Home Range and Habitat Use of Breeding Common Ravens (Corvus
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HOME RANGE AND HABITAT USE OF BREEDING COMMON RAVENS IN REDWOOD NATIONAL AND STATE PARKS by Amy Leigh Scarpignato A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment Of the Requirements for the Degree Masters of Science In Natural Resources: Wildlife August, 2011 ABSTRACT Home range and habitat use of breeding Common Ravens in Redwood National and State Parks Amy Scarpignato Very little is known about home range and habitat use of breeding Common Ravens (Corvus corax) in Redwood National and State Parks (RNSP) despite their identification as nest predators of the Marbled Murrelet (Brachyramphus marmoratus). I used radio telemetry to examine home range, habitat use, and foraging behavior of breeding Common Ravens in RNSP during 2009 (n = 3) and 2010 (n = 8). I estimated home range and core-use area size, calculated home range overlap between adjacent ravens, and quantified site fidelity by calculating overlap between years for the same individuals. I used Resource Utilization Functions (RUFs) to examine raven resource use within the home range. Average home range size of ravens in RNSP was 182.5 ha (range 82-381 ha) and average core-use area was 31.4 ha (range 5-71 ha). The most supported habitat use models were the global and human models followed by the old-growth model. All beta coefficients in models of individual birds differed from zero suggesting that the variables in the models had a strong influence on home range use. Home range use of individual ravens was generally higher near roads (n = 6), old-growth edge (n = 7), bare ground (n = 6), and in mixed hardwood (n = 5) and prairie habitats (n = 5). Use generally decreased near human use areas (n = 5) and in old-growth habitat (n = 5). Radioed ravens were observed foraging in human use areas 85% of the time but only 35% of identified iii food items were anthropogenic. While I found little overlap between adjacent ravens, the areas of overlap were centered on anthropogenic food sources that occurred at adjacent territory boundaries. Removal of anthropogenic food sources along roads and in human use areas within and adjacent to Marbled Murrelet nesting areas may reduce raven use of these areas and thereby reduce potential encounters of ravens and murrelet nests. iv ACKNOWLEDGEMENTS I would like to thank Dr. T. Luke George for his help throughout my experience at Humboldt State University. I would like to thank my committee members Dr. Mark Colwell and Dr. Richard Golightly. I would like to thank David Haines for trapping expertise and an overall generous amount of support. I would like to thank CORA crew members; Micah Carnahan, Christina Varian, Bridget Roberts, Wendy Pearson, Skylar Giordano, Lindy Keilson, Stephanie Nefas, Elizabeth Maldonado, and Caroline Allander for great tracking and data collection. I would also like to thank The Wright Family for providing funding for this research and the National Park Service, California State Parks, Keith Benson, Jay Harris, and Rich Byrnes for access to study sites. Anthony Desch, Kristin Sesser, and The Luke George Lab 2009-2011 provided both logistical and emotional support. I would also like to thank Brian Kertson, Chad Rittenhouse, and John Marzluff for invaluable guidance and insight with statistical analysis. I would like to thank my family, especially Joe and Jackie Scarpignato, for providing me with a great support system and lots of love. v TABLE OF CONTENTS Page ABSTRACT …………………………………………………………………………... iii ACKNOWLEDGEMENTS …………………………………………………………… v LIST OF TABLES ……………………………………………………………………. vii LIST OF FIGURES ………………………………………………………………….. viii LIST OF APPENDICES ………………………………………………………………. ix INTRODUCTION ……………………………………………………………………. 1 METHODS ……………………………………………………………………………. 4 RESULTS …………………………………………………………………………….. 12 DISCUSSION ……………………………………………………………………….... 15 MANAGEMENT IMPLICATIONS …………………………………………………. 23 LITERATURE CITED ……………………………………………………………….. 24 vi LIST OF TABLES Table Page 1 Fixed-kernel density estimates with choice of the plug-in method for smoothing parameter of home range and core-use area of eight Common Ravens in Redwood National and State Parks, California, 2009 and 2010. Mean (±SE) of each variable for each year are also provided…………………. 31 2 Three-dimensional home range overlap for adjacent breeding Common Ravens in Redwood National and State Parks, California, 2010. Three- dimensional overlap measures the volume of overlap of the utilization Distributions. Mean (±SE) is also provided..…………………………………… 32 3 Site fidelity using 3-dimensional and 2-dimensional home range overlap of three breeding Common Ravens in Redwood National and State Parks, California between 2009 and 2010. Three-dimensional overlap measures the volume of overlap of utilization distributions and 2-dimensional overlap measures the area of overlap between years. Mean (±SE) of each variable are also provided………………………………………………………….