Seed Dispersal and Movement of Philippine Frugivorous Birds in a Fragmented Forest Landscape - progress report
Just over a year a ago, Birds on the Brink awarded a grant to Jelaine Gan to help support her research project studying fruit-eating birds in the Philppines. Here, Jelaine provides readers with an update.
Identifying Bird-fruit Links for Philippine species
As part of our research we have created a database of bird-fruit links for the Philippines. From the fruit surveys in the field, we recorded 128 bird frugivory events. This was supplemented with online citizen science data by searching for photographs of birds eating fruits, leading to the addition of 430 records that involved 76 plant species and 82 bird species. Once finalised, this database will be available online for public use. Institutions involved in reforestation activities can use the study to identify what plants to use for greatest biodiversity benefit.
Above: We found this Spotted Imperial Pigeon feasting on the fruits of the Binunga (Macaranga tanarius) during our surveys. The project is collating information on bird-fruit links, or what fruits birds in the forest eat, to understand the mutualistic relationship between fruit-eating birds and fruiting plants.
Radio-tracking of Spotted Imperial-pigeons
We caught two Spotted Imperial Pigeons (Ducula carola) in San Mariano, Isabela. Due to the security issues faced by the team at the original site in Baggao, we had to change locations midway through the project. We found the imperial pigeons in relatively high numbers at Barangay Daragutan East, and we decided to do trapping and tracking here. From March to May 2023, we set-up canopy mist-nets every day, when possible, near the fruiting trees.
However, we had limited success despite the huge effort and ended up catching only two individuals. A male was tracked successfully for 26 days, with 746 location points recorded. The female was tracked for 10 days, and there were 258 location points obtained. We hope to catch and radio-track more imperial pigeons next year in January 2024.
Above: The team tracked two individuals of Spotted Imperial Pigeon in the fragmented forest landscape in San Mariano, Isabela. Their movements can tell us how they are affected by forest fragmentation and also how far they can disperse seeds.
Seed Passage Experiments with Captive Frugivorous Birds
We worked with a wildlife rescue centre and with seven individual birds of four species, using 10 different fruits (Table 1). The protocol was fine-tuned after conducting a pilot-test run. We supplemented the fruits with the regular diet given by the centre and observed them until an hour has passed without any seeds present in the droppings.
Above: The status of seed passage experiments with captive birds in the local wildlife rescue centre. The green coloured boxes indicate successful seed retention time experiment.
The seed retention time (SRT) ranged from 30 to 390 minutes. It varied a lot by bird species and fruit species, likely influenced by fruit size and seed size. The smallest fruit was Hagimit, a type of fig with tiny seeds, and the average SRT across species was 233 minutes. In comparison, the Ylang-ylang, which has the largest fruit, had an average SRT of 193 minutes.
Social Media Brief
Through the support of the Birds on the Brink (BOTB), our team were able to conduct research on fruit-eating birds in the Philippines. We fed native fruits to birds at a local rescue centre and timed how long it takes for the seeds to be ‘pooped out’ (the fancy term is ‘seed retention time’). This can tell us how far the birds can disperse the seeds and understand their role as seed dispersers. In addition, we are collating information on what plants are eaten by which birds based on both field surveys and online citizen science data, creating the first ever database on bird-fruit links for the Philippines.
This database will be made available to the public and serve many purposes. Government and non-governmental organizations involved in reforestation initiatives can use the information to select what native plant species to plant that will be beneficial for birds and biodiversity in general. Planting fruiting trees will attract birds and increase seed dispersal, which will accelerate natural forest regeneration.
Above: This call for citizen science data was posted online on Facebook to gather records on bird frugivory links, populating the first database on such for the Philippines.
Above: With the help of captive birds at the local rescue centre, we determined the seed retention time (SRT) of different fruits. SRT refers to the time it took for the seed to be defecated since the fruit was eaten, and it is an important factor to understand bird’s importance as seed dispersers.
In addition, we have conducted feeding experiments with rescued birds to determine seed retention time. We timed how long the seeds of certain fruits take to be ‘pooped out’ after eating them. This seed retention time is different and varies across bird species, fruit size, seed size, among other factors. Using this information, we can model how far a seed can be dispersed by the bird, and therefore understand the importance of these avian seed dispersers.
Acknowledgments
Thank you for the generous support from the Birds on the Brink (UK Charity No: 1188009), the Rufford Foundation, and the Forest Foundation Philippines. We are also grateful to our local partners, the local government units of Baggao and San Mariano, and the Mabuwaya Foundation.