Oh, bird poop!  Study shows invasive island predators can disrupt life outside

Oh, bird poop! Study shows invasive island predators can disrupt life outside

DeKalb, Illinois – A New study It identifies the “circular economy” of seabirds connecting land and sea and shows how invasive predators on the island can disrupt even what’s going on offshore beneath the waves.

Gray-faced hummingbird in Kurapuki, Mercury Islands, Aotearoa, New Zealand. Image credit: © Steph Borrelle

What’s more, at the heart of it all is, well, bird poop.

led by Professor Holly Jones From Northern Illinois University, researchers studied four islands north of New Zealand in the same archipelago — two with a prolific history of invasive mammals such as rats, rabbits, or cats, and two untouched by non-native predators.

The seabirds themselves are some of the best hunters in the ocean, feeding on squid and fish. On the islands where they breed, seabird guano, also known as bird poop, is so rich in nitrogen and other nutrients that it is sometimes called “white gold.” Besides the dead meat of seabird prey, guano fertilizes the island’s soil and flies from the islands to the sea, where it drives plant diversity and enriches the near-shore aquatic ecosystems used by marine life as sources of habitat and protein.

Scientists hypothesized and demonstrated that the loss of seabird populations on islands would affect the composition and quality of inshore seagrass, or macroalgae, which play a vital role in fishery habitats, carbon sequestration, and atmospheric oxygen production.

NIU Professor Holly Jones

“We found that nearly half of the variation in the composition of algae or seagrass in the near-shore ecosystem can actually be attributed to characteristics on the island — specifically seabird density, seabird-derived nutrients in the soil and invasion history,” Jones said.

The new study was recently published online in the journal, environmental restoration. Jones is a faculty member of Northern Illinois Center for Community Sustainability It holds NIU’s joint designations Biological Sciences And the Environmental Studies. It was co-authored by Dr. Lindsey Rankin, a former Ph.D. at NIU. The student who led a dive team in recovering marine specimens, Dr. Stephanie Borrell From Birdlife International.

An island country, New Zealand’s only indigenous mammals are bats, so invasive predators have particularly strong effects. Globally, 31 percent of seabirds are threatened with extinction, the highest percentage of any bird group. Over the past four centuries, most species (including seabirds, mammals, and reptiles) have been island species, and most of these extinctions were caused by invasive predators.

Lindsay Rankin collects data on the composition of the macroalgae community surrounding Kurapuki, Mercury Islands, Aotearoa, and New Zealand. Image credit: Evan Brown.

“By looking at the characteristics of some seagrass communities, we can identify islands with a history of invasive mammals, and the amazing amount of difference underscores the importance of the land and marine connections that seabirds provide,” Jones said. “It was surprising to find that land variables are just as important in driving the formation of seaweed communities as marine variables.”

Runoff from islands fertilizes the near shore ecosystem, affecting the abundance and species of seagrass; It also enriches the levels of nitrogen isotopes in plants, making them more nutritious for marine organisms.

“Herbivores in the ocean need nutritious greens, and the nutritional content in seaweed is passed through the trophic levels in the ocean,” Jones said.

“We found that the formation of the near-shore ecosystem recovers more quickly from the uptake of nutrients by the seagrass,” she added. “On the island where invasive mammals were removed three decades ago, the composition of seaweed species was similar to that of pristine islands. But levels of nitrogen uptake in those species remained low.”

Jeanette backlit off the coast of Kurapuki Island, Mercury Islands, Aotearoa, New Zealand. Image credit: © Steph Borrelle

Jones and her colleagues note that some types of algae are better indicators of seabird influence than others. On the two islands with a history of predator invasion, the researchers found that four of the six seaweed species studied showed depleted levels of seabird-derived nitrogen, indicating that they had not fully recovered.

The considered islands are part of the Mercury group of islands, located eight kilometers from the east coast of Coromandel, New Zealand. The burrowing seabirds that inhabit the islands include the wobbly shearwaters, the two-footed shearwaters, the small shearwaters, the northern common petrel, the Beecroft petrel, the gray-faced petrel, the white-faced petrel, and the little blue penguin.

Among the many variables studied, scientists determined the density of burrows on the islands. On the newly exterminated island of Ohao, a single apparently uninhabited burrow was discovered. The average burrow density of seabirds on Kurapuki Island, where predators were wiped out 30 years ago, still represents only 14% of the burrow density on islands that have never been invaded.

Seabird burrows in Kurapuki. Image credit: © Steph Borrelle

The researchers also calculated the density of sea urchins feeding on seaweed. Previous studies indicated the importance of herbivores in the composition of the macroalgae community.

“Seabird burrow density, soil nutrients and invasion history, together explain greater variability in macroalgae compared to sea urchins, the dominant herbivores of seagrass,” Jones said.

Elimination of the predator can lead to the restoration of the colonization of seabirds and is critical to the recovery of the population. But to better inform policies and restoration efforts, it is important to understand whether removing predators is sufficient to expedite the restoration of terrestrial and marine links.

“The results of our study indicate that seabirds take a long time to recover from mammalian invasions, and their impact on terrestrial and marine food webs, also takes a long time,” Jones said. “This work is unique in that most researchers study the effects of invasive mammals and island recovery both on land and at sea, but rarely link the two together.”

Media contact: Tom Parisi

About NIU

Northern Illinois University is a nationally recognized, student-centered, public research university, with expertise that benefits its region and spans the world in a variety of fields, including the sciences, humanities, arts, business, engineering, education, health, and law. With its main campus in DeKalb, Illinois, and learning centers for students and working professionals in Chicago, Naperville, Oregon, and Rockford, NIU offers more than 100 areas of study while serving a diverse and international student body.

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