Record Details
Dispersal of juvenile northern spotted owls in western Oregon
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Dispersal of juvenile northern spotted owls in western Oregon |
| Names |
Miller, Gary Scott
(creator) |
| Date Issued | 1989-03-16 (iso8601) |
| Note | Graduation date: 1989 |
| Abstract | Dispersal of juvenile northern spotted owls (Strix occidentalis caurina) was studied in western Oregon from 1982-1985. The study was initiated to document the pattern of juvenile spotted owl dispersal, survival, habitat use, and possible effects of forest fragmentation on the dispersing juveniles in the Pacific Northwest Douglas-fir Region. Forty-eight juveniles were radio-marked 3-8 weeks after fledging and followed through dispersal or until they died or the transmitter failed. Spotted owl reproduction in western Oregon varied considerably during the 4 years of the study, with an average of 31% of pairs checked for reproductive status in 1983-1985 attempting nesting (range 14%-69%). A geographic gradient in reproductive performance appeared to exist, with greater reproduction in the south. Juvenile owls spent an average of 104 days in the natal area after fledging. Size of areas used by juveniles prior to dispersal averaged 28 ha. Eighty-four percent of all juveniles began dispersal between mid-September and mid-October; one juvenile did not disperse. Initial dispersal usually was rapid but most juveniles settled into well-defined areas for their first winter after the initial dispersal movements. Those juveniles surviving their first winter often began moving again in late winter or early spring. Mean maximum straight-line dispersal distance was 28 km (first-year movements only) and direction was random in most areas. First-year survival of spotted owls was calculated from daily survival rates and yielded an estimate of 19%. The 2 main causes of mortality were starvation and avian predation. Great horned owls (Bubo virginianus) were the only documented avian predator. Most mortality took place in the first 6 months after fledging. The possible effects of forest fragmentation on dispersal distance and survival, and habitat use by dispersing juvenile spotted owls was also investigated. There were no statistically significant relationships between final distance dispersed and forest fragmentation or days survived and forest fragmentation. Juveniles used a wide variety of habitats while dispersing but, based on availability, 12 of 18 juveniles showed a significant selection (P<0.05) for old-growth/mature forests. |
| Genre | Thesis |
| Topic | Birds of prey -- Oregon -- Geographical distribution |
| Identifier | http://hdl.handle.net/1957/8985 |
