Left and center: A garden spider egg case opened by a chickadee to gain access to the eggs. Right: An intact egg case.
A month later I again saw a lone chickadee in that tangle. It appeared to be searching and stopped to pick at some curled dry leaves. Another chickadee joined it, picking at the empty curled leaf the first one had inspected, and seconds later a third chickadee did the same.
Chickadee see, chickadee do. Evidently one advantage of chickadees associating in flocks is making discoveries and pooling what they see and what they learn about it. Society does the same for us. It provides us with many opportunities that may come our way without our seeing them on our own. But sometimes we do see them—and seize them—and that makes all the difference.
European starling
Yellow-bellied sapsucker pair
Young sapsucker (painted after it was killed at a window)
Barred owl
Broad-winged hawk
Blue-headed vireo
Red-breasted nuthatches
Blue jay on American chestnut
Chickadees at nest site
Ruffed grouse feeding on hornbeam flower buds
Great-crested flycatchers
Male red-winged blackbirds in transit
Red-winged blackbirds in marsh
Evening grosbeaks feeding on young poplar leaves
Woodcock
Baby woodcocks in hiding
11
* * *
Redpolls Tunneling in Snow
NATURE IS A MAGICIAN WITH A BIG BAG OF TRICKS. SHE pulls rabbits out of a hat, and it is a joy to see what turns up. Sometimes what you get is different from what you expect, and that is when the magic starts to come alive.
Chickadees and their kin may stay all their lives in the same small flock in the same area, where the individuals probably know each other and have a dominance hierarchy. Northern finches, in contrast, often form huge anonymous flocks, and they specialize in and hunt for specific food over enormous distances. Their food tends to be seeds that are packaged by the plant’s fruits in various ways that make them mechanically difficult to access. Some grosbeaks have massive thick bills that crack cherry pits. Goldfinches have delicately pointed bills to handle the small seeds of thistle heads. With their specialized bills, crossbills pry the bracts of conifer cones apart to reach the seeds at their bases. But all these finches have one thing in common: the need to be at the right place at the right time to keep up with plants’ unpredictable fruiting schedules. The seed eaters move, as I’ve said, sometimes over vast distances, and so become unpredictable as well (at least to us), often being rare or absent for years in a geographical area before becoming abundant. In North America these birds include two species of crossbills, pine grosbeaks, evening grosbeaks, pine siskins, and redpolls.
The common redpoll, Corduelis flammea, is one of the smallest finches at home in the high Arctic snow-swept tundra. It lives year-round north of Hudson Bay, where it is a seed specialist on the cones of spruce, birch, and alder. Redpolls come south in winters when their food crops fail in the north. The white-winged crossbills had most recently come to Maine in the winter of 2006–2007 and the pine siskins in 2011–2012. And a large movement of common redpolls into the northern United States occurred in the winter of 2012–2013.
In 2012 the first snow fell at my cabin in Maine on November 5, and eleven days later a flock of about thirty common redpolls appeared at my feeders filled with black sunflower seeds. They had not ventured this far south from their high Arctic domain for many years, so it was a treat to see them. They continued to arrive in ever-greater numbers until by January 20, 2013, a flock of about a hundred, and sometimes as many as 150, came to my clearing and my feeder daily. Throughout this time the snow was fluffy and temperatures ranged from −8°C to −24°C. A flock of up to twenty-two evening grosbeaks, twenty pine grosbeaks, and eight purple finches were also regular visitors. So it was not surprising when on January 23, beginning four minutes after sunrise, approximately 150 redpolls as well as evening and pine grosbeaks and purple finches arrived again. Working at my desk at the window, I at first paid them scant attention, because I had by then seen them often. The wind was blowing and the temperature was −26°C.
As usual after their early-morning feeding, the redpolls started hopping around on the deep powdery snow. They concentrated their activity in and near a patch of chokecherry bushes, even though the feeders were still loaded with food and seed had spilled onto the snow. Although no food was visible where they were gathering, I noticed one bird after another duck headfirst into the snow and then, while fluttering its wings, push itself several centimeters forward with its head still submerged in the snow.
The redpolls’ odd behavior looked somewhat like typical birds’ bathing, during which the head and front of the body are ducked down and quickly brought up and the wings then beat and spray water. However, the redpolls’ behavior in the snow differed. It included simultaneously pushing and walking forward, and it lacked the repeated head lifting but had the wing beating. After each burrowing episode, the redpoll popped up and resumed hopping on top of the snow, having left a groove or a tunnel in it. I had not seen this before, so I took the opportunity to gather details.
By the end of that day, fifty-one of these groovelike depressions were scattered about where the numerous individuals had gathered in small groups. Most of these artifacts of their snow bathing were 4–5 cm wide, 6–20 cm long, and usually 4–6 cm deep. Five were tunnels, having clear entrance and exit holes with an intact bridge of snow between them. The birds’ hopping along on top of the snow had left only tracks that barely indented the surface.
