This project will explore, through a series of observations and experiments on over 300 nesting attempts per year, how climate change will affect Tree Swallows nesting near Ithaca, New York, and their insect prey. The proposed research will network 25 active nests with temperature sensors, motion-detecting web cameras and Radio Frequency Identification readers to provide details on avian responses to environmental change. The proposed research investigates the effects of different thermal environments, not only on the birds directly, but indirectly through observations and experiments on the effects of temperature on insect flight.
The project will directly support five graduate students and nine undergraduates and indirectly support the research of at least 20 more from a diversity of ethnic backgrounds. The Ithaca site will continue to serve as the test-bed for techniques and approaches at other Tachycineta study sites in the pan-American Golondrinas de la Americas research network. Data from this project will cap a 25-year dataset, made available to the public at the Ithaca page of the Golondrinas web-site:
One of Earth's most dynamic environments is the aerosphere, the dynamic layers and currents of the atmosphere and the animals that live there. The major predators in this realm are the aerial insectivores: birds and bats that prey on flying insects. Of these, swallows are by far the most tractable organisms to study. The aerial insects upon which swallows prey are the flying reproductive stages of aquatic and terrestrial larvae. These insects, without the ability to actively thermoregulate, can only fly when air temperatures are sufficiently warm to allow their wing muscles to contract fast enough for flight. As a result, swallow food, and swallow reproductive success, are highly sensitive to air temperatures, and one of the principal foci of this research is a better understanding of these links between daily weather variation, the availability of insects in the air column, and the effects of both temperature and insect densities on swallow reproduction and survival. In this project, we continued a daily aerial insect monitoring program that was begun in 1989, and we supplemented that 12 m suction sampler with drift and emergence trap samplers. This increased sampling yielded the most thorough characterization of the aerial insect fauna over Ithaca that we have ever had, and perhaps the most thorough data set anywhere in North America on the relation between flying insects and temperature. We have published the first of the studies that will come of this work, a detailed study of how cold snaps in spring and summer affect flying insect densities and the mortality of chicks who cannot be provisioned by parents when available insect densities plummet. We have many more papers in progress on the effects of weather on insect flight behavior, including a detailed set of experiments measuring in the lab, with insects of different Orders, differneces in the temperatures that can sustain flight. One of our biggest pushes in this period was a two-year monitoring of the densities of emerging aquatic insects both at our pond study area and in the waters of Cayuga Lake, a very large deep lake about 5 km away. We have hypothesized that the much larger thermal inertia of the lake maintains much more stable water temperatures than in our much smaller ponds, and that foraging swallows can find food over the lake on days that are too cold for insects to be emerging from the ponds. We are in the midst of analyzing all the resulting insect samples and temperature data and are exploring stable-isotope and radio-tag methods to nail down swallow movements when they disappear from our study area during cold snaps. To better understand the swallows in this predator-prey system, we have been studying direct weather effects on foraging behavior: we find that the height and distance that swallows fly in search of prey for their offspring depends much more strongly on daily variation in local weather conditions than it does on the number or age of the offspring being fed or the age of the parent swallows doing the feeding. Another surprisingly strong effect of weather is revealed by a model we are now writing up based simply on daily maximum temperatures and calendar date that can explain a great deal of the annual variation in population lay-date distributions. These results are valuable contrasts to much of the work we do on variation in individual quality, as we find that when a swallow lays in a give season is the best indicator we have of how many eggs it is going to lay, how strong its immune response to novel antigens is going to be and how well it performs in standardized flight tunnel tests. Timing of breeding has a important connections to global change. We recently published a comparative paper with colleagues across North America showing that swallow food supplies tend to plateau in late spring after a pretty regular increase early in the season. Thus they are not subject to a sharp peak in food availability for rearing chicks, and, unlike some European birds, they are not experiencing the same sort of mismatch in phenology between their breeding dates and peaks in their prey. There is still the possibility, however, that the entire aerial insect fauna is shifting earlier in its emergence dates and leaving fledglings and molting adults with dramatically reduced food availability in the critical early fall period. We are testing this possibility using our long-term data on seasonal insect availability. We are also preparing one of the most detailed analyses ever that simultaneously estimates survival and breeding dispersal of a songbird. These analyses are producing the best estimates we’ve ever had for survival across various strata in our long-term study population and it is serving as a valuable template for studies evaluating the effects of various covariates on swallow survival.
