Data for: Interspecific competition and facilitation coexist in mixed-species bird flocks of montane coniferous forests in Taiwan

Besides competition, positive interactions also play an important role in
shaping the social structure of mixed-species bird flocks. This study
aimed to illuminate the interspecific interactions of competition and
facilitation in mixed-species bird flocks. We recorded the foraging
behavior and microhabitat use of flocking species in montane coniferous
forests of Taiwan under different social contexts. Foraging niche breadth
and niche-overlap with other flocking species were compared between
individuals inside and outside of mixed flocks. For the three microhabitat
variables (foraging locations, vertical strata, and horizontal strata),
relationships between niche-overlaps of heterospecific pairs of these
flocking species and their corresponding interspecific associations were
determined using a simple linear regression. While in mixed flocks, two
understory species, Taiwan Fulvetta Fulvetta formosana and
Yellowish-bellied Bush-Warbler Horornis acanthizoides, shifted their
foraging from shrubs upwards into coniferous trees. Meanwhile, Flamecrests
(Regulus goodfellowi) moved downwards vertically within the canopy, and
Black-throated Tits (Aegithalos concinnus) spread out horizontally along
branches. In addition, Flamecrests applied many more sally-hovers inside
of mixed flocks than outside of flocks. All four species are insectivores
which might find it more difficult to obtain sufficient food during the
colder winters when food resources become scarcer. Therefore, they may be
using the increased vigilance afforded by the flock to expand their
foraging niches and thus to increase their foraging opportunities inside
mixed flocks. Furthermore, niche-overlaps of heterospecific pairs of the
11 common flocking species were positively correlated with their
corresponding interspecific associations on all three microhabitat
variables. These results indicate that a greater foraging niche-overlap
between two flocking species would result in higher coexistence of the two
species in mixed flocks. Consequently, facilitative interactions occurred
in these mixed-species flocks in addition to competitive interactions.