Indicator species are animals whose health and population levels can be indicative of the health of the environments in which they live, and shifting factors within that environment that are changing significantly. Seabirds such as gulls are often indicator species, particularly for environmental changes that cause their populations to respond to shifts in their ocean habitat.
A recent study in The Auk: Ornithological Advances reports on how multiple species of Arctic seabirds are responding to changes in their environment over the last four decades. The researchers have found evidence that the warming ocean is both directly and indirectly affecting seabird populations in Alaska.
Researcher Holly Goyert – formerly of the University of Idaho and now at the University of Massachusetts – and colleagues used mathematical models to investigate the relationships between large, long-term datasets covering climate fluctuation, zooplankton abundance and distribution, and populations of certain seabird species in the ocean off Alaska from 1974 to 2014.
Their results showed that declines in populations of the Black-legged Kittiwake – a type of Arctic gull – are linked to declining zooplankton productivity. The species’ cousin – the Red-legged Kittiwake – is also experiencing a population decline, but this is more a result of warming ocean surface temperatures.
Goyert explains their findings, “although Black-legged Kittiwakes are one of the more abundant gulls in the world, their populations are undergoing significant declines, which calls their global status into question. Our paper suggests that the deterioration of food web resources such as krill, which is related to warming oceans, has contributed to these declines.”
However, not every seabird species is experiencing population declines. Both Common and Thick-billed Murres, which are related to puffins, have shown to be resilient to climate change – and may even be benefitting. But other species are still struggling to adapt to a changing habitat, and this study is just the first attempt to determine how climate and habitat variability affect seabird population dynamics on a large scale.
“Mass seabird deaths and breeding failures in recent years have the scientific community puzzled, and both appear to be climate-related,” says Melanie Smith, Director of Conservation Science at Audubon Alaska, who was not involved in the study. “This study is an important step in clarifying the effects of changing climate on seabird population dynamics across Alaska. We can use what we’ve learned here to design detailed monitoring and to better anticipate population declines, improving managers’ ability to protect vulnerable species.”