A sapsucker in early spring making sap licks in a quaking aspen crown, and a chickadee taking sap.
Sapsuckers do not chisel into wood for food like most other woodpeckers. Instead, they nick the bark of live trees to make the sugary sap run, and they lick it for fuel and also eat the insects attracted by the same food source. Excavating a nesting cavity out of the solid wood to create a safe home for their young is thus, for them, a huge job. It is one not unrelated to the feeding of nestlings. Birds in open, exposed nests must raise their young quickly, because as long as the young are in the nest they are vulnerable to predation. That requires fast growth, which in turn requires the parents to deliver massive amounts of food to the babies in a short time. But when the young are in a safe place such as a solid wood cavity, the food-gathering pressure is greatly eased, because the amount of food open-nest young need within a week or so can be supplied over two or three weeks instead. Thus a female sapsucker needs a mate that is strong, able, and willing to hammer in wood, to help her make a nest cavity. And what better indicator of these qualities is there than the volume and duration of his drumming?
I was excited; I had a hypothesis. If it was accurate, my hypothesis would indicate that the sapsucker males were the primary nestmakers. This would be very unusual, since almost exclusively female birds make the nest while the males are passive onlookers. (There are exceptions, though, such as weaverbirds and wrens, where the male starts the nest, which serves as a sexual attractant, and the female finishes it and thereby accepts him.)
Predictions can bias and mislead, if they come too early. But once you have a data set, there is nothing like having a prediction for making progress in at least a tentative direction. If the facts match, you are a step closer to solving the riddle. I now had a hypothesis, and if it was a correct one, it had to match not just one but numerous facts of the natural history of these woodpeckers.
In Vermont I once made, for the fun of it, a survey of 176 live poplar trees along the woodland roads I ran on. I found twelve with the Fomes hoof fungus, of which five had sapsucker holes, while there were no sapsucker holes in the remaining 164 trees. I concluded that most sapsucker nest holes are in live aspen trees that have a fungus-softened core while the rest of the tree is alive and solid. The Fomes hoof fungus, which infects a tree’s center and leaves a hoof-shaped fruiting body on its trunk, serves as a marker of a tree where a nest hole can be excavated. If a sapsucker chooses just any poplar tree for a nest site it may face a very difficult if not an impossible task, but if it chooses a tree with a fungal body on it the task will be much easier. However, the fruiting bodies of this fungus are not obvious to an observer. Thus a sapsucker male that finds a suitable tree and shows it to a potential mate is providing a service to her even if he doesn’t make the nest hole. I was eager to find out if sapsucker males do lead females to suitable nest trees, and also if males take the lead in excavating the nest hole. It was now the beginning of the sapsuckers’ nesting season, and I needed to observe them not only at the drumming tree, but also in the surrounding forest.
The leaf buds had not yet unfurled, so it was still easy to see between the trees and not difficult to find and follow the birds. It also helped that they were noisy at this time; the sapsucker pairs seemed to keep in contact with each other by calls and drumming. I had not known that females also drummed. Compared with the males’ resounding hammering, theirs was more like a tapping and had a different sound pattern, although the males’ varied as well.
I started at a sap lick on a white birch tree. A female was on the birch, a male on the next tree over. They both made a couple of drumrolls, and I presumed they were a pair. I then headed toward the clearing and the apple tree to look for others. I soon found them. Hearing a commotion, I ran to it and saw three sapsuckers receding into the distance. My crashing through the woods ended up as a nearly hour-long woodpecker chase.
The trio would fly through the trees and stop somewhere for animated interactions, and usually by the time I caught up to them they were off to another location, where their screeching and drumming would start all over again. I found myself going up and down and sideways across the east side of a hill, but when at times I did catch up I could not hold my binoculars steady enough, nor would the birds hold still enough, for me to reliably differentiate the female from the male. But after a while I realized that I was covering and re-covering the same ground, returning several times to the same patch of poplars in the woods just below the apple tree. I had heard no drumming from there, so I suspected that the three birds I was chasing were the drummer and the females that had been coming to him.
