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.
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, -. https://doi.org/10.1111/1365-2664.14218