Population Demography of Northern Spotted Owls

The Northern Spotted Owl, a threatened species that occurs in coniferous forests in the western United States, has become a well-known environmental symbol. But how is the owl actually faring? This book contains the results of a long-term effort by a large group of leading researchers to document population trends of the Northern Spotted Owl. The study was conducted on 11 areas in the Pacific Northwest from 1985 to 2008, and its objectives were both to evaluate population trends and to assess relationships between reproductive rates and recruitment of owls and covariates such as weather, habitat, and the invasion of a closely related species, the Barred Owl. Among other findings, the study shows that fecundity was declining in five populations, stable in three, and increasing in three areas. Annual apparent survival rates of adults were declining in 10 out of 11 areas. This broad, synthetic work provides the most complete and up-to-date picture of the population status of this inconspicuous forest owl, which is at the center of the complex and often volatile debate regarding the management of forest lands in the western United States.

Researchers:
Steven H. Ackers
Lawrence S. Andrews
David R. Anderson
Robert G. Anthony
Brian L. Biswell
Kenneth P. Burnham
Peter C. Carlson
Raymond J. Davis
Lowell V. Diller
Katie M. Dugger
Eric D. Forsman
Alan B. Franklin
Elizabeth M. Glenn
Scott A. Gremel
Dale R. Herter
J. Mark Higley
James E. Hines
Robert B. Horn
Joseph B. Lint
James D. Nichols
Janice A. Reid
James P. Schaberl
Carl J. Schwarz
Thomas J. Snetsinger
Stan G. Sovern
Gary C. White

Eric D. Forsman, who collaborated with a team of twenty-seven researchers to produce this report, is a Wildlife Biologist with the USDA Forest Service’s Pacific Northwest Research Station, and also holds a courtesy faculty position as an Associate Professor in the Department of Fisheries and Wildlife at Oregon State University.

INTRODUCTION

STUDY AREAS

FIELD METHODS

ANALYTICAL METHODS
DEVELOPMENT OF COVARIATES
Barred Owl covariate
Habitat covariates
Weather and climate covariates
Land ownership, ecoregion, and latitude covariates
Reproduction covariate

FECUNDITY
Individual study areas
Meta-analysis of fecundity

APPARENT SURVIVAL
Individual study areas
Meta-analysis of apparent survival

ANNUAL RATE OF POPULATION CHANGE
Individual study areas
Estimates of realized population change
Meta-analysis of annual rate of population change

STATISTICAL CONVENTIONS

WORKSHOP PROTOCOLS

RESULTS
FECUNDITY
Individual study areas
Meta-analysis of fecundity

APPARENT SURVIVAL
Individual study areas
Meta-analysis of apparent survival on all areas
Meta-analysis of apparent survival on the eight NWFP monitoring areas
Potential cost of reproduction on survival
Effects of Barred Owls on recapture and survival

ANNUAL RATE OF POPULATION CHANGE
Individual study areas
Estimates of realized population change
Meta-analysis of annual rate of population change

DISCUSSION
FECUNDITY

APPARENT SURVIVAL

ANNUAL RATE OF POPULATION CHANGE AND REALIZED RATES OF POPULATION

CHANGE
Individual study areas
Meta-analysis of annual rate of population change

STATUS OF OWL POPULATIONS IN THE EIGHT NWFP MONITORING AREAS

ASSOCIATIONS BETWEEN DEMOGRAPHIC PARAMETERS AND COVARIATES
Cost of reproduction on survival
Weather and climate
Barred Owls
Habitat

POTENTIAL BIASES IN ESTIMATES OF DEMOGRAPHIC PARAMETERS
Fecundity
Apparent survival
Annual rate of population change
Estimating goodness-of-fit and overdispersion

SUMMARY, CONCLUSIONS, and RECOMMENDATIONS

ACKNOWLEDGMENTS

LITERATURE CITED

APPENDICES

TABLES

FIGURES