by Sage Rohrer
I first set out to Costa Rica for the OTS Tropical Biology course almost six weeks ago (or years ago??) filled with excitement about seeing hummingbirds. The Ruby-throated Hummingbird found in my temperate zone home of Missouri is respectably flashy, but no lone species can compare to the brilliant colors and diversity found in the tropics.
So we reached our first field site at Palo Verde National Park and saw lots of monkeys, crocodiles, trogons, and mosquitoes… but basically no hummingbirds. And then we went to CIRENAS and saw manakins and more monkeys and antlions and a sea turtle laying eggs… but no hummingbirds. And then we went to the cloud forest of Monteverde….
and the world changed.
A tiny, idyllic café set in the foggy mountains had feeders arranged along the porch, which were swarmed with flashing jewels of all shapes and colors.
Well after this, I was sure I had reached the zenith of OTS hummingbirds. Seven gorgeous species in an hour, all sufficiently close and fearless to let me photograph them. Day made. But this was just the beginning.
We left the cloud forest (too soon), collectively holding our breath as our top-heavy bus lurched its way down narrow mountain roads with smoking brakes, until at last we reached the hot lowland rainforest of La Selva. During our time there I saw many ant species and learned the fun fact (through experience…) that trap-jaw ants have a tiny anterior hairlike sensor that triggers their mandibles to slam shut with one of the strongest proportionate forces on earth, but the hummingbirds were a bit sparse. However, I did at least get my first hummingbird pollination action shot of the trip.
With the final OTS weeks in sight, we made our way back up the chilly mountains to explore more cloud forests and the new tundra-like ecosystem of the páramo. On our way we picked up the last set of brilliant scientists to lead our final faculty projects. And one happened to specialize in hummingbirds!
Our faculty leader wanted to examine possible reasons behind a surprising dominance hierarchy existing between the four most common species on el Cerro de la Muerte – the most dominant species (the Fiery-Throated Hummingbird) is not the largest! We decided to measure proportionate bill size, wing shape, and agility to see if any of those things might provide an advantage in aggression interactions.
To do this, we built an obstacle course – AKA the “torture box”- to measure agility, set up mist nets at another excellent cloud forest café (I guess cafés and hummingbirds are a theme here?), and waited for the hummingbirds to land in the net.
As you can see, conditions were tough.
We captured about 35 hummingbirds and a number of other accident birds who also flew into the mist nets. After analyzing our data, we found some exciting results – dominance in hummingbirds does seem to be related to agility! Relative speeds in completing the obstacle course occurred in the same order as the dominance hierarchy, with Fiery-throated Hummingbirds completing the course faster than other species, regardless of size.
Though I have mist netted other birds before, working with tiny stunning hummingbirds for the first time was the highlight of an already incredible trip. Plus they were pretty cooperative photography subjects.
Until next time, Costa Rica.