Fairbanks, Alaska. Almost every spring, we revisit the Platte to watch in awe as swirling legions of mid-continent sandhill cranes congregate while they fuel up for their long April journey north. After we return home to our own 40 acres in the middle of Alaska, we wait with trepidation for the return of two particular cranes from the Nebraska legions. April may not quite be “the cruelest month” for us, but it is the longest one.
For a decade, the same pair of wild sandhill cranes has nested in our backyard. We have come to know these two birds as “Millie” and “Roy” and have recorded their daylong activities as they raise their young. Over that busy summer season, they spend a little more than five weeks reestablishing ownership of the territory and incubating the eggs, then another month protecting and feeding the vulnerable toddling chicks and finally two intensive months emphasizing dance and flight. The summer sociology of these cranes is like that of an isolated settler family homesteading on the Great Plains in the 1860s—a stark contrast to the month of March that they spent among the tumultuous hordes of birds on the Platte.
It takes a month for sandhill cranes to migrate from central Nebraska to central Alaska. En route, they stop for extended foraging at a staging ground west of Saskatoon and then fly up the eastern side of the Rocky Mountains before turning west to pass over the lowland boreal forests and reach central Alaska. They arrive here between April 25 and 28, when the pond is covered with ice, snow still lies a foot deep on the cranberry bog and rusty brown bog rosemary and willows demarcate the boundary between marsh and black spruce forest. In the next four months the snow will melt and the top foot of soil and vegetation will thaw, but the underlying permafrost base persists throughout the year.
Upon arrival at their traditional summer nest territory, Roy and Millie reconnoiter, walking slowly as they scan the cattails and the leafless willow twigs. In these exploratory strolls, their red foreheads are expanded and prominent, a reflection of high arousal upon returning to the place they had left eight months ago.
The navigation skills that reliably guide Roy and Millie year after year to one particular three-acre pond in the center of largely roadless Alaska seem almost uncanny. Scientists have proved that some birds can use the stars, the sun, the magnetic fields of the earth, the topography of the landscape and even scents for orientation and navigation. Which of these are used by migrating cranes? Even if we precisely identified the most salient environmental cue, we would still be ignorant of the computational processes within a bird’s brain. Somehow a crane integrates diverse sensory information to produce a biological analogue of a GPS, a mental map that guides every one-day flight segment so that the birds arrive precisely on schedule. We hope that 21st-century neuroscience will tell us how they do it.
Once satisfied by careful perusal of his summer home, Roy begins to dance. On the Platte, crane dancing is characterized by spectacular jumps, wingspreads and dramatic bows, directed briefly toward a mate or at a transient rival in the hurly-burly world of the shallows on the river. On the nest, territory dancing is much more private. Cranes are social creatures and the family is the fundamental social unit. For the pair and their colts, dancing cements social cohesion. In April dancing probably also helps to synchronize the reproductive physiologies of the two birds.
The first extended dance that we see in spring is largely a solo performance by Roy—running forward on the icy platform, spreading his wings, vocalizing, springing up, crouching down into a tuck-bob, pointing his bill skyward in an arch and spinning in a sequence of steps like a ballet dancer’s tour jeté. Millie may run across the stage as Roy pauses and then resumes his acrobatics. This overall dancing bout lasts almost a minute and is followed by a unison call—a strong vocal statement that proclaims “this site taken.” Dancing epitomizes the crane version of high arousal behavior.
Temple Grandin, a uniquely gifted animal behaviorist at Colorado State University, and Jack Panksepp of Washington State identify “seeking” as one of the fundamental animal emotions, perhaps even a kind of master emotion. Panksepp calls it “the basic impulse to search, investigate, and make sense of the environment”. Our pair of cranes spend many hours inspecting their territory over the first week after their arrival.
From time to time Millie and Roy break away from peering at bushes and point their bills forward and slightly upward as they stiffly step in a “parade march.” Then Millie spreads her wings like a solar collector as an invitation to Roy, who responds by mating. As a coda, they bow to one another.
As territorial reconnaissance continues, Roy occasionally piles cattail stalks or other vegetation as if he were starting to construct a nest. For a few days Millie’s response is to look away and ruffle. But eventually she accedes to his suggestion, and they build a loose nest together. After Millie lays her two eggs, they trade off incubation duties every two to eight hours for 30 days.
During incubation, the pond thaws; snow disappears from the marsh, and sedges, cranberries, cattails, willows, bog rosemary gradually green up. In the surrounding boreal forest, wood frogs awake from hibernation and hop to shallow pondlets so males can croak like hoarse ducks and females can lay their eggs. In off-duty shifts Millie and Roy feast on the frogs as well as last year’s berries, voles and tubers. When other cranes call in the surrounding valley, our pair answers. On some days, Roy flies off, apparently in response to the distant calls. What goes on in the valley is unknown to us.