After approximately an hour of this activity the birds returned to the feeders or perched almost motionless in small groups in trees at the edge of the clearing. By early afternoon they had all left the clearing. No bird had stayed in its groove or tunnel for more than a few seconds.
I had no idea what to make of the behavior (although there were some similarities to the winter behavior of tunneling ruffed grouse; see Chapter 12). There had to be a meaning, a story, behind it. Were the redpolls bathing, looking for food, or making shelters to protect them from the cold? It was a puzzle, providing an impetus to look closer.
Redpolls hopping on snow, and one burrowing in it.
As I have mentioned, in this winter of 2012–2013 the common redpolls were not alone at my feeders. Four additional species of northern finches and four species of other birds were also present for weeks at a time. So this was an excellent opportunity to compare the behavior of redpolls with that of other birds, especially the concurrent finches.
The next day, January 24, when the temperatures had dropped to −28°C during the night, about a hundred redpolls showed up after first light. Again, soon after feeding on sunflower seeds they did some snow bathing, but a strong wind obliterated the record of their ground activity so I could not get data. The cold and snow lingered, and on January 25, at −23°C, after the dawn feeding the redpolls gathered on the snow in the same chokecherry bushes. This time they left a total of fifty-nine snow furrows. A group of them gathered in another patch of chokecherries, where they left fifty-four more furrows. A third flock gathered in still another small clump of chokecherries and left sixteen furrows. Seventeen more furrows were also left in the open at the periphery of the clearing, but only three furrows were made within the large open areas of the field itself. As during the two previous days, the burrowing/snow bathing occurred only after the birds’ morning feeding. It was over by 10 a.m., but small groups of the birds continued to come and feed (but not burrow) until about 2 p.m.
Low temperature alone could not have sparked the behavior, because on January 26 the weather was scarcely changed—it was still as cold and clear with no wind and the snow was as before—but there was no snow burrowing. And on January 27, with similar weather conditions, only forty-two new depressions/tunnels were made. That was the last day I witnessed snow bathing, although the
redpolls and other birds continued to come daily all winter. The weather had generally been cold with dry snow on the ground, and for snow bathing the redpolls would have needed wet snow.
The redpolls commonly roosted high in the trees around the clearing, never staying more than a few seconds in their snow depressions. They went to the forest at night but the snow surface there remained free of their tracks and anything resembling furrows or burrows. On the other hand, in the forest I routinely saw the tracks and overnighting snow caves of the much less common ruffed grouse, so it is likely that the redpolls overnighted in the trees.
The redpolls’ behavior increasingly seemed odd to me because during my five months of observation, the grosbeaks, American goldfinches, and purple finches had done no snow bathing or burrowing. I went to the literature to search for previous reports of snow tunneling and suggestions about its causes. In the winter of 2001–2002, flocks of redpolls had arrived in Adirondack Park in mid-January and been seen fluttering in the snow. J. E. Collins and J. M. C. Peterson concluded in 2003 that the birds stimulated one another in this activity and were apparently doing it “for enjoyment.” I presume that enjoyment is a given—eating is for enjoyment too, but we know its function. R. S. Palmer (1949) and G. Furness (1987) had described similar bathing activity of common redpolls in Maine. In contrast, small birds in northern Europe, including redpolls and Siberian tits (Parus cinctus), had been reported to take up residence in snow burrows to escape wind and cold. To try to test these hypotheses, I examined the data on the redpolls as a function of the weather. Temperatures varied from −28°C to 4.5°C, skies from clear to overcast, snow from powdery to sticky wet. The redpolls needed powdery snow to tunnel in. But they did not bury themselves in the tunnels they made; moreover, they never bathed in wet snow, and they tunneled only in cold conditions but did not overnight in the tunnels even in the coldest weather. With hundreds of redpolls present around the feeders for many days over a wide range of weather conditions and temperatures, no factor of the external environment stood out as an obvious trigger for the snow tunneling.
However, individuals within the redpoll flocks are strongly influenced by one another. They arrived in tight flocks as in a small cloud, remained in tight flocks when they were feeding, and left the same way. Flight stimulated flight. When one flew to feed at a spot where I had not seen any birds in weeks, another and another quickly joined it until dozens were assembled there. In one instance approximately twenty redpolls gathered where one bird had first flown to pick at the seed head of a pigweed (Chenopodium) exposed above the snow. The twenty returned to this site at least fifteen times in succession in short, in-unison flights, but none made an attempt to burrow into the snow where the seeds of the mostly still-buried plant could have been found. Similarly, bathers attracted each other and also acted in unison.
The tunneling behavior could not be explained as a foraging strategy, since it did not occur in the presence of food but rather in its absence after feeding was finished. The default hypothesis is that the making of furrows and burrows in the snow is related to building shelters for energy economy and warmth. As we’ll see in the next chapter, the local grouse submerge themselves in loose snow and make a new snow cavity each night. Small body size should make the redpolls much more vulnerable to cold than the grouse because it accelerates heat loss, and they may compensate behaviorally by huddling, as golden-crowned kinglets do on tree branches at dusk. Redpolls, though, don’t huddle, and likely have other ways to survive at sub-zero temperatures.
