her kids. After about three days, the young ones scatter, coming back to the nest in evening to nurse. They can eat solid food when they are a week or so old and are weaned after about four weeks.

The hare spotted by P&R hikers had patches of brown fur mixed with the winter white. Mid-February seems early for the transition to summer coloration. Timing of the molt is regulated chiefly by day length, not by the amount of snow on the ground, so sometimes out-of- synch brown hares are conspicuous on snow and white ones are very visible on leaf litter.

The ecology of fear

the far-reaching effects of a universal emotion

What do animals do when they are frightened? They increase vigilance, scanning their surroundings with all available senses. Some ‘freeze’ in hopes that immobility renders them invisible. Some hide, in the best available cover. And some run. Any of those responses interferes with other necessary activities. In addition, the bodies of frightened animals respond to fear by increasing the production of stress hormones, and that increases the heart rate, the metabolic rate, and thus the expenditure of energy. Prolonged fear adds negative impacts on the immune system and reproductive physiology. All of these negative effects have consequences not only for individual animals but for their populations.

It doesn’t much matter if the cause of fear is a real threat or something merely perceived to be threatening. Failure to evade a threat bears a high cost and is often lethal, so even a perceived threat generally necessitates a reaction, just in case it is real. Play it safe, so you have a chance to play another day!

The importance of a perceived risk of predation was shown experimentally in a population of song sparrows in British Columbia. The perceived risk of predation was manipulated by using playbacks of predator calls, every few minutes all day and night long, four days on followed by four days off, throughout the entire nesting season. Some nests were exposed to various kinds of predator calls, such as hawk, owl, crow, and raccoon; as a control for the generation of extra noises, other nests were exposed to calls of non-predators (loon, goose, seal). Playbacks began well before female sparrows built their nests.

Nests were located before any eggs were laid. Direct predation on nests was prevented by netting and electric fencing, and video cameras recorded the entire nesting cycle.

The results for song sparrow reproduction were striking. Female sparrows exposed to predator calls built their nests in denser vegetation than those exposed to non-predator calls. Nests exposed to predator playbacks contained fewer eggs and hatching success was lower. Females with nests exposed to predator calls were jumpier, left the nest more often and stayed away longer, with the result that their chicks got chilled. Chicks in nests exposed to predator calls were fed less often by their parents, so they weighed less. As a consequence of chilling and fewer food deliveries, chick mortality was higher than in nests exposed to non-predator calls. The reproductive output of the population of sparrows with the perceived risk of predation was reduced by forty percent, compared that of the population without the perceived risk. It is likely that the ultimate difference between the two populations was even greater than forty percent, because deprivation during growth usually has continuing negative effects into adulthood.

Other studies have shown similar effects of perceived predation risk on the biology of other species, including elk and snowshoe hares. When hares were regularly exposed to the mere presence of a dog (a potential predator), their stress hormones increased. Females then produced smaller litters and the young hares (leverets) were unusually small and thin.

In addition, the risk of predation commonly affects where animals live and so can limit the availability of suitable habitat. For example, marmots avoid habitats where the detection of predators is impaired. Juvenile salmon and several other freshwater fishes avoid habitats pervaded by alarm cues from the bodies of dead or injured companions (although risk taking is likely to increase if the animals are not well fed). In the presence of tiger sharks near Australia, dugongs became wary and tended to move into different areas. Bears become less active in daytime and more active at night when close to roads and development. Wildlife abundance and activity is known to be lower near trails frequented by dogs.

By constraining habitat use, predation or risk of predation also affects foraging opportunities. For example, brown bears are dominant over black bears, which may avoid salmon streams visited frequently by brown bears; in such areas, black bears consume fewer salmon than where brown bears are scarce. Female bears, both black and brown, with cubs often avoid salmon-spawning areas frequented by male bears, to reduce the risk of infanticide; they have reduced intake of salmon and lighter-weight cubs as a result. For bears, fat mamas tend have bigger cubs and to be more successful in cub-rearing than thinner females, so risk avoidance has a cost (presumably a lower cost than with infanticide, however).

