Invasive Mouse Threatens Albatross Population

Because of invading mouse species, albatross numbers are falling. New research published in the Journal of Applied Ecology shows long-lived animals may be more vulnerable to predation than previously assumed.

Using a Population Model to Simulate the Decline

Researchers used a sophisticated population model that is not limited to evaluating only breeding pairs to shed light on decades of uncertainty regarding the impact of invading mice on the critically endangered Tristan albatross. Because this new study is not limited to breeding pairs, it exposes previously unknown population decreases.

Conservation groups are sometimes hampered by a lack of funding, making it difficult to aid all vulnerable species actively. Decisions on where to deploy resources and spend money are thus a typical issue.

The rate at which a species' population declines is frequently a useful measure of how urgent intervention is required. However, new research published this week reveals that a population may decline long before this pattern is visible in prior population surveys for long-lived species.

Albatrosses are the world's largest flying birds and may live to be quite elderly, with one female named Wisdom, who was tagged over 65 years ago, still reproducing today. Albatrosses live so long because they reproduce so slowly-it might take 5-15 years to start breeding.

A breeding couple of the biggest species can only raise one chick every two years since it takes about 12 months to develop mature enough to fly, and parents require a considerable rest between rearing chicks.

While being among the biggest birds, Albatrosses are endangered by some of the tiniest mammals-mice. Non-native house mice (Mus musculus) devour albatross chicks and adults on various islands, including Gough (UK Overseas Territory of Tristan da Cunha), Marion (South Africa), and Midway (USA). Many chicks are lost to predators, resulting in very low breeding success for albatross species nesting on these islands.

Although this problem has been known for two decades, the repercussions of mouse predation have been difficult to assess due to the albatrosses' extended lifetime. In population studies, as in many seabird species, a subset of the whole population, often the breeding adults, is considered.

Losing Chicks

Since monitoring began in 2004, the severely endangered Tristan albatross (Diomedea dabbenena) has lost half of its chicks to mouse predation. During the same time, however, the breeding population has remained relatively steady at around 1500 pairs each year.

Conservationists are perplexed by the impact of mouse predation on albatross populations. Eliminating mice from Gough Island, the principal breeding place for albatross, would be an impressive operation, but the question remains: What advantages would such a project give to albatross populations?

This week's new article published in the Journal of Applied Ecology gives a strong response. A group of scientists supported by the Agreement on the Conservation of Albatrosses and Petrels employed a sophisticated population model that no longer limits the study to breeding individuals.

Extrapolating 30 years ahead, the researchers predicted that removing mice from their main breeding island would result in a Tristan albatross population that was 2-8 times greater in 2050 than if the mice stayed.

However, the population forecasts are uncertain, owing to the difficulty in determining whether baby albatrosses are still alive. Albatrosses spend 2-20 years at sea after fledging, where they are unaccounted for. This uncertainty makes population size estimates fairly imprecise, and when extending the population 30 years into the future, the range of error covers several thousand birds. Nonetheless, the latest estimates are the most robust yet, giving a wealth of new data to help guide management decisions.

Importance of the Study for Conservation

The Agreement on the Conservation of Albatrosses and Petrels' Information Officer, John Cooper, emphasized the necessity of incorporating these results into future conservation efforts.

Overall, the study's findings support that investing in mouse eradication on islands where mice kill albatrosses is likely to be a very effective method for restoring albatross populations.