"This is probably the best example to date of ecology causing a sexual dimorphism," said Temeles of his findings. "When I think about it, this is a pretty convincing example."
According to Temeles, the question raised by the research is "Did ecology play a role in the evolution of human sex differences?"
"I've been telling my students for six years that something was up with these hummingbirds," said Temeles. "No one decided to take up the project. So last year I got a sabbatical and went down [to St. Lucia]."
To perform the study, Temeles and three Amherst students traveled to the island of St. Lucia in the West Indies from May 5 to May 14 and again from May 28 to June 28 of last year. The study involved observing male and female hummingbirds as they went to feed and subsequently pollinate two species of plant in the genus Heliconia, H. bihai and H. caribaea.
Jillian L. Brennan '01, Jedediah N. Horwitt '01 and Irvin L. Pan '00 served as field assistants on Temeles' project. Together, they observed the birds, entered data, and brainstormed the implications of certain results.
"'I've spent a lot of time talking and thinking about evolution with Ethan, and it was great to be part of a project where we got to document an interesting case study in evolution," said Pan.
For an entire month, the four woke up at dawn to go on long hikes and difficult car rides to reach the center of the island where the birds resided.
"The best way I can describe the experience is intense," said Horwitt. "It was an adventure."
One memorable moment was when the group climbed to the top of the rainforest canopy.
"It was quite a thrill to look at these birds face to face," said Horwitt.
Temeles and the three students discovered that male hummingbirds mainly fed and defended the flowers of H. caribaea, while females mainly fed and defended the flowers of H. bihai. At three separate feeding sites the flowers of H. caribaea were significantly shorter and straighter than the flowers of H. bihai. The birds' feeding times were also shorter at their preferred flower.
In the hummingbird species Eulampis jugularis males are 25 percent heavier than females. However, the bills of females are 30 percent longer and 100 percent more curved than the bills of males. In other birds, the larger body of the male corresponds with a larger bill.
Temeles, who has studied sexual dimorphism throughout his academic career, first noticed hummingbird dimorphism in 1990. He immediately suspected that the evolution of these birds differed from typical bird evolution.
The bills of the male and female hummingbirds were perfectly suited to the flowers Temeles and his students observed them feeding on.
Research from another area called the Forestière Reserve, which lacks H. caribaea, provides additional evidence for Temeles' theory. In this area males were observed feeding at the flowers of the red-green-bracted H. bihai.
In addition to his research, Professor Temeles is serving as a consultant to several governments in the Lower Antilles.
Temeles intends to continue his fieldwork for at least 15 more years. Every island in the Lesser Antilles contains different patterns of variation in local hummingbirds and flowers, and Temeles hopes to research each region more extensively. He is always looking for eager assistants, and urges students who are interested to think about the opportunity.
Although hummingbird research has come to a near standstill in recent years, Temeles hopes that the compelling results of his study will spark renewed interest in the field.
His findings are being sent to the Encyclopedia Brittanica and will be included in evolution textbooks in the future.