Scientist at Work Blog: A Native Big Island Songbird

David J. Flaspohler, an avian ecologist and conservation biologist at Michigan Technological University, writes from Hawaii, where he is studying the influence of human activities on birds and the natural ecosystems that support them.

Sunday, May 27

They say that in Hilo, you don?t tan, you rust. With about 127 inches of rain per year, Hilo is said to be the third-rainiest city in the United States and one of the wettest in the world. There is at least some rain 275 days a year.

In the high canopy of the kipuka forests, overcast skies make it difficult to confidently identify the tiny color bands on birds? legs or to judge the condition of an active nest; rain and fog make it all but impossible. After a 45-minute drive up to Powerline Road with my colleagues Nolan, Iciar, Dan and Justin, we return to Hilo.

Unlike scientific research in a laboratory, where a lot of variation can be controlled, field ecology involves working around unpredictable forces like weather. For us, the isolation that makes the kipuka attractive for research also makes it challenging. My aborted mission for today was to check the status of a Hawaii elepaio nest in one of the largest and most distant kipuka.

Checking this single nest involves a 45-minute drive from Hilo, another 35-minute rumble down the lava road, then a 40-minute hike across the rolling, fractured pahoehoe lava to reach the kipuka. It then can take 10 to 30 minutes to find the nest, using a GPS device and a sketch made by the person who found the nest.

Depending on luck and how active the birds are, it can take 30 minutes or more of concentrated watching with binoculars to determine whether a nest is still viable and whether the birds are incubating or feeding nestlings. I am lucky when I do reach the nest the following day. The female?s tail can be seen sticking out from the nest cup.

As you can see, we invest an enormous amount of time and resources simply to get one data point from a single nest. We check nests every three days, so a successful nest found during the building stage may need to be checked 8 to 10 times. For each species, we strive to find at least 25 nests; with more nests we can look at how kipuka size, nest height and rat presence influence the probability of success.

The subspecies of elepaio on the Big Island have a special place in native Hawaiian culture. Songbirds are generally shy and retreat from humans, but the elepaio is curious and will often closely approach and even follow a single person through the forest. From ancient times to the present, shapers of outrigger canoes, called kalai wa?a, have relied on tall, straight Acacia koa trees for building voyaging canoes ? a foundation of Hawaiian culture. Canoe builders consider this bird a guardian spirit, and it is said that if the insect-eating elepaio shows interest in a koa tree, it is a sign that it is infested with insects and thus a poor choice for a canoe. Felling and working an enormous Acacia koa tree into a canoe using traditional tools involves thousands of hours, so it is easy to understand why Hawaiians developed detailed protocols for selecting the right tree ? and why they would revere the elepaio.

Early work on our research project by Devin Leopold, a Stanford University graduate student, revealed that although rats climb trees, they show up less often the higher you get in the canopy. We use tracking tunnels baited with coconut to attract rats that must step on an ink pad and then on a sticky white card to reach the coconut, leaving their footprints behind. Devin placed these on the ground and at 6 and 12 meters up on tree trunks, and found that rat foraging is less intense in the highest forest canopy. Most of the kipuka birds nest in the canopy, and larger kipuka generally have taller trees. So we suspect that nest success would be higher in larger kipuka, considering only rats as a source of nest failure.

Rats are omnivores and could be influencing native birds in a more indirect way as well. Many endemic Hawaiian birds feed largely on the nectar of flowers, supplementing their diet with insects. During the breeding season, they must increase their intake of insects to secure enough protein and fat for fast-growing nestlings. Rats also eat insects on the ground and trees, so they compete with native birds for this key food resource.

To help understand how rats might be influencing arthropods in the kipuka, Erin Wilson, a postdoctoral researcher with Dan Gruner at the University of Maryland, is monitoring insects in the kipuka with and without rats. She has also deployed netting around individual ohia tree branches to exclude foraging birds so we can look at how insect abundance varies when exposed to bird and rat predation, when exposed to only birds, and when exposed to neither bird nor rat predation.

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