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Synergistic impacts of aggressive species on small birds in a fragmented landscape

Citation

Westgate, Martin; Crane, Mason; Florance, Daniel; Lindenmayer, David (2021), Synergistic impacts of aggressive species on small birds in a fragmented landscape, Dryad, Dataset, https://doi.org/10.5061/dryad.jm63xsj93

Abstract

1. Attempts to conserve threatened species in fragmented landscapes are often challenging because factors such as habitat loss, habitat degradation and dominant species interact to reduce threatened species’ capacity to survive and reproduce. Understanding how threatening and mitigating processes interact is critical if conservation measures are to be effective.

2. We used data from long-term monitoring of bird populations and multivariate latent variable models to quantify how Australian woodland birds respond to the presence of the Noisy Miner, a despotic species known to exclude other bird species. We then investigated the extent to which the presence of other aggressive species exacerbates the impacts of the Noisy Miner, and to what extent these impacts can be mitigated by dense midstorey plantings.

3. We found strong synergies between the Noisy Miner and two other aggressive species (Grey Butcherbird and Pied Butcherbird), despite weak effects of butcherbirds in isolation.

4. The impacts of aggressive birds are most pronounced for small-bodied species; but these impacts are lessened in the presence of high midstorey cover.

5. Synthesis and applications. Accounting for interactions reveals that revegetation may be capable of improving conservation outcomes even when the proximate cause of species declines (i.e. exclusion or predation by aggressive bird species) cannot be managed directly.

Methods

This dataset consists of 1520 observations of 36 bird species at 220 locations. They are presented as three inputs necessary to run a latent variable model as implemented in the R package 'boral'. Species observations ('species.csv') are presence/absence (0/1). Site data ('sites.csv') show percentage overstorey and midstorey cover as taken from field surveys; percentage cover of native vegetation in a 500m buffer around each site from remote sensing; the year of observation; and whether the Noisy Miner or either of the Grey or Pied Butcherbirds were seen on that occasion. Trait data ('traits.csv') show log body mass and are taken from the scientific literature. Data have been grouped from 6 observations per year (3 plots x 2 observers) for this analysis.

Usage Notes

Observations that contain missing values have been removed. Prior to analysis all percentage cover variables were log(x + 1)-transformed and scaled to a mean of zero and a standard deviation of one. The variables 'year' and 'log body mass' were also scaled but not log-transformed.