Sunday, August 6, 2017

Murmurations

Behavior
Biological Evolution
Edward Hessler

You've probably seen a video of a starling murmuration.  These murmurations are mesmerizing.  The birds appear to be in communication as they turn and fly in perfect synchrony without colliding.  It is as though there is a "super-mind" regulating this dance in the sky.

Here is a video of one.

So, what is known about this phenomenon? Andrea Alfano writing in The Living Bird, a publication of the Cornell Laboratory of Ornithology describes current knowledge as well as what is not known. Such flocks are leaderless and this challenges our minds and imaginations.  A smart swarm, so to speak.

Alfano provides a link to Grainger Hunt, a scientist with the Peregrine Fund. He makes this observation about a murmuration resulting from an encounter by a large flock of starlings with a hungry peregrine falcon. "Here is a peregrine, intent upon a meal, and the focus of each desperate starling is avoidance. The wondrous cloud is thus secondary—an extraneous property, emerging from independent attempts by each individual, within the multitude of self-interested starlings, to escape the falcon— and how better than by getting in the middle of the flock and staying there until the peregrine leaves? At each point during a peregrine attack, there are safe places to be, and there are unsafe ones, and so each starling strives to place others between itself and the falcon." 

This is a common-sense analysis based on ideas we have about adaptation. Alfano reports on a recent computer analysis (see link in her article) that begins to provide needed details on the mechanics of the behavior..  The researchers found that starlings co-ordinate "their movements with their seven nearest neighbors."  However, this doesn't explain such movements.  There is still much to be learned on how the birds do this.

In a more recent paper published in PlosOne, the authors call attention to a basic difficulty of studying this behavior. Empirical analysis is very difficult.  In this situation, computer models become useful.  The model the researchers used was based on the idea of self-organization. Among the findings was that group size influences the variability of the shape of the murmuration. A bonus of the study is that it led to several hypotheses that can be tested empirically. The authors made the following comment on the limitations of their study, notably shortcomings of the model.  It also points out the complexity of murmurations and some of the variables that might be involved.

"Despite its usefulness, our model has shortcomings. First, of such complex animals as birds, it concerns merely their movement behaviour in relation to the position and heading of others and of the roost, while using a simple model of flying behaviour, ignoring e.g. flapping flight. It ignores any behaviour related to other motivations, such as nutritional, reproductive or motivations to avoid a predator. It also ignores environmental disturbances, e.g. by physical forces, such as wind. Thus, in nature, there will definitively be additional reasons that cause flock shape to be variable beyond those that we consider in this paper. Indeed, in the model the variability of shape of, for instance, small flocks of 200 birds is below that observed in real flocks in nature.
The use of models is beginning to play a much more important role in K-12 science education.  They are used widely by scientists in all disciplines. Here is a summary table on developing and using models as described in the Next Generation Science Standards.
 

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