HOME RANGE AND HABITAT USE OF BREEDING COMMON 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 ( 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 for the same

individuals. I used Resource Utilization Functions (RUFs) to examine 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 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

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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, 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.

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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 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 resource use in Redwood National and State Parks, California, 2010…………. 34

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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

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INTRODUCTION

Marbled Murrelet (Brachyramphus marmoratus) populations have declined substantially in the southern portion of their range, leading to their listing as a federally threatened 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 ( 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 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 Heinrich 1999,

Kristan and Boarman 2003, Marzluff and Neatherlin 2006, RNSP 2008a), has lead to a dramatic increase of their populations in western North America and Redwood National and State Parks (Liebezeit and George 2002, McShane et al. 2004). Marzluff and

Neatherlin (2006) found that Common Ravens exploited anthropogenic food sources when nesting within 1 km of settlements and campgrounds and that breeding ravens near human settlements and campgrounds exhibited reduced home range size, increased reproduction, and increased abundance. In addition, Common Ravens have been found to be more abundant along major roads and highways that provide an easy and dependable source of road-killed food (Austin 1971, Knight and Kawashima 1993, Knight et al.

1995, Boarman and Heinrich 1999).

An analysis of both real Marbled Murrelet nests with known fates and simulated nests indicated that the highest risk of predation was found near forest edges, especially in areas adjacent to human activity (Raphael et al. 2002, Malt and Lank 2009). Almost all of RNSP’s high-use visitor areas and major roadways are located within old-growth

3 forest (Bensen 2008). Thus, habitat fragmentation in combination with the availability of anthropogenic food sources may be attracting Common Ravens to high quality Marbled

Murrelet nesting habitat leading to higher predation rates of Marbled Murrelet nests and a decline in reproductive success (Raphael et al. 2002, Golightly and Gabriel 2009).

Despite their identification as an important nest predator of the Marbled Murrelet, very little is known about the Common Raven in Redwood National and State Parks

(Singer et al. 1991, Peery et al. 2004, Hébert and Golightly 2007). Understanding the relationship between nest predator ecology and behavior and predation risk can improve our ability to conserve sensitive species and make effective management decisions

(Liebezeit and George 2002, Marzluff and Neatherlin 2006). Common Raven home range use has been examined in other environments, but no home range studies have been conducted in coastal old-growth forests in California. Home range provides a direct measure of the area used by an during its normal activities (Burt 1943) while space use may determine the size of the home range, link the movement of to the distribution of resources within the home range (Borger 2006, Borger 2008), and be a good predictor of predation risk (Marzluff et al. 2004). I used radio-telemetry to examine factors that influence Common Raven space use within the home range. My objectives were to (1) estimate home range and core-use area size, (2) estimate the amount of home range overlap and site fidelity, and (3) examine resources influencing habitat use within the home range of breeding Common Ravens in Redwood National and State Parks.

METHODS

STUDY AREA

I studied Common Ravens in the southern portion of Redwood National and State

Parks (41°24′N, 124°01′W), Humboldt County, California, from the town of Orick, north, to the Klamath River (Fig. 1). The climate is characterized by cool, wet winters

and coastal fog that moderates summer temperatures. Annual precipitation of 175 cm

falls almost entirely as rain, occurring predominately between November and May.

Average summer temperatures range from 8-19° C and average winter temperatures

range from 4-13° C (RNPS 2008b). Old-growth forest comprises 30% of RNSP,

representing 45% of remaining old-growth redwood forests in California (RNPS 2008b).

Major habitats include old-growth and second-growth forests dominated by coast

redwood (Sequoia sempervirens) and Douglas-fir (Pseudotsuga menziesii), natural

prairies, and mixed hardwood forests dominated by red alder (Alnus rubra), willow (Salix

spp.), big-leaf maple (Acer macrophyllum), tanoak (Lithocarpus densiflorus), madrone

(Arbutus menziesii), and California bay (Umbellularia californica). Major river drainages

include the Klamath River, Redwood Creek, and Prairie Creek. There are four main

campgrounds and numerous backcountry campsites, picnic areas, visitor facilities, and

roads scattered throughout the park complex. Approximately 400 000 people visit the

park every year with highest visitation from May to September (RNSP 2008b). The park

is long and narrow, transected by California Highway 101, the Newton B. Drury

Parkway, and numerous smaller roads. The park boundaries are surrounded by human-

4

5 modified landscapes including towns, cattle pastures, managed timberland, and beaches

that provide many food sources for ravens.

CAPTURE AND RADIO TELEMETRY

I conducted area searches from February to April 2009 and 2010 to locate

breeding pairs of Common Ravens (hereafter “raven”). Surveys were conducted along

roads and trails in the study area focusing on areas containing old-growth forest, known and potential Marbled Murrelet (hereafter “murrelet”) nest sites, and areas that were logistically feasible to capture ravens safely and conduct radio telemetry. When I located a breeding raven pair, I recorded the pair’s location (<10 m accuracy) in Universal

Transverse Mercator (UTM) coordinates with hand-held Global Positioning System

(GPS) units (Garmin GPSMAP 60Cx) and observed birds to identify habitual perches and food sources.

