Petrels are a diverse group of seabirds, part of the order Procellariiformes, often referred to as “tubenoses” due to their distinctive tubular nostrils. These birds are predominantly pelagic, meaning they spend most of their lives over the open ocean, ranging across all the world’s oceans from polar to tropical waters. Their widespread distribution necessitates a varied diet and adaptable foraging strategies.
Primary Food Sources
Petrels exhibit a wide range of dietary preferences, primarily consuming marine organisms such as fish, squid, and various crustaceans. Small fish, particularly mesopelagic species like lanternfish (Myctophidae), are a significant component of their diet, especially for species like the Soft-plumaged Petrel. Squid, including families like Cranchiidae and Onychoteuthidae, also represent a substantial food source for many petrel species, with some gadfly petrels largely feeding on small squid. Crustaceans, such as krill (euphausiids) and amphipods, are consumed by many petrels, particularly those in temperate and cold waters. For instance, the White-faced Storm Petrel’s diet primarily consists of crustaceans like krill and copepods, along with small fish and cephalopods.
Some petrel species, particularly the larger ones like the giant petrels, are also opportunistic scavengers. They feed on carrion, including the remains of dead whales or seals, and often consume offal or discards from fishing vessels. Giant petrels have also been observed preying on other seabirds, such as penguin chicks.
Diverse Foraging Methods
Petrels employ a variety of techniques to capture their prey, adapted to the type of food and their marine habitat. Many species are surface feeders, picking food directly from the water’s surface. This often involves a technique called surface seizing, where petrels, including storm petrels and gadfly petrels, snatch prey while flying low over the sea or while sitting on the water. Storm petrels, for example, frequently patter on the water with their webbed feet to maintain position while dipping down to seize tiny crustaceans and fish.
Other petrel species engage in various forms of diving to pursue prey. Shallow diving, or plunge-diving, involves plunging just below the surface to seize food, a method used by Antarctic petrels and some shearwaters. Some petrels and shearwaters are capable of deep diving, pursuing prey at considerable depths, with shearwaters recorded diving over 65 meters. Diving petrels, characterized by their short, stubby wings, “fly” through the water using a scissoring action of their partially open wings to pursue small crustaceans and fish. Certain species also filter feed, straining small organisms like zooplankton from the water.
Influences on Dietary Choices
Dietary choices in petrels are not static and are influenced by several factors, including species-specific adaptations, geographic location, and seasonal prey availability. Different petrel species exhibit distinct dietary preferences.
Geographic location plays a role, as prey availability differs across marine environments. Providence Petrels, for instance, forage in warmer waters, with their diet largely consisting of squid and fish. Conversely, some small and medium-sized petrels in temperate and cold waters consume a significant amount of crustaceans. Seasonal variations also impact diet, with foraging patterns adapting to the availability of resources throughout the year. During breeding seasons, petrels may undertake long foraging trips to distant, productive waters to feed their chicks.
Human activities, particularly industrial fishing, can also influence petrel diets. Studies have shown that some petrel populations, such as the Hawaiian Petrel, have shifted to consuming smaller prey over time, which researchers correlate with the onset of large-scale industrial fishing impacting oceanic food webs. Petrels are attracted to fishing vessels, feeding on discards or baits, which can lead to interactions with fisheries. Changes in oceanographic conditions, such as rising sea temperatures, can affect the distribution and abundance of prey like krill, further altering petrel foraging opportunities.