Compass Brain

Savannah Sparrow (Passerculus sandwichensis)

More Savannah Sparrows have arrived to join those I first saw in early October. Note the plural. Males and females look alike, so I can’t say whether the two of them that appear in the closing seconds of the video above are a mating pair, but it seems likely. They are ground-nesting birds, and would no doubt reproduce here in the park if the Parks administration were to put a moratorium on mowing a portion of the grassland from February through June every year, as it did on one lifesaving but exceptional occasion in 2019. Hints on the management of breeding habitat may be found in this publication.

These individuals came here on migration from parts unknown further north. They are able to find their way in both directions as soon as they learn to fly, without having to be taught by older and wiser birds. As it happens, scientists have fastened on this species as the model bird for the study of migratory orientation. Scientists take the bird as it hatches and raise it in the laboratory, and put it through various experiments to learn what it knows and how it navigates. The results have been astonishing:

Migratory songbirds enter the world with two apparently innate representations of the direction of the first migration, one coded with respect to the magnetic field, the other withrespect to the axis of celestial rotation …. An ability to orient in an appropriate migratory direction based on the magnetic field develops in young birds raised entirely indoors with no exposure to relevant visual orientation information.

(PDF) The flexible migratory orientation system of the Savannah Sparrow (Passerculus sandwichensis). Available from: https://www.researchgate.net/publication/13905890_The_flexible_migratory_orientation_system_of_the_Savannah_Sparrow_Passerculus_sandwichensis [accessed Dec 02 2021].

But the birds’ ability to orient to the earth’s magnetic field is only part of their toolkit. They can recalibrate their orientation as the magnetic field shifts, and they supplement or substitute magnetic orientation with other senses. They have, in short, “a system of interacting compass senses: magnetic, star, polarized light and, perhaps, sun compasses.” This ability appears to be typical of night-migrating songbirds generally. I want to remember this point the next time someone disses a “bird brain.”

Savannah Sparrow (Passerculus sandwichensis)

More about Savannah Sparrows: Wikipedia Cornell Audubon In Chavez Park

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