Cats – people either love them or hate them, but cats have been a major problem for Hawaiian wildlife since their introduction in the 1800s. European colonists kept cats on their ships in order to control mice and rats that plagued the ships and contaminated food supplies. Like the rats, cats made their way to shore and established populations throughout the islands. Birds are now facing predation from both mongoose and cats. Native birds and other species evolved in ecosystems where these types of predators did not exist, therefore have not adapted any defenses against them. As many of these birds do not have the natural instinct to flee, they will remain still even when predators approach – quite literally, sitting ducks. Unlike mongoose, cats are more agile and can access animals in a greater variety of habitat types, including wetlands, forests, and lava fields. Mortality of native forest birds, seabirds, and other ground nesting birds soared as cat populations continued growing.
One species that was hit especially hard is the ‘Ua’u, the Hawaiian petrel. These large seabirds nest in rock crevices on the ground, with hatchlings remaining flightless until they are around 15 weeks old. Parents spend their days at sea hunting for food to bring to the chicks, leaving them unprotected and vulnerable during the day. Since petrels create burrows on the ground to nest in, they are easy targets for cats and mongoose, which are even known to attack and kill adults. These introduced predators have caused severe declines in the petrels, to the point where only a few isolated nesting locations remain. These birds are not able to breed until they reach sexual maturity at around 5 years of age, so even without considering the predation pressure by cats, it would take several decades for populations to return to healthy levels.
Conservationist John Muir once said, “When one tugs at a simple thing in nature, he finds it attached to the rest of the world”. This quote is tremendously relevant when analyzing the huge cascade of ecosystem effects caused by the addition of just one species. Petrels, like other seabirds, are vital players in the nutrient cycle, as their phosphorus and nitrogen-rich excrement provides fertilization for trees and forest plants. The disappearance of the petrels is challenging other aspects of the environment, which will bring larger problems that have no simple solution.
Several management strategies are currently in play to attempt to protect the birds and give populations a chance to rebound back to more sustainable levels. Predator proof fences have been built surrounding nesting sites of seabirds, and while a fence may not necessarily sound like the most secure way to guard the nests, they have been incredibly effective. Additionally, trapping and euthanizing cats and mongoose is practiced at most nesting sites as well.
As a personal side note, I was recently offered a job at Haleakala National Park on the island of Maui, where one of the largest breeding populations still exist. I would be participating in management and protection of the birds by monitoring population sizes and trapping mammal predators on a daily basis. I would be thrilled to be a part of something so important and exciting!
A new, more intensive management approach began just over a year ago in November 2015, which has left researchers and conservationists with high hopes for the program’s success. Petrel chicks and eggs are collected from nests located in especially vulnerable areas and are translocated to a fenced in nesting spot at Kilauea Point on the island of Kauai. The chicks are monitored and cared for daily and are fed a nutritious diet of fish and squid. All chicks in the first translocated group fledged within about a month of being moved, and will spend the next 3 to 5 years of their lives at sea, returning to breed once they reach sexual maturity. Most seabirds imprint on their nesting location and will return there as adults to raise their own chicks. In order for this project to be successful, the chicks will need to have imprinted on the new, safe nesting site at Kilauea Point rather than the site where the chicks were hatched and collected. The next 2 to 3 years will be crucial in evaluating how successful the project will be, as chicks should begin returning to lay their eggs. Experts are confident that their efforts will be worthwhile and will allow petrel populations to begin the extensive recovery process.
I’d like to note that the introduction of cats has had severe repercussions for more than just birds; even aquatic animals like monk seals and sea turtles are impacted in different ways. For the purpose of this blog, I chose to focus on Hawaiian petrels.