Petrels are a type of oceanic bird known for their extraordinary life spent gliding over the open water. They inhabit the pelagic zone, the vast expanse of the ocean far from coastlines. Petrels navigate the marine environment for years at a time, coming to shore only to reproduce. Their presence is significant, as they act as widespread predators and indicators of ocean health, requiring specialized biological features to endure the remote conditions of the high seas.
Defining Characteristics and Adaptations
Petrels belong to the scientific order Procellariiformes, a group commonly referred to as the “tubenoses.” This name comes from their prominent tubular nostrils situated on the bill. These tubes are connected to a specialized salt gland above their eyes, allowing them to excrete the excess sodium chloride consumed from their saltwater diet, a process known as osmoregulation. This adaptation is necessary for survival far from freshwater sources.
The tubular structure also enhances their highly developed sense of smell, which they use to locate food and navigate back to their remote nesting colonies. Petrels possess long, narrow wings, which are perfectly shaped for dynamic soaring, an energy-efficient flight method that uses the wind gradient over the ocean waves.
Global Habitats and Pelagic Life
Petrels maintain a cosmopolitan distribution, inhabiting every ocean basin across the globe, with particular diversity noted around New Zealand. They are considered truly pelagic, spending the non-breeding portions of their lives exclusively in the open ocean, sometimes for many years straight. Their life at sea involves long-distance, often trans-equatorial, migrations between feeding and breeding grounds. These extensive movements are influenced by global wind patterns, which helps them conserve energy. Petrels use oceanic frontal zones, where different water masses meet, as reliable foraging areas, demonstrating their reliance on productive, remote marine habitats.
Foraging and Feeding Behavior
The diet of petrels consists mainly of marine invertebrates, particularly squid, small schooling fish, and various crustaceans. Many species specialize in feeding on mesopelagic prey, organisms that ascend from the deep ocean to the surface waters at night. This behavior leads many petrels to forage nocturnally, taking advantage of the vertical migration of their food source. Petrels primarily use surface seizing, plucking prey from the water while in flight or resting. Larger species are known to scavenge discards from commercial fishing vessels. Certain groups, like the diving petrels, can make shallow dives to capture food.
Nesting and Reproductive Cycle
Petrels are colonial breeders, returning to specific, often remote, islands or coastal cliffs year after year. They exhibit strong philopatry, meaning they return to their natal colony, and form long-lasting, monogamous pair bonds. Smaller petrel species excavate burrows in the soil or utilize natural rock crevices for their nests. The reproductive strategy involves laying a single, relatively large egg per breeding season.
The incubation period is long, lasting from 40 to over 50 days, with both parents taking turns on the nest. Incubation shifts can be lengthy, sometimes exceeding ten days for species that must fly great distances to feed. Before laying, females often depart on a “pre-laying exodus,” a lengthy foraging trip to accumulate necessary energy reserves. Chick-rearing is protracted, lasting several months, during which parents feed their young with energy-rich, regurgitated stomach oil. After fledging, the juvenile petrel spends several years at sea before returning to land to begin its own reproductive cycle.