Too much traffic dampens sunbirds’ appetite

A juvenile orangebreasted sunbird feeding on an Erica. Photo: Sjirk Geerts

Thought it was just people who don’t like living next to busy, noisy thoroughfares? Not so: orange-breasted sunbirds feel the same!

This seems to be the case based on research done by Dr Sjirk Geerts and Dr Anton Pauw of Stellenbosch University (SU), which was recently published in the ecological journal Austral Ecology. These two researchers established that expanses of multicoloured Ericas, which are usually a favoured source of nectar for orange-breasted sunbirds, aren’t exactly in great demand when they grow too close to thoroughfares. And the closer these flowers grow to the road, the less attractive they are to the birds.

The study forms part of the two botanists’ work as participants in the Cape fynbos research group at the SU Department of Botany and Zoology, which focuses on the interaction between plants and animals.

The impact of roads on the mortality rate and breeding behaviour of bird species is already well known but no research has yet been done on the impact of roads in Cape fynbos areas on the feeding behaviour of birds – and therefore also on the consequent pollination of plants by birds, says Dr Geerts.

About 70 of the 400 Erica species in the south-western Cape are pollinated almost exclusively by the orange-breasted sunbird, which is endemic to the region. It was one of these species – Erica perspicua – which occurs in shades from white to dark-pink, that was used for this study.

The research was conducted along a dual-lane road between Pringle Bay and Kleinmond on the Overberg coast. It goes through the Kogelberg Biosphere Reserve, an area that is noted for its rich variety of fynbos. Every day, more than 3 300 mostly light vehicles use the road, which has a speed limit of 100 km.

“Orange-breasted sunbirds love the nectar in the tube-like flowers of so many of our most beautiful Erica species,” Dr Geerts says.

 “When a sunbird inserts its beak into one of these flowers, it breaks the stamen ring inside, which causes a little explosion of pollen. The pollen that lands on the sunbird’s beak as a result is then rubbed off onto the anthers of the next flower that the bird visits – and so pollination takes place.

“We did our survey by looking to see if there was pollen on the anthers of flowers with both broken and intact anther rings,” says Dr Geerts.

According to Dr Geerts, the research follows from a project by two groups of undergraduate SU Ecology students. The Matie students then helped with this research during the collection of the necessary data and the counting of the number of flowers in the study area with broken anthers because of a visit from a sunbird.

 “Traffic is probably one of the most common yet most underestimated influences that human beings have on nature,” Dr Geerts believes. “The study shows us yet again that we should think carefully before we build a new road through a natural area,” he says. “This is especially important within sensitive ecosystems, where both animals and plants depend on one another to ensure food and pollination.

“Roads can be quite problematic in areas where endemic or threatened plants occur,” concludes Dr Geerts. “If plants aren’t pollinated, they can’t form seed and their capacity to flourish becomes restricted.”

Media enquiries:
Engela Duvenage, Media: Faculty of Science, Stellenbosch University
+27 21 808 2684 science@sun.ac.za.