Range‐wide sources of variation in reproductive rates of northern spotted owls

Abstract

We conducted a range‐wide investigation of the dynamics of site‐level reproductive rate of northern spotted owls using survey data from 11 study areas across the subspecies geographic range collected during 1993–2018. Our analytical approach accounted for imperfect detection of owl pairs and misclassification of successful reproduction (i.e., at least one young fledged) and contributed further insights into northern spotted owl population ecology and dynamics. Both nondetection and state misclassification were important, especially because factors affecting these sources of error also affected focal ecological parameters. Annual probabilities of site occupancy were greatest at sites with successful reproduction in the previous year and lowest for sites not occupied by a pair in the previous year. Site‐specific occupancy transition probabilities declined over time and were negatively affected by barred owl presence. Overall, the site‐specific probability of successful reproduction showed substantial year‐to‐year fluctuations and was similar for occupied sites that did or did not experience successful reproduction the previous year. Site‐specific probabilities for successful reproduction were very small for sites that were unoccupied the previous year. Barred owl presence negatively affected the probability of successful reproduction by northern spotted owls in Washington and California, as predicted, but the effect in Oregon was mixed. The proportions of sites occupied by northern spotted owl pairs showed steep, near‐monotonic declines over the study period, with all study areas showing the lowest observed levels of occupancy to date. If trends continue it is likely that northern spotted owls will become extirpated throughout large portions of their range in the coming decades.

Using passive acoustic monitoring to estimate northern spotted owl landscape use and pair occupancy

“…We believe it was reasonable to expect that spotted owls may respond to the intensity of barred owl vocal activity, not just presence or absence of barred owls, as these calls are used for territorial defense and interspecific competition. We estimated that there was a 0.89 probability that spotted owls were less likely to be paired when using hexagons with high amounts of barred owl calling activity, which is consistent with evidence that competition by barred owls may suppress spotted owl recruitment and other demographic rates (Franklin et al, 2021;Rockweit et al, 2022;Wiens et al, 2021). We found no effect of barred owl calling intensity on detection probability of spotted owls and only weak evidence of a negative effect on the probability of landscape use.…”

“…These persistent population declines are driven primarily by continued loss of old forest due to large wildfires and timber harvest on non‐federal lands as well as by competition and displacement by congeneric barred owls ( Strix varia ), a recent newcomer to the Pacific Northwest (Davis et al, 2022; Franklin et al, 2021; Lesmeister et al, 2018). Barred owls have been linked to changes in spotted owl behavior and ecology such as reduced niche space, increased adult dispersal, and decreased survival and reproduction (Jenkins et al, 2021; Jenkins, Lesmeister, Forsman, et al, 2019; Jenkins, Lesmeister, Wiens, et al, 2019; Lesmeister et al, 2018; Rockweit et al, 2022; Wiens et al, 2021). Without management intervention, competition by barred owls in combination with declining habitat conditions is expected to cause extirpation of northern spotted owls from parts of their range in the coming decades (Franklin et al, 2021; Yackulic et al, 2019).…”

Integrating new technologies to broaden the scope of northern spotted owl monitoring and linkage with USDA forest inventory data

“…GNN models are mapped predictions of forest structure and composition across broad landscapes based on FIA plot data and Landsat imagery (Bell et al, 2021). The spotted owl monitoring program has a long history of using GNN data as territory-scale habitat covariates for modeling the effects of forest disturbance, structure, and tree species composition on spotted owl dispersal, distribution, and population trends within the eight historical study areas (Jenkins et al, 2019a(Jenkins et al, , 2021Franklin et al, 2021;Davis et al, 2022;Rockweit et al, 2022). By integrating next generation survey methods throughout the entire spotted owl range, the monitoring program could further leverage the potential of range-wide FIA-derived models as spatially explicit predictors of spotted owl distribution and population change.…”