RESULTS
Historically native species were more vocally seasonal than
recent parkland colonizers . The seasonality indices of native forest
species ranged from 0.25–0.69. The seasonality indices of parkland
colonizers were lower, ranging from 0.01–0.25 (Figure 3, Figure 4).
Only the most seasonal species, Little Spiderhunters and Drongo-cuckoos,
were entirely silent for months at a time. Species with slightly weaker
seasonal trends in vocal behavior, including Rufous-tailed Tailorbirds
and Pin-striped Tit-babblers, had a distinct season of heightened vocal
activity but could still be heard to a lesser extent during the off
season. In contrast, parkland colonizers like Straw-headed Bulbuls and
Asian Koels did not follow any seasonal pattern – peak vocal activity
occurred in different months between the two years and concentrated
irregularly throughout the year.
The peak vocal season for most species was around June. Of the
five focal native forest species, all but one had their peak seasons in
May-June. Little Spiderhunters, the only nectarivore, had a peak vocal
season earlier in the year, in March (Figure 3, Figure 5, Table 2).
Lineated Barbets did not show a seasonal trend but did have an
interannual trend – they were heard more often in year two than in year
one of the study.