I captured ravens from May-July 2009 and March-June 2010 using a bow net

(Superior Bownet & Design, Clinton, MD) and remote control trigger design (Jackman et al. 1994). I baited trap sites with meat scraps or human food for approximately one week before trapping. I removed ravens from traps within a few minutes of capture and released ravens within 60-90 min after capture. Because breeding pairs occupy similar

home ranges and sex has not been found to influence home range size (Linz et al. 1992,

Roth et al. 2004, Marzluff and Neatherlin 2006), I captured one member of each of 10

target pairs. I banded ravens with a United States Geological Service stainless steel butt

end band and a unique engraved plastic band (Bedrosian and Craighead 2007). I attached

6 backpack mounted radio transmitters (model A1135, Advanced Telemetry Systems,

Isanti, MN) weighing 19 grams (< 3% body weight) with a 6.35mm-wide Teflon ribbon harness (Driscoll 2009, M. Lanzone 2009, pers. comm.). I measured wing chord, culmen length, tarsus length, and mass, determined age based on mouth color, iris color, and plumage (Kerttu 1973, Heinrich and Marzluff 1992), and sex based on the presence of a brood patch or cloacal protuberance and behavior (Appendix A). All capture and handling methods were approved by the Humboldt State University Institutional Animal

Care and Use Committee (# 08/09.W.64.A).

I relocated ravens with radios from May-September 2009 (n = 3) and March-

September 2010 (n = 8) using telemetry receivers (model RS 1000, Communication

Specialists Inc., Orange, CA or model TRX-1000S Wildlife Materials, Inc.,

Murphysboro, IL) and 3-element, collapsible Yagi antennas. I followed all birds captured in 2009 in both 2009 and 2010. Each bird was relocated in random order, 1-2 times per day, separated by at least 1 hr, during three randomly selected periods in the day: morning (06:00-11:00), midday (11:00-16:00) and evening (16:00-21:00). If the bird was visually located, a GPS location (<10 m accuracy), habitat type, and behavior were recorded. Habitat type was classified as second-growth, old-growth, prairie, bare ground, mixed hardwood, campground, picnic area, parking lot, paved road, roadside, or human habitation. I defined old-growth as areas that had never been logged and second-growth included any logged forests. Prairie included areas of natural prairies and dead or green grass, forbs, or shrubs. Bare ground included soil, pavement, rock, and gravel. Mixed hardwood included areas dominated by hardwoods such as alder and willow. Behavior

7 was categorized as foraging (searching for or carrying food), perching, courtship, nesting,

resting, preening, social interaction, or human interaction. If a bird was foraging, I recorded the food item it was manipulating. If a bird was perched, I recorded the perch type and estimated perch height (m) with a rangefinder (Opti-Logic Models 400 LH and

400 XLA; 0.9m accuracy). To find nest sites, I recorded the location of adults carrying food to fledglings, fledgling vocalizations, or any nesting behaviors. If a bird could not be seen, I triangulated its location with at least three bearings. I estimated locations and error polygons using LOAS™ 4.0.3.3 (Ecological Software Solutions LLC 2009). I eliminated

all points with error polygons larger than the smallest habitat patch size (1.3 ha) within

my study area based on vegetation maps provided by RNSP in ArcGIS® 9.3.1 (ESRI

2009).

STATISTICAL ANALYSIS

Home range and home range overlap

I calculated home range and core-use area size using fixed-kernel density

estimators. I determined smoothing parameters by calculating a pilot bandwidth to

estimate the density function. I plugged in the density function estimate to calculate the

ideal bandwidth (plug-in method; Wand and Jones 1995, Kernohan et al. 2001, Gitzen et

al. 2006). I calculated the smoothing parameter using the Hpi.diag function in the ks

package Version 1.7.1 (Duong 2010) in Program R 2.8.1 (R Development Core Team

2009). In addition, I compared home range and core-use area size estimates for seven bandwidth selection techniques (Appendix B, C). Kernel estimators are most robust with

8 at least 30 points, preferably more than 50, so I estimated all home ranges with at least 49

points in 2009 and 67 points in 2010 (Seaman et al. 1999, Kernohan et al. 2001). Home

range and core-use areas were defined as the extent of area with a 95% and 50%

probability of occurrence, respectively, during the study period. Home range estimates

provided a 95% utilization distribution, 95% home range, and 50% core-use area for each

bird at a 10 x 10 m cell size and were calculated in Home Range Tools Version 1.1

(Rodgers et al. 2005) in ArcGIS® 9.3.1. In addition, I calculated 99% utilization distributions, and 99% kernel home range estimates using Hawth’s Analysis Tools for

ArcGIS (Beyer 2004). I calculated autocorrelation among telemetry locations using the

Swihart and Slade index (Swihart and Slade 1985) in Home Range Tools in ArcGIS®

9.3.1. Significant autocorrelation was present among sampling points with a score less

than 1.6 or greater than 2.4.

I calculated the 3-dimensional home range overlap (Volume of Intersection Index;

Seidel 1992, Millspaugh et al. 2004, Kertson and Marzluff 2009) between adjacent

ravens within the same year. In addition, I calculated the 2-dimensional and 3-

dimensional home range overlap between years for the same individual to quantify site

fidelity. Home range overlap was calculated in ArcGIS® 9.3.1 using the 99% utilization

distribution (3-dimensional overlap) and the 99% kernel home range (2-dimensional

overlap) (Kertson and Marzluff 2009). Two-dimensional overlap assumes equal use of

the home range (Kertson and Marzluff 2009) while 3-dimensional overlap takes into

account spatial variation in home range use. Results are presented as means ± SE.