After another wild chase I remained at the poplars to wait for a possible interception there. Soon a lone female did arrive, but I lost sight of her. Then I heard a brief drumming here, an answer there, and also screeching vocalizations. I was determined to find out who was chasing whom, and after a while I found that in three chases it was males apparently trying to chase off another male; the entourage I was following included two males and at least one female. And then I found the epicenter of it all: a poplar tree with three sapsucker nest holes. This was the one tree a male kept returning to repeatedly.
Sapsuckers often return year after year to the same tree, where they annually excavate a new nest hole. The nest holes on this tree were from previous years, and there was, so far, no new one. The female drummed near this tree, and the male was at one point on the same limb with her. When just the two were there, there were no chases. Therefore, it was males chasing males, and females accompanying their males.
One male looked into one of the old holes of the aspen tree that seemed to be the sapsuckers’ focal point. Additionally, he tapped here and there on the tree trunk, possibly testing it. Eventually I noticed a yellowish patch on the tree trunk a half-meter beneath an old nest hole. I didn’t understand what it was until I saw him pecking there for several minutes and realized he was removing the gray-greenish outer bark to reveal the light-colored inner bark, in a pattern roughly the shape and size of a nest-hole entrance. The tree was thus marked, as though with initials, as his. He had staked out a nest tree.
While he was busy at the tree, another sapsucker at least a hundred meters away made screeching calls, and the nesting male—I later identified him as the drummer—instantly launched himself in typical woodpecker flight toward the sound, and I heard another vocal interaction as he tried to chase away the other male.
After pursuing the birds through the woods like a wild man, I had at last found their focal spot, which would soon turn out to be their actual nest tree. I had to leave to go back to Vermont, but when I returned nine days later the male was working deep inside the tree at precisely the spot where the outer bark had been removed. A second question occurred to me: Does the male or the female do the heavy work of making the nest?
During my nine days in Vermont I watched another pair of sapsuckers. I found four different trees where nests had been started, as well as one that had fourteen old (or partial) nest holes from previous years. I watched as a pair of sapsuckers examined them, behavior which suggested to me that they were interested in nesting. Indeed, they began to work up to ten minutes at a time to excavate what looked like a probe hole in a very thick bigtooth aspen with the hoof fungus. The pair worked there briefly, but then abandoned that tree and moved to a nearby quaking aspen (also with the fungus). The male started working and soon had a hole deep enough that his entire head disappeared into it. They abandoned this tree as well, most likely because, as I discovered, it was hollow—the fungus had rotted out the interior and there was no “floor” for a nest. Clearly, finding the right tree can be an ongoing process, not just a one-time event. And the female is far from passive in the process of choosing and making a nest hole.
What actually happens, as I learned by chasing sapsuckers around the woods for a week, was even more interesting than I had anticipated. I saw a female fly directly to the nest hole a male had begun, perch in front of i
t, and make several hey calls. She ducked her head into the hole again and again, at least twenty times in succession. Then she ducked in deeper—up to her shoulders. I saw her tail quiver and her body vibrate as if she were pecking to excavate. She continued for eleven minutes, pulled out of the hole, made four loud screeches, and flew off. In three minutes she was back at the hole and perched there silently. The male arrived, flew to her, screeched, and left with her following. Next he returned to the hole and without the slightest hesitation slipped in and got to work. He reached down far deeper than she had, so she must have merely tapped near the entrance. She then visited him, again perching silently nearby. He hammered loudly without pause for twenty-five minutes. She left after a while, came back, screeched three times, and resumed her perch at the hole. He came out and, as before, they both left in the direction of their sap licks in a sugar maple tree. Soon he reappeared and continued his excavation work for nineteen minutes before leaving to refuel at the licks. He returned at noon and worked for forty-one minutes straight. I made four more spot checks on the nest that day, until 7:45 p.m., and watched two more of his work sessions, lasting twenty-four and nineteen minutes.
