DOI: 10.5061/dryad.3n5tb2rhj
title: Bird community recovery following invasive tree removal

description: Invasive plants can lead to significant changes in the abundance and
 diversity of the existing flora. Restoration programs, therefore, largely
 focus on the recovery of the vegetation. Faunal responses have received
 less attention. Here we examined whether or not bird communities recovered
 following removal of a native, invasive tree in South Eastern
 Australia with a view to evaluating whether this could be used as
 a tool for assessing the effectiveness of the remediation programs.
 Pittosporum undulatum is an Australian native tree that has become highly
 invasive in areas well outside its original range within Australia and in
 many other regions of the world. In the Azores, for example, it is
 associated with changes in bird communities. In Australia, high density P.
 undulatum is the cause of major declines in biodiversity of flora and the
 total suppression of regeneration of Eucalyptus. Its removal from nature
 reserves across temperate south eastern Australia has been effective in
 allowing many plant communities to recover, but the impact on birds is
 unknown. We compared the species richness, density and functionality of
 local resident bird communities across original remnant vegetation and
 invaded areas with those that had been cleared of invasive P. undulatum
 populations at different times. Areas infested with P. undulatum had fewer
 carnivorous birds but overall there did not appear to be any strong
 influence on species richness, or density. However, when invaded areas
 were examined at a finer scale by partitioning the observations into
 ‘above’ or ‘within’ and ‘below’ the dense P. undulatum canopy, strong
 differences were detected with fewer birds and fewer species relative to
 the diversity and abundance of birds in the Eucalyptus overstory. Our work
 demonstrates that while P. undulatum provides habitat for birds, there is
 a difference in the relative proportions of different functional groups.
 This is important, particularly in light of the long-term decline in
 ground dwelling bird communities across the temperate regions of the
 continent. We conclude that birds are a useful bioindicator of habitat
 health and that the inclusion of avian monitoring programs could improve
 the evaluation of the efficacy of restoration projects.
description: <i>Site selection and bird surveys</i>
 Ten sites across peri-urban areas of Melbourne, in south-eastern
 Australia, were selected to evaluate their bird communities (Table 1). The
 vegetation at these sites has been surveyed and analysed in a previous
 study (O’Leary et al. 2018 <i>Forest Ecology and
 Management</i> 408: 112-120). Sites were selected to contain (1) an
 area of uninvaded, remnant vegetation supporting a
 <i>Eucalyptus</i> overstorey of varying species composition
 consistent with local conditions (“reference control”); (2) an area
 currently infested by <i>P. undulatum</i> (“invaded”); and (3)
 a formerly invaded area where <i>P. undulatum</i> had been
 removed (“cleared”). Two sites (Ferntree Gully and Sherbrooke Forest)
 lacked invaded patches but are included here for analyses that do not
 depend on a sequence from control to invaded to cleared patches. We used
 Ecological Vegetation Class (EVC) mapping supported by on-ground
 observations to ensure that the vegetation patches within a site supported
 similar vegetation (DELWP 2017). Sites ranged in size from 1–12 ha. The
 management area at each site was characterised as having a severe
 <i>P. undulatum</i> infestation (30–70% canopy cover) prior to
 removal work. Bird surveys were conducted on three
 separate mornings at each site from mid-May to late June of 2017. Surveys
 were conducted within the first three hours after sunrise. Following a
 modified version of the process established by Loyn (1986) and outlined in
 Loyn et al. (2007), i.e. 10 minutes surveying time was implemented for
 each hectare of sampling area at each site, to a maximum of 20 minutes.
 This timeframe has been observed as appropriate to survey bird communities
 within south eastern Australian forests, whilst reducing the risk of bias
 towards conspicuous species with distinctive and/or frequent
 calls.  All birds observed by sight and call within and
 below the vegetation canopy were identified to species level. Birds flying
 overhead were not included in the study. Bird species relative abundance
 was determined by dividing the total number of birds observed over the
 three surveys at each site. Surveys distinguished bird use of the habitat
 within or below the <i>P. undulatum</i> canopy (PU) from use
 of the overstorey (NPU) due to the predicted large effects of dense
 <i>P. undulatum</i> canopies. Density was determined by
 dividing the numbers of birds by the area surveyed.
 Values of five traits reflecting ecological functionality (life
 history, habitat preference, and feeding guild) were extracted for each
 bird species identified (Higgins et al. 2006 Handbook of Australian, New
 Zealand and Antarctic Birds, Vol 1-7, Oxford University Press, Melbourne,
 Australia.).  <i>Statistical
 analysis</i> Differences in bird species
 richness and individual abundance among reference, invaded, and cleared
 vegetation types and between the <i>P. undulatum
 </i> understory and overstorey in invaded sites were tested with
 one-way ANOVAs. To compare species richness in individual feeding guilds
 across the three vegetation types, we used Kruskal-Wallace tests, due to
 the smaller numbers of species involved in each guild. The effect of time
 since <i>P. undulatum</i> removal was tested with linear
 regression on relativized measures of species richness and individual
 abundance (richness or abundance in cleared patch divided by richness or
 abundance in the corresponding reference control). To summarize the
 differences and similarities among bird communities in the three
 vegetation types we employed principal components analysis (PCA) of bird
 species presence/absence data using the prcomp function in R (R Core Team
 2017). Loadings on the first two principal components were examined to
 account for the contribution of individual species to the community
 configuration. We repeated the PCA using bird abundance data using
 nonmetric multi-dimensional scaling (NMDS) and checked that the results
 were biologically meaningful as suggested by Björklund (201, Evolution,
 73(10), 2151-2158). Since all results were in qualitative agreement, we
 present PCA of the presence-absence data here. Scores on the first two
 principal components were compared among reference, invaded, and cleared
 vegetation types using Wilcoxon signed-rank tests. PCA
 was also used to investigate the functional response of bird communities
 to <i>P. undulatum</i> infestation and removal. Mean
 functional trait values in the species assemblage were calculated from the
 traits of individual species weighted by the abundance of individuals of
 the species. All data were centred and scaled to unit variance prior to
 analysis. All analyses were conducted using the R statistical platform (R
 Core Team 2017).
 <i>Processing</i> The data was
 originally assembled in csv files for analysis in R and they are provided
 as supplementary data in that form. Here we have collected the files into
 a single Excel file for ease of upload.
description: The data is presented as four sheets in a single Excel file. Each
 sheet corresponds to a figure in the paper and is clearly labelled as
 such.  The file is called O'Leary Data - birds in Pittosporum
 undulatum sites.xls