Applying camera traps to detect and monitor introduced mammals on oceanic islands

Lucas Lamelas-López,Iván Salgado

doi:10.1017/s0030605319001364

Abstract

AbstractThe introduction of mammal predators has been a major cause of species extinctions on oceanic islands. Eradication is only possible or cost-effective at early stages of invasion, before introduced species become abundant and widespread. Although prevention, early detection and rapid response are the best management strategies, most oceanic islands lack systems for detecting, responding to and monitoring introduced species. Wildlife managers require reliable information on introduced species to guide, assess and adjust management actions. Thus, a large-scale and long-term monitoring programme is needed to evaluate the management of introduced species and the protection of native wildlife. Here, we evaluate camera trapping as a survey technique for detecting and monitoring introduced small and medium-sized terrestrial mammals on an oceanic island, Terceira (Azores). Producing an inventory of introduced mammals on this island required a sampling effort of 465 camera-trap days and cost EUR 2,133. We estimated abundance and population trends by using photographic capture rates as a population index. We also used presence/absence data from camera-trap surveys to calculate detection probability, estimated occupancy rate and the sampling effort needed to determine species absence. Although camera trapping requires large initial funding, this is offset by the relatively low effort for fieldwork. Our findings demonstrate that camera trapping is an efficient survey technique for detecting and monitoring introduced species on oceanic islands. We conclude by proposing guidelines for designing monitoring programmes for introduced species.

Highlights

Introduced species threaten native biodiversity and natural resources (Vitousek et al, ; Doherty et al, ), are the second most important cause of biodiversity loss, after habitat destruction and fragmentation, and on islands have been the main driver of wildlife population declines and species extinctions (Millennium Ecosystem Assessment, )
The introduction of mammals is a major cause of species extinctions on oceanic islands (Biber, ), and most introduced mammal species became established after European colonization (Vitousek, )
We evaluated camera trapping as a survey technique for detecting and monitoring introduced small and medium-sized terrestrial mammals on a remote oceanic island

Summary

Introduction

Introduced species threaten native biodiversity and natural resources (Vitousek et al, ; Doherty et al, ), are the second most important cause of biodiversity loss, after habitat destruction and fragmentation, and on islands have been the main driver of wildlife population declines and species extinctions (Millennium Ecosystem Assessment, ). Island ecosystems are vulnerable to introduced mammals because of loss of antipredator behaviour in many island species (Blumstein & Daniel, ), high rates of endemism High rates of species invasion and extinction of native fauna and flora on oceanic islands have resulted in biotic homogenization (i.e. the gradual replacement of native biota by introduced species; McKinney & Lockwood, ). The introduction of mammals is a major cause of species extinctions on oceanic islands (Biber, ), and most introduced mammal species became established after European colonization (Vitousek, ). Each new introduction of mammals increases the number of native species lost, and the probability of extinction is higher for oceanic island endemic species than for mainland species (Blackburn et al, ). The number of bird species that have become extinct following human colonization of oceanic islands is estimated to be in the hundreds to thousands (Blackburn et al, ), and most extinction events have occurred or are occurring in island ecosystems (Courchamp et al, )

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Conclusion