Prey Abundance, Space Use, Demography, and Foraging Habitat of Northern Goshawks in Western Washington Thomas David Bloxton, Jr. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science University of Washington 2002 Program Authorized to Offer Degree: College of Forest Resources University of Washington Graduate School This is to certify that I have examined this copy of a master’s thesis by Thomas David Bloxton, Jr. and have found that it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made. Committee Members: Dr. John M. Marzluff Dr. Daniel E. Varland Dr. Marco Restani Dr. James K. Agee Date: _________________________ In presenting this thesis in partial fulfillment of the requirements for a Master’s degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of this thesis is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Any other reproduction for any purposes or by any means shall not be allowed without my written permission. Signature_______________________________ Date__________________________________ TABLE OF CONTENTS Page List of Figures.….…………………..……………………………..………………….iii List of Tables…....…………………………………………………..………………...v Chapter 1: Influence of La Niña on Prey Abundance, Space Use, and Demography of Northern Goshawks………………………………….1 Methods………………………………………………...……………...3 Study Area………………………………………………..…...3 Weather………………………………………………...……...5 Prey Surveys…………………………………………………..5 Space Use………………………………………………...……6 Selection and capture of goshawks…………………....6 Radiotracking………………………………………….7 Home range analysis…………………………………..8 Demography……………………………………………….…10 Results………………………………………………………..………11 Weather…………………………………………..…………..11 Prey Abundance……………………………………..…….....12 Space Use…………………………………………………….13 Demography……………………………………………...…..16 Survivorship………………………………………….16 Reproduction………………………………………....16 Discussion………………………………………………………..…..17 i Chapter 2: Foraging Behavior and Habitat Use by Northern Goshawks in Managed Forests of Western Washington……………………..…….33 Methods……………………………………………………...……….36 Study Area…………………………………………………...36 Radiotelemetry…………………………………………...…..38 Selection and capture of goshawks………………..…38 Radiotracking………………………………………...38 Determining kill locations…………………………....39 Habitat Assessment………………………………………..…39 Univariate analysis………………….…………..……40 Multivariate analysis….………..…………………….41 Results……………………………………..…………………………42 Foraging Behavior………………………………..………….42 Habitat………………………………………..………………44 Univariate analysis………………….…………..……45 Multivariate analysis….……………………………...46 Discussion……………………………………………………..……..47 Foraging Behavior………………………………………..….47 Habitat………………………………………………..………48 Managing young stands for hunting goshawks.…...…50 Literature Cited…...……………………………………………………………….....60 ii LIST OF FIGURES Number Page 1.1 Western Washington map showing goshawk territories…………………..…24 1.2 Interannual variation in winter precipitation and spring temperature in Washington, 1996-2000.……………………………………………………..25 1.3 Change in relative abundance of selected goshawk prey in western Washington following the La Niña winter of 1998-99……………………....26 1.4 Mean sizes of Northern Goshawk home ranges during the breeding season in managed forests of western Washington……………………………..…...…27 1.5 Box plots showing differences between pre- and post-La Niña home range sizes of Northern Goshawks…………………………………………………28 1.6 Home range size before and after La Niña for five Northern Goshawks…....29 1.7 Comparison of pre- and post-La Niña home ranges (95% fixed kernel) at 5% increments of the utilization distribution………………………………….…30 1.8 Kaplan-Meier survival function and pre-/post-La Niña fitted regression lines of the survival function for Northern Goshawks radiotagged in western Washington, June 1997-November 2000………………………………….…31 iii 1.9 Mean annual number of young fledged per occupied territory before and after La Niña………………………………………...……………………..………32 2.1 Western Washington map showing goshawk territories where foraging study took place in relation to major land ownership patterns……...……………...56 2.2 Diet of goshawks in western Washington from 1997-2000……………….…57 2.3 Relationship between size of prey and the distance away from the nest where it was captured…………………………………………………………….…58 2.4 Forest structural stages at 52 goshawk kill sites and 52 randomly located sites within territories in managed forests of western Washington, 1997-2000…..59 iv LIST OF TABLES Number Page 1.1 Years each goshawk (or territory) was studied for space use, survivorship, and reproduction from 1996-2000 in western Washington..…………………..…23 2.1 Vegetative attributes at 52 goshawk kill sites and 52 randomly located sites within territories in managed forests of western Washington……………….54 2.2 Akaike’s Information Criterion (AIC) values for four competing goshawk foraging habitat models……………………………………………………....55 2.3 Odds ratios for the single variable model and the full model containing all three variables………………………………………...………...……………55 v ACKNOWLEDGEMENTS This research would not have been possible without the cooperation and commitment of many public agencies and private companies and the dedication of their personnel. The Washington State Department of Natural Resources (DNR), Rayonier, Champion Pacific Timberlands, Inc., Port Blakely Tree Farms, Weyerhaeuser, Sustainable Ecosystems Institute, Washington Department of Fish and Wildlife, Olympic National Park, U.S. Forest Service – Pacific Northwest Research Station, Plum Creek Timber Company, International Paper, Crown Pacific, Merrill and Ring Tree Farms, Campbell Group, Olympic Resources Management, Sarvey Wildlife Center, Sardis Wildlife Center, Northwest Raptor Center, and the University of Washington’s Olympic Natural Resources Center provided funding, access to lands, and logistical support. The following people were indispensable in my efforts during the course of study: R. Meier, L. Raynes, L. Young, P. Swedeen, J. Eskow, A. Stringer, N. Wilkins, K. Risenhoover, T. McBride, D. Runde, L. Hicks, H. Stabins, F. Silvernail, S. Horton, P. Harrison, E. Kuo-Harrison, D. Hays, S. Desimone, P. Happe, K. Jenkins, S. Hall, S. Gremel, and J. Swingle. I also thank the following people for their diligent efforts and assistance in the field: D. Yonkin, B. Davies, J. Luginbuhl, E. Neatherlin, J. Bradley, B. Griffith, H. Tall, K. Beesley, J. DeLap, C. Wilkerson, D. D’emilio, S. Pollock, J. Bent, D. Pike, and P. Smith. Graduate committee members M. Restani and J. Agee provided invaluable guidance. I especially thank S. Finn for vi his dedication to the initial phase of this project from 1996-1998 and for his assistance throughout the years that followed. Finally, I wholeheartedly thank J. Marzluff and D. Varland for their unending guidance and support during this valuable learning experience. vii