It is clear that predation risk and the perception of risk affect not only the behavior of individuals but also have probable consequences for animal populations, by affecting reproductive output. Furthermore, the consequences of fear may extend beyond the species that is directly exposed to the risk of predation, with cascading effects through the network on interacting species, although the magnitude of such effects probably varies greatly.

An example is found in invertebrates: when grasshoppers are stressed by the risk of predation by spiders, their body composition changes. Then, when the grasshoppers die and decompose, their altered chemistry slows the subsequent decomposition of the leaf litter. So materials are recycled more slowly, with other consequences still to be recorded.

A far more dramatic example was seen when elk in Yellowstone changed their patterns of habitat use to avoid wolves, moving uphill and losing much of the lush foraging near the streams. However, many other components of that ecosystem changed for the better. Vegetation near streams was no longer over-browsed; willows, aspens, cottonwoods recovered, which helped stabilize stream banks and improve fish habitat. When their major food plants (just mentioned) recovered, beavers moved back in, creating ponds that support fish, amphibians, and lots of insects on which other animals feed. Berry bushes also rebounded and were again able to produce good crops of berries, which feed bears, birds, and other animals. Good shrub cover in the streamside zones provides important nesting and foraging sites for songbirds, including Neotropical migrants. In short, dozens of species and the entire ecosystem benefit from a reduction of elk browsing in this area.

Herbivores and their plants

complex interactions between the eaters and the eaten

When herbivores consume their food plants, sometimes they just nibble a bit and there is little impact on the plant or on the consumer. Aside from that trivial outcome, there are two possibilities. One: the herbivore consumes so much plant material that the remaining plants are very badly damaged (think of overgrazed pastures, for instance) or are stimulated to produce defensive chemicals that deter further consumption. For example, browsing by snowshoe hares induces the production of chemical defenses in feltleaf willows, and the hares then eat less of plants with increased defenses. In both cases, the food supply for consumers is markedly reduced.

The second possible outcome is that consumption by the herbivore increases the future supply of the food resource. This sounds crazy—how could damage to the plants increase the resource and ultimately benefit later consumers? It is not entirely crazy; in certain circumstances, it has been documented to happen.

The classic example comes from studies of the grazing herds of the Serengeti in Africa. As the herds move across the plains, they crop the grasses. This stimulates the grasses to grow (in order to produce seeds eventually), helped along by fertilization from the animals’ waste products. So when the next bunch of grazers passes by, the supply of grasses has recovered and even improved. A similar effect is achieved when humans mow their lawns. Ecologists call this an increase of primary productivity, because the basic producers of energy and nutrients for the food web (namely, the plants) have increased. This kind of response to grazing can happen when the system is rich enough to support the continued growth of the plants; it doesn’t work in nutrient-poor or water-limited systems.

A neat example of herbivore-induced increase of resources comes from an Arizona study of the effects of a stem-galling sawfly that parasitizes arroyo willows; the gall is produced by the plant in response to the irritation by the sawfly. Female sawflies insert their eggs into young shoots and the larva feeds on the resulting gall tissue. When there is little egg-laying by sawflies, the willow branches naturally become more resistant to galling as they age. However, when galling is heavy, something else happens. Heavy galling kills the end of the shoot, and this allows sprouting of dormant buds near the base of the shoot. These buds make new, young shoots that are susceptible to the galling action of the sawflies. In effect, severe galling activity can thus renew and increase the food supply for later sawfly larvae (and anyone else that likes young willow shoots).

