What is the STARFLAG Project?
The STARFLAG project consists of a group of European scientists from various different disciplines, including biology, physics and economics, coming together in order to study collective animal behavior. STARFLAG has recently come together in order to study the starlings as a "paradigm of animal behavior" (Cavinga 63).
Early Studies
In order to study the patterns of the starling birds, digital pictures were taken of the aerial acrobatics during the winter months in Rome. To correctly locate the position of each bird, pictures were taken from two separate angles in order to create a 3D image of where each bird was located. The first problem with this, however, is that corresponding each bird in one picture to the same bird in the other picture seemed to be very difficult, as the lighting in each image was very different, the birds all looked very similar, and the shape of the flock looks very different in the two different sets of photos.
|
Second, the technology to actually match up the two images did not exist. In order to match the two images, a singular motivated researcher would analyze the two images and would manually decide which birds matched up. While in small numbers this would not be an issue, the amount of birds that had to be matched was somewhere in the thousands in each of the pictures. Not only was the matching of birds in one single picture a mundane task, but in order to get actual empirical data, this process would have to be repeated for hundreds of pictures, resulting in manual matching to be entirely out of the question.
New Developments
In recent years, the STARFLAG project was able to develop an algorithm that mimics the procedure that the human brain uses in matching that was able to perform the matching of the two flocks automatically in very large numbers. However, the algorithm is able to handle 2 to 4 times more information than the human brain can process, making the algorithm much more powerful than the brain. After using the algorithm to produce 3D positions of the birds, the border of the flock is identified in order to measure the volume of the flock as well as the surface area. The number of birds inside of this border is proportional to the volume of the flock, while the number of birds on the border is proportional to the surface area. Along with this, however, it is important to identify birds that belong to the border of the flock in order to remove the statistical bias that they produce in terms of the nearest neighbor distance between birds.
Distance Between Birds
The nearest neighbor distance (NND) is the smallest value in the set of distances between a bird and its neighbors, and because birds on the border of a flock have fewer neighbors, their average NND is greatly skewed. However, when looking at the NND, it seems that as the flock increases, the result is that the average NND decreases, meaning that as the flock gets bigger, the distance between neighbors begins to lessen.
Along with this idea of NND, it seems that there is actually no fixed distance within which the birds interact, as it all depends on the density of the flock. By this, it can be assumed that birds use "topological distance" rather than "metric distance," meaning that the distance between birds is measured somewhat by function, rather than my actual distance. For example, when riding a subway, most human beings measure their travels by the amount of stops to their destination rather than by actual distance. Similarly, starlings measure their distance between neighbors based on how useful it is to have their neighbors around, rather than how close they actually are, as the distance between birds in a large flock would be smaller than in a smaller flock in order to avoid predation.
|
Relation to Neighbors
After looking at the 3D images that the new algorithm was able to produce, the spatial structure suggested that a very common feature of the flock was that the shortest NND between birds was typically found at the sides of the bird, rather than ahead or behind. Research suggests that this occurs due to the fact that the eyes of the starling are located on the sides of the head, rather than in front, which allows for the bird to see better towards the sides rather than in front or behind them.
Along with this, each bird seemed to have a fixed number of neighbors, regardless of distance. According to the data collected by STARFLAG, it seems that each bird had approximately seven neighbors. There is no definitive answer as to why each bird has approximately seven neighbors, however, experiments on birds have shown that birds do not have the mental capacity to distinguish sets with different numbers of objects past the number seven. In this sense, the research suggests that the number seven may actually act as a cognitive limit for the starlings, so they are mentally unable to manage having more neighbors than seven.
Along with this, each bird seemed to have a fixed number of neighbors, regardless of distance. According to the data collected by STARFLAG, it seems that each bird had approximately seven neighbors. There is no definitive answer as to why each bird has approximately seven neighbors, however, experiments on birds have shown that birds do not have the mental capacity to distinguish sets with different numbers of objects past the number seven. In this sense, the research suggests that the number seven may actually act as a cognitive limit for the starlings, so they are mentally unable to manage having more neighbors than seven.
References
Cavagna, A., & Giardina, I. (n.d.). The seventh starling. Significance, 5(2), 62-66. doi:10.1111/j.1740-9713.2008.00288.x
Multimedia Sources
Cover Image: http://www.laboiteverte.fr/wp-content/uploads/2014/11/murmuration-alain-delorme-03.jpg
Header Image: https://c2.staticflickr.com/6/5171/5429758700_8f8b9b0c21_b.jpg
First Image: http://www.technologyreview.com/sites/default/files/legacy/starlings.gif
Second Image: https://upload.wikimedia.org/wikipedia/commons/f/f5/PSM_V84_D217_2_Flocking_habit_of_migratory_birds_fig5.jpg
Header Image: https://c2.staticflickr.com/6/5171/5429758700_8f8b9b0c21_b.jpg
First Image: http://www.technologyreview.com/sites/default/files/legacy/starlings.gif
Second Image: https://upload.wikimedia.org/wikipedia/commons/f/f5/PSM_V84_D217_2_Flocking_habit_of_migratory_birds_fig5.jpg