That sparked questions in the mind of a University of Delaware researcher: Were they competing for the same limited food and habitat resources? And were the gentoos the cause the Adélies' decline?
“We set out to explore whether the Adélies and gentoos were eating out of the same lunch box, so to speak,” said Megan Cimino, a doctoral candidate in the University of Delaware's College of Earth, Ocean and Environment and the lead author of a study reported recently in Scientific Reports.
It turns out, that even where the populations of the two species overlap, their feeding strategies – both target krill – are different enough that one species isn't out-competing the other. But figuring that out took high tech tools such as tagging both species of birds to track movement and feeding patterns and use of an underwater robot that allowed researchers to pinpoint exactly where the food was and where the birds were going to get it.
The technology produced hundreds of thousands of data points that Cimino reviewed before concluding that one species wasn't out-competing another for the same food resources. The findings leave lingering questions about why gentoos expanded their range and why the Adélie population is declining so dramatically.
The Western Antarctic Peninsula is one of the most rapidly warming places in the world and Cimino's previous work with Adélie penguins there looked at shifts in climate and weather conditions. Megan Cimino, University of Delaware
Since 1950, the average annual temperature in the Antarctic Peninsula has increased 3.6 degrees. The average winter temperature has risen by 10.8-degrees. Meanwhile, the climate is changing from dry and polar to warmer and sub-polar with more rain.
Cimino said that when she was there last year it was the Antarctic summer but at times it was much colder in Delaware than it was at Palmer Station where she worked. In the earlier work, Matthew Oliver, Patricia and Charles Robertson Professor of Marine Science and Policy at the university, worked with Cimino to compare data from 1987 to 2011 on the Adélie penguin’s diet, weather and the large-scale climate indices to see connections year-to-year in penguin chick weight. “The ability of a penguin species to progress is dependent on the adults’ investment in their chicks,” Oliver said. “Penguins do a remarkable job of finding food for their chicks in the ocean’s dynamic environment, so we thought that the type and size distribution of food sources would impact chick weight.”
What they found instead was that local weather and overall atmospheric climate affects chick weight gain. Among the keys were high winds, cold and precipitation such as rain and humidity. Because penguins live in rocky areas with little or no shelter there is no protection from extreme conditions when parents were away from the nest foraging for food. They were able to link weight gain to local weather conditions.
For example, westerly wind and air temperature can cause a 7-ounce change in average chick weights, as compared to 3.5-ounce change caused by wind speed and precipitation. A 7-ounce decrease in chick weight could be the difference between a surviving and non-surviving chick.
Teams of scientists including Oliver, Mark A. Moline, the director of the College of Earth, Ocean and Environment and William R. Fraser and Donna L. Patterson-Fraser from Polar Ocean’s Research Group, have been monitoring the decline of Adélie penguin populations. In 1975, there were an estimated 15,000 breeding pairs in the Antarctic summer. Today, a few thousand pairs remain.
With the latest research, paid for by the National Science Foundation and by the NASA Biodiversity Program, the team wanted to see if the two species were in a turf war for the same food supply.
Penguins were tagged with satellite transmitters and depth recorders to see how deep they dove in search of food. The also used an autonomous underwater vehicle, REMUS, to collect water samples and measure temperature, salinity and light levels in the water. In addition, they measured levels of phytoplankton and krill, the primary food source for both penguin species.
They also discovered that both species foraged and returned to nesting areas with enough food for their young suggesting there was enough food to support both populations.
With the underwater robot "it's like seeing the ocean as the penguins do," Moline said. The work allowed the team to rule out competition for food as a limiting faction.