One important consideration is that these redpolls in Maine were far to the south of their usual range. How they survive winter nights in the Arctic tundra is not known, although some researchers have suggested that they overnight in snow tunnels. But since even in wind and at temperatures to −26°C they remained in their local burrows no longer than several seconds and did not return to them in the evening, this explanation for their tunneling in Maine seems questionable.
Here in New England, the burrowing serves no immediate function. The usual reason given for apparently senseless behavior is play. Though motivated by enjoyment rather than anticipated reward, play provides practice for adaptive behavior that may be needed in the future. For example, redpolls obviously have not only the ability but also a strong urge to burrow in snow. This behavior may be fully expressed in the Arctic, where it is useful to help them survive the cold, and only partially expressed, as play, in places where remaining in the burrow may be costly. For instance, small birds in burrows under snow in New England forests would be vulnerable to ground predators such as short-tailed shrews and weasels.
But the main reason for not overnighting in their snow tunnels in New England, I suspect, has to do with temperature fluctuations. During most winters here, days of snowfall, snowmelt, and deep frost alternate, often overnight. A small bird in snow that is alternately subjected to thawing and freezing is exposed to the lethal risk of becoming trapped under an ice crust. Frequency is of little relevance, when just one such ice-storm event could kill an entire population if all the birds made the mistake of burying themselves in wet snow the evening before an overnight frost. Perhaps the redpolls truncate their overnighting behavioral repertoire in the south because of the more variable winter temperatures.
Redpolls were back two years later. They were in smaller numbers, up to twenty at a time. As before, temperatures were low and the snow was powdery for the two months or more that they regularly visited my birdfeeders. They hopped on the snow daily, but I saw none of the bathing/tunneling behavior. I was and am hugely pleased to have used the rare opportunity to observe their snow bathing in the brief period two years earlier. The absence of the behavior since then makes it all the more intriguing, and shows that there must be more to it than I imagined.
12
* * *
Tracking Grouse in Winter
THERE ARE RUFFED GROUSE IN MY WOODS, AS IN ALMOST all woods in northern North America. I love the sound of the males’ music on warm spring mornings, and I have also heard that deep, pulsing, thunderlike drumming in the night. I see them most often in November, when I’m likely to be up in a tree in the woods at dusk waiting for deer. It is quiet then and I’m straining my ears hoping to hear a twig snap from perhaps a deer’s distant footstep. At such times I have often been startled by grouse, because beginning in the fall they venture off the ground and fly into the treetops for their brief evening feasts on buds. At dusk in the otherwise silent forest you hear every stray wing beat against a branch, and the sound is startling, especially in deer season after you have been hyper-alert for hours at a stretch, day after day.
Grouse are our most hunted northern game bird, and they are the favorite prey of goshawk, red-tailed hawk, and great horned owl. Perhaps for these reasons, they are one of the shyest of birds. But rare individuals at times apparently become attached to humans. A friend of mine, a logger, told me of a grouse that would meet him every day in the woods and follow right behind him in his skidder. Another friend, a naturalist, had one follow him on his bicycle (he stopped and grabbed it for catch-and-release). A grouse visited another friend’s family on their porch every day for months. A photo in Northern Woodlands magazine (winter 2013) shows the naturalist Mary Holland with a wild grouse on her knee—the bird had followed her on her hike through the woods. She later reconnected to it on several occasions. From me grouse have mostly flown away, and pronto, except for some females that seemed intent on attacking me when I inadvertently approached their young. On the other hand, grouse do not flush easily from a nest when incubating the eggs. Only when I’ve come near one repeatedly has the female flown off and out of sight before I got there.
Ruffed grouse stay year-round in the north woods no matter how severe the winter. I knew something about their lives in summer and fall, but nothing of them in winter except that they seek overnight shelter from the cold by burying themselves under the snow. Snow insulates, so this behavioral adaptation to winter reduces thei
r need to shiver to keep warm and hence conserves energy. Grouse in the winter woods of Maine face no shortage of tree buds, but energy extraction from this mostly roughage diet is limited by the processing capacity of the gut. As with most herbivores, a grouse’s gut has a full-time job just to keep up a positive energy balance.
By January 2015, as in many Maine winters, we had not only an abundance of snow but also nights and days of sub-zero temperatures. Curiously, although it had been a good year for grouse, I had not seen one for nearly six weeks. But then, while I was out on snowshoes looking for woodpecker holes as possible overnight shelters of chickadees and nuthatches, a grouse exploded out of the snow within two meters of me. This would hardly have given me pause except that I knew grouse will spend the night under the snow. Given the context of the birds’ and perhaps my own problems in overnighting at sub-zero temperatures, I was puzzled. It was, I noted at the time, a “sunny and practically warm day, and the sun had been up for four hours—so why was this bird just leaving its bed?” Flushing a grouse out of the snow at noon was not unheard of—I had done it in earlier years—and it was easily dismissed as common knowledge, at least to some. But common knowledge is often worth examining.
One Wild Bird at a Time Page 12
