Eliška Padyšáková awarded for the Outstanding Article published in Biotropica

My first trip to tropical Africa took place back in the days of my Master´s study of European mammals at the University of South Bohemia. I joined the team of Czech botanists and ornithologists and their students who studied plant–pollinator interactions. For two months, we were alone on a mountain ridge in the open air with limited equipment except for basic cooking supplies, sleeping bags, bags of rice, microcapillary tubes, and pocket refractometers. These limitations taught me to deal with unstable conditions and the sometimes limited accessibility to needed equipment in Cameroon.

I greatly appreciate the opportunity to do real science with such simple equipment and limited funds, and since then I was fascinated by the unique plant–pollinator relationships found there. When I later wondered what I would be doing during doctoral studies, there was no doubt it would be pollination ecology in the Cameroonian mountains. While many things were still simple, by then there were some new conveniences, including solar panels for charging batteries, gasoline generators, waterproof remote video recording systems, computers, and an Internet connection.

Impatiens sakeriana with its long peduncle.

Our study area—the Bamenda Highlands of North-West Province, Cameroon—was once heavily forested. However, repeated cutting and burning had limited the forest to ravines or areas along the waterways and allowed grasslands to expand. Even though the area had maintained its wealth of plant and animal species, we were sad witnesses to dramatic changes to the landscape, including the loss of remnants of species-rich montane forest, the spread of Pteridium aquilinum, and the loss of the last remaining medium-sized mammals.

During our research, we discovered a pollination system that seemed adapted to hovering by birds, something that was thought to be unique to hummingbird pollination plants in the New World. With its long peduncle, Impatiens sakeriana is exclusively pollinated by two sunbirds—the Cameroon sunbird (Cyanomitra oritis) and the northern double-collared sunbird (Cinnyris reichenowi). Both sunbird species perched to exploit floral resources, but to our surprise, they also had a remarkable ability to hover at flowers. Cyanomitra oritis was a more frequent visitor and hovered more often than C. reichenowi, which preferred to perch while feeding on nectar and or robbed nectar by piercing the flowerspur. Interestingly, C. oritis was an equally effective pollinator whether it hovered or perched.

The Cameroon sunbird (Cyanomitra oritis).

After observing that C. oritis hovered for 86% of its visits to another balsam on Mt. Cameroon— Impatiens frithii—we decided to test some common assumptions about how floral morphology influences bird hovering behavior: (1) that a plant’s floral morphology (rather than active choice by birds) is what determines bird foraging strategy; (2) that sunbirds perch whenever possible; and (3) that birds heavier than 9 g should preferentially perch, because the energetic costs of hovering are higher than for perching. To test these ideas, we used a portable remote video recording system, which enabled us to accurately measure key variables such as the rate and duration of bird visits to flowers.

Our results showed that none of the common assumptions above applied to Cameroonian sunbirds. The choice of behavior mode at flowers is based on both plant architecture as well as optimal foraging—although C. oritis is the largest local sunbird (11.9 g), it often hovered at flowers where perches were available. This observation clearly indicated hovering is less problematic for sunbirds than was generally assumed. Similarly, adaptations in this Paleotropical plant to bird hovering bear a striking resemblance to the well-known and highly specialized hummingbird-pollinated systems in New World. Unfortunately, sunbirds are studied far less than hummingbirds. This is especially true in tropical Africa, where (paradoxically) the most sunbirds occur. We hope that by drawing attention to these fascinating and understudies species, we will continue to see fascinating discoveries in the future.

Eliška Padyšáková, Institute of Entomology
Photo: Štěpán Janeček