Invasive Mice Pose Risk of Extinction to Albatross Species

Cryptic population decrease due to invasive species predation in a long-lived seabird supports need for eradication

Steffen Oppel, Bethany L. Clark, Michelle M. Risi, Catharine Horswill, Sarah J. Converse, Christopher W. Jones, Alexis M. Osborne, Kim Stevens, Vonica Perold, Alexander L. Bond, Ross M. Wanless, Richard Cuthbert, John Cooper, Peter G. Ryan

Summarized by Michael Hallinan

What data were used? This study uses data collected on the breeding population of Tristan Albatross (Diomedea dabbenena) from 2004 to 2021 on Gough Island, in the southern Atlantic Ocean, where they almost exclusively live. All adult birds were marked and identified using metal rings for identification across annual visits during breeding season. This resulted in 4,014 albatross having encounter histories, and a very high probability that any breeding individual will have been detected if the nest had not failed early as they are faithful to their breeding sites. In addition to population metrics the number of nests per study area was recorded.

Methods: From the population size and demographic data an estimation of population trajectory, annual survival probability, and probability of returning to breeding grounds were calculated. These models were used to create population projections under three different scenarios. One scenario where mouse predation of the hatchlings did not change average breeding success and survival, one where mouse eradication lead to an increase in annual breeding success, and one where gradual increase of mouse predation decreases adult survival by 10%

Results: Generally, between 2004 and 2021 albatross breeding pairs didn’t seem to decrease statistically significantly. However, when also considering immature and non-breeding birds there was a detectable decrease in the global population of ~1% per year. Since albatross survival was quite high, this long-term decrease seems to be explained by low breeding success which is later investigated in the three scenario projections. Within these projections, under scenario A (where mouse predation stayed the same) the population steadily declined up through the model. Under scenario B (where successful mouse eradication occurred) the albatross population experienced an increase to 1.8-7.6 times its current size by 2050. Lastly, under scenario C (where no mouse eradication occurred and impacts worsened) the population declined significantly by 2050 with less than 2000 birds remaining.  

A shaded range line graph which presents observed breeding population and estimated total population from 2005 to 2021, as well as modeled total populations from 2021 to 2050. Breeding populations were consistently between 2000 individuals and 4000 individuals for this period with little variation outside of this range. The estimated total population however, begins at about 10000 individuals in 2005 and steadily decreases with some plateaus and peaks till about 8000 individuals in 2021. In addition, this graph then presents modeled data from 2021 to 2050 of each of the three scenarios. In scenario A (where no change occurs) the median population declines steadily from about 8000 to a little under 7000 individuals by 2050. In scenario B (where mice are successfully eradicated) the population experiences a median population increase up to just under 10000 individuals by 2050 but estimation errors result in a very wide credible interval which ranges from as high as approximately 17000 to a little under 8000 individuals in 2050. Lastly, in scenario C (where mice population increases and no eradication occurs) the median estimated population falls under 2000 individuals plus or minus 1000 by 2050.
This diagram shows observed population size on Gough Island between 2004 and 2021 (all data left of the dashed vertical line) where the black data points and regression represent the breeding population and the green line represents total estimated population size including unobservable immature and non-breeding birds.The three lines and intervals shown to the right side of the dashed line present the three scenarios through 2050. The lines represent the median values and the shading represents the 95% credible interval.

Why is this study important? The Tristan Albatross is classified as critically endangered based on a previous demographic analysis, finding that the species might go extinct within 30 years. This study creates a better projection for albatross population health under the three scenarios, which allows for significantly improved conservation efforts and a data-based sense of urgency regarding their conservation. 

The big picture: A series of Albatross population health and nest quantity data from 2004 to 2021 was recorded. It was used to model future population health development among three different scenarios regarding invasive mice predation on the albatross chicks. One where mice predation stayed the same, one where it got worse, and one where the mice were successfully being eradicated leading to increased albatross breeding successes.  If the mice were to be eradicated, albatross populations could experience a significant increase by 2050 with a population of up to 7.6 times today’s size. 

Citation: Ryan, Peter G. (2022/06/18). Cryptic population decrease due to invasive species predation in a long-lived seabird supports need for eradication. Journal of Applied Ecology, n/a, -.

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