9

Resource Utilization Function Analysis

I used the Resource Utilization Function approach (RUF; Marzluff et al. 2004) to examine the relationship between raven home range use and habitat variables because it

allowed the individual animal to be the sampling unit, used a continuous measure of

space use, and considered the entire home range in the analysis. Because this approach

examined space use within the home range, it corresponded to third-order habitat

selection (Johnson 1980). Within each raven’s 99% utilization distribution (30 x 30 m

cell size to match the spatial resolution of the landscape data), I used the height of the

utilization distribution at each pixel as the dependent variable and the landscape attributes

within the same pixel as the independent variables. I conducted multiple regression

analyses between home range use and habitat variables with the ruf package in Program

R 2.8.1(Handcock 2004), which adjusts for spatial autocorrelation using the Matern

correlation function. The magnitude of the standardized coefficients indicated the relative

importance of the resource. A positive sign indicated resource use increased with an

increase in quantity and a negative sign indicated resource use decreased with an increase

in quantity.

Model development and selection

I developed four a priori models based on previous research and park management concerns using eight habitat variables to describe raven habitat use. The

eight variables included: distance to road, distance to human use areas, distance to old-

growth edge, and five habitat types. I measured the Euclidean distance within each pixel

10 in the utilization distribution to the nearest human use area (m), road (m), and old-growth edge (m) in ArcGIS® 9.3.1 from GIS layers provided by RNSP (D. Best 2009, pers.

comm.) . Human use areas included: campgrounds, parking lots, private homes, park

facilities, picnic areas, farms, a lumber mill, and the town of Orick. Distance to road

quantified the distance to Highway 101, Newton B. Drury Parkway, and Bald Hills Road, which were paved roads with high traffic that may provide road kill for ravens. Distance to old-growth edge was the distance to the nearest edge between old-growth forest and

any other habitat type. I identified five habitat categories: second-growth forest, bare

ground, mixed hardwood forest, old-growth forest, and prairie (refer to p. 6 for habitat

descriptions). Habitat types were assigned based on vegetation maps from RNSP in

ArcGIS® 9.3.1 (D. Best 2009, personal communication). All of the distance variables were log-transformed prior to analysis. I ran correlation matrices in Program R 2.8.1 to test for correlations among model covariates. I only included variables with a correlation coefficient less than 0.7 in the models. If a variable did not occur within the utilization distribution of the individual raven, it was left out of the model for that individual.

I developed candidate models based on insights from previous studies on raven habitat use and concerns about the potential impact of ravens on nesting murrelets. The human model included distance to roads and distance to human use areas. The old-growth

model included a dummy variable for old-growth forest and distance to old-growth edges. The habitat model included all of the five habitat types. The global model included distance to human use areas, distance to roads, distance to old-growth edges, and all of the habitat variables. I used Akaike’s Information Criterion (AIC) to identify the best

11 model for individual ravens from the set of candidate models. Models were ranked using

∆AIC and relative likelihood was determined using Akaike weights (Burnham and

Anderson 2002). Models within 2.0 ∆AIC points were averaged, using model averaging to obtain unconditional estimates of coefficients, standard errors, and 95% confidence intervals.

RESULTS

I surveyed large portions of the study area, including interior forest trails and

areas away from roads, but found all ravens near roads or along edges (Fig. 2). Surveys

totaled 105 hrs. I captured ten ravens, three in 2009 and seven in 2010. Trapping totaled

184 hrs, with a range of 0.5-106.5 trap hrs per individual bird. Average time for a raven

to be captured from initial trap set-up was 1.5 hrs. In 2009, I collected an average of 51 locations (range 49-53 points) for each bird (n = 3). In 2010, I relocated the three ravens

captured in 2009 and five of the seven ravens captured in 2010. I could not relocate two ravens after capture in 2010 either due to transmitter failure, departure from the study area, or residing in a location with too much interference to receive a signal. I collected an average of 95 locations (range 67-117 points) for each bird (n = 8)

I observed ravens perched on human structures (29%) and trees or snags (71%) with an average perch height of 22 ± 3 m (n = 127). Average perch height for human structures was 5 ± 1 m (n = 30) and included light posts (55%), fences (38%), and road signs (7%). Average perch height for natural perches was 29 ± 3 m (n = 97) and included redwood (49%), hardwood (37%), and Douglas-fir (14%) trees. When perched in redwoods, average perch height was 55 ± 5 m (n = 48). I observed ravens foraging (n =

39) in human use areas 85% of the time, including campgrounds (18%), parking lots

(36%), and roads and roadsides (46%). Ravens foraging outside of human use areas were observed in prairies or grassy areas along roads. When I observed birds foraging (n = 39),

I could identify food items 30% of the time. Of those observations, 35% were

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13 anthropogenic (trash, scrambled eggs, chips, and human vomit) and 65% were natural

food items (Gray Fox (Urocyon cinereoargenteus), snake, and chipmunk (Tamias sp.) roadkill, worms, mushrooms, and a fish carcass). I could not locate exact nest trees but all nesting areas were located within core-use areas (n = 8) and in old-growth forest except one for which the habitat type could not be determined.

HOME RANGE AND HOME RANGE OVERLAP

In 2010, raven home range size averaged 182.5 ± 41.5 ha (range 82-381 ha) and

core-use area size averaged 31.4 ± 7.4 ha (range 5-71 ha; n = 8; Table 1, Fig. 3). Home range size for the three ravens captured in 2009 averaged 121.3 ± 5.0 ha (range 114-131 ha) and core-use area size averaged 24.0 ± 4.0 ha (range 16-29 ha; n = 3; Table 1). Raven core-use areas contained human use areas, such as campgrounds, housing, and parking lots (75%) and high traffic road interchanges (25%; n = 8). I detected autocorrelation among locations for two birds. However, I did not adjust the estimates for autocorrelation because all raven locations were collected at least an hour apart.

