Abundance, biomass and energy use of native and alien breeding birds in Britain

Tim M Blackburn,Kevin J Gaston

doi:10.1007/s10530-018-1795-z

Abstract

We quantify the contribution of alien species to the total breeding population numbers, biomass and energy use of an entire taxonomic assemblage at a large spatial scale, using data on British birds from 1997 and 2013. A total of 216 native and 16 alien bird species were recorded as breeding in Great Britain across the two census years. Only 2.8–3.7% of British breeding bird individuals were alien, but alien species co-opted 11.9–13.8% of the energy used by the assemblage, and contributed 19.1–21.1% of assemblage biomass. Neither the population sizes nor biomasses of native and alien species differed, on average, in either census, but alien species biomass is higher than native species biomass for a given population size. Species richness underestimates the potential effects of alien bird species in Britain, which have disproportionately high overall biomass and population energy use. The main driver of these effects is the ring-necked pheasant (Phasianus colchicus), which comprised 74–81% of alien biomass, yet the breeding population of this species is still only a small fraction of the estimated 35 million birds released in the UK in autumn. The biomass of this release exceeds that of the entire breeding avifauna, and suggests that the pheasant should have an important role in structuring the communities in which it is embedded.

Highlights

Floras and faunas worldwide are increasingly colonised by alien species—those moved by human activities to areas beyond the natural biogeographic boundaries to their distributions (Blackburn et al 2011)
We based our analyses on the British breeding bird population size estimates published in the earliest (Stone et al 1997) and most recent (Musgrove et al 2013) Avian Population Estimates Panel (APEP) reports; we refer throughout to population estimates from 1997 and 2013, the data underlying the estimates derive from different ranges of earlier years
We considered Category C3 species to be native, as these can technically be considered re-introduced rather than alien species

Summary

Introduction

Floras and faunas worldwide are increasingly colonised by alien species—those moved by human activities to areas beyond the natural biogeographic boundaries to their distributions (Blackburn et al 2011). Alien species are concerning for conservation biologists and environmental managers because they may exert negative impacts on native species, leading to population declines and even extinctions. Evans et al (2016) applied the new Environmental Impact Classification for Alien Taxa (EICAT) protocol (Blackburn et al 2014; Hawkins et al 2015) to categorise the impacts of 415 bird species with known alien populations. There was a complete absence of information on the impacts of more than 70% of alien bird species. These species may or may not be having detectable effects on native species, but in the absence of data it is impossible to say (Evans et al 2016)

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