The kittiwake is a highly pelagic seabird of the northern oceans, represented by two main species: the widespread Black-legged Kittiwake (Rissa tridactyla) and the rarer, Bering Sea-endemic Red-legged Kittiwake (Rissa brevirostris). These gulls spend most of their lives at sea, returning to cliffs only for breeding. Their existence is intrinsically tied to the availability of small marine organisms, and their diet provides a clear window into the health of their oceanic environment.
Primary Prey: Small Pelagic Fish
The majority of the kittiwake’s diet, particularly during the energy-intensive breeding season, consists of small, schooling pelagic fish. In the North Sea and surrounding areas, the Black-legged Kittiwake relies heavily on the lesser sandeel (Ammodytes marinus), a small, lipid-rich fish that is a staple for chick-rearing. When sandeels are less available, the birds broaden their diet to include other small fish, such as sprat and herring fry, and juvenile cod. This dietary flexibility is often determined by the local availability near their nesting colonies.
The Red-legged Kittiwake, restricted primarily to the Bering Sea, exhibits a more specialized diet centered on myctophid fishes. These small, deep-water fish form a dominant part of the Red-legged Kittiwake’s food intake, sometimes accounting for nearly 100% of the prey by wet-weight occurrence. Other important fish prey for both species in various regions include Pacific sandlance and capelin. The energy content and availability of these schooling fish are directly linked to the reproductive success of the adult birds.
Secondary and Opportunistic Food Sources
Although fish are the preferred and most energetically dense prey, kittiwakes supplement their diet with a variety of non-fish marine life, especially when primary prey is scarce. These secondary food sources include several types of marine invertebrates, reflecting the birds’ adaptability as surface feeders. Small squid are frequently consumed, particularly by the Red-legged Kittiwake population.
Planktonic crustaceans also form an important part of the diet, particularly euphausiids (krill), copepods, and amphipods. These tiny organisms are an important energy source, especially for non-breeding birds or in regions where larger fish are less common. The birds will also occasionally consume polychaete worms and jellyfish.
Kittiwakes are also known to be opportunistic feeders around human activity and marine mammals. They will readily take fish offal and discards from commercial fishing vessels, turning discarded material into an alternate, though lower quality, food source. They will also follow whales and other large marine predators, feeding on the small fish fragments or disturbed prey items brought to the surface.
Foraging Techniques and Feeding Behavior
Kittiwakes are primarily considered surface feeders, meaning they capture their prey at or just below the water’s surface. Their main technique while flying is “dipping,” where they snatch prey from the water without landing. They can also engage in “surface-seizing,” capturing small items while sitting on the water.
While they are capable of some submerged foraging, their ability for deep pursuit diving is limited, typically only plunging to depths of less than one meter. The Red-legged Kittiwake has evolved a unique foraging pattern, often feeding nocturnally to capture myctophids that migrate closer to the surface at night.
Kittiwakes frequently forage in large, mixed-species flocks, a behavior that helps them locate patchy and unpredictable food resources. They are often among the first species to discover a dense patch of fish, attracting other seabirds to the feeding frenzy. This communal feeding strategy increases the efficiency of prey detection.
Environmental Influence on Diet
Environmental factors dictate the availability of the kittiwake’s preferred food, forcing shifts in their diet composition. Sea surface temperature (SST) is a major driver, as warmer winter SST can negatively affect the recruitment and survival of the sandeel population, leading to a reduced biomass of this staple prey. When the highly nutritious sandeels are unavailable, kittiwakes must switch to less energy-rich alternatives, which directly impacts their health and ability to provision their young.
Fishery pressure also plays a significant role, particularly the industrial fishing of forage fish like sandeels and clupeids. Competition with commercial fisheries reduces the overall stock of prey accessible to the birds. The breeding season presents the highest energetic demand, and a lack of preferred prey during this time often results in reproductive failure.
The distribution of prey can also be affected by oceanographic changes, forcing kittiwakes to fly farther from their colonies. When preferred fish stocks are depleted or shift their location due to warming waters, the birds must either extend their foraging range or rely on less suitable prey. This dynamic illustrates the kittiwake’s sensitivity to both localized human activities and large-scale climate fluctuations.