There were few areas where raven home ranges overlapped but in all six cases, home range overlap between adjacent pairs was not more than 6% (xˉ = 3.4 ± 0.8 %; range 1-6%; n = 6; Table 2) and the area of overlap included human use areas, such as a lumber mill, highway interchange, campground, visitor’s center, and housing area. Site fidelity among individual ravens was high between 2009 and 2010 with an average 3- dimensional overlap of 65 ± 0.1% (range 54-74%; n = 3; Table 3, Fig. 4) and an average

2-dimensional overlap of 81 ± 0.03% (range 77-86%; n = 3; Table 3, Fig. 4).

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RESOURCE UTILIZATION FUNCTION ANALYSIS AND MODEL SELECTION

The global and human models received the most support (3 of 8 individuals,

37.5% each; Table 4, Appendix D) followed by the old-growth model (2 of 8 individuals,

25%; Table 4, Appendix D). The habitat model was not ranked as a top model for any raven (0 of 8; Table 4, Appendix D). The global model received the highest average

Akaike weight (0.39; Table 4, Appendix D) followed by the old-growth (0.30; Table 4,

Appendix D), human (0.26; Table 4, Appendix D) and habitat models (0.05; Table 4,

Appendix D). Individual use patterns were variable but all of the 95% confidence intervals of the coefficients in the top models differed from zero indicating that variables were good predictors of home range use. After model averaging, old-growth and distance to old-growth edge were important covariates in all eight top models, distance to road in seven top models, distance to human use in six top models, and bare ground, mixed hardwood, and prairie habitats in three top models (Appendix E). Within top models of individual ravens, raven use increased closer to roads and old-growth edge (6 of 7 ravens and 7 of 8 ravens, respectively; Appendix E). Raven use in proximity to human use areas was variable with four ravens showing decreased use closer to human use areas and two ravens showing increased use closer to human use areas (Appendix E). Use decreased in old-growth forest (5 of 8 ravens; Appendix E) while use increased in bare ground, mixed hardwood, and prairie habitats (3 of 3 ravens; Appendix E).

DISCUSSION

RESOURCE UTILIZATION FUNCTION ANALYSIS AND MODEL SELECTION

Individual ravens exhibited preferences for resources within their respective home

ranges. The global and human models were ranked as the top model most often but no

single model consistently explained raven use. However, the top model for raven use

within the home range of each individual was well supported with beta coefficients that

did not overlap zero. In general, individual ravens showed greater use of roads, old-

growth edges, bare ground, prairies, mixed hardwood and decreased use of old-growth

and human use areas.

Space use by ravens has been attributed to locations of food sources and nest site

placement (Roth et al. 2004, Marzluff and Neatherlin 2006), which is consistent with my

results. I was only able to quantify use of human influenced resources because exact nest

locations could not be confirmed. Models built using only foraging locations may provide

more consistent and repeatable measures of foraging habitat use yet a complete

description of raven habitat use, including nest site location, breeding stage, and seasonal

variation may be necessary to identify potential conflicts with sensitive species, such as

the Marbled Murrelet (Roth et al. 2004).

Due to the large variability in diet and food sources within each raven’s home

range, I found no relationship between distance to human use areas and raven use of human use areas within the home range. This pattern may also be due to small sample size (Powell and Backensto 2009) but was not due to collinearity among the independent

15

16 variables. There was no correlation between distance to human use sites and any of the

other independent variables. These conclusions did not change when distance to road and

distance to human use models were analyzed separately.

The lack of an association between raven use and distance to human use areas was

unexpected based on my observations and the results of other studies (Engel and Young

1992, Roth et al. 2004, Marzluff and Neatherlin 2006). There are three reasons why a

relationship between home-range use and distance to human use areas may not have been

found. First, I examined third order habitat selection (use within the home range) and

ravens may be responding to human use areas at a larger (second order) scale. Ravens

may place their territories near anthropogenic resources but within their home range (the

scale I examined) nest placement, old-growth edge, and roads may be more important.

All raven core-use areas contained roads or human use areas and my surveys indicated

little or no raven use away from these areas. Although detection may have been difficult

in interior forests, most often ravens would be attracted to a human presence or vocalize,

making detection probable. Because raven core-use areas contained human use areas,

variation in use relative to human use areas may have been difficult to detect. Second,

human activity may cause ravens to leave human use areas quickly after obtaining food

items. RNSP’s greatest visitation occurs from May to September, when 96% of radio-

telemetry locations (n = 758) were collected. Thus, the temporal use of the areas (as measured by radio locations) may not reflect the amount of resources ravens derive from human use areas. Ravens were observed foraging in human use areas but most often after visitors had vacated the area or ravens would obtain a food item and quickly leave to

17 consume it elsewhere. One raven was observed pulling trash from a parking lot trash

receptacle and many ravens were observed foraging in campsites, parking lots, or picnic

tables, but all were unoccupied. When campground visitation was high or when parking and picnic areas were full, ravens were observed perched in nearby trees. Third, resident pairs of ravens have been observed exploiting anthropogenic resources during most of the year and switching to natural prey during the breeding season when feeding nestlings and fledglings (Boarman and Heinrich 1999, Kristan and Boarman 2003). Because I collected

most of the locations during the period when ravens had nestlings or fledglings, ravens

may have switched to forage in locations where they could obtain natural prey, which

would reduce the association with human use areas and may increase the likelihood of

nest predation.

Ravens exhibited increased use closer to roads. Roads provide a dependable food

resource for ravens and in areas with limited resources may provide a significant portion

of the food available to ravens (Kristan et al. 2004, Marzluff and Neatherlin 2006).

