Nest-site competition and killing by invasive parakeets cause the decline of a threatened bat population.

Dailos Hernández-Brito,Javier Juste,Martina Carrete,José L Tella,Carlos Ibáñez

doi:10.1098/rsos.172477

Abstract

The identification of effects of invasive species is challenging owing to their multifaceted impacts on native biota. Negative impacts are most often reflected in individual fitness rather than in population dynamics of native species and are less expected in low-biodiversity habitats, such as urban environments. We report the long-term effects of invasive rose-ringed parakeets on the largest known population of a threatened bat species, the greater noctule, located in an urban park. Both species share preferences for the same tree cavities for breeding. While the number of parakeet nests increased by a factor of 20 in 14 years, the number of trees occupied by noctules declined by 81%. Parakeets occupied most cavities previously used by noctules, and spatial analyses showed that noctules tried to avoid cavities close to parakeets. Parakeets were highly aggressive towards noctules, trying to occupy their cavities, often resulting in noctule death. This led to a dramatic population decline, but also an unusual aggregation of the occupied trees, probably disrupting the complex social behaviour of this bat species. These results indicate a strong impact through site displacement and killing of competitors, and highlight the need for long-term research to identify unexpected impacts that would otherwise be overlooked.

Highlights

Biological invasions are considered as one of the most serious threats to biodiversity worldwide owing to their impacts on native biota and ecosystem functioning [1]
Little attention has been paid to the potential impacts of non-native species invading urban environments because it is often assumed that these habitats hold low biodiversity, which is mainly represented by common, widespread human commensal species, leaving vacant niches for invaders [35]
We demonstrate a process by which an invasive bird species, mostly occupying urban environments [28], impact a threatened bat species

Summary

Introduction

Biological invasions are considered as one of the most serious threats to biodiversity worldwide owing to their impacts on native biota and ecosystem functioning [1]. Biodiversity can be challenging owing to the variety of potential, multifaceted impacts [1]. 2 invasive bird species may impact native species through different mechanisms such as predation, competition, hybridization or disease propagation [2]. Most research has focused on only a few invasive species. The most recent review of studies on the impacts of invasive birds shows that published research focusing on potential impacts only exists for 18% of non-native bird species introduced worldwide [3]

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Conclusion