I had dug into grouse snow dens in the past, and given the birds’ diet, had not been surprised to find numerous scat. Grouse scat is nothing like the white liquid splotches we usually associate with bird droppings. A diet of tree buds, often those of flower catkins, creates firm, sausage-shaped pellets that look and almost feel like catkins themselves. I examined this den, too, and found fewer scat than I expected. This could be significant, because with the bird sleeping late there should have been more rather than less scat. I counted only twenty-two scat. I didn’t know how many the grouse normally produced overnight, but I did know I had a question—and a reason for counting the scat of many more of their snow dens.
There had been a series of light snowstorms on top of a couple of heavy ones; conditions were ideal for grouse to den in the snow, and the depressions that marked them on the otherwise smooth white snow blanket could be seen from over a hundred meters away. I immediately started taking more and longer hikes through the woods.
In the course of two days I found a couple dozen previously occupied grouse dens and collected the scat piles, put them into plastic bags, and thawed them at the cabin to count the pellets. The number of scat in a den varied from three to seventy-one, although most dens contained forty-five to fifty-five. These data and other observations associated with the dens suggested various possibilities that I had not thought of before, and so I was eager for more samples and more observations. Unfortunately, even after collecting many more scat samples I still could not make sense of it all, because most of them were from old dens that had been formed in the previous weeks when the light snows had only partially obliterated this track. What I really wanted to know was the time of day when each grouse had entered its den and when it had left. But could I find out?
I knew when a grouse had left its den only if I was lucky enough to flush one out of its resting place. But I would not know when the bird had entered its den, or how long it would have stayed if left undisturbed. Theoretically, I could have learned entrance and exit times by staying hidden in the woods and waiting and watching, for maybe a month, maybe more, until a grouse happened to come by and make a den within sight. If I then continued to watch until the grouse emerged from the snow, I would know the precise length of time spent in the den—by one grouse, at one time. Clearly, that strategy was not practical.
An alternative possibility—the one that I tried—involved making, and then often traveling, a long snowshoe track through the woods. On twice-daily runs I recorded the presence and progress of dens as they revealed themselves from the disturbance in the snow that marked a den entrance and the equally conspicuous exit hole. I took into account the time of day, the timing and force of occasional winds that disturbed the snow, and the intensity of snowfalls, all of which information would help me estimate how long a given den was occupied. During each run I took the scat for counting. After all previous dens had been accounted for, any entrance or exit holes on the next run would be new. Given that my view extended at least twenty meters from the sides of my path, a two-kilometer loop covered a considerable area. I used my data on den residency times along with scat counts as a roughly calibrated scat clock from which the length of time a grouse stayed in a den could be estimated by the number of scat.
Snow denning by ruffed grouse.
By March 1 I had surveyed ninety-four dens. I found that dens that were made shortly before dark and spontaneously left shortly after dawn contained forty to fifty-five scat. Thus, given a night of around twelve hours, the grouse produced about four scat per hour. Further, I flushed eleven grouse from their dens at various times in the day from morning until late afternoon. By plotting the number of scat left in these dens with respect to the time the birds were flushed I found that the scat numbers increased linearly: from none at 7 a.m., meaning they had very recently entered the den rather than overnighting there, to near thirty by early afternoon. In contrast, in the three dens where I flushed the bird in late afternoon or near dusk, I found only three or four scat, indicating that the grouse had left their dens and then reentered the snow either for overnighting or for brief stays before re-emerging after sundown to feed before their long overnight session in a den.
The scat clock suggested that in January and February the grouse fed mostly in the early morning and at the end of the day and spent a large part of the day under the snow. Aboveground observations were in agreement: in a month of twice-daily hour-long walks I never saw a grouse in the daytime except those I flushed out of their snow dens. Grouse sitting in bare deciduous trees feeding on buds would have been easily visible from at least sixty meters. But on only one evening (sixteen minutes after official sundown) did I see a grouse in the top of a white birch plucking buds from the tree. That is, the grouse were as if absent to any traveler through the woods during the daytime.
In addition to denning times, grouse behavior also left other records in the snow. First, most of the den entrance holes were angled grooves into the snow, so the birds dove into the snow with wings held close to their sides. The entrance depression from the dive led into a usually short tunnel of roughly the grouse’s diameter, suggesting the bird pushed itself forward on its chest and belly rather than walking or fluttering. The tunnel was usually less than a meter long, although one extended to three meters. The longer tunnels often had one or two of what looked like peepholes along its length, showing where the bird had stuck its head up out of the snow on the way to its denning place, the cavity at the end of the tunnel. The cavity always had a solid base to perch on and launch from, likely formed by packed snow and perhaps also snow that had softened from body heat and then frozen.
Most of the scat was of relatively solid matter in the form of the aforementioned sausage-like pellets (1–2 centimeters long and weighing on average 1.2 grams). In a den they were piled side by side and on top of one another into a tight stack, so the bird apparently did little turning after it had settled. The pellets were not messy; even when thawed they did not soil my fingers. However, dens with large numbers of scat (near fifty, as in overnighting dens) often also contained three or four much larger fecal pellets (seven grams each) that when fresh or thawed are a sticky brown semi-liquid paste. These pellets, when present, were always separate from the large stack of scat. They did not show smear marks, as would be expected if they had been in contact with the bird, so they had probably been deposited as or shortly before the bird left the den. Total scat usually weighed about a seventh of a grouse body weight.