Radio-marked ravens were observed foraging on snake, chipmunk and Gray Fox killed on roads. In addition, ravens were observed patrolling roadways, flying along road corridors, or perched on light posts, road signs, fences, and trees near highway interchanges during every visit to the study site. My findings and observations are consistent with other studies that have found high use of roads by ravens (Sherman 1993,

Marzluff and Neatherlin 2006, Kristan and Boarman 2007, Bui et al. 2010). In the

Mojave Desert, ravens spent 49% of their time foraging directly on linear-right-of-ways

(Sherman 1993). In addition, breeding ravens in the Mojave Desert placed their nests

18 closer to roads than to human use areas and distance to road was associated with high fledgling success (Kristan and Boarman 2007). Roads and road-killed carrion may be contributors to raven reproductive success (Kristan et al. 2004, Kristan and Boarman

2007) therefore, further studies are necessary, but management of food resources provided by roads may also decrease raven populations (Kristan et al. 2004, Kristan and

Boarman 2007, Bui et al. 2010).

Ravens also showed greater use of bare ground and prairie habitats, which is consistent with other studies of raven habitat use (Engel and Young 1992, Boarman and

Heinrich 1999, Marzluff and Neatherlin 2006, Mueller et al. 2009). Ravens are primarily ground foragers in open habitats and feed most often while walking on the ground

(Boarman and Heinrich 1999, Mueller et al. 2009). Diet studies found that arthropods were one of the most frequent food items in raven pellets (Engel and Young 1989, Camp et al. 1993, Kristan et al. 2004). Radioed ravens were regularly observed foraging for arthropods in the short grasses along roads and in natural prairies or eating worms and other food items in grassy roadsides. Thus, the high use of prairie and bare ground habitat that I found is consistent with raven foraging ecology and findings from other studies.

Models indicated greater use of mixed hardwood habitats by ravens. Mixed hardwood may be important foraging habitat for ravens during other times of the year but during my study, I did not observe ravens foraging in hardwood, only perched. I observed radioed ravens perched in hardwood trees adjacent to prairies, pastures, roads, parking lots and highway interchanges. High use of trees in riparian areas has previously been documented because of the importance of its perch sites (Engel and Young 1992). Mixed

19 hardwood trees in RNSP may provide perch sites for ravens and are often in close proximity to important food sources. Perch locations adjacent to food sources allow ravens to avoid human interaction while still being able to take advantage of anthropogenic food. It appears that ravens used mixed hardwood possibly because hardwoods provide important perch sites rather than food resources.

The only habitat where raven use decreased was old-growth forest. The low use of

old-growth forest interior by radioed ravens was consistent with my initial surveys and

point count surveys conducted in RNSP (Bensen 2008). During the 2007 and 2008

murrelet nesting season, 10 point stations in interior old-growth forest were surveyed 10

times and no ravens were detected within 50 m of the point count (Bensen 2008). Low

use of old-growth was most likely due to limited food resources and lack of suitable

foraging habitat in coniferous forests (Mueller et al. 2009).

Despite low use of old-growth, models indicated high use of old-growth edge.

Ravens were observed daily perched in tall redwood trees and snags along old-growth

edges. Although greater use of old-growth edge may be a reflection of the edges created

by roads or human use areas, ravens may take advantage of the good viewing along old-

growth edges to search for potential food items, especially along roads and near human

use areas. The combination of the attraction of anthropogenic resources with a preference

for perching along old-growth edges may draw ravens closer to murrelet nesting habitat,

especially near human use areas (Raphael et al. 2002, Marzluff et al. 2004, Malt and

Lank 2009).

20 HOME RANGE AND HOME RANGE OVERLAP

I examined general patterns in home range size estimates of ravens in northern California

and western coniferous forests. Raven home range size in RNSP was substantially

smaller (xˉ = 265 ha (99% kernel)) than ravens in coniferous forests in Washington (xˉ =

1211 ha (99% kernel); Marzluff and Neatherlin 2006). Raven home ranges in RNSP were larger (xˉ = 183 ha (95% kernel)) than ravens inhabiting open areas in northern

California (xˉ = 121 ha (95% kernel); Roth et al. 2004). Small home range size is likely related to the presence of reliable food sources (Roth et al. 2004). Core-use areas of

radioed ravens in RNSP contained reliable food sources, such as campgrounds, housing,

parking lots or high traffic road interchanges.

Within smaller home ranges in RNSP, foraging effort may be greater; therefore a

raven may be more likely to encounter a murrelet nest if one is present in the home range.

Based on the home range size of the birds I captured and the amount of area surveyed, it

is clear that I sampled a large proportion of the breeding ravens in my study area.

Therefore, at the landscape scale, smaller home ranges of ravens in RNSP may mean that

less of the old-growth habitat is occupied by territorial ravens, especially in areas away

from roads and human use areas. Because home range placement of ravens in RNSP may

be associated with roads and human use areas and home range size is smaller than other

areas with similar habitat, raven use of RNSP is rather limited and could be greatly

reduced if anthropogenic food sources are removed.

The three ravens radioed in both years exhibited high site fidelity with an average

of 81% range overlap and 65% use overlap between years. This is higher than ravens in

21 coniferous forests in Washington where home range overlap between years averaged

66% for nine ravens. High site fidelity has also been documented for ravens in California,

Alaska and elsewhere (Boarman and Heinrich 1999, Roth et al. 2004, Powell and

Backensto 2009). I found little 3-dimensional home range overlap between adjacent ravens (xˉ = 5.5%) in RNSP but the few areas where ravens did overlap were human use areas. Marzluff and Neatherlin (2006) also detected a low amount of home range overlap among adjacent territories (xˉ = 7.7%) in Washington.

