Comparison of abundances between 1982 and 2018:
In order to compare abundances and biomasses between the two time
periods, we used two approaches. First, we fitted the log-normal model
(Oksanen et al. 2013) to the rank abundance distribution of
species in 1982 and 2018 (McGill et al. 2007) and compared the
parameter estimates using 1000 parametric bootstrap replicates. An
overlap in log-normal SADs’ confidence intervals suggested no change in
community structure. Second, we regressed the abundances and biomasses
in 2018 against those in 1982 using GLMs (Supplementary Information). To
determine if the slope of the abundance regression was equal to one, we
used a Likelihood Ratio Test with a null model constraining intercept=0
and slope=1 and the alternative with a free slope. We partitioned the
data by foraging guild, foraging strata, sociality and habitat
specialists and re-ran regressions using the same approach as for the
entire data set. We excluded outlier species from each test using Cook’s
distance (Venables & Ripley 2002). We performed a non-parametric
bootstrap test to evaluate the number of outliers expected by chance
using alpha=0.01. To account for phylogenetic dependency, we computed
the linear model with a correlation structure based on the community’s
phylogeny and compared the BIC of the latter model with the model
without phylogenetic correlation structure. We repeated this procedure
for 1000 phylogenetic trees from BirdTree.org and report the mean and
the 2.5% and 97.5% quantiles difference in BIC between the
non-phylogenetic and phylogenetically corrected models.