Gannets, albatross and pelicans, like many other seabirds, spend most of their life out on the open ocean. The fact that they feed in saltwater is the feature they all share. But they are not only ubiquitous on the ocean, they also found their way into our language and superstition: Sailors considered the sight of albatross as lucky charm and killing one led to disaster. ‘Wearing an albatross around your neck’ derived from the poem ‘The Rime of the Ancient Mariner’ written by Samuel Taylor Coleridge and would always remind the sinner of his wrongdoing.
Seabirds are special in many ways: They live longer than their terrestrial relatives, have fewer young and invest more energy in raising them. They usually breed in large colonies and can perform long annual migrations. Seabirds have adapted to their particular lifestyle in many sophisticated ways. But one of their traits in particular collides with the modern world and leads into disaster.
A tube on the beak
Being out at sea makes it tricky to find fresh water to drink. Some seabirds have developed a trait any ship-wrecked survivor would envy: They can drink salt water. The order Procellariiformes that includes albatross, petrel and shearwater is also called tube-nosed birds. The tube is a nasal gland located at the base of the beak. It filters and removes excess salt from the blood. Depending on the seabird’s species the excess salt either dribbles out of the tube
Built-in goggles and sunglasses
Whereas humans and other terrestrial creatures only see a blurry image when opening their eyes underwater, seabirds need a clear vision to catch their prey. Some seabirds like gannets evolved a simple adaptation: They can adjust the shape of their lenses depending on their current environment. This process only takes a fraction of a second and allows them to see clearly above and below the water surface.
In land-based birds the ability to see UV light is crucial. It plays a role in orientation, foraging and sexual selection. In contrast, most seabirds can’t see UV light. Certain cells in the eyes of seabirds contain droplets of oil. These droplets act like microscopic lenses. Researchers assume that these micro-lenses block out UV light from the birds’ vision by acting like sunglasses. This is crucial as excessive exposure to UV light can cause visual impairment up to blindness, a flaw seabirds can’t afford. Due to the reflection of UV light on the water surface seabirds are particularly exposed to UV light.
Plunge diving and bubble wrap protection
Birds are light-weights. That’s crucial to be able to fly. Seabirds that need to dive to catch their prey face a dilemma. The problem with light-weights is that they usually can’t dive very deep. Luckily, some seabirds found an efficient solution: plunge diving. Gannets, for instance can dive from an altitude of 40 m. Due to the massive acceleration, gannets hit the water with about 90 km/h. This speed enables them to dive down to 35 m to catch their prey. To prevent injury caused by the impact of the water, some seabirds have a built-in air cushion provided by their plumage that feels like feathery bubble wrap.
Sulphide smell leads the way
Seabirds are able to find their food even in foggy conditions, relying solely on their sense of smell. Procellariiformes such as albatross and shearwater can smell schools of fish from a distance up to 30 km. The main chemical that helps them to find their way is called dimethyl sulphide (DMS). Although other chemicals are involved in this process as well researchers haven’t fully explored them yet. DMS is produced by marine algae. When the algae die or get predated by zooplankton such as krill, the chemical is released into the water. To humans DMS smells like rotten eggs or decaying seaweed. For seabirds the smell of DMS is a promise for food: An abundance of krill also attracts lots of fish. Only recently researchers discovered that plastic waste that has been floating in the ocean for several months gets coated with algae and that this algae-plastic conglomerate eventually starts excreting DMS. Seabirds are attracted by the smell and feed on the plastic particles. As the birds’ digestive tract can’t break down the plastic, it eventually gets clogged up. As a result the birds die of starvation with their stomach filled with plastic. Plastic ingestion has become one of the main causes of death in seabirds.
The adaptations seabirds have undergone were crucial to guarantee their survival in the harsh conditions of the oceans. However, some of these special traits like the skill to find their prey via the smell of DMS collide with the modern world ruled by humans and their plastic waste. This time they might not be quick enough to adapt again.
Listen to the story on the Boiling Point podcast (the Science Show on Eastside Radio 89.7FM)
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