Closer to home, the browsing of ptarmigan (and moose) on feltleaf willows in northern Alaska affects the growth patterns of the willows: removal of the terminal buds and shoots kills the twig and allows the buds and shoots lower on the branch to sprout. The new shoots are more numerous and have more buds on browsed branches than unbrowsed shoots. Repeated browsing produces a ‘broom’ architecture and eventually reduces the height of the willow shrub. Thus, not only are there more shoots with more buds for ptarmigan to eat, but also the buds on shorter shrubs are just at a height where ptarmigan like to forage. So the bud supply for ptarmigan in the future is increased. However, the effect on the willows is negative—production of flowers and seeds is much reduced.

The take-home lesson is that the interactions between the eater and the eaten are not necessarily simple! The plants are not merely inert victims of munching animals. A close look is needed to understand what is going on and then explore the ramifying consequences.

Stories in the snow

a snowy ramble reveals winter action

I love to go a-wandering along a snowy trail, looking for signs left by others who’ve been out on their business of living. A recent prolonged cold spell had kept the snow soft, preserving evidence of a very busy wildlife community along a local creek.

Mink tracks rambled along the creek-side, dipping down to the stream and curving up into the forest. The footprints were bigger than those of a second mink that traveled part of the same route, so my naturalist friend and I guessed that the first mink was a male. His trackway led a long way upstream on one side of the creek and seemed to circle back down on the other side—at least the footprints were the same size there. This might have been a male patrolling his territory.

Everywhere, we found the delicate, stitchery trackways of small rodents. According to the books at hand, mice are likely to drag their long tails, flipping them to the side as a counter-balance during sharp turns, but voles don’t usually show tail-drag marks. If that’s right, we had both mice and voles, especially on one side of the creek. The tiny trackways of shrews were less numerous.

Snowshoe hares had been busy, especially on the other side of the creek. Trackways led up to the streambank, then away, then back to creekside, then away. It was as if the hares wanted to cross the fragile ice but, lacking the nerve to do so, just dithered along the bank.

A bird had hopped about extensively in and out of some brushy areas. The tracks seemed too small to be those of a junco. Then we found wing-prints where the bird had flitted a short distance to a new site, and the length of the wing was clearly too long to belong to a junco. My guess was possibly a varied thrush, some of which overwinter here.

The only actual bird we saw was a brown creeper, hitching its way up a tree trunk and flying down to go up the next tree—their typical foraging pattern as they search for tiny bugs in the bark. According to the literature, creepers commonly concentrate their efforts on trees with ridged bark, the deeper the ridges the better; this kind of bark harbors more insects than smoother bark.

A few deer tracks, both large and small, appeared as we walked along. But there was much less deer traffic here than, say, in Gastineau Meadows, where peripatetic deer had cruised all over the place.

My friend called to me: Come look at this! I saw a shallow groove in the snow on the streambank and, without thinking, said: Oh, a shrew trail. Look again, said my friend. Ah—there’s a faint yellow stain at the bottom of the groove. And here, where I had casually supposed my ’shrew’ had dived under the snow, was—not a burrow at all, but just a deep dimple. My friend, who is smarter than I am, said: I think a bird, maybe a kingfisher, perched on that branch near the edge of the stream and projectile-defecated a jet of hot poop, melting the groove in the snow. So we said: Well, if that’s so, then in the dimple at the end of groove there should be a little wad of solid waste. And yes, indeed there was! Good detective work, friend!

A final little treasure on this walk was a dead red alder that sported a beautiful array of conks (or shelf-fungi). The living conks all had a slightly soft pile of white stuff at their lower edges. This stuff had occasionally smeared sideways over the bark, showing that it had been soft when the temperatures were above freezing. What is this stuff?

Phellinus conks. Photo by Katherine Hocker

I took a sample to a local forest pathologist, who put it under his microscope. He said that the white material was certainly fungal mycelium (the technical word for the mass of filaments that grow through the wood before producing the spore-bearing conk). However, without DNA work, there’s no way to know if it belongs to a parasitic fungus growing on the conk or to the conk species itself, because this kind of conk (of the genus Phellinus) often grows some of its own filaments right down through the conk itself. So we ended our walk with one more mystery.