QUANTIFYING DISTURBANCE FACTORS AND EFFECTS IN COMMON TERNS (STERNA HIRUNDO) USING VISUAL, AUDIO, AND REPRODUCTIVE DATA

The common tern is designated as a species of special concern in Upstate New York. The largest inland tern colony in New York is located on Oneida Lake, which is habitat to many other colonial waterbird species and an area of high human use during the tern breeding season. In addition to disturbances caused by recreational use, Oneida Lake’s common terns are exposed to potential disturbances from tern research and cormorant management. Researchers intensively monitor tern nests during the breeding season, and USDA-APHIS participates in a lake-wide hazing program to control doublecrested cormorants (Phalacrocorax auritus). The goal of this study was to discern and describe disturbances which might affect the projected sustainability of the common tern colony on Oneida Lake. To evaluate the status of common terns on Oneida Lake, reproductive and population data were gathered. In order to classify, quantify, and evaluate the extent of human disturbance to the tern colony, I observed the colony during the summer of 2003 and collected visual and audio data of potentially disturbing events and the terns’ reactions. Analyses of these data were performed using conventional statistics and Raven spectrogram analysis software. Common tern population and reproductive parameters from 2003 were examined for deviation from patterns established by 1979-2002 data. Additionally, I examined differences in reproductive data among the different islands where terns nested in 2003. An estimated 449 pairs of terns established 621 nests in 2003. A total of 952 chicks hatched from 1587 eggs in 362 nests over the season, and 389 chicks fledged. These numbers are comparable or higher than those of past years and indicate that the Oneida Lake colony seems to be maintaining its population. Nests on Little Island were more likely to hatch than those on other islands. Further study is needed to determine why significant (at alpha=0.05) differences in nest fates among breeding islands occur I classified disturbances to the tern colony on Oneida Lake as relating to tern researchers, the USDA-APHIS cormorant hazing program, recreational watercraft, aircraft, and natural phenomena. The terns’ behavioral and audio responses were quantified. Significant differences among disturbance categories were demonstrated through ANOVAS (F=14.82, df =5, p < 0.001; F=22.77, df=5, p<0.001). Tukey’s test of multiple comparisons yielded significant differences in disturbance-related window counts including differences between controls and both researcher and natural disturbance categories (27.9 vs. 105 terns/minute, d=7.47, p<0.001, 27.9 vs. 72.9 terns/minute, d=5.50, p<0.001) and the researcher disturbance category and watercraft, hazing, and aircraft disturbance categories (105 vs. 43.5 terns/minute, d=5.68, p< 0.001, 105 vs. 39.2 terns/minute, d=6.00, p< 0.001, 105 vs. 39.0 terns/minute, d=3.81, p=0.0027). Audio analysis demonstrated significant differences in alarm calls given between controls and researcher disturbance (53.1 kip/min vs. 140 kip/min, p<0.001) and watercraft disturbance categories (53.1 kip/min vs. 106 kip/min, p<0.001). Tern research activities appeared to cause the most disturbance. Further research is needed to quantify potential impacts of cormorant hazing programs on common terns The tern colony seems self-sustaining, but studies to determine the effects of less intense nest monitoring on common tern reproductive output are needed. Innovative and less intrusive techniques for measuring nesting efforts could benefit both the study species and those attempting to manage it.