Raven pairs in RNSP actively defended territories throughout the study period.

Throughout this study, I did not observe non-breeding ravens in any breeding territories. I observed ten territorial displays between adjacent raven pairs. Five times, I observed radioed ravens chasing Red-tailed Hawks (Buteo jamaicensis) out of their territories and twice I observed Turkey Vultures (Cathartes aura) being chased away from food sources. In addition, I once observed a radio-marked raven preying on a Steller’s Jay nest. Active territoriality and predation of other murrelet nest predators might effect murrelet predation risk because raven territoriality and site fidelity may decrease overall raven and predator abundance within the park.

Although raven territoriality and site fidelity may decrease overall predator abundance, breeding ravens whose territories include nesting habitat of sensitive species may pose a predation risk to those individuals within the territory (Kristan and Boarman

2007, Bui et al. 2010). Nests of radioed ravens were located in old-growth forest; therefore despite overall low use of old-growth, nest placement within old-growth forest draws ravens through murrelet nesting habitat and may pose a predation risk in the area

22 around nest. In addition, breeding ravens may effect murrelets because ravens have been observed to switch from anthropogenic food to natural prey when they start feeding young (Kristan and Boarman 2007). In RNSP, young ravens hatch as early as late

April and I observed adult ravens feeding fledglings into August. Thus, ravens in RNSP may be switching to forage on natural food items from April to August. Raven nest placement in old-growth along with the switch to natural prey items during the murrelet breeding season may increase the potential for ravens to encounter a murrelet nest.

MANAGEMENT IMPLICATIONS

Due to individual variation of raven home range use within RNSP, a number of different

management approaches are necessary to reduce impacts of ravens on murrelets. More

studies are necessary to identify important food sources for ravens but I observed ravens foraging in human use areas and exploiting anthropogenic food. In addition, ravens exhibited more use closer to roads, bare ground, and prairies possibly because these features provide food resources for ravens. More effort is needed to reduce the food availability within human use areas and along roads, especially in areas adjacent to old- growth forest. Reducing food sources may reduce raven presence in old-growth forest, thus reducing the potential for a raven to encounter a murrelet nest. Testing closures of human use areas or roads may be helpful in assessing the impacts of these features on raven populations. Caution should be used with future development of roads, campgrounds, or activities that create unnatural edges. Because of high site fidelity and territoriality, conditioned taste aversion in raven territories within high-risk areas may be an effective method of reducing nest predation by ravens (Avery et al. 1995, Golightly and Gabriel 2009).

23

LITERATURE CITED

Austin, G.T. 1971. Roadside distribution of the Common Raven in the Mojave Desert. Calif. Birds 2:98.

Avery, M.L., M.A. Pavelka, D.L. Bergman, D.G. Decker, C.E. Knittle, and G.M. Linz. 1995. Aversive conditioning to reduce raven predation on California Least Tern Eggs. Colonial Waterbirds 18:131-245.

Bedrosian, B. and D. Craighead. 2007. Band wear in Common Ravens. North American Bird Bander 32:149-152.

Beissinger, S.B. and M.Z. Peery. 2007. Reconstructing the historic demography of an endangered seabird. Ecology 88:296-305.

Bensen, K.J. 2008. Forest and beach corvid monitoring and management and Redwood Creek corvid and backcountry campsite mapping trail, and backcountry management plan implementation– Redwood National and State Parks. Unpublished report on file at South Operations Center, Redwood National and State Parks, Orick, CA. 23 pp.

Best, D. 2009. GIS Coordinator, Redwood National and State Parks, Orick, CA. [Personal Communication].

Beyer, H. L [Online]. 2004. Hawth's analysis tools for ArcGIS. http://www.spatialecology.com/htools (February 2011).

Boarman, W.I. and B. Heinrich [Online]. 1999. Common Raven (Corvus corax), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of ; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/476doi:10.2173/b na.476 (February 2011).

Börger, L., N. Franconi, F. Ferretti, F. Meschi, G. De Michele, A. Gantz, and T. Coulson. 2006. An integrated approach to identify spatiotemporal and individual- level determinants of animal home range size. The American Naturalist 168:471-485.

Börger, L., B.D. Dalziel, and J.M. Fryxell. 2008. Are there general mechanisms of animal home range behaviour? A review and prospects for future research. Ecology Letters 11:637-650.

24

25 Bui, T.D., J.M. Marzluff, and B. Bedrosian. 2010. Common Raven activity in relation to land use in western Wyoming: implications for Greater Sage-grouse reproductive success. The Condor 112:65-78.

Burnham, K.P. and D.R. Anderson. 2002. Model selection and inference: a practical information-theoretic approach. Second edition. Springer-Verlag, New York, New York, USA.

Burt, W.H. 1943. Territoriality and home range concepts as applied to mammals. Journal of Mammalogy 24:346-352.

California Fish and Game Commission. 1992. Animals of California declared to be endangered or threatened. Government Code Section 11346.2 (d), regulation 92:1-8.

Camp, R. J., R. L. Knight, H. A. L. Knight, M. W. Sherman, and J. Y. Kawashima. 1993. Food habits of nesting common ravens in the eastern Mojave Desert. Southwestern Naturalist 38:163-165.

Driscoll, D.E., R.E. Jackman, and W.G. Hunt. 2004. Mounting backpack telemetry on Bald and Golden Eagles. Unpublished protocol. 5 pp.

