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.