Nature Blog Network

Saturday, May 1, 2010

Walkabouts, local ecology, and the importance of novelty

Millie and Roy returned on Earth Day 2010. Within minutes, they erupted into energetic spinning jumps and deep forward bows on  Bog Central - a dance that probably reflected emotional release.  Then they began to check out the local ecology.

Although they have nested here for many years, these cranes are meticulously cautious when they first arrive in the spring. Apparently the neighborhood needs vetting and re-vetting. Sometimes bad things happen while we are traveling; it pays to inspect the home premises when we return. This appears to be true for cranes as well as people.

These wild Alaska Cranes are ever vigilant. Ongoing quiet reconnaissance seems almost compulsive. They take no notice of the daily barking by neighborhood dogs, yet a novel sound, like a delivery truck on a nearby road, piques their curiosity as they assume a Tall Investigative posture. Intruding ravens release agitation and attack.

The contrast to suburban Florida Sandhill Cranes who tolerate endless human traffic is striking (see footnote1).

For these wild Alaska Sandhill Cranes, it appears that familiar is benign but any novelty triggers interest (Tall Investigative posture) that can escalate to edginess (Tall-alert posture). In order to detect deviations in their environment, we think that Roy and Millie must hold in memory some representation of their local ecology .  How do they create the reference worldview?

Our cranes' neighborhood has three concentric zones:
  1. a core nest territory that is readily visually inspected, 
  2. nearby ponds within walking distance, and 
  3. the wider surround of Goldstream Valley accessible by short flights.
Reconnaissance allows accumulation of local geodata.

During the first few days after their arrival, Roy and Millie scrutinize their nest pond and the adjacent marsh. Following a bout of feeding or loafing, they pace slowly ahead with necks extended as if they were sniffing. This ritualized posture is often a prelude to copulation but it might also reflect exploration. 
In both the photos above, Roy, distinguishable from Millie by his larger white patch, is closest to the camera. This posture is different from the familiar "intention to fly" (see Social Body Language) in that the neck is not arched. 
  • The picture above shows a crane's-eye view of bog central. Daily patrol around the bog allows collection of seeds and insect prey. General surveillance is punctuated with deliberate examination of notable items. For example, the remnants of Phyl's skeleton (Blogpost July 2009) merited 30 seconds of intense staring on Earth Day.
  • Goal-oriented tasks, like selection of a premium site to build the nest, are another priority. At many spots across the bog, Roy explores local construction possibilities by seizing, waving, and deliberately piling a few fragments of cattail. As the first and second weeks roll on, he focuses upon fewer sites and Millie begins to take some interest as she nears time for egg-laying. 
On two occasions during the second week, pacing-gazing was followed by a slow walk to the northwest, toward Upper Pond which is almost a half-mile away. In past years, the Upper Pond has been a nesting site for ducks and grebes. The route to Upper Pond is the same each year; the cranes do not explore in other directions. Generally, Millie and Roy revisit the Upper Pond in July and August when they take the colts for a stroll.

The third level for reconnaissance is Goldstream Valley. On every evening for the first 10 days after their arrival, the cranes fly across southeast to valley to roost for the night in the Cross-Valley Ponds and Bogs. They come back the following afternoon to feed, explore, sleep, mate and dance in Bog Central and to call in unison several times each day. On many occasions, they are answered by other cranes - one pair to the east, one to the south-southwest, and another to the southwest.

During the 30 day incubation period while one crane is incubating the eggs, the other often flies across the valley to the south or to the southeast and then returns in a few hours to assume incubation duties. In past years after the colts are hatched, Roy conversed with other valley cranes on a daily basis and often flew off toward their calls for an hour or two.

We conclude that the crane's "mental representation" of the local ecology of Goldstream Valley is informed by visual information through walkabouts and flyabouts reinforced by the territorial calling through the summer.

What is the the crane's mental map of the local neighborhood?

Some birds have phenomenal capacities for spatial memory. The best studied species are jays and crows that remember the locations of tens of thousands of hidden food tidbits they have hidden.
  • Do they retrace the exact path that was followed to hide each item?
  • Do they remember a particular location for each item by relating to an array of specific landmarks ? 
  • Do they hold in their minds a general neighborhood reference map that includes spatial coordinates for each cached item?  
Simple cues and even retracing paths for a few items have been validated in laboratory experiments that control all other variables for jays and crows. But in natural environments, the contexts are diverse; there are multiple and variable cues, and the spectrum of responses is large. We suspect that their penchant for exploration could allow cranes and other birds to construct mental maps of their surroundings. In philosophical jargon, these would be termed decoupled representations, "registrations of the environment that are relevant to many possible actions but specific to none" 2.

Such cognitive accomplishments would go well beyond lists of specific cues that release fixed responses. Cranes are wary, long-lived birds who remain paired for a decade or more because they are canny. Although creatures of habit, they are not automatons. We suggest that one critical capacity might be a cognitive "novelty detector", like that employed by a policeman who strolls down the street quietly scanning for anything out of normal.

Danger anticipated can be disaster avoided.

1. Cranes in more civilized climes can habituate to human activity. Florida Sandhill Cranes inhabit golf courses and suburban neighborhoods, seem unperturbed by proximity to people, and even become part of the cross-species social scene.

Diana Burton of Indian Harbour Beach Florida emailed as follows:
 I am not a biologist, but an ophthalmologist living in Florida. [The cellphone snapshot to the left was taken at the entrance to her clinic.]
I wanted to share an interesting Sandhill Crane behavior and see if you've ever heard of it. One of the technicians in my clinic came in very excited and told this story. A pair of cranes which is often around her house was in the backyard. Her girls wanted to jump on the trampoline. Carleen told them they might scare the cranes away but they went out carefully and the cranes stayed. The girls started jumping on the trampoline and Carleen said the birds looked at the girls, then each other, then started jumping (I guess dancing.) Carleen ran and got her video camera but the battery was dead. One other time, the pair was there and her daughter went and started to jump. That time, one of the cranes started to jump but the other didn't. 
Dr. Burton's email describes a crane that exploits the automatic door opener of a hospital emergency room to beg for food.
 I take call for an area hospital and went to the emergency room to see a patient. I've seen cranes in the parking lot there on several occasions, but one of them walked up to the sliding door to the emergency room entrance and it opened. He stood there and looked in. A patient came to the door and the crane walked away about 10 feet, but immediately returned after the patient passed. The door opened. He stood looking in. This happened over and over for several minutes, with the sliding door opening and closing because of the crane. Finally, a nurse at the desk said, "OK, Henry." She went over to the popcorn stand and got a bag, and walked out the sliding doors past "Henry." He loped after her and she spread some popcorn on the grass for him (her?). She said, "He does this all the time."

2. Sterelny K, 2003. Thought in a Hostile World. The evolution of human cognition. Blackwell Publishing, page 50.

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