Seabird predation effects and population viability analysis indicate the urgent need for rat eradication from Europa Island, western Indian Ocean

Saunier, Merlène; Amy, Maxime; Barbraud, Christophe; Pinet, P.; Ringler, David; Russell, James M.; Corre, Matthieu Le

doi:10.5751/ace-02174-170132

Cited by 5 publications

(10 citation statements)

References 43 publications

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“…While red-tailed tropicbird nesting success was slightly lower with increasing rat activity at nests, this effect was not significant. Again, this result contrasts with reports of rat predation on tropicbird nests elsewhere, which are extremely varied (Fleet 1972(Fleet , 1974Wirtz 1972;Ringler et al 2015;Flores et al 2017;Luna et al 2018;Saunier et al 2022).…”

Section: Impacts Of Rats On Christmas Island Birdscontrasting

confidence: 94%

“…On Christmas Island, rat activity at nests was lower, averaging 0.04 visits h −1 nest −1 (range 0–0.40 h −1 nest −1 ) which could help to explain lower rat predation rates. However, note that on Europa there was no correlation between nest fate and the number of rat visits (Saunier et al . 2022).…”

Section: Discussionmentioning

confidence: 99%

“…The native predator (goshawk; A. fasciatus natalis) also had an impact on the nesting success of both the thrush and to a lesser degree, red-tailed tropicbirds. Saunier et al (2022) noted that brood neglect contributed to nest failure rates on Europa Island caused by black rats and birds of prey (2022). Failure due to brood neglect on Christmas Island was comparatively low.…”

Section: Impacts Of Rats On Christmas Island Birdsmentioning

confidence: 99%

“…Rat densities on islands can be very high, with reports of up to 119 rats ha −1 (Harper and Bunbury 2015). Predation rates of island bird nests by rats can also be high; for example, 36% of Hawaiian Puaiohi (Myadestes palmeri) nests failed due to rat predation , while 22% of tropicbird nest failures on Europa Island were attributed to rat predation (Phaethon rubicaudra; Saunier et al 2022). Rates of rat nest predation potentially vary due to differences in rat density, the availability of alternative resources, the presence of terrestrial land crabs (Woodward 2017), the sensitivity of bird species to rat impacts (with nesting location, egg size and shell density all potentially moderating impacts), and degree of adult nest defence (Jones et al 2008).…”

Section: Introductionmentioning

confidence: 99%

“…Predation rates of island bird nests by rats can also be high; for example, 36% of Hawaiian Puaiohi ( Myadestes palmeri ) nests failed due to rat predation (Vanderwerf et al . 2014), while 22% of tropicbird nest failures on Europa Island were attributed to rat predation ( Phaethon rubicaudra ; Saunier et al . 2022).…”

Section: Introductionmentioning

confidence: 99%

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Investigating the impact of black rats (Rattus rattus) on the endemic and threatened avifauna of Christmas Island

et al. 2023

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Context. Invasive mammalian predators are a primary cause of extinctions, especially on islands. Baseline data on the impact of invasive mammalian predators are critical for deciding whether their eradication or control should be attempted, and for monitoring ecosystem changes over time if control does occur. Christmas Island is a tropical island with multiple invasive species, including two mammalian predators (black rats, Rattus rattus and feral cats, Felis catus). Black rats are known to prey upon island bird species (including their nests) elsewhere, but the severity of their impacts on Christmas Island birds is unclear. Describing these impacts would help managers decide whether rat control is warranted, especially as a cat eradication program underway on the island could conceivably result in increased rat density. Aims. In this study, we quantify the impacts of rats on Christmas Island bird abundance and nesting success. Methods. The abundance of four endemic forest bird species/subspecies (Christmas Island imperial pigeon, Ducula whartoni, emerald dove, Chalcophaps indica natalis, thrush, Turdus poliocephalus erythropleurus and white-eye, Zosterops natalis) was measured using transect surveys. Nest success was measured using remote sensing camera surveillance for one forest bird species (thrush) and one seabird species (red-tailed tropicbird, Phaethon rubicaudra westralis). We explored whether these measures were related to spatial variation in rat density and activity (measured by trapping and inkcards), the presence of other invasive species, habitat and seasonal variables. Key results. Neither rat density nor activity explained the abundance of any forest bird species. Instead, seasonal and habitat features were more consistent predictors of bird abundance. White-eyes were more abundant near yellow crazy ant (Anoplolepis gracilipes) supercolonies. Nest success for thrushes and red-tailed tropicbirds was either not, or only very weakly, influenced by rats. Conclusions. Black rats currently have little effect on the population sizes and nesting success of Christmas Island birds. Implications. This study suggests that rat control is not currently a management priority, but ongoing monitoring of rat density, activity, and impacts is needed to ensure management can respond promptly if rat density or impacts change as cat control progresses towards eradication.

