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Thursday, June 18, 2009

Alaska Crane Kindergarten

---For photos on the Christy Yuncker Photo Journal webpage, click here.

Sandhill Crane colts are intensively tutored from day 1. For their parents, summer school teaching is a 24/7 job. The three core subjects (crane versions of the three R's) in Colt School are: Foraging, Display/Dance, and Flying, each of which addresses biological imperatives: nourishment, socialization, and migration. We think of the 14 days after hatching to be crane kindergarten, when the curriculum stresses Foraging first and Display/Dance next.
Crane colts run about on the day they hatch; they are physiologically precocial. Body plan, brain anatomy, and motor abilities are genetic, encoded in their DNA just as for every crane generation over 10 million years. Yet colts don't scatter like a brood of leghorn chicks for they are far from self-sufficient.

Young colts require parental protection and instruction for many months; effectively they are behaviorally altricial. For cranes as for people, nature enables and nurture refines. The genetic program provides only a framework that roughly defines capacity and potential.
On hatch day in mid-June in Alaska, colt schooling begins to shape and expand the native talents.

Foraging: Life is especially fragile in the first week. As the colts struggle to cope with the sensory storm in the bright new world outside the egg, they learn not only to avoid predators but also to distinguish food from pebbles and sticks. From hatch day forwards, parents devote most of their days to searching for suitable food items and offering them to the hungry colts, as illustrated by 10-day old Phyl accepting food from Millie in the picture below

Food items may be frightening or the packaging formidable. To the right, Roy has caught a dragonfly that he offered to 3-day old Jacques.
The colt looked baffled. Next, Roy dismembered the insect and successively fed the isolated head (a neat package), the thorax and the abdomen. Jacques was more interested in the next dragonfly presented to him. Perhaps the most impressive meal of this season was a dead ducking. This ungainly package of protein frightened even Millie at first. But Roy picked the duckling up by the neck (photo below) and then shook repeatedly until he could extract small bits of flesh that he passed to each colt.
For at least 14 hours each day during the first week after hatch, Roy and Millie scoured the grass for insects. At seven days of age, both colts were thriving. By ten days of age, they were beginning to peck at morsels on the ground, although most of their nourishment came via parent's beak.They had transformed from bumbling stumbling little butterballs to full partnership in the foraging foursome at twelve days of age, as shown at the end of this blogpost.

Displaying/Dancing: Many scholarly publications emphasize the easily-viewed aggressive encounters in mobs of cranes at staging and roosting areas. These flashy in-your-face displays often involve 1-2 year old birds that are probably pre-reproductive. Similar postures are used by older birds to defend nest territory. But agonistic signals are only one chapter in the display/dance lexicon. Amid the the crush of adolescent face-offs on the Platte River shallows during the annual "March Melee," mated pairs of cranes dance in synchrony with one another, like teen-age lovers oblivious of the hubub in the surrounding crowd on New Year's eve in Times Square.

Crane dancing often involves a mated pair, but cranes dance solo as well. Dancing generally reflects  a positive emotional state.  In the June 11, 2009 blogpost, we described Roy's joyous dance upon return from migration; this was largely a solo performance but also involved Millie as she dashed across the ice. Another example is shown to the right - Roy dancing alone in early evening at the center of the marsh on colt day seven (2009). It was his first dance since hatch days. He jumped and ran while Millie nestled, thirty meters away, with sleeping colts under her wings (see hyperlink for image). It is tempting to think that Roy's dance expressed elation: after an exhausting first week of non-stop parenting, both colts had survived and were healthy.  Dancing of a pair promotes reproductive synchrony. The dancing of Roy, Millie, and Jacques after the death of Phyl effectively promoted family solidarity and provided emotional release (blogpost of July 10, 2009)

In some cases, we may not see dancing for weeks. In 2009, Roy did not dance during incubation yet he danced briefly alone (spontaneously) on the evening of June 10, the hatch day of Jacques and again on June 11, the hatch day of Phyl. In 2008, we observed no dancing by Roy in late July or through August, during the 6 weeks while his colt recovered from an injury, but then Roy began to dance again when the colt finally began to fly (see hyperlink and May 20, 2009 blogpost). 

