A COMPARISON OF GOODNESS-OF-FIT TESTS FOR ANALYSIS OF NEST ORIENTATION IN WESTERN KINGBIRDS (TYRANNUS-VERTICALIS)

Computer simulations and Western Kingbird (Tyrannus verticalis) nest orientation data were used to compare the properties and assumptions of four goodness-of-fit test. The results and relative abilities of each test to detect different patterns of nest orientation were evaluated. The computer simulations showed that each method was powerful in detecting unimodal patterns. However, Rayleigh's Z and Watson's U2 lacked the robustness for detecting bimodal patterns demonstrated by Rao's U. Computer simulations demonstrated a lack of robustness and low power in detecting directional avoidance patterns, but also demonstrated that each method performed with low Type I error and high power when analyzing data with no pattern. Nest orientation of Western Kingbirds exhibited a high degree of variation between years, but appeared to be generally polymodal with modes in the north, south and east. The detection of a significant pattern of nest orientation was dependent on the analytical method used. Chi-square analysis showed significant departures from a uniform distribution in each of four years and all years combined. Rayleigh's Z indicated significant nest orientation only in 1986. Watson's U2 and Rao's spacing test both indicated significant nest orientation for all years combined, and years 1985 (Rao's spacing test only) and 1986. Rao's spacing test has distinct advantages in the analysis of nest orientation and other circular data over other commonly used goodness-of-fit tests, especially if the data are polymodal. Rao's spacing test accounts for many of the statistical implications a researcher must consider when analyzing nest orientation data. It is more flexible; able to handle more types of circular data with fewer limiting assumptions; can detect polymodality; and is more powerful with small sample sizes. In addition, the nest orientation of Western Kingbirds and other species is probably affected by multiple factors such as microclimate, predation and habitat structure which make the use of Rao's spacing test indespensible in determining the nature of the pattern of nest orientation of Western Kingbirds.