Remote Sensing Penguin Guano

There is so much we don’t know about the Earth and the biosphere. Even for relatively big and easy to see species such as birds, it is hard to know how and where they live, or even how many individuals exist. There are only so many biologists, and humans can only go and see so much.

Remote sensing of the planet from space has gives important insights about large scale processes that can’t be seen easily form a human perspective. For instance, a few images from space make absolutely clear how important dust storms in Africa are for the Amazon forests in South America.

In the past, it has been difficult to learn much about animal populations, because individuals are small and elusive. Biologists are getting better at detecting and tracking animals, especially mass movements of them.

This month NASA calls attention to a successful long term project that uses satellite imagery to locate colonies of Penguins [3]. Penguins are, of course, far too small to be reliably detected from most satellite imagery. However, Penguins live in colonies, and produce immense amounts of guano, which can be seen from space.

In fact, Penguin colonies could be seen from space 30 years ago [2], and space imagery and analysis have gotten a lot better since then.

The basic technique is to detect the color of guano covered rocks, and to infer how many Penguins live there from the area covered. Cross checking on the ground has confirmed that this indirect and remote measure is a pretty good estimate of and many Penguins there are and where they nest.

As the researchers note, Penguins live on sea ice, which means that they are a sensitive indicator of how ice conditions change. As sea ice is melting in parts of Antarctica, we can document how Penguins relocate in response. Penguins are also eat krill and fish, so they are a visible indicator of the health of these foods in an area.

Mathew Schwaller, Heather Lynch and colleagues have completed a global census of Adelie Penguins using imagery from several satellites [1]. They use machine learning techniques to identify the visual signature of nesting areas. Based on the very characteristic nesting habits of Adelies, it is possible to estimate the number of Penguins based on the area. Naturally, the satellite data is combined with on-site investigations and other reports, in order to validate the remote sensing and the estimation.

From [1] FIGURE 1. Map of extant Adélie Penguin colonies, as well as penguin colonies not found in imagery and presumed extinct. Solid bars represent sections of coastline in which populations are generally increasing in abundance, and dashed lines those in which populations are generally decreasing. Areas with no bar are either a mix of increasing and decreasing populations, are not changing in abundance, or do not have sufficient data to assess population change (see Supplemental Material Appendix A). Right: example of high-resolution imagery from Devil Island (−63.797°, −57.290°; location indicated by black arrow). Areas identified in the analysis as guano are shaded in light green. Imagery © 2014 by DigitalGlobe, Inc.

One huge advantage of the satellite data is that there is continued coverage of the whole world, so it is possible to track the changes in Penguin populations. For instance, the 2014 report indicates that over the last twenty some years, nesting sites in West Antarctica have dwindled. This is where sea ice is shrinking. In the same period, new nesting sites have appeared in East Antarctica, where sea ice has increased. Overall, the total population of Adelies seems to have increased in recent years, even as the birds have migrated to more favorable ice.

Ideally, the census can be maintained for a number of years to accumulate a much more detailed baseline, to improve the technique, and refine the understanding of the Penguin population. This census is only one species, so it remains to be seen how similar techniques might track other species.

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1. Heather J. Lynch and M. A. LaRue, First global census of the Adélie Penguin. The Auk, 131 (4):457-466, 2014/10/01 2014. https://doi.org/10.1642/AUK-14-31.1
2. Heather J.  Lynch,  and Mathew R. Schwaller, Mapping the Abundance and Distribution of Adélie Penguins Using Landsat-7: First Steps towards an Integrated Multi-Sensor Pipeline for Tracking Populations at the Continental Scale. PLOS ONE, 9 (11):e113301, 2014. https://doi.org/10.1371/journal.pone.0113301
3. Adam Voiland, Penguin Droppings Are Fertile Ground for Science : Image of the Day. NASA Earth Observatory.2017,  https://earthobservatory.nasa.gov/IOTD/view.php?id=90372

PS.  Wouldn’t “Penguin Guano” be a good name for a band? How about ‘Adelie Census’?

 

 

Space Saturday