The community structure of bird assemblages on urban Strangler figs

Figs have been regarded as keystone plant resources that support diverse
tropical vertebrate frugivore communities. Planting or conserving large
fig trees, such as stranglers, has therefore been proposed for enhancing
urban biodiversity. We compared the diversity and community structure of
bird assemblages on strangler figs with non-fig urban trees as well as
between the fruiting and non-fruiting fig trees in an urban setting in
Singapore. The total bird abundance across all the fig trees when in fruit
was 4.5-fold higher than on non-fig trees and 3.5-fold higher than when
the same fig trees were not fruiting, but only attracted two more species.
On individual trees, after accounting for the presence of mistletoes, tree
height, the area covered by buildings and road lane density, and distance
to natural vegetation, mean diversity was not different between non-fig
trees and fig trees when they were not in fruit. On the other hand, when
fruiting, each fig tree on average had 1.4 more species, 3 more counts of
non-native birds, and 1.6 more counts of insectivorous birds than when not
fruiting. There was significant compositional turnover between non-fig
trees and non-fruiting fig trees, while community dispersion was
significantly lower among fig trees in fruit. Our results demonstrate that
fig trees provide fruit and non-fruit resources for birds in an urban
landscape but do not necessarily support a more diverse total bird
assemblages than non-fig trees. Instead, bird communities on fruiting
urban figs would be highly homogeneous and dominated by a few species.