……. 33 4 Number of times a model was the top model, average Akaike’s Information Criterion (AIC) weight, and range of model weights for Common Raven resource use in Redwood National and State Parks, California, 2010…………. 34 vii LIST OF FIGURES Figure Page 1 Location of the study area within the southern portion of Redwood National and State Parks, Humboldt County, California………………… 35 2 Routes surveyed during area searches to locate breeding Common Ravens. Despite extensive surveys in forest interior, ravens were only detected along roads and forest edges…………………………….. 36 3 Fixed-kernel density estimates of home range (95% kernel) with choice of the plug-in method for smoothing parameter of eight breeding Common Ravens in Redwood National and State Parks, California in 2010. Each individual raven is identified by a different pattern. Core-use areas (50% kernel) are indicated within each home range by darker lines…………………………………………………… 37 4 Overlap in home range use between breeding Common Ravens in 2009 and 2010 in Redwood National and State Parks, California. The shading represents the amount of 3-dimensional overlap based on utilization distributions from each year…………………………………. 38 viii LIST OF APPENDICES Appendix Page A Common Raven banding information and morphometric measurements, Redwood National and State Parks, California, 2009 and 2010………………………………………………………… 39 B Fixed-kernel density estimates of home range (95% kernel) size (ha) for seven bandwidth selection techniques of eight Common Ravens in Redwood National and State Parks, 2010………………….. 40 C Fixed kernel density estimates of core-use area (50% kernel) size (ha) for seven bandwidth selection techniques of eight Common Ravens in Redwood National and State Parks, 2010…………………. 41 D Model selection results of standardized resource utilization functions (RUF) of eight Common Ravens in Redwood National and State Parks, California, 2010. Models are ranked according to the difference in Akaike’s Information Criterion (AIC) between the model and the best-fitting model (ΔAIC). Number of parameters (k) and Akaike weight (wi) are presented for all models……………….….. 42 E Maximum likelihood estimates (MLE) of standardized resource utilization function (RUF) coefficients, standard errors (SE), and 95% lower and upper confidence intervals from the top model for eight Common Ravens in Redwood National and State Parks, California, 2010………………………………………………………… 43 ix INTRODUCTION Marbled Murrelet (Brachyramphus marmoratus) populations have declined substantially in the southern portion of their range, leading to their listing as a federally threatened species in Oregon, Washington, and California and a state-endangered species in California in 1992 (California Fish and Game Commission 1992, USFWS 1992). Loss of breeding habitat was identified as the greatest threat to the persistence of murrelet populations in the original listing decision, therefore, initial conservation efforts focused on protection and restoration of coastal old-growth forests. Despite the protection of remaining coastal old-growth forest in Oregon, Washington, and California, Marbled Murrelet populations have continued to decline in the southern portion of their range (McShane et al. 2004). More recent analyses suggest that the greatest threat to maintaining a viable Marbled Murrelet population in California is low productivity due to poor reproductive success (Nelson and Hamer 1995, Ralph et al. 1995, Peery et al. 2004). The few direct observations that have been made suggest that corvids, in particular Common Ravens (Corvus corax) and Steller’s Jays (Cyanocitta stelleri), are important predators of Marbled Murrelet nests (Singer et al. 1991, McShane et al. 2004, Peery et al. 2004, Hébert et al. 2006, Golightly and Gabriel 2009, Golightly and Schneider 2009, USFWS 2009). Because space use by corvids has been found to predict nest predation (Marzluff et al. 2004), a better understanding of the home range and habitat use of Common Ravens in Redwood National and State Parks (RNSP) may provide insights into 1 2 management approaches to reduce Marbled Murrelet nest predation by Common Ravens in RNSP. No long-term surveys have been conducted on corvids in RNSP but analyses of Breeding Bird Surveys indicate that Common Ravens have increased 380% over the period 1966-2007 in the Southern Pacific Rainforest Ecoregion (George 2009). Common Ravens are considered generalist omnivores, eating live prey, carrion, eggs, insects, grains, and anthropogenic foods. In addition, the ability for Common Ravens to use different environments, including human development (Boarman and