Most of the snow dens had no foot tracks leading in or out, indicating that the birds had entered the snow by diving into it and exited by jumping up and out at the end of their dens. As expected from such behavior, the dens were in open space, providing for free access.
Den locations were also in part related to the presence of others. I had expected to find small groups of grouse denning in close proximity, as I had commonly seen several feeding in groups at dusk in the fall. Twice I flushed two from separate dens close together, although I more often found empty dens near one another.
Walking my grouse loop and seeing the new den locations showed me that there was no single exclusive reason for the cluster denning. Paired dens had been made a day apart, and some were probably night dens that a bird had made near its earlier dens.
Given these observations, I tested whether the birds were attracted to marks in the snow that mimicked den entrances. Traveling the same loop, I made a hundred fake entrances by tossing onto the snow, and then yanking back, a surrogate for a diving grouse (a dead bantam rooster attached to a strong string). However, although the facsimiles mimicked the entrance marks of grouse dens almost exactly, no new den appeared near any of them. Apparently dens become associated with one another either by two grouse denning close together or by one grouse making a new den near its previous one. (Grouse never reuse a den.)
Originally I had wanted to know if grouse spend time in snow dens both day and night. They do. Long daily denning is uniquely possible for
grouse because of their food. Unlike the other birds in these winter woods they do not need to forage continuously just to get by. Their plentifully available food, namely tree buds, can be gathered almost anywhere, probably quickly and at the birds’ convenience, with almost no search. On the other hand, digesting this cheap and easy food is a lengthy process—storing it in a crop, then passing it on to the gizzard, from there to the glandular stomach, and finally to the intestines—and hence the grouse have ample time to linger in their dens. But I wondered if, in addition to serving as a place for digestion, the denning might also have permitted the grouse to evolve a strategy to reduce predation in the winter.
In the absence of snow the grouse spend most of their time hidden on the ground in dense thickets. But in the winter their food is buried under snow; they are not able to feed on the ground as they do at other times of year, so instead they find food in the tops of trees. Most of their feeding then occurs at dawn and dusk, and they have a tendency to do it in the company of others. Both of these trends—to be crepuscular and to join others—should reduce their vulnerability to predation by their main predators, great horned owls and goshawks, when they are exposed in leafless treetops where they can be seen from afar.
They also need to avoid predators the rest of the day. What better way to do that than to become invisible by hiding under a layer of snow? But there are caveats: a clever strategy almost always engenders a counter-strategy. For example, a predator might learn to track the grouse (as we can), by making deductions from signs on the snow. This in turn would be likely to produce a counter to the counter-strategy. The grouse might apply the lottery or shell-game principle: the more holes or disturbances there are on the snow that are not associated with a grouse in residence, the more the real signal of a grouse is degraded and becomes potentially meaningless. Of the dens I found, fewer than one in ten was occupied by a grouse, in part because grouse never use the same den twice, so that numerous decoys (from a predator’s point of view) accumulate in any one area. A grouse making two dens in every twenty-four hours may leave, depending on the frequency of snowfalls, up to sixty decoys in a month. Many more depressions in the snow are created by animal tracks and by snow cushions falling off branches.
Individual grouse choosing to den near others may also forage in a crowd, so that if one is attacked the others will be alerted and able to escape. Further, even if a predator did manage to pick an occupied den, it would have to know where, in relation to the entrance, to pounce upon the grouse. This might be difficult to determine, because, at least under the condition of deep snow in which I observed the grouse, the tunnels were of various lengths and angled in different directions, so the entrance holes did not pinpoint the birds’ location. Finally, a grouse’s exit from a den is explosive. (My one attempt to photograph an exiting grouse that was right in front of me failed miserably: even though I knew the bird was about to appear, my finger on the camera trigger was far too slow to capture its movement.) But, as a final observation that combines all of the above potential advantages of the anti-predator advantage of the snow dens, I at no time saw signs of a predator having disturbed an active or previously used den, although coyote and weasel tracks were common in the same woods.
By March 4 I thought I was done with the grouse. Counting their scat was less “engrousing” than it had been before. I needed to walk the route once more and time myself in order to be able to estimate the length (five kilometers). It was a sunny noontime, and temperatures had soared to 35°F. Hairy and downy woodpeckers drummed, and blue jays held their always noisy first spring convention. An even surer sign that winter was winding down was the snow fleas. It was the first day I had seen them on the snow. Two moose, a cow and her calf, sauntered ahead of me, and I saw them for a brief few moments. But none of these was as exciting as the sight and sign of three grouse doing something they had not done for at least the preceding two months.