Displays and dances are communications. Crane displays involve posture, movement, timing, and context. In order for us to understand fully the displays of cranes, we need to construct a catalog of the complex moves and try to asses their meanings from the worldview of a crane. Body language, loud calling (long distance), and soft purring (short distance) are the channels for the social messaging networks of cranes. Displays can deliver information with a single unambiguous posture (leaning forward as a signal to fly or jumping back when startled), or with sequences linking several dance steps (jumping and turning), or through a series of multi-step sequences flowing together and lasting for seconds or even minutes.

Dancing is a spectacular distinguishing behavior of cranes. As noted by Ellis and his coworkers, the rich repertoire of stereotyped displays and postures puts cranes at one apex of social complexity in the animal world1.

A display can be a a single statement or a part of a conversation. Dance is not just an announcement of territory or of mood, but also allows two-way information exchange. Just as bird music is divisible into notes, phrases and full songs, so crane dancing is divisible into steps, sequences, and full dances. For a mated pair, dance sequences are complementary and responsive to the partner. Dance is an important cement for crane social structure, and dance proficiency requires years of practice.

There are parallels between dancing and bird song. The full adult song of many passerine birds depends not only upon innate ability but also learning. The "song system" has been extensively studied2. The sequence is listening, storage, retrieval, early motor output, and then practicing and practicing until the full adult song crystallizes. Young 3-month-old birds listen to songs of experienced adults and store those memories in a precisely localized brain nucleus. It is only later at 7 months of age, that they begin to sing under the control of another nucleus in their brains. The first attempts are choppy but with time and practice, young birds become good enough to mimic the songs heard 4 months earlier. Thus song output is initiated and refined at one site in the brain that draw upon memories stored in another site.

Cranes are born with the capacity for dance but early attempts are halting. Anatomy and neurocircuitry allow dance postures and movements, but for cranes as for the Bolshoi ballet, repetition helps movements appear to be effortless and the sequencing to become liquid. For a colt, we see a three step lesson-plan for display/dance training: 1) motivation by adult and observation by colt, 2) imitation, and 3) complementary response to adult steps. Display training for crane colts can begin as early as day 4. Just before the photo on the left was taken, Roy and Millie gave little jumps that caused both colts to watch  in rapt attention. Then tiny Jacques (colt in the middle right, above) faced off to Roy in a forward display . As Roy stretched out both his wings, Jacques
mimicked his father with his own tiny wing stretch (left image above). The enlargement to the right lets you see the little guy better. During kindergarten, dance training stops at imitation, step 2 of the lesson-plan.

Only this year, we discovered that colts display with one another. The picture to the left shows Roy probing for food while Jacques and Phyl (4 days old) face off to one another. Jacques is jumping in a baby wing stretch directed toward Phyl. It is possible that this baby display is a baby face-off - precursor of the behaviors of teenagers jumping on the shallows of the Platte.

Graduation from kindergarten is marked by efficient family team foraging. The "four gunslingers" in the photograph below are a formidable sweeping machine for harvesting dragonflies. Twelve-day old colts move smoothly as they flap their front appendages (wings) and run between their parents. In the coming weeks, the colt-parent pairs will forage together on the home marsh. In addition, the family will begin exploratory day-trips to adjoining bogs. Except for physical conditioning during foraging and dance training, flight school lies a month ahead.

References cited
1. Ellis DH, Swengel SR, Archibald GW, Kepler Cb 1998. A sociogram for cranes of the world.
Behavioral Processes 43:123-151.
2. Marler P 2004, Slabbenkoorn H (eds.)2004. Nature's Music: The Science of Bird Song, Elsevier, Amsterdam.
Revised July 12, 2009

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