On a mild but windy day a fishing boat moves across the Mediterranean Sea, when, suddenly, a flock of tiny, dark birds seem to appear from nowhere.
Storm petrels!
Ancient myths warn that these birds predict an oncoming storm, but their rapid appearance likely has more to do with their reliance on wind currents and an extraordinary sense of smell.
Tubenoses
Storm petrels belong to a group of birds known as tubenoses. The “tubes” appear as bumps on top of their beaks and are the reason for their ability to detect scents over long distances. Their nostrils explain the storm petrel’s mysterious appearances—they are just in search of a good meal.
The Mediterranean storm petrel (Hydrobates pelagicus melitensis) is a subspecies of the larger population of European storm petrels (Hydrobates pelagicus). They are wholly black except for their broad, white tail and a light underwing stripe. Mediterranean storm petrels differ markedly from their European cousins in several ways, including diet, mating calls and behavior, and the timing and pattern of migration. There have even been differences found in molecular markers. On close examination, the Mediterranean subspecies also has a darker, thicker bill and is slightly larger than the European storm petrels. But in the field, the two are indistinguishable and so are categorized as one species.
Along with their strong sense of smell, storm petrels have a strong smell! These two “abilities” are especially helpful during the breeding season as storm petrels usually only visit their nests at night to avoid ariel predators. They also nest in locations that are dark in daylight, such as caves or burrows. Storm petrel mates also have unique calls by which they can distinguish each other. Finding mates and chicks in a large colony or in a cave full of twists and turns, might be difficult for other birds, but the storm petrel is able to pick out the unique smells and calls of its own family from dozens or even hundreds of others.
Seabird Flight Patterns
A strong sense of smell doesn’t explain the storm petrel’s propensity to appear during storms. That myth most likely stems from the fact that storm petrels, and most seabirds, rely on wind currents for their flight. In fact, on a perfectly still day, it may be hard for them to lift off the water. When they are flying, storm petrels have a signature, rapid, batlike wingbeat. They are also well-known for their hovering behavior while hunting, skittering along the sea’s surface in search of fish, squid, crustaceans and jellyfish.
While they are adept at flying, storm petrels, like many seabirds, are no good at walking. They have small, webbed feet great for swimming and lifting off the water but incapable of standing on land. They shuffle along on their tarsi unless there is enough space to flap their wings so that they can fly low over the ground. Luckily for storm petrels, they don’t have to do a lot of walking as they spend most of their lives at sea. The one time of year that they do go inland, is during mating season.
Storm Petrel Breeding Habits
Storm petrels usually mate for life and invest heavily in their offspring; a recent study showed that storm petrels make the longest foraging trips of any seabird. They usually feed their chicks a high-calorie oil they store in their stomachs during their long journeys to and from nest sites. Both parents incubate one egg for 38-50 days, beginning in May; the more frequently they are gone, the longer it takes for the egg to hatch. Once the chick is around a week old, the parents leave it on its own while they go off to find food, coming back for regular feedings until the fledgling is about 56-86 days. Fledging lasts through the end of September.
The main population of European storm petrels nest in the Faroe Islands, United Kingdom, Ireland and Iceland. This population has around 4-500,000 breeding pairs and is listed as Least Concern by the IUCN Red List. The Mediterranean subpopulation is less than one tenth that size with no more than 16,000 breeding pairs. The Mediterranean storm petrels breed primarily in Malta, Sicily and the Balearic Islands, with half of nesting pairs on the Maltese islet of Filfla.
It is difficult to estimate storm petrel populations due to the remoteness and inaccessibility of their nesting sites and the fact that they spend most of their lives far out to sea. Research indicates that the large European population is likely stable, but the condition of the Mediterranean population is less clear.
Storm petrels and rabbits?
Storm petrels choose to nest under rocks, in caves, or even to excavate their own burrows, loosening the earth with their bills and kicking out the debris with their feet. Other animals may share their burrows, in which case the storm petrels erect a protective barrier. Their neighbors might be other storm petrels, Atlantic puffins, Manx shearwaters and even rabbits! Not all of their neighbors repay their generosity, however, as puffins and shearwaters sometimes tear down the dividing wall, destroying not only the nest, but sometimes killing the chick and sometimes their parents.
Predation
In addition to being attacked in their own nests, storm petrels face predatory threats from the air. Native predators include other seabirds such as the great skua, great black-backed gull and particularly in the Mediterranean, yellow-legged gulls. Raptors such as peregrine falcons and owls also prey on them. Mammalian predators include non-native house cats, rats and American mink, and these animals can wipe out an entire breeding colony. The little storm petrel’s only defense is to spit its stomach oil (the same oil it feeds its babies) at its attacker.
The World’s Smallest Seabird
Though Mediterranean storm petrels have few defenses, they have had powerful influences on human culture. For instance, it was once believed that storm petrels were the souls of drowned sailors, and it was bad luck to kill one. And the image of the small, intrepid bird on the stormy ocean has also become a chosen symbol for revolutionary calls to action around the world. While storm petrels themselves are largely silent birds, their behaviors and life history tell a fascinating tale.
Written by Rachel Endicott
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