History, nesting biology, and predation ecology of raptors in the Missouri Coteau of northwestern North Dakota by Robert Kevin Murphy A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biological Sciences Montana State University © Copyright by Robert Kevin Murphy (1993) Abstract: Although species composition of birds of prey (raptors) that nest in the northern Great Plains is being altered due to land use, detailed case histories of such change are lacking, few long-term data exist to help understand population dynamics of raptors in prairie areas, and implications of changes for other prairie wildlife on which raptors prey are poorly understood. I studied mechanisms and implications of land use impacts on raptors on the Missouri Coteau of northwestern North Dakota by (1) tracing change during the past century in raptor species composition and habitat on the 108-km2 Lostwood National Wildlife Refuge (LNWR), (2) assessing current (1981-90) population stability, annual reproductive success, and habitat relationships of raptors on LNWR and comparative species' nesting densities on an adjacent area of different land use, and (3) determining prey needs of common, large (>700 g) raptor species on LNWR and prey use in relation to habitat on an area of contemporary land use. Northern harriers (Circus cvaneus), Swainson's hawks (Buteo swainsoni), ferruginous hawks (B. recalls), and burrowing owls (Athene cunicularia) comprised the community of raptors that nested on LNWR before settlement in the early 1900s, great horned owls (Bubo virginianus) were rare but gradually increased over the last 40-50 years, red-tailed hawks (B. iamaicensis) pioneered about 30 years ago, and Cooper's hawks (Accipiter cooperii) pioneered in the past decade. Today, red-tailed hawks and great horned owls have replaced Swainson's and ferruginous hawks as dominant large raptors, coinciding with succession from mixed grass prairie to aspen parkland with brush-dominated uplands. Harrier abundance probably has changed little, but nesting burrowing owls have been absent >40 years. I suggest the most fundamental causes of change in the raptor community were altered susceptibility of prey to foraging behaviors of specific raptor species and decreased abundance of certain key prey species. During the 1980s red-tailed hawks and great horned owls exhibited high, stable nesting densities (mean, 0.23 and 0.13 occupied nests/km2) but erratic and low annual productivity (mean, 0.9 and 0.7 young/occupied nest); both species nested most in areas with highest densities of tree clumps, and the owl was associated with wetlands. Nearly all Swainson's hawk nests occurred on LNWR's boundary, and an adjacent area (93 km2) of different land use had twice as many occupied Swainson's hawk nests/km2 as LNWR. Great horned owl diets were studied during late spring and Swainson's hawk diets during summer, 1986-87 on areas of mixed land use; 2,900 and 1,284 prey items were recorded, respectively. Diet varied among families of both species. The owl relied heavily on avian prey from wetlands (total wetland prey: 57% of overall frequency and 76% biomass of diet) especially ducks and used less Leporid prey than reported elsewhere. Great horned owls depredated about 2-4 ducklings/km2 and 1.3-1.4 adult ducks/km2 during mid-May through June; adult females of several duck species were more vulnerable to owl predation than males. Swainson's hawks used many prey from wetlands (49% overall frequency, 42% biomass); mammals were the most important prey Class and overall diet was more diverse compared to study findings elsewhere. Variation in use of several important prey among Swainson's hawk families was mostly explained by nesting area habitat. A cursory survey of great horned owl and red-tailed hawk diets on LNWR suggested these raptors relied on prey from wetlands, especially ducks. Land use practices that favor nesting red-tailed hawks and great horned owls in prairies of the northern Great Plains are not amenable to raptor species that nest mainly in the region and perhaps not to many other species of indigenous migratory birds. HISTORY NESTING BIOLOGY AND PREDATION ECOLOGY OF RAPTORS IN THE MISSOURI COTEAU OF NORTHWESTERN NORTH DAKOTA by Robert Kevin Murphy A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biological Sciences MONTANA STATE UNIVERSITY Bozeman, Montana August 1993 J S r tK ii APPROVAL of a thesis submitted by Robert Kevin Murphy This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies. Approved for the Major Department ID JiML Date Head, Major Department Approved for the College of Graduate