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

Abstract

Invasive species are one of the greatest drivers of biodiversity loss worldwide, and the eradication of invasive species from islands is a highly efficient management strategy. Because eradication operations require large financial investments, uncertainty over the magnitude of impacts of both invasive species and their removal can impede the willingness of decision makers to invest in eradication. Such uncertainty is prevalent for long‐lived species that display an inherent lag between life stages affected by invasive species and those used for population status assessments. Albatrosses are amongst the longest‐living bird species and are threatened on land by invasive species and at sea by industrial fisheries. As in many seabird species, usually only a segment of the population (breeding adults) is used for status assessments, making it difficult to assess albatross population trends and the potential benefit of conservation action, such as the management of predatory invasive species. We used population monitoring and mark‐recapture data to estimate the past population trajectory of the critically endangered Tristan albatross Diomedea dabbenena by accounting for unobservable birds at sea in an integrated population model. We then projected the future population trajectory of Tristan albatrosses for scenarios with or without predation by invasive house mice Mus musculus on their main breeding site, Gough Island. The adult breeding population remained stable between 2004 and 2021, but breeding success was low (31%) and our model indicated that the total population (including unobservable immature birds) decreased from a median estimate of 9,795 to 7,752 birds. Eradicating invasive mice leading to a two‐fold increase in breeding success would result in a 1.8–7.6 times higher albatross population by 2050 (median estimate 10,352 individuals) than without this intervention. Low reproductive output for long‐lived species may lead to a cryptic population decrease, which can be obscured from readily available counts of breeding pairs by changes in the population structure. Mouse eradication is necessary to halt the ongoing population decrease of the Tristan albatross, even if this decrease is not yet apparent in the breeding population size.

Advances in remote sensing of emperor penguins: first multi-year time series documenting trends in the global population

“…Seabird populations also include substantial ‘unobservable’ life history stages (pre-breeding juveniles, non-breeding adults) that strongly affect population viability but are difficult to monitor directly because these stage classes are absent from colonies at the time of the count. For example, demographic monitoring of Tristan albatross ( Diomedea dabbenena ) revealed that reproductive failure diminished the abundance of unobservable (non-breeding and pre-breeding) stage classes across an 18-year period, despite apparent stability in the number of observable breeders [ 53 ]. Because we are similarly capturing a subset of the population (and in our case, not the breeding population), the framework we present here may represent an index of demographic parameters for emperor penguins, such as breeding success, of which sustained changes would ultimately influence the unobservable breeding population of emperor penguins (during austral winter).…”

Foraging behaviour and habitat use during chick-rearing in the Australian endemic black-faced cormorant (Phalacrocorax fuscescens)

“…However, as for most seabirds, both partners contribute to raising the chicks, and therefore, negative impacts on one sex could be expected to reduce reproductive success ( Schreiber and Burger, 2001 ). While cormorants, as long-lived seabirds, are resistant to occasional breeding failure, repeated failures can be expected to eventually impact demography and population sizes ( Oppel et al, 2022 ; Schreiber and Burger, 2001 ).…”

Migratory patterns of two major influenza virus host species on tropical islands

“…Seabirds are highly sensitive to environmental changes and significant modifications of their biology in response to climatic [40] and anthropogenic changes, such as habitat modifications and alien predator introductions [41], have been described. Seabird numbers have decline by 70% over the past 60 years, with the highest decreased reported for terns (86%; [42]).…”