Duong, T [Online]. 2010. ks: Kernel smoothing. R package version 1.7.1. http://CRAN.R-project.org/package=ks (December 2010).

Ecological Software Solutions LLC [Online]. 2009. Location of a Signal™ (LOAS). Version 4.0.3.3. Hegymagas, Hungary. www.ecostats.com (February 2011).

Engel, K.A. AND L.S. Young. 1989. Spatial and temporal patterns in the diet of Common Ravens in southwestern Idaho. Condor 91:372-378.

Engel, K.A. AND L.S. Young. 1992. Movements and habitat use by Common ravens from roost sites in southwestern Idaho. Journal of Wildlife Management 56:596-602.

Environmental Systems Research Institute (ESRI). 2009. ArcGIS. 9.3.1. Redlands, CA.

George, T.L. 2009. Corvid abundance and management. Pp. 11-39 In Colwell, M.A., T.L. George, and R.T. Golightly [eds.]. A predator management strategy to address corvid impacts on productivity of Snowy Plovers (Charadrius alexandrinus) and Marbled Murrelets (Brachyramphus marmoratus) in coastal northern California. Final Report submitted to U.S. Fish and Wildlife Service, Arcata, CA. 115 pp.

Gitzen, R.A., J.J. Millspaugh, and B.J. Kernohan. 2006. Bandwidth selection for fixed- kernel analysis of animal utilization distributions. The Journal of Wildlife Management 70:1334-1344.

26

Golighty, R.T., C.D. Hamilton, and P.N. Hebért. 2009. Characteristics of Marbled Murrelet (Brachyramphus marmoratus) habitat in northern California. Report to the National Parks Service, Orick, California and California Department of Fish and Game, Sacramento. California.

Golightly, R.T. and P.O. Gabriel. 2009. Marbled Murrelets. Pp. 65-106 In Colwell, M.A., T.L. George, and R.T. Golightly [eds.]. A predator management strategy to address corvid impacts on productivity of Snowy Plovers (Charadrius alexandrinus) and Marbled Murrelets (Brachyramphus marmoratus) in coastal northern California. Final Report submitted to U.S. Fish and Wildlife Service, Arcata, CA. 115 pp. Golightly, R.T, and S.R. Schneider. 2009. Observations of Marbled murrelet incubation using longterm nest monitoring in Northern California. Unpublished report. California Department of Fish and Game, Sacramento, CA.

Golightly, R.T. and S.R. Schneider. 2011. Years 9 and 10 of a long-term monitoring effort at a Marbled Murrelet nest in northern California. Report to the California Department of Fish and Game, Sacramento, California.

Handcock, M.S. [Online]. 2004. ruf: An R package for the estimation of the Resource Utilization Function. http://csde.washington.edu/~handcock/ruf (January 2011).

Hébert, P.N., R.T. Golightly, and H.R. Carter. 2006. Breeding biology of Marbled Murrelets nesting in Redwood National and State Parks, California. Pages 69 – 131 in Hébert, P.N. and R.T. Golightly. 2006. Movements, nesting and response to anthropogenic disturbance of Marbled Murrelets (Brachyramphus marmoratus) in Redwood National and State Parks, California. Unpublished report, Department of Wildlife, Humboldt State University, Arcata, CA.

Hébert, P.N. and R.T. Golightly. 2007. Observations of predation by corvids at a Marbled Murrelet nest. Journal of Field Ornithology 78:221-224.

Heinrich, B. and Marzluff, J. 1992. Age and mouth color in Common Ravens. Condor 94:549-550.

Heinrich, B., D. Kaye, T. Knight, and K. Schaumburg. 1994. Dispersal and association among Common Ravens. Condor 96:545-551.

Jackman, R.E., W.G. Hunt, D.E. Driscoll, F.J. Lapsansky. 1994. Journal of Raptor Research 28:268-273.

Johnson, D.H. 1980. The comparison of usage and availability measurements for evaluating resource preference. .Ecology 61:65-71.

27

Kernohan, B.J., R.A. Gitzen, and J.J. Millspaugh. Analysis of animal space use and movements, p. 125-166. In J.J. Millspaugh and J.M. Marzluff [eds.], Radio-tracking and animal populations. Academic Press, San Diego, CA.

Kertson, B.N. and J.M. Marzluff. 2009. Animal movement, home range, and resource utilization function (ruf) analysis in ArcMap 9.3. School of Forest Resources. University of Washington. 30 pp.

Kerttu, M.E. 1973. Aging techniques for the Common Raven (Corvus corax principalis) Ridgeway. M.Sc. thesis, Michigan Technical University, Houghton, MI, USA.

Knight, R.L. and J.Y. Kawashima. 1993. Responses of raven and Red-tailed Hawk populations to linear right-of-ways. Journal of Wildlife Management 57:266-271.

Knight, R.L., H.A. L. Knight, and R.J. Camp. 1995. Common Ravens and number and type of linear right-of-way. Biological Conservation 74:65-67.

Kristan, W. B., III and W.I. Boarman. 2003. Spatial pattern of risk of Common Raven predation on Desert Tortoises. Ecology 84:2432-2443.

Kristan, W.B., III and W.I. Boarman. 2007. Effects of anthropogenic developments on Common Raven nesting biology in the west Mojave Desert. Ecological Applications 17:1703-1713.

Kristan, W. B., III, W.I. Boarman, and J.J. Crayon. 2004. Diet composition of common ravens across the urban-wildland interface of the West Mojave Desert. Wildlife Society Bulletin 32:244-253.