A couple centimeters of snow had fallen in the night, and I found one fresh grouse track that led into a spruce thicket, where the bird had hunkered down without covering itself with snow and had left sixteen scat. It had come there that morning and stayed awhile, but had left long before the early-evening feeding time. I flushed two more grouse, which also had sought shelter for a long part of the day but had not buried themselves even though the snow was soft and fluffy. Instead they had made molds in the snow under low-hanging branches of balsam fir. Soon after this, they no longer overnighted in the open areas of the deciduous woods and again roosted, as in the rest of the year, several meters high in the thick branches of spruce and balsam fir trees growing in thickets under which their scat was scattered over the ground.
The overnight change of grouse denning behavior, a reaction to changes in both snow conditions and temperature, was a gift to find so unexpectedly. It was another reminder of the rewards of continuity of observations—of one bird behavior at a time.
13
* * *
Crested Flycatcher’s Nest Helpers
A FOOTLONG PIECE OF HOLLOW LOG WITH A HOLE IN ITS side, and with two pieces of board nailed onto the top and bottom, is a great bird house. One that I made of a piece of black cherry from the winter firewood was used by a pair of great crested flycatchers. The previous year they (or another pair) had occupied a bird box of boards that was meant for wood ducks, until a pair of grackles used it in early April, when the beaver bog in Vermont had drained and they could no longer build nests directly over the water in cattails.
Now, on April 25, 2010, the leaves were popping out, and serviceberry, trilliums, trout lilies, and lilacs were in full bloom. And, oh, the birds! Migrants were still coming through, mostly white-throated sparrows and ruby-crowned kinglets. I heard the first warbler, saw a chickadee slip into the bird box that tree swallows had nested in the year before. The broad-winged hawk was back, and the snipe displayed over the bog. The phoebes had already built their bulky nest of mud and moss, this year attaching it to a narrow “ledge” of board under the roof and over a window. The neighbor’s bluebirds had just laid their first clutch of five eggs, and I heard a woodpecker tapping and discovered a sapsucker making phloem taps in a pine tree, the only time I ever saw them do that on a pine.
May 4, 2010. I found the first blue eggshell of a robin on the ground. Just-hatched Canada goose goslings, as yellow as the carpet of butter-colored dandelions now on lawns, were visible on a neighbor’s pond. Purple and white apple blossoms adorned the trees. I checked the bird box where I had seen the chickadee slip in the week before. Lifting off the cover, I saw nothing but fluff almost to the top, but teasing it apart revealed two speckled eggs. So the female had just started to lay her clutch; she would hide the eggs daily after laying her morning egg and before leaving for the day. The northern orioles had just returned and were already starting to build their hanging nest from fibers pulled out of the stems of last year’s milkweed, and a pair of kingbirds were attempting to steal the fibers to use in their own nest. Tree swallows stopped by. But there was yet no sign of the great crested flycatchers that had nested here the year before.
May 8, 2010. At noon it was snowing and chilly (26–28°F) under a dark sky. Every two steps forward toward summer were still being followed by one step back to winter. No tree swallows were in sight: they could not find food on the wing on a day like this.
May 11, 2010. It was still a chilly 25°F at dawn, but now under a clear blue sky and the rising sun the air warmed up quickly. Some of the frost-sensitive leaves had been killed. Those of birch, maple, and cherry would revive. The swallows were back, and the orioles’ nest looked finished. I was glad to see the phoebe fly to its nest. When I tapped on the chickadee box and lifted the cover the incubating female flew out, and within the insulating and concealing fluff I saw an exquisite, tiny, deep round cup cradling six eggs. The clutch was now full, and the eggs’ volume and weight exceeded those of the female that had laid them.
May 17, 2010. Finally! I heard the ringing calls of grea
t crested flycatchers and noticed a pair examining the nest box I had made from the hollow black cherry log. As one bird entered the box the other flew to the nearby apple tree and called loudly.
From then until June 19, despite being near the flycatchers’ nest box every day, I scarcely mentioned them in fifty-three pages of dense notes about five nests in view—tree swallows, phoebes, orioles, chickadees, and the crested flycatchers—except to note that when I tickled their nest box on May 27 the incubating bird snapped its bill in warning or alarm and then flew off. On June 19 I merely mentioned that the flycatchers were perching conspicuously by the nest entrance and that they seemed unperturbed when I opened the nest box and saw the now partially feathered young hunkered down. They too snapped their bills in some kind of warning display; the sides of their mouths were white, not yellow as in most birds. But then, starting the next day, I took twenty pages of notes on the crested flycatchers in just three days.
The flycatcher story started the morning of June 20. At 7:30 a.m., on my usual morning bird walk with what was then my regular entourage, two dogs, two Canada geese goslings, and a rooster, I noticed the male and female flying back and forth from one treetop to another. They kept their distance from each other and flew slowly, with deliberate shallow fluttering wing beats, and with their tails slightly elevated as though acting as air brakes. The performance looked like a display flight, and at the least there was a hubbub, but I detected nothing unusual at the nest. Crested flycatchers are normally noisy near the nest, and were being noisy now, but seemed to be making themselves even more conspicuous than usual. Why? What was going on?
One Wild Bird at a Time Page 13