The female was a frequent visitor at the nest site, but mostly as an observer or inspector, and when participating in making the hole she did so feebly. My prediction was confirmed: the male does most of the work. I never saw him feed her except indirectly by creating the sap licks. The female, though, also works indirectly for their reproductive effort: while he is excavating, she is collecting insects, gathering the protein she needs to produce their clutch of eggs.
As I later found by observing a fourth attempt to make a nest hole in another quaking aspen with the fungus, the female shows interest in if, where, and maybe by whom a nest hole is being made, and indicates her approval by token participation, which seems to signal the male to take over and do most of the work. When she came to inspect, he would resume hammering as though with renewed vigor. I conclude that the male’s drumming attracts the female, and that when she arrives he leads her to his previously found nest site. If she approves, she lets him know by offering token help, and he then begins excavating in earnest.
I eventually saw mating. The female was perched directly in front of the nest hole. Expecting her to go inside, I waited, and waited—as she just sat there, preening her feathers. Finally, after three-quarters of an hour, she started to tap weakly all around the outside of the hole. She peeked into it and tapped some more, again very lightly. The male then arrived and flew to her, and she began to hammer loudly as though using the nest hole as a drum. He fluttered away in his display (“follow me”) flight to a nearby branch. He came back, she again drummed, and he again fluttered off. On his third try she followed him to the branch, and they copulated there. Then she left immediately and he entered the nest hole. The tips of his wings showed at the entrance as he worked, indicating that the nest was perhaps half finished. She was presumably busy as well, but in the forest. Preparing to lay five to eight eggs required a great deal of protein; she had to hunt for insects. He, meanwhile, fueled up regularly at sap licks he had made. He always had several close and handy.
When after about sixteen days the nest hole was almost completed, the female helped by throwing wood chips out of the entrance. As I had expected, the male’s drumming had by then almost stopped. It was time for the beginning of incubation, when the sugar maples and beeches had leafed out, restricting visibility through the woods. The pair took turns incubating the eggs. And they played what looked like equal parts in feeding the noisy young.
Like all woodpecker babies, the hatchlings made a racket right from the start. Young woodpeckers can afford to beg loudly and almost continuously because their nest, unlike those of most birds, is a fortress, one constructed at great cost and with expert ingenuity by both parents. The babies of other woodland birds, in flimsy, quickly made nests, are vulnerable and must stay silent. They beg only briefly and weakly, and only when a parent is directly at the nest.
My observations now fitted into a consistent story, one that still gives me pleasure whenever I hear a sapsucker drumming in the early spring. Sapsucker males are amazing drummers who go out of their way to be loud. Particularly in sapsuckers, which are not adapted as routine wood excavators, the female may need help to make the nest hole, and may look for evidence that a potential mate is both willing and able to help with this crucial step in the reproductive process. Drumming vigor, as determined by its loudness, would be an excellent measure linked to mate choice by female sapsuckers. But only if the drummer actually “delivers” by doing the work of nest-hole building.
To find out what others had discovered that might refute or confirm my hypothesis, I went to the obvious two sources: Arthur Cleveland Bent’s Life Histories of North American Woodpeckers and Lawrence Kilham’s Life History Studies of Woodpeckers of Eastern North America. In both accounts I found confirming observations as well as conflicting interpretations. To my relief, neither work referenced anything like my hypothesis about drumming, even while both largely supported what I had seen. There was confirmation that males helped build the nest holes, but nothing regarding why or how this might be related to drumming or why male sapsucker nest-hole-making might be different from that of other woodpeckers.
The observations in 2012 led to others the following spring, but these were in more detail and with an experiment added. In large part they confirmed what I had found the previous year, so here I summarize only the experiment and its outcome.
