Recovery Plan for the Northern Spotted Owl - DRAFT

ABiases in AUsing the conventions above, either ( or p could be modelled in eight ways, g*t,g+t, t g*T, g+T, T, g or the null case, denoted -. Combinations of these eightstructures for o and p lead to 64 models of the five data sets on adult females.Table C.6. presents the number of model parameters, -2log&(L), and AIC foreach of the models considered.While the AIC-selected model was (OT'Pg J)' some neighboring models weretested to allow a deeper understanding of the data. These tests retain a verygeneral model structure for the recapture probabilities. Three tests were ofparticular interest:Test 1. (o(pg vs. (0tpg T) x 2 = 11.9666, 5 df, P = 0.035.Here, one concludes that there is significant year-specificity in adultfemale survival.Test 2. (O.Pgr) vs. (OTPg.p'). X 2 = 4.930, 1 df, P = 0.026.Here, one concludes that there is a significant linear trend in logit(O).Test 3. (OT, Pg.T) VS. (0t, Pg'r), X 2 = 7.036, 4 df, P = 0.134.Here, one concludes that there is no reason to use four additionalparameters to let R vary by year, when a linear trend is satisfactory.Finally, a Wald test (2-sided) of the significance of the slope in the relationshipbetween logit(O) vs. T is,z = -2.287, P = 0.011. Thus, one concludes that the slope is significant.This comprehensive analysis indicated a decreasing trend in annual adultfemale survival rate for the populations in the five study areas (Table C.7.).This finding is important because X is critically influenced by the adult femalesurvival (i.e., juvenile survival and fecundity are relatively less important intheir influence on X). Because the evidence strongly indicates that R decreasedduring the 1985-91 period, one must infer that X also decreased over thisperiod. That is, the rate of population decline was accelerating during thestudy period.Estimates of juvenile survival have been contentious because estimates arebiased low if some juveniles leave the study area, survive a full year, and neverreturn to the study area. To the extent that these three events happen, juvenilesurvival is underestimated, and estimates of X are too low (i.e., the truevalue of X is probably larger than estimated).Two approaches were employed to obtain more reasonable estimates of juvenilesurvival, 0,. First, the maximum estimate ofjuvenile survival from the fivestudy areas (4, = 0.311, sse = 0.103) was used (cases 1 and 2 in Table C.8.).Second, data on juvenile survival from the best production year for the Medfordand Roseburg areas were pooled to obtain a maximum estimate (4, = 0.3065,se = 0.0764) and this was used (cases 3 and 4, in Table C.8.). The Medfordand Roseburg areas are large in size and adjacent to each other. Thus, thenumber of dispersing juveniles that survived and never returned is minimizedin this approach. In each of the four cases, an attempt was made to use arealistic estimate of juvenile survival as one of the estimates affecting A. Cases1 and 3 allowed adult female survival to decline, while Cases 2 and 4 used anestimate of the average adult female survival from the pooled data. Table C.2.provides estimates of X = 1. In each of the four cases, there was strong statisticalevidence of a declining population.325