Recovery Plan for the Northern Spotted Owl - DRAFT

Obviously, these statements hold only for powers well below 1.0 and forappropriate ranges of the variables, and as noted above, the specific predictionsof the regression model were often in error by 0.08 to 0. 1O or even more.Nonetheless, the conclusions above provide at least a rough guideline to theways that power is affected by altering the variables.This analysis suggests that a minimum of 8 years probably will be required for80 percent probability of detecting trends in owl populations unless suchtrends exceed 3 percent and more than 10 owls are recorded per 100 stations.Such a program probably would require that more than 1,000 stations bevisited per year. If 12 years of data are available to estimate trends, then 600stations per year, if visited on a 4-year cycle, might be sufficient to detectannual trends in the 2 to 3 percent range, particularly if eight or more birdsare recorded per 100 stations. Obviously these conclusions are based on theassumptions inherent in the model, and these assumptions can be refined andimproved as data from the monitoring program are collected. Furthermore, itmust be remembered that these surveys do not detect trends in the totalpopulation; they provide information only about the territorial population.Breeding Bird Survey data: Breeding Bird Survey data from a 25-year period(1966-1990) for hawks and owls were used as a surrogate for long-term spot-Table A.5. Description of data sets used to estimate number of years required toobtain reliable estimates of long-term trends.Average AverageState or Number Birds per Percent Autocor-Species Province Years Routes Route Change relationa4Turkey vulture Florida 1966-90 22 5.2 -1.4 1.99Maryland 1966-90 43 4.7 3.3 2.03Ohio 1966-89 24 1.5 3.1 1.50Oklahoma 1967-90 23 4.0 0.2 1.25+Black vulture Alabama 1966-90 28 2.1 2.1 2.56Florida 1966-90 21 4.7 0.1 1.78Red-tailed hawk Kansas 1967-90 29 2.1 1.1 2.07Oklahoma 1970-90 23 1.6 3.1 2.00Wisconsin 1966-90 57 0.7 4.3 2.18Red-shouldered hawk Florida 1971-90 23 2.0 0.9 3.01American kestrel New York 1974-90 46 1.4 -1.6 2.42Ohio 1974-90 24 1.3 1.4 2.38Ontario, Canada 1968-90 25 1.0 3.0 1.73Osprey Florida 1966-85 20 1.0 6.9 2.17Great horned owl Kansas 1967-90 29 0.7 2.2 2.48aBased on Durbin-Watson test with a = 0 05;1 = autocorrelation present260