Sometimes a single crane or a “foreign” pair of cranes lands on the cranberry bog to begin their own territorial scrutiny. With red crowns flashing, Roy and Millie expel them by bowing, ruffling, chasing and unison calling. In one instance when the intruder appeared in the central cranberry bog while Millie was on the eggs and Roy was away visiting, Millie flew off the nest, calling loudly as she crossed the marsh to challenge the foreigners. From afar Roy answered her and landed feet first to join in repulsing the invaders.
When Roy and Millie first arrive, they are pale gray in color, but during the weeks of incubation, they become smeared with brown muck as a result of a behavior called “feather painting.” Nina Faust in Homer, Alaska, has uploaded to YouTube a fascinating video (“Sandhill Crane Painting 101”) that shows a crane plucking tufts of muddy plant material from the marshy ground and wiping the mud across his feathers. In some senses, the vegetation is a tool, like a paintbrush. The function of feather painting has yet to be definitively established, but it is widely assumed to provide camouflage for the nesting birds.
Roy and Millie have made a nest every year since 2001. Like most cranes, they are faithful to their nest territory and to each other, more or less for life. In 2001 a fox was seen near the nest. In the next two years the eggs hatched but the chicks survived only a few weeks. Twin chicks hatched in 2004, 2006, 2009 and 2010, but only one of them lived through the summer and migrated. In both 2008 and 2010 a single chick hatched and migrated.
When youngsters are present, Millie and Roy spend 13 weeks as full-time summer school teachers. As typical for species of birds that lay small clutches of large eggs, the parents invest heavily in each youngster. Crane colts need protection and nourishment, and equally important, they need a progressive education.
Summer school has five core subjects: Foraging, Seeking, Defense, Dancing and Flying. Colt education requires both physical training and enhanced mental skills.
In the first two weeks after breaking out of the egg, each tiny chick toddles closely after a parent, tumbling over grass and vegetation but running on. It is sometimes hard work for the newly hatched to keep up with the adults. In one instance the family took an overnight exploratory hike through the woods to a pond half a mile away when their colt was only five days out of the egg. The young colts are innately curious about their world, gazing intently at their parents, each other and objects in the environment.
The parents forage meticulously and offer seeds, berries, spiders, caterpillars and even whole dragonflies to the colts. Millie is especially adept at tracking and snatching dragonflies in mid-flight. The large insects are first presented whole to the tiny chicks and then dismembered into bite-sized fragments. When Roy catches a vole, he shakes the limp corpse until it falls apart into small strips of flesh that can be offered to the chicks. The chicks begin to peck at vegetation, perhaps just striking at a pattern, imitating a parent or testing for palatability.
The parents are very wary. The family forages as a group of four or in parent-colt pairs. If a predator like a mew gull swoops down toward the family, the chicks shelter under their parents, who bill-stab up at the attacking gull. For nap-breaks and overnight, the chicks roost under Millie’s wings, a behavior that we call “tenting.”
After mid-June, Roy and Millie may take brief breaks from foraging to dance very briefly with each other and then try to recruit a colt. In these cases, an adult faces a colt, squats down with wings out, vocalizes as if coaxing the small bird to join in. The colt looks puzzled at first but eventually responds with clumsy jumps, flailing wing stumps and little leaps that sometimes become splats.
Also at this age twin colts often gently bill-spar with each other, but these sparring bouts are short-lived and never, in our limited experience, seemed to be seriously destructive.
At seven in the morning on July 2, 2009, our sleep was interrupted by unison calling. On the previous day, both twin colts had been trailing their parents around the bog, but “Phyl” usually lagged behind. “Jacques,” the larger, more vigorous colt, kept up with the adults and got most of the food. When we were awakened, we saw that Phyl was an immobile lump in the grass, apparently dead. Again and again throughout the day one parent or the whole family would pause from their foraging routine to return to Phyl’s body for a few minutes. They stood still, stared intently at the feathery remains, preened themselves by picking at feathers on their back and wings and, on occasion, piled a few strands of grass on Phyl.
After the last of these visits at 9:52 p.m., Roy stepped into the middle of the cranberry bog and began dancing on the grassy platform, streaked with shadows from the sinking western sun. His dance was uncommonly vigorous. Millie joined him, with display sequences like “run-flap-glide” that we knew from scientific literature but had never before seen. Even Jacques participated in the family dance, facing off to Roy’s wingspreads with little erect wing-tuck postures and running to and fro. The high activity lasted for three minutes, the longest dance that we have witnessed in a decade of watching these cranes.
Crane dance reflects attitude and arousal. It is also a mechanism for social bonding. Excited and extended dancing on the ice was correlated with the end of migration and prolonged intense dancing likewise followed the death of this colt. Birds have similar brain centers with the same neurotransmitters as mammals, but the workings of their brains are yet opaque to us. At the present time we do not have direct objective data about the physiological causes of “emotional displays” in birds. We can only watch and wait for more clarity from laboratory neuroscientists.
Throughout July and August colts continue to improve their Foraging, Seeking and Defense and, most notably, their Dancing. Dance practices merge into preflight school in preparation for migration.
To be continued…