s part of their summer research internship, Ashley Miniet '10 and Meredyth Duncan '12 engaged in two projects that relate to bird breeding and behavior in Fairbanks, Alaska. Both involve Tree Swallows (Tachycinetta bicolor), a small aerial predator of insects. Despite the Tree Swallow's diminutive size (less than 20 grams), it makes a remarkable spring migration from South America to North America each year to breed. While summering in Alaska, the birds can take advantage of the long days and bug-filled air, both of which are beneficial for raising young successfully!
Tree Swallows and Climate Change
Ashley, funded by a summer research stipend from the Howard Hughes Medical Institute, was in charge of a long-term nest-box study of tree swallows in cooperation with the Alaska Bird Observatory (ABO) in Fairbanks, Alaska. Ashley coordinated ABO's swallow program for elementary through high-school students and led student groups that studied Tree Swallow nesting activity. The observatory owns over 100 nest boxes in local fields and the education program has monitored breeding at this site for over a decade. Consequently the data are quite valuable for understanding how behavior of breeding birds in Alaska may be affected by global warming.
Ashley Miniet '10 (right) coordinated ABO's swallow program for elementary through high-school students and led student groups that studied Tree Swallow nesting activity.
Tree swallows breed in a remarkably intensive time period. Nest building begins in mid-May and by the end of June, five to six naked, blind nestlings hatch from eggs no larger than a blueberry. In just 16 days the young grow to the size of adults, thanks to the round-the-clock provisioning efforts of both parents. Young must rapidly accumulate fat stores to help them make the long migratory journey into South America. Some Tree Swallow populations fly to southern Argentina! Ashley helped students measure young birds in nests and placed a light-weight aluminum band on one leg of each chick. Bands are printed with an individually-specific number to allow future swallow-watchers at ABO to track birds that return in the summers that follow.
Ashley also examined the long-term Tree Swallow dataset and, building on the work of Daisy Yuhas '09, has confirmed that the birds in central Alaska are breeding earlier and earlier each year. The pattern coincides with warmer summer weather that tends to occur earlier each season. She also discovered that birds that follow the early-breeding pattern most markedly are those that are more likely to experience nest failure. The exact mechanisms behind the discovery are unclear, but ABO ornithologists are interested in understanding the important result in more detail.
Ashley examines a swallow chick.
Early Odor Learning in Tree Swallows
Meredyth, funded by a summer stipend from Swarthmore's Natural Science and Engineering Division, assisted me in uncovering basic questions about the sense of smell in birds. Olfaction in birds is a sensory modality long overlooked by ornithologists and a subject that is yielding new insights into avian behavior. The abundance and accessibility of Tree Swallows in Alaska make them an ideal species to examine closely.
The swallow study developed out of a recent discovery made by my Behavioral Ecology seminar. Students found that domestic chicks detected and retained familiarity with environmental odors that they had experienced while still inside the egg. Specifically, students revealed that newly hatched birds that had developed in incubators containing scent were not particularly responsive to the scent after hatching, compared to a control group (that had developed in an incubator without scent). It was as if the scent-treated group had become familiar with the odor and therefore responded less when they experienced it again after they had emerged from the egg.
Meredyth Duncan '12, who took all of the field photos included here, builds new swallow boxes. photo by Eric Engman
Though nearly unstudied in birds, such patterns are well-documented in other groups of animals. For example, newborn rat pups actually respond to garlic odors differently if, during pregnancy, their mother is fed a garlic-laden diet.
On the University of Alaska campus (not far from the Alaska Bird Observatory), Meredyth monitored another set of Tree Swallow nest boxes, each of which had a small tube of peppermint oil attached inside. Adult swallows built their nest, laid eggs, and reared chicks in the minty surroundings. By contrast, the nest boxes at ABO contained no mint oil. When hatchlings at both sites were nine days old, the students tested their response to mint odor. The protocol involved holding each nestling in a warm, specially-made swallow “sleeping bag” until it closed its eyes and fell asleep, while gently puffing scented air near into the bird's nostrils (known as nares) with a squeeze bottle. The degree to which a bird responded by clapping its beak, squirming, or shaking its head was scored. Such behavior is a measure of how potent a bird found the odor to be.
Newly-hatched swallow chicks in a nesting box.
Similar to prediction, birds reared in minty environments reacted less to mint than those that had never smelled mint before. This result - new information about how a bird's chemical senses work - will be written up for publication and paves the way for future tests. Logical next steps include determining: (1) the developmental stage at which odor memories are created in birds, and (2) whether the odors learned at the nest site affect the breeding decisions of offspring that return to Alaska to reproduce the following year. For example, if mint tubes are placed at random in nest boxes next year, one might determine whether birds that were reared in mint preferentially return to breed in minty boxes.
An Alaskan Extravaganza
Julie and Ashley check on a swallow nest box.
Both Ashley and Meredyth had a host of new experiences in Fairbanks this summer with me and my family. In addition to going on day-trips to view wildlife and picking wild raspberries, the two students took at four-day trip to Denali National Park via the Alaska Railway. Inside the Park, the two were lucky enough to see close-up roadside views of caribou, wolves, a grizzly bear, and big horned sheep. They also experienced one of the few days per year when visitors enjoy a breathtakingly clear view of Mt. McKinley, the tallest peak in North America, against the backdrop of Wonder Lake, some 90 miles inside the National Park.
During the ten-week Alaskan experience, the two Swatties not only enjoyed many different adventures, they developed and honed skills in research design, bird monitoring, handling, and scientific data analysis. On one occasion a moose even joined us at the field site while it quietly browsed on tender willow shoots and grass - both of which sounded delicious!