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Albatross populations are declining due to invasive mouse species

Albatross populations are declining due to invasive mouse species

The critically endangered Tristan albatross may be more affected by mouse predation than previously thought. Credit: Peter Ryan

New research published in the Journal of Applied Ecologyshows that long-lived species may be more affected by predation than previously thought.

Researchers have used an advanced population model, not limited to analyzing breeding pairs only, to shed light on decades of confusion surrounding the impact of invasive mice on the critically endangered Tristan albatross. Because this new research isn’t limited to just analyzing breeding pairs, it reveals previously missed population declines.

Conservation organizations are often plagued by limited resources and thus struggle to directly help all endangered species. Decisions about the allocation of resources and expenditure are therefore a common problem.

The rate at which a species is declining is often a good indicator of the urgency of intervention. However, a new study published this week shows that for long-lived species, a population may decline long before this trend becomes apparent in previous population studies.

Albatrosses are among the largest flightless birds in the world and can reach an incredibly old age, with a female named Wisdom being tagged over 65 years ago and still breeding. Albatrosses achieve this longevity by reproducing very slowly – they often take 5-15 years before they can breed. In the largest species, a breeding pair can only raise one chick every 2 years, as it takes almost 12 months for the chick to be large enough to fly, and parents need a long rest period between raising the chicks.

Despite being among the largest birds, albatrosses are threatened by some of the smallest mammals: mice. On several islands such as Gough (UK Overseas Territory of Tristan da Cunha), Marion (South Africa) or Midway (USA), introduced alien house mice (Mus musculus) eat albatross chicks and sometimes even adults. Albatross species that breed on these islands have very low breeding success because many chicks are lost to predation.

Albatross populations are declining due to invasive mouse species

The critically endangered adult Tristan albatross in flight. Credit: Peter Ryan

Knowledge of this problem dates back two decades, but the consequences of predation by mice were previously difficult to estimate due to the long lifespan of the albatrosses. As with many seabird species, population studies consider only a portion of the total population, usually the breeding adults. The researchers determined that this lack of informed data may contribute to difficulties in assessing population trends and potential benefits of conservation actions, such as the management of invasive predatory species.

Since monitoring began in 2004, the critically endangered Tristan albatross (Diomedea dabbenena) has lost an average of half of its chicks each season to predation by mice. Still, the breeding population has remained remarkably stable at about 1,500 pairs per year over the same period.

Conservationists are confused about the impact of mouse predation on albatross populations. The eradication of mice on Gough Island, the main breeding ground for albatross, would prove to be an ambitious operation, although the question remains: What benefits would such a project bring to albatross populations?

A new article published this week in the Journal of Applied Ecology gives a convincing answer. A consortium of researchers funded by the Agreement on the Conservation of Albatross and Petrel used an advanced population model that no longer restricts research to just breeding adults. This model includes all young albatrosses, as well as adults taking a break from breeding, which roam the southern oceans and therefore cannot be counted by ornithologists.

Contrary to previous studies, the scientists found that the total population of the Tristan albatross has decreased by more than 2,000 birds since 2004, despite the stable number of breeding pairs.

Extrapolating 30 years into the future, the researchers further concluded that wiping out mice from their main breeding island would most likely result in a Tristan albatross population that would be 2-8 times larger by 2050 than if the mice stayed.

Albatross populations are declining due to invasive mouse species

This Tristan Albatross wears a leg ring for identification. Credit: Steffen Oppel

However, the population projections involve great uncertainty, especially since it is very difficult to know whether young albatrosses are still alive. After fledging, albatrosses spend 2-20 years at sea where they cannot be explained. This uncertainty makes population size estimates somewhat inaccurate, and when the population is extrapolated 30 years into the future, the range of uncertainty spans several thousand birds. Nevertheless, the new estimates are the most robust to date and provide a lot of new information to guide management decisions.

Bethany Clark, BirdLife International Seabird Science Officer, said: “It is incredibly difficult to track albatrosses because a large proportion of the population is always away from the breeding colony. The advanced population model in this study overcomes some of these challenges and gives managers quantitative evidence of the impact of invasive mice and the potential benefits of eradication.”

Anton Wolfaardt, project manager for mouse-free Marion, added: “This new study is incredibly important for Marion Island, where mice also kill albatrosses. It confirms the importance of exterminating mice on Marion Island to create a positive conservation future for the the island’s globally important albatross populations.”

John Cooper, information officer of the Agreement on the Conservation of Albatross and Petrel, emphasized the importance of implementing these findings in future conservation efforts.

“In addition to the ongoing problems of albatross bycatch in fisheries, this study gives us hope that some albatross populations can be restored with technically feasible management measures that can now be implemented if governments fulfill their obligations under the Migratory Species Convention and fund these efforts.” support. “

Overall, the study’s conclusions support the decision that investing in the eradication of mice on islands where mice kill albatross is likely to be a highly effective strategy for restoring populations of these ocean vagrants.

Conservation plans to protect the albatross

More information:
Steffen Oppel et al, Cryptic population decline due to invasive species predation in a long-lived seabird supports the need for eradication, Journal of Applied Ecology (2022). DOI: 10.1111/1365-2664.14218

Provided by British Ecological Society

Quote: Albatross Populations Decline Due to Invasive Mouse Species (2022, June 20) retrieved June 20, 2022 from https://phys.org/news/2022-06-albatross-populations-declining-due-invasive.html

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