Studies ill STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a doctoral degree at Montana State University, I agree that the Library shall make it available to borrowers under rules of the Library. I further agree that copying of this thesis is allowable only for scholarly purposes, consistent with "fair use" as prescribed in the U.S. Copyright Law. Requests for extensive copying or reproduction of this thesis should be referred to University Microfilms International, 300 North Zeeb Road, Ann Arbor, Michigan 48106, to whom I have granted "the exclusive right to reproduce and distribute my dissertation for sale in and from microform or electronic format, along with the right to reproduce and distribute my abstract in any format in whole or in part." Signature^ Date 13 /MglCj ITQy iv ACKNOWLEDGMENTS As major advisor, R. Eng served shared practical ideas and provided patient support that helped me endure hardships. I am very grateful to A. Sargeant of Northern Prairie Wildlife Research Center (NPWRC), U.S. Fish and Wildlife Service (FWS) for eager support over the past decade. Other committee members were integral: A. Harmata injected insight and unique philosophies, R. White coordinated contracts with FWS and with B. Sindelar and J. Taylor added fresh perspectives. Dozens of spirited individuals helped with raptor nest searches and other tasks. I especially thank J. Ensign and M. Funk, also D . Callow, P. Knupp, and D. Peterson. Personnel of NPWRC kindly helped with logistics and techniques: M. Sovada, A. Kruse, R. Greenwood, J. Piehl, and G. Grau. I had strong backing from the National Wildlife Refuge (NWR) system through D . Pierce and T. Gutzke formerly of Des Lacs NWR Complex, and D. Henry, FWS-Region 6. Fellow graduate students T. Olenicki, M. Restani, and W. Thompson gave suggestions and shared camaraderie. My thesis benefited from past discussions and work with colleagues M. Gratson and R. Rosenfield. Consulting physician and friend W. Cornatzer and many others helped me battle health problems in latter years of my program, and my family gave valuable moral support. I thank many landowners in the Coteau hills of northwestern North Dakota for hospitality, access to their lands, and helpful insights. A. Kruse and B. Bowen (NPWRC) lent many harrier and short-eared owl nest data. D. Cohan (FWS-Bismarck) helped measure vegetation change on aerial photographs. D . Gustafson, W. Newton (NPWRC), and W. Thompson gave statistical advice. J. Barrett and B. Gilbert entered myriad data. I thank D . Topp for administrative help during final thesis stages. My dear wife and partner in study of prairie ecology, K. Smith, was infinitely vital to all stages of this work. Karen, I so value your unique perceptions and your strength during difficult times. Thank you. This study was partly funded by FWS-Region 6 and NPWRC. V TABLE OF CONTENTS Page LIST OF TABLES............. ix LIST OF FIGURES.................................................. xiii ABSTRACT......................................................... xv THESIS INTRODUCTION.............................................. I PART I: A HISTORICAL SKETCH OF BREEDING RAPTORS AND THEIR PRAIRIE HABITAT ON LOSTWOOD NATIONAL WILDLIFE REFUGE, NORTH DAKOTA..... 7 INTRODUCTION............................................... 8 STUDY AREA................................................. 9 Location, Physiography, Geology, and Soils........... 9 Habitat Composition............. 10 Climate and Weather............................. 11 History and Land Use................................. 12 METHODS.................................................... 12 RESULTS: SURVEY OF HISTORICAL ACCOUNTS...................... 16 Historical Raptor Habitat Base....................... 16 Vegetation Reconstruction: Presettlement Flora.. 16 Vegetation Reconstruction: 1900-1935........... 21 Vegetation after 1935.......... 22 Historical Raptor Community.......................... 25 Pre-1935 Observations: northwestern North Dakota and Peripheral Areas......................... 25 Pre-1935 Observations: LNWR.................... 28 LNWR Raptors: 1935 through Present......... 29 Northern Harrier..................... 30 Ferruginous Hawk......................... 31 Swainson's Hawk.......................... 31 Red-tailed Hawk.......................... 31 Great Horned Owl......................... 32 Burrowing Owl............................ 33 Short-eared Owl. .......................... 33 Long-eared Owl........................... 33 Cooper's Hawk.......................... 34 Historical Raptor Prey............................... 34 DISCUSSION: