IMPLICATIONS OF CLIMATE CHANGE FOR NORTH AMERICAN WOOD WARBLERS (PARULIDAE) Paul K. Strode INTRODUCTION Recent investigations of long-term ecological data in relation to climate change reveal statistically significant shifts in the timing of seasonal biological events that are temperature driven (1). However, some species are linked to environmental clues that are unrelated to climate. For example, wood warbler migration from the tropics is initiated by photoperiod (2) whereas the phenology of their caterpillar prey and budbreak of the prey’s leafy hosts in the northern latitudes are synchronized with accumulating spring temperatures (3). I analyzed years of wood warbler migration timing for eastcentral Illinois and eastern North Dakota and spring temperature data for a hypothetical migration route northward through the upper Midwest. I tested the hypothesis that bird migration timing is largely unrelated to the timing of spring and predicted that birds would show no significant change in migration timing even while the timing of spring is advancing due to climate change. REFERENCES 1. Parmesan, C., and G. Yohe A globally coherent fingerprint of climate change impacts across natural systems. Nature 421: Hagan, J. M. III, T. L. Lloyd-Evans, and J. L. Atwood The relationship between latitude and the timing of spring migration of North American landbirds. Ornis Scandinavica 22: Lawrence, R. K., W. J. Mattson, and R. A. Haack White spruce and the spruce budworm: defining the phenological window of susceptibility. Canadian Entomologist 129: Root, T.L., et al Fingerprints of global warming on wild animals and plants. Nature 421: DISCUSSION Climate change appears to be altering the spring temperature pattern in opposite directions along the hypothesized migration route. There is potential for the timing of migration to become uncoupled from the timing of food resources during migration and on breeding grounds because global climate change is not occurring uniformly throughout the region. Therefore, birds are under selective pressure to adjust the timing of their northward movements to coincide with the spring peak in caterpillar biomass. But the limits to this adaptability are unclear, especially if selection for migration timing is contradictory along the migration route (later springs in the south, earlier in the north). Even if these mixed environmental signals can be overcome, there may not be enough variation in the photoperiodic response for migrating birds to adjust rapidly to earlier springs. Future studies should seek to more accurately predict the ecological and even economic consequences of declining Neotropical migrant songbird populations, especially if climate change continues to alter the spring temperature pattern in the northern latitudes, and only by discovering, analyzing, and maintaining long-term phenological data can we expect to validate the predictions of climate change (4). METHODS Migration data for the years were taken from the original records of numerous observers during scientific surveys. Data from were recorded by the Champaign County Audubon Society and from by the author. The Fargo arrival dates were recorded by the Fargo-Moorhead Audubon Society. Each year included the first sighting by any observer during censuses beginning in February and conducted at least weekly. All Midwest weather stations available through National Climate Data Center within the hypothetical migration route of the warblers were assessed and only those with surface temperature records dating back to at least 1912 were included in the analyses. A base 5º C thermal model for caterpillar activity was used to determine the beginning of the peak in spring caterpillar activity at a 300 Degree Day accumulation. Figure 1. Hypothesized migration route for wood warblers through Urbana, Illinois (USA), with weather station data (date of 300 DD) for the years Numbers are change in days of the timing of spring (300 DD) over the 100-yr period. Figure 2. First arrival dates for eight wood warbler species through Urbana, Illinois, and Fargo, North Dakota. P- value is the probability that the slope of the change over time = 0. Figure 3. Spring trophic asynchrony.