For the first time ever, an entire species has been counted from space. Using the highest-resolution satellite images available, scientists have counted the number of northern royal albatrosses living on remote islands in the Pacific Ocean.
The research, led by the British Antarctic Survey, is not the first to use satellite images to count animals, but it is the first time that the entire population of a species has been assessed from space. Despite the birds having an impressive range of 64 million square kilometers (25 million square miles), albatrosses (Diomedea sanfordi) only breed in an area 8 square kilometers (3 square miles), spread over Chatham Island, New Zealand, making it fairly straight-forward to get an estimate of the total global number of the species.
The results of the analysis, published in the journal Ibis, found there are actually fewer of the endangered birds than previously thought. While past studies conducted by physically going out and counting them found that there were 5,700 nests, the figure obtained from the satellite images puts this at around 3,600.
The birds only make up a few pixels in the images, but that is enough to count them. Fretwell et al. 2017
This lower figure could be for a number of reasons. It could indicate that the population of northern royal albatrosses is in decline, with the birds being heavily hit by longline fishing and getting caught on fishing lines as they are dragged behind boats. It could also simply be that this has been a bad year breeding-wise for the birds. The researchers hope that by repeating the analysis over a few years, they will get a better idea as to how the species is faring.
Despite their limited breeding site, it has been difficult to keep track of albatross numbers due to their extreme nesting habits. Not only are the sea stacks on which they bed down on every year fairly remote, being around 680 kilometers (422 miles) off the eastern coast of New Zealand, they are also incredibly difficult to access. The sea stacks are surrounded by vertical cliffs, which means any scientist that wants to count them has to literally rock climb up there.
But when the US military allowed the highest-resolution images taken from space to be released, it gave the researchers a novel way to keep tabs on the birds. The satellites can capture objects as small as 30 centimeters (12 inches), meaning that the big, white albatrosses sitting on exposed, vegetation-free islands are actually fairly easy to see. All the researchers needed to do was get copies of the few stacks on which the population nests and count the white blobs.
3