Lanzone, M. Avian Bioacoustics Lab Supervisor, Carnegie Museum of Natural History’s Powdermill Avian Research Center, Rector, Pennsylvania. [Personal Communication].

Liebezeit, J.R. and T.L. George. 2002. A summary of predation by corvids on threatened and endangered species in California and management recommendations to reduce corvid populations. California Department of Fish and Game report. Sacramento, CA. 144 pp.

Linz, G.M., C.E. Knittle, and R.E. Johnson. 1992. Home range of breeding Common Ravens in coastal southern California. Southwestern Naturalist 37:199-202.

28 Luginbuhl, J.M., J.M. Marzluff, J.E. Bradley, M.G. Raphael, and D.E. Varland. 2001. Corvid survey techniques and the relationship between corvid relative abundance and nest predation. Journal of Field Ornithology 72:556-572.

Malt, J.M. and D.B. Lank. 2009. Marbled Murrelet nest predation risk in a managed forest landscapes: dynamic fragmentation effects at multiple scales. Ecological Applications 19:1274-1287.

Marzluff, J.M. and B. Heinrich. 1991. Foraging by Common Ravens in the presence and absence of territory holders: an experimental analysis of social foraging. Animal Behaviour 42:755-770.

Marzluff, J.M., J.J. Millspaugh, P. Hurvita, and M.A. Handcock. 2004. Relating resources to a probabilistic measure of space use: forest fragments and Steller’s Jays. Ecology 85:1411-1427.

Marzluff, J.M. and E. Neatherlin. 2006. Corvid response to human settlements and campgrounds: causes, consequences, and challenges for conservation. Biological Conservation 130:301-314.

McShane, C., T. Hamer, H. Carter, G. Swartzman, V. Friesen, D. Ainley, R. Tressler, K. Nelson, A. Burger, L. Spear, T. Mohagen, R. Martin, L. Henkel, K. Prindle, C. Strong, and J. Kearny. 2004. Evaluation report for the 5-year status review of the Marbled Murrelet in Washington, Oregon, and California. Unpublished report. EDAW, Inc. Seattle, Washington. Prepared for the U.S. Fish and Wildlife Service, Region 1. Portland, Oregon. 370 pp.

Millspaugh, J. J., R. A. Gitzen, B. J. Kernohan, M. A. Larson, and C. L. Clay. 2004. Comparability of three analytical techniques to assess joint space use. Wildlife Society Bulletin 32:1–10.

Mueller, T., N. Selva, E. Pugacewicz, and E. Prins. 2009. Scale-sensitive landscape complementation determines habitat suitability for a territorial generalist. Ecography 32:345-353.

Nelson, S.K [Online]. 1997. Marbled Murrelet (Brachyramphus marmoratus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/276doi:10.2173/b na.276 (April 2009).

Nelson, S.K. and T.E. Hamer. 1995. Nest success and the effects of predation on Marbled Murrelets. In Ecology and conservation of the Marbled Murrelet (C.J. Ralph,

29 G.L. Hunt, Jr., M. Raphael, and J.F. Piatt, eds.), pp. 89-98. General Technical Report PSW-152, U.S. Forest Service, Pacific Southwest Research Station, Albany, CA.

Peery, M.Z., S.R. Beissinger, S.H. Newman, E.B. Burkett, and T.D. Williams. 2004. Applying the declining population paradigm: diagnosing causes of poor reproduction in the Marbled Murrelet. Conservation Biology 18:1088-1098.

Powell, A.N. and S. Backensto. 2009. Common Ravens nesting on Alaska’s North Slope oil fields. In Coastal Marine Institute [ed.], Final Report. OCS Study MMS 2009-007. University of Alaska Fairbanks. Fairbanks, AK. 38 pp.

R Development Core Team [Online]. 2009. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.R-project.org (December 2010).

Ralph, C.J., and L.L. Long. 1995. Productivity of Marbled Murrelets in California from observations of young at sea. In Ecology and conservation of the Marbled Murrelet (C.J. Ralph, G.L. Hunt, Jr., M. Raphael, and J.F. Piatt, eds.), pp. 371-377. General Technical Report PSW-152, U.S. Forest Service, Pacific Southwest Research Station, Albany, CA.

Ralph, C.J., G.L. Hunt, Jr., M.G. Raphael, and J.F. Piatt. 1995. Ecology and conservation of the Marbled Murrelet in North America: an overview. In Ecology and conservation of the Marbled Murrelet (C.J. Ralph, G.L. Hunt, Jr., M. Raphael, and J.F. Piatt, eds.), pp. 3-22. General Technical Report PSW-152, U.S. Forest Service, Pacific Southwest Research Station, Albany, CA.

Raphael, M.G., D.E. Mack, J.M. Marzluff, and J.M. Luginbuhl. 2002. Effects of forest fragmentation on populations of the Marbled Murrelet. Studies in Avian Biology 25:221-235.

[RNSP] Redwood National and State Parks. 2008a. Corvid management strategy – Redwood National and State Parks. Unpublished report on file at South Operations Center, Redwood National and State Parks, Orick, CA. 45 pp.

[RNSP] Redwood National and State Parks. 2008b. Redwood National and State Parks Fact Sheet. Redwood Park Association in cooperation with Redwood National and State Parks, Orick, CA. 2 pp.

Rodgers, A.R., A.P. Carr, L. Smith, and J.G. Kie. 2005. HRT: Home Range Tools for ArcGIS. Ontario Ministry of Natural Resources, Centre for Northern Forest Ecosystem Research, Thunder Bay, Ontario, Canada.

30 Roth, J.E., J.P. Kelly, W.J. Sydeman, