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Conservation Assessment for the Northern Goshawk in Southeast Alaska

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Conservation Assessment for the Northern Goshawk in Southeast Alaska The Northern Goshawk (Accipiter gentilis atricapillus) in the Western Great Lakes Region: A Technical Conservation Assessment February 2003 Aimee M. Roberson1,2 and David E. Andersen U.S. Geological Survey, Minnesota Cooperative Fish & Wildlife Research Unit3, University of Minnesota, St. Paul, MN 55108 Patricia L. Kennedy4 Department of Fishery & Wildlife Biology, Colorado State University, Fort Collins, CO 80523 ______________________________________________________________________________ EXECUTIVE SUMMARY This conservation assessment is a summary of the information currently available regarding the northern goshawk (Accipiter gentilis) in the Western Great Lakes Region (WGLR), including the states of Minnesota, Wisconsin, and Michigan and the forested southern portion of the Canadian province of Ontario. Because relatively few scientific studies of the goshawk in the WGLR have been conducted and even fewer published, information that may be relevant from studies conducted in other parts of North America and Eurasia have also been summarized. The purpose of this assessment is to present information relevant to the formation of a conservation and management strategy for the goshawk in the WGLR. This assessment describes the species’ systematics, physical characteristics, distribution, and abundance. It also includes information regarding the foraging ecology, habitat characteristics, population ecology, potential threats, and monitoring of the northern goshawk, summarizes ongoing research, and identifies additional research needs for this region. ____________ 1Present address: U.S. Fish and Wildlife Service, 2105 Osuna Road NE, Albuquerque, NM 87113 2E-mail: [email protected] 3Cooperators of the Minnesota Cooperative fish and Wildlife Research Unit: University of Minnesota, the Wildlife Management Institute, U.S. Geological Survey, and the Minnesota Department of Natural Resources 4Present address: Eastern Oregon Agricultural Research Center, Oregon State University, P.O. Box E, 372 So. 10th St., Union, OR 97883 TABLE OF CONTENTS EXECUTIVE SUMMARY…………………………………………………………………………………………….. i TABLE OF CONTENTS………………………………………………………………………………………………. ii ACKNOWLEDGEMENTS………………………………………………………………………………………….…. iii INTRODUCTION....…………………………………………………………………………………………...…...…... 1 Background…………………………………………………………………………………………….……………. 1 Approach and Scope of Assessment………………………………………………………………….……..………. 3 History of Goshawk Conservation Efforts and Management………………………………………….……………. 4 NOMENCLATURE AND TAXONOMY……………………………………………………………………………… 6 DESCRIPTION OF SPECIES………………………………………………………………………………...………... 6 DISTRIBUTION AND ABUNDANCE ………………………………………………………………………...……... 7 Rangewide…………………………………………………………………….………………………...…………… 7 Regionwide……………………………………………………………………………………………..…………… 8 FEEDING HABITS AND PREY ECOLOGY…………………………………………………………………...…….. 10 Does Food Limit Goshawk Populations?……………………………………………………………………………. 10 Prey Taxa and Abundance in Diets………………………………………………………………………………….. 12 Prey Species Habitat Needs………………………………………………………………………….....….………... 15 Seasonal Dietary Shifts………………………………………………………………………………….…………... 17 Foraging Behavior…………………………………………………………………………………………………… 17 Hunting Tactics……………………………………………………………………………...………………… 18 Foraging Success, Prey Delivery Rates, and Prey Caching……………………………...…………………... 18 Foraging Distance from Nest……………………………………………………………...………………….. 18 HABITAT……………………………………………………………………………………………………...……….. 19 Does Habitat Limit Goshawk Populations?…………………………………………………………………………. 19 Breeding Season Habitat……………………………………………………………………….……………………. 20 Nest Area…………………………………………………………………………………..…………………... 21 Nest Tree…………………………………………………………………………………………………… 21 Nest Structure and Location in Tree……………………………………………………………………….. 23 AlternativeNests/Nest Areas…………………………………………………..…..…….…………………. 23 Dominant Forest Types…………………………………………………………………………………….. 24 Forest Structure and Landscape Features………………………………………………………………… 25 Stand Age, Canopy Closure, Tree Size and Density………………………..…………………………... 25 Aspect and Slope……………………………………………………………..…………………………. 27 Plucking Perches…………………………………………………………..….………………………... 28 Water……………………………………………………………………………………………………. 28 Forest Openings……………………………………………………………..………………………….. 28 Breeding Season Foraging Habitat…………………………………………………………………………… 29 Post-Fledging Area (PFA) Habitat…………………………………………………………………..………... 31 Nonbreeding Habitat………………………………………………………………………………………………… 32 Home Range Size………………………………………………………………………………………….………… 34 POPULATION ECOLOGY AND VIABILITY…………………………………………………………………….….. 35 Definitions…………………………………………………………………………………………………………… 35 Annual Cycle………………………………………………………………………………………….……………... 35 Breeding Period…………………………………………………………………………..……………………. 35 Pre-laying Period……………………………………………………………………….…………………... 36 Incubation Period…………………………………………………………………………………………… 36 Nestling Period……………………………………………………………………………………………... 36 Fledging-Dependency Period………………………………………………………………………………. 37 Nonbreeding Period………………………………………………………………………..…….…………….. 38 Movements…………………………………………………………………………………………………………... 38 Migration/Irruptions……………………………………………………………………..…………………….. 38 Dispersal……………………………………………………………………………..………………………… 39 Natal Dispersal……………………………………………………………………………………………….... 40 Breeding Dispersal……………………………………………………………………………………………... 41 Spatial Structure………………………………………….…...……………………………………….…………….. 41 ii Dispersion……………………………………………………………………………………………... 41 Density……………………………………………………………………………………...…….…………….. 42 Demographics……………………………………………………………………………………………………….. 43 Breeding System………………………………………………………………………..………………………. 43 Age Structure…………………………………………………………………………...………………………. 44 Reproduction…………………………………………………………………………..……………………….. 44 Proportion of Pairs Breeding…………………………………………………………...……………………... 45 Clutch Size……………………………………………………………………...………………………………. 45 Nesting Success………………………………………………………………………..……………………….. 45 Productivity…………………………………………………………………………………..………………… 46 Survival and Population Growth Rate………………………………………………………..….…………….. 48 Longevity………………………………………………………………………………………..……………… 49 Population Status and Viability………………………………………………………………………….………….. 49 POTENTIAL THREATS………………………………………………………………………………………...….….. 50 Habitat Alteration………………………………………………………………………………………….………… 50 Nesting and Post-Fledging Areas……………………………………………………………..………………. 51 Foraging Areas……………………………………………………………………………..………………….. 53 Human Disturbance………………………………………………………………………………….…….………… 53 Predation…………………………………………………………………………………………….……… ……… 54 Competition………………………………………………………………………………………………………….. 55 Disease……………………………………………………………………………………………………..………... 56 Siblicide/Cannibalism……………………………………………………………………………………………….. 57 Pesticides and Other Contaminants………………………………………………………………………..………… 57 Falconry………….…………………………………………………………………………………….…………….. 57 MONITORING…………………………………………………………………………………………………...…….. 57 Survey Approach to Population Monitoring………………………………………………………….……………... 58 Demographic Approach to Population Monitoring………………………………………………….…….………… 60 Habitat-Based Monitoring………………………………………………………………………….………………... 61 ONGOING RESEARCH AND RESEARCH NEEDS…………………………………………………………………. 62 Ongoing Research………………………………………………………………………………….………………... 62 Research Needs……………………………………………………………………………………….……………... 63 Population Dynamics…………………………………………………………………………….…………….. 63 Population Monitoring…………………………………………………………………………………………. 63 Habitat Relationships and Models……...……………………………………………………………………… 64 Goshawk Diet and Habitat Requirements of Their Prey………………………………………………………. 64 LITERATURE CITED………………………………………………………………………………………...……….. 66 LIST OF TABLES Table 1. List of Goshawk prey species reported for the WGLR…………………………………………………….….. 13 Table 2. Proportion of mammalian and avian prey in diets of goshawks during the breeding season……………….… 14 Table 3. Reported goshawk nest trees in the WGLR………………………………………………………………..….. 22 ACKNOWLEDGMENTS We would like to thank the following individuals for their contributions and input: Al Williamson and Jim Gallagher, of the Chippewa National Forest; Steve Lewis and Joel Trick, of the U.S. Fish and Wildlife Service; Clint Boal, of the Texas Cooperative Fish and Wildlife Research Unit; Teri Kanikula, formerly of the Minnesota Fish and Wildlife Cooperative Research Unit; and Ted Dick and David Plumpton, authors of the Review of Information on the Status of the Northern Goshawk (Accipiter gentilis atricapillus) in the Western Great Lakes Region and Ontario. iii INTRODUCTION Background The northern goshawk (Accipiter gentilis atricapillus; hereafter referred to as goshawk) is listed as a migratory nongame bird of management concern by Region 3 of the U.S. Fish and Wildlife Service (USFWS) and is on the U.S. Forest Service’s (USFS) Regional Forester’s Sensitive Species list for Region 9 (Lewis 1998). The goshawk is listed at the state level as a species of concern in Michigan (Weise 1998), but is not listed in the other states or provinces of the Western Great Lakes Region (WGLR – northern forested portions of Michigan, Minnesota, and Wisconsin, and the southern forested portions of Ontario) where it also occurs (Dick and Plumpton 1998). The concern over this species is currently focused in the western U.S. where litigation to list goshawk populations as threatened or endangered throughout or in parts of its range has been ongoing for almost 10 years. Subsequent findings based on a status review of goshawk populations west of the 100th meridian conducted by the USFWS (1998a) determined that listing the goshawk as threatened
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