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Section: Impacts Of Rats On Christmas Island Birdscontrasting

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Section: Impacts Of Rats On Christmas Island Birdsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigating the impact of black rats (Rattus rattus) on the endemic and threatened avifauna of Christmas Island

et al. 2023

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Marked differences in foraging area use and susceptibility to predation between two closely-related tropical seabirds

Fayet,

Sanchez,

Appoo

et al. 2023

Oecologia

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Ecological theory predicts that closely-related species must occupy different niches to coexist. How marine top predators achieve this during breeding, when they often gather in large multi-species colonies and are constrained to central-place foraging, has been mostly studied in productive temperate and polar oceans with abundant resources, but less so in poorer, tropical waters. Here, we track the foraging movements of two closely-related sympatric seabirds—the white-tailed and red-tailed tropicbirds Phaethon lepturus and P. rubricauda—breeding on Aldabra Atoll, Seychelles, to investigate potential mechanisms of niche segregation and shed light on their contrasting population trends. Combining data from GPS, immersion, depth and accelerometry loggers, we show that the two species have similar behaviour at sea, but are completely segregated spatially, with red-tailed tropicbirds flying further to feed and using different feeding areas than white-tailed tropicbirds. Using nest-based camera traps, we show that low breeding success of both species—which likely drives observed population declines—is caused by high nest predation. However, the two species are targeted by different predators, with native avian predators mainly targeting red-tailed tropicbird nests, and invasive rats raiding white-tailed tropicbird nests when they leave their eggs unattended. Our findings provide new insight into the foraging ecology of tropicbirds and have important conservation implications. The extensive range and spatial segregation highlight the importance of considering large-scale protection of waters around tropical seabird colonies, while the high level of nest predation provides evidence in support of rat eradication and investigating potential nest protection from native avian predators.

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Long‐term monitoring highlights the positive responses of the seabird community to rat eradication at Tromelin Island, Western Indian Ocean

Saunier,

Amy,

Baumann

et al. 2024

Conservat Sci and Prac

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The eradication of rats (Rattus norvegicus, R. exulans and R. rattus) on islands is essential for the preservation of island ecosystems, including seabird populations, which are particularly vulnerable to rat predation. However, the long‐term positive effects of rat eradication on seabird colonies and populations are often understudied. Brown rats (R. norvegicus) were eradicated from Tromelin Island in 2005. No other significative active restoration actions (such as artificial social attraction, translocation or habitat manipulations) have been implemented, which provides a unique opportunity to investigate natural seabird recolonization and recovery processes after rat eradication. We used seabird annual nest counts conducted from 2005 to 2022 and georeferenced data of occupied nests, to precisely describe the rebuilding of the seabird community of Tromelin Island. Despite the lack of any active restoration actions after the eradication of rats, and the remoteness of the island, 17 years after rat eradication, the seabird community increased from two to seven breeding species, and from 353 to 4758 breeding pairs (total for all species). The recovery of masked and red‐footed booby populations was mostly due to the improved breeding success and in fine to auto‐recruitment. Inter‐ and intra‐specific social attraction accelerated the arrival of new species and boosted their population growth. On a finer spatial scale, recolonizing species showed different patterns of colony settlement linked to intra‐specific attraction. The dynamics of the community of Tromelin Island after rat eradication can be regarded as a natural experiment that informs the processes of colony settlement, population dynamics and connectivity in tropical seabirds. Our results demonstrate the huge benefits of eradicating rats from seabird islands, even when no additional active restoration actions are feasible.

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Seabird predation effects and population viability analysis indicate the urgent need for rat eradication from Europa Island, western Indian Ocean

Cited by 5 publications

References 43 publications

Investigating the impact of black rats (Rattus rattus) on the endemic and threatened avifauna of Christmas Island

Investigating the impact of black rats (Rattus rattus) on the endemic and threatened avifauna of Christmas Island

Marked differences in foraging area use and susceptibility to predation between two closely-related tropical seabirds

Long‐term monitoring highlights the positive responses of the seabird community to rat eradication at Tromelin Island, Western Indian Ocean

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