Photo caption: Photo was taken under the requisite permits provided by the New Zealand, United States and/or United Kingdom Antarctic programs or authority - Michelle LaRue.
Research led by Professor Michelle LaRue from the School of Earth and Environment at Te Whare Wānanga o Waitaha | University of Canterbury (UC) published in Remote Sensing in Ecology and Conservation shows that high-resolution Synthetic Aperture Radar (SAR) imagery can track emperor penguins through the Antarctic winter, opening a new way to monitor an endangered species during a critical stage of breeding.
Emperor penguins have recently been added to the International Union for Conservation of Nature's Red List of Threatened Species and are one of the clearest living indicators of change in Antarctica. Their breeding success depends on stable sea ice, which is increasingly under pressure as the climate warms. Being able to monitor them through the dark Antarctic winter gives scientists a better chance of understanding how quickly conditions are changing, and what that could mean for the future of the species.
For nearly 20 years, emperor penguins have largely been monitored from space using optical imagery, essentially photographs taken by satellite. That approach has revealed a great deal, but it relies on sunlight, which makes it impossible to use during the complete darkness of Antarctic winter.
"The problem is that the best time to understand emperor penguin breeding populations is in winter, when light is limited," Professor LaRue says.
"What this study shows is that with SAR imagery we can now see them during that critical winter period, when we know exactly who we are looking at: the males incubating their eggs."
Early in the season, birds gather in loose groups at their colonies. During courtship and mating, they form smaller, denser clusters. Later, the females leave to forage at sea and the males remain behind, huddling together while incubating the eggs through the coldest months.
If scientists can estimate how many males are present in those huddles, they can infer how many breeding pairs came to the colony. That information provides a much better measure of population health than spring counts alone.
"We have seen fewer birds in springtime imagery over the last 10 to 15 years in many places, and we are still trying to figure out why that is," Professor LaRue says.
"A lot can happen between winter, when birds come together to breed, and spring, when chicks have hatched and are being fed by their parents. However, if we can estimate breeding pairs in winter, we can get a much better metric for understanding population change."
SAR technology works differently from normal satellite photography. Instead of relying on sunlight, it sends radar signals down to Earth and measures the signal that bounces back. In this study, researchers used high-resolution commercial SAR imagery provided by Umbra, with each pixel representing an area as small as 25 to 30 centimetres.
That detail allows penguins to stand out against the ice. Fast ice, which is sea ice attached to the coast or an ice shelf, can be relatively smooth. Penguins create a rougher surface on top of it, making them visible in the radar imagery.
"Because the fast ice is very smooth, there is little scattering, but the penguins are rough on a smooth surface, so they stand out nicely," Professor LaRue says.
The team found they could not only detect the birds but also follow changes in colony patterns through the season. Loose aggregations, denser mating groups, and winter male huddles could all be identified from the images.
A key strength of the study was the ability to compare those interpretations with observations made on the ground by a film crew shooting a documentary at one of the colonies. The project was supported by a Catalyst: Strategic - New Zealand - NASA Research Partnerships 2023 grant through the Ministry of Business, Innovation and Employment and involved collaborators from NASA JPL, Umbra, British Antarctic Survey, Ocean Motion Technologies, and the University of Waikato.
When Professor LaRue analysed the images, the patterns she identified closely matched the observations recorded on the ice. That gave the team confidence that what they were seeing from space reflected real penguin behaviour.
The current paper does not yet provide a final breeding population estimate. Instead, it establishes that scientists can detect emperor penguins with high-resolution SAR and monitor their colony behaviour through winter.
That is only the first step. UC researchers are now working towards what could become the first breeding population estimate for emperor penguins using this approach. They also want to link winter observations with spring imagery to better understand what changes between those seasons.
Better winter monitoring could support more accurate conservation decisions by showing whether population changes are linked to breeding numbers, sea ice conditions or losses later in the season.
For Professor LaRue, the work is both scientifically exciting and practically important.
"We have been studying emperor penguins for only about 100 years, and there is still so much we do not know," she says.
"This is just the beginning. We can now see them and track what they are doing through winter, and that opens the door to much more discovery."
