Revealing altered community phenology with autonomous recording units and machine learning

Submitted by Michi on 18 July 2024.

Photo above: a short-tailed babbler in Singapore (Photo credit: Sin Yong Chee Keita). Short-tailed babblers are historically native to Singapore, but today can only be found in protected nature preserves. Like most native species, they time their breeding so that fledglings emerge at the time when mast fruiting is most likely to occur.

Text by Laura Berman

Most of the time, birds breed seasonally – even in tropical climates where it seems like almost any time of year would be just as good. An exception to this rule was found in a recent study based in tropical Singapore, where only some of the birds breed seasonally.

Laura Berman and coauthors deployed autonomous recording units (ARUs) in forests in Singapore to collect 24/7 soundscapes for two full years, then trained machine learning classifiers to identify the courting songs of nine bird species (read the research article here). The timing of courting song is typically a good indicator of when birds are breeding. Curiously, historically native forest species bred seasonally, as expected, but recent parkland colonizers bred all year round.

                                                           Coauthor Wei Xuan Tan deploying an autonomous recording unit (ARU) in Sungei Buloh Nature Preserve in Singapore. ARUs had to be revisited every month for two years to collect the full dataset. Soundscapes were used to determine the seasonality of each bird species. Photo credit: Laura Berman.

The small tropical island of Singapore used to be almost entirely covered in closed canopy rainforest, with endemic birds dependent on that dense foliage. In the last 100 years, Singapore has urbanized rapidly, and many of those forests have been converted into high-rise apartments interspersed with grassy lawns. This change in habitat was matched by a corresponding shift in species composition. Singapore was colonized by bird species who preferred the new open parklands.

But why should parkland birds breed aseasonally? Those same species do have known breeding seasons inside their native ranges. This kind of pattern has been seen before among invasive birds. For example, when house sparrows first colonized North America they bred year-round. It is possible that newly established populations can benefit from aseasonal breeding if they are expanding into an unoccupied niche, and there is enough food available to successfully raise chicks even during the off season.

Regardless of why exactly parkland birds breed aseasonally, one thing is clear. The urbanization of Singapore has led not only to a shift in species composition, but also to an altered community phenology.

                                                 An Asian Koel in Singapore. Asian Koels are recent colonizers of Singaporean parklands and nest parasites of invasive House Crows – they also breed all year round, unlike native forest species. Photo credit: Sin Yong Chee Keita.

Read the article here.

Comments