Urbanization and phenology
Phenology is an aspect of a species’ ecological niche which is
dynamically associated with both habitat and climate, and vocal
seasonality is typical of most birds globally, even in equatorial
regions where the climate is nearly aseasonal (Thomson 1950, Hau et al.
1998, Beebe et al. 2005, Berman et al. 2023). Among the panel of nine
focal species in this study, some sang seasonally as expected, while
others did not. Historically native species adapted to forest interiors
sang seasonally, while species which have only established breeding
populations within the last few decades, and which are adapted to more
open habitats, sang aseasonally. Singapore has undergone dramatic
urbanization over the last 200 years. That urbanization has led to
changes in land cover, including the introduction of open parkland
habitat resembling woodlands, which in turn has led to a shift in
species composition and the colonization of woodland-adapted birds. Our
results suggest that this conversion of forest into parkland and urban
areas has not only altered the species composition of Singapore, but in
doing so may have also led to an altered community phenology. While it
is clear from the data that historically native forest species are more
seasonal in their song than the more recently established species, it is
less obvious why these two groups of species should have distinct
phenologies. Some potential explanations include dietary differences, or
an initial transitional period of aseasonality for newly established
populations that may last for decades. In the following paragraphs we
discuss the potential factors driving these phenological differences.