As is the case on so many islands throughout the world, Hawaiʻi’s seabirds evolved without mammalian predators and thus have no natural defenses against them. The appearance of non-native mammals such as cats, dogs, rats, mongoose and pigs has proven to be a significant threat to these ground-nesting birds (along with a wide range of other endemic Hawaiian bird species). In even the most remote breeding colonies, these predators attack and kill adults and chicks and can cause significant damage to the breeding population in a very short span of time.
Introduced predators are a significant threat to nesting seabirds, as this predated Hawaiian Petrel in Upper Limahuli Preserve demonstrates (Photo by Emily Haber)
Loss of habitat
Non-native mammals, especially pigs and goats, can destroy the native vegetation that is such important breeding habitat for Hawaiʻi’s endangered seabirds. Digging and trampling by these mammals destroys native vegetation and leads to invasion by exotic plants that can swiftly take over native forest. If left unchecked, this can ultimately result in dense stands of species such as strawberry guava, making it impossible for seabirds to nest on the forest floor.
Dense stands of invasive plants such as this guava dramatically change seabird breeding habitat (Photo by Jay Penniman)
Artificial Light Attraction
Hawaiʻi’s endangered seabirds fly to and from their breeding colonies only at night. Human light pollution can confuse this behavior, particularly in fledglings during the very first journey from the colony to the sea. These fledglings become disoriented by bright lights and fly into buildings or become exhausted and land on the ground in a phenomenon known as ‘fall-out’. The island of Kauaʻi, for example, experiences some of the highest fall-out in the world and hundreds of newly fledged shearwaters and petrels are grounded every year. Once on the ground, these exhausted and confused birds cannot fly again and either die from exposure and starvation or are eaten by feral cats and dogs. Since 1979 more than 32,000 seabirds have been collected by the Save Our Shearwaters (SOS) program on Kauaʻi, with 75% of these being Newell’s Shearwaters.
Every year, hundreds of newly fledged seabirds are disorientated by lights and crash to the ground, such as this Newell's fledgling at Port Allen (Photo by Andre F. Raine)
Collision with Powerlines
During the breeding season, adult birds fly back and forth from their fishing grounds at sea to their breeding colonies in the mountains. Across their paths lie utility lines, which can pose a collision risk to flying birds such as in areas where they are elevated well above the height of surrounding vegetation. This is a particular threat in areas where birds funnel out from valleys or gather near breeding colonies, and an unknown number of adult birds die every year from collision with these wires.
Powerlines can create a significant collision risk for birds flying to and from breeding colonies (Photo by Marc Travers)
Less is known about threats to these birds at sea, but as with seabirds around the world it is highly likely that various threats at sea are also taking their toll on Hawaiʻi’s shearwaters and petrels. These threats can include marine pollution (such as plastics and oil slicks), reductions in prey from overfishing, mortality through by-catch, and the far-reaching ramifications of climate change.
Threats at sea are still poorly known for Hawaii's endangered seabirds.