Large invasive herbaceous plants decrease the taxonomic, functional and phylogenetic diversity of birds via their reproductive traits

Birds are among the organisms most impacted by plant invasions, the
effects of which are particularly conspicuous during the breeding season.
Birds can incorrectly assess the suitability of large, invasive hogweeds
Heracleum sp. in south-eastern Poland when selecting nesting sites early
in spring when the developing invaders do not yet differ substantially in
form from the rest of the vegetation. One would expect lower bird breeding
success in areas with invasive hogweeds. Furthermore, this may shift bird
community composition towards species with filtered traits, which may then
be reflected in various measures of diversity. To assess these
expectations, we conducted bird surveys at 74 sites, arranged as 37 pairs
(with invasive Heracleum vs. control). The presence of Heracleum was
associated with lower bird taxonomic and phylogenetic diversity.
Functional richness (calculated based on species' reproductive
traits) was also lower at sites with these invaders. The species detected
at Heracleum sites were characterised by traits associated with rapid
breeding, e.g., small clutches, short incubation periods, and short
fledging periods. We show that the bird community at sites with hogweeds
became less diverse and composed of random species sharing similar
reproductive traits. Bird communities with low diversity at Heracleum
sites tended to exhibit a common trait syndrome. These patterns provide
insights into the mechanisms of how invasive plants may lead to the loss
of some traits and species in bird communities.