The nest of the drummer and his mate in 2012 had been approximately two hundred meters from his drum on the old apple tree. The parents and fledged young later came to the birch tree by my cabin window to pick off red ants, which had a trail going up the trunk to the aphids they tended on leaves in the tree’s crown. Thus the sapsuckers were getting a protein supplement along with the sugar the ants were carrying back to their nest (which they got from the aphids, which got it from the tree sap). This was sapsucker heaven—with drum and food source next to each other—and I wondered what would happen if the nest tree, too, were located directly at the male’s drumming site. Would he still fly off into the woods whenever a female arrived? Or would the drum’s proximity to the ideal nest site keep him there? If he did not leave, would his staying induce the female to accept the location as a nest site?
Expecting the sapsucker pair to return in 2013 to raise another brood of young, I felled the poplar in which they had nested and (with a little help from friends) set up a four-meter length of it, which included their recently used nest cavity, at the super drum at the apple tree. When a male sapsucker arrived the next spring he immediately went to the drum. He also immediately took an interest in both the poplar stem next to him and the hole itself, which had likely held his nest the year before. A female quickly joined him, examined the poplar trunk, and peeked into the hole.
Sapsuckers did not, to my knowledge, reuse old holes. As expected, this male started to make a nesting cavity in the nearby woods. With no poplar close by, he chose to make a test hole in a dead maple tree, but when the female seemed uninterested he quit and started drumming at his drum. He then returned to the used nest site and began tapping inside it and throwing out small chips and debris. And to my surprise, the sapsuckers did nest in that old hole.
Watching them there gave me great pleasure—until, one hot summer day, I saw both of them picking at the tree in a bizarre frenzy and realized that they were picking at ants. They were not just eating the ants but also regurgitating them and flinging some aside.
A colony of the red ants had found the nest just as the young were hatching, and before I noticed what was happening, the eggs or hatching young had been destroyed. In the deserted nest cavity I found only a few eggshells, along with the usual debris of a red ant nest.
5
* * *
Barred Owl Talking
TALKING OWLS SEEM A CONTRADICTION. OWLS DON’T TALK. According to folklore they hoot, but ra
rely, and nowadays most people haven’t even heard a hoot. But I’ve heard them here in the Maine woods since I was a boy, and up on my hill near my cabin for thirty years. However, they don’t all hoot. The saw-whet owl emits a high-pitched, one-second-long whistle, monotonously repeating it without apparent variation at about half-second intervals for hours on end. This tiny bird sounds like a city garbage truck backing up. Hearing this song induced me to put up nest boxes in spruce woods in the hope of attracting a pair to nest there. None did. I heard a great horned owl’s deeply resonating who-who-who-whooo after midnights in the winter of 2007, when a pair nested in a pine grove next to my cabin. I was not closely acquainted with this pair, although several years earlier a great horned owl, which I called Bubo, had made its home here for at least two years, and I hoped it had returned.
Owls are almost invisible to us, and their presence is easy to miss, except when they happen to be vocal. That winter a pair took over the nest my ravens had made and used the previous year. In March, when temperatures had dipped to −29°F, I heard the ravens making a commotion at the nest site. Rushing out to investigate, I saw a great horned owl flying away from their nest tree. As I climbed the tall pine toward the nest, to my great surprise a second owl flew off, hooting at me. The owls’ two eggs lay in a snow cavity; either they had scooped out a hole in the deep snow covering the raven nest or falling snow had piled up around the incubating parent. In other years I found evidence of the owls’ presence: a half-eaten grouse stashed in a crotch of a large sugar maple, the remains of a grouse kill in the snow. One year the owls killed at least two just-fledged young from the nest of Goliath and Whitefeather, a pair of ravens whose family I had been observing. As recently as 2010, my neighbor Dionel Witham talked of “the big owl with ears” that perched in a pine tree on his property. I suspected it was Bubo, but I had no way of knowing.
One Wild Bird at a Time Page 5
