In this post, Bea Maas writes about her recent paper with Teja Tscharntke, Shahabuddin Saleh, Dadang Dwi Putra & Yann Clough “Avian species identity drives predation success in tropical cacao agroforestry“.

Birds can make farmers happy. Due to their contribution to the suppression of pest insects in agriculture, their presence can increase the quality and quantity of crop yields. Especially in the tropics, insect eating birds are considered as one of the most important providers of this valuable ecosystem service. Their high impact on ecosystems is partly due to their high mobility and diversity – insectivorous birds exist in almost every terrestrial habitat, feeding on all kinds of existing insects and spiders, including many crop pests.

It is exactly that function that attracts more and more scientists, farmers and other stakeholders worldwide, especially since the economic impact of bird services in agriculture has been recognized – presenting a chance for both species conservation and agro-economics. Accordingly, an increasing common interest exists to integrate valuable ecosystem services, such as the suppression of pest insects by birds, into agricultural management – also because of the need of alternatives to pest management with pesticides and other agro-chemicals.

Cacao plantations close to the primary forest block of the Lore-Lindu National Park in Central Sulawesi, Indonesia (Photo: Bea Maas)
Cacao plantations close to the primary forest block of the Lore-Lindu National Park in Central Sulawesi, Indonesia (Photo: Bea Maas)

But here comes the tricky part: it is poorly understood which mechanisms drive the successful suppression of pest insects by birds. Both species diversity and single species identities play an important role in ecosystem processes. Both local and landscape management affect the biological and functional diversity of different farms. To provide practical implications for the management of ecosystem services, the success of insect eating birds needs to be reduced to its key drivers.

Dummy caterpillars made of plasticine; lengths of 2cm (Photo: Bea Maas)
Dummy caterpillars made of plasticine; lengths of 2cm (Photo: Bea Maas)

We conducted our study on the predation success of birds in Indonesia, the third largest producer of one of the most important tropical ‘cash crop’ systems: cacao agroforestry. On the island of Sulawesi, we selected 15 cacao smallholder plantations that differed in their local shade tree management and distance to primary rainforest within the agricultural landscape. The number of birds in our study area was determined using standardized point counts and capture-recapture methods. To quantify the predation success of birds, we used dummy caterpillars made of plasticine. The plasticine experiment is an easy method to study bird predation on larvae of butterflies and beetles, which present one of the most abundant and serious pests in many agroforestry systems, including the cacao in Indonesia. We could identify bird predation marks on the artificial prey in our plantations and link these results to our observations of the bird community.

The Lemon-bellied White Eye (Photo: Bea Maas)
The Lemon-bellied White Eye (Photo: Bea Maas)

We have good news for both cacao farmers and conservationists in Sulawesi. (1) Although 69 different bird species could be recorded, the predation success of birds was dominated by one common species: The Lemon-bellied White Eye. That species should be easy to attract with additional nesting sites provided by shade trees or boxes. (2) Both the Lemon-bellied White Eye as well as the quantified predation success profited from nearby primary forest.

Accordingly, the proximity of rainforest is not only important for biological diversity and conservation, but also to safeguard ecosystem services and high activity rates of insect eating bird species. “Why do birds suddenly appear, every time you are near?” – the love song by The Carpenters reflects an important part of our results, assuming that ‘you’ is a tropical rainforest. These findings demonstrate once more that birds can not only satisfy us by being pretty and a popular symbol for peace – they can contribute to pest suppression in agriculture, providing their services all day long, and therefore should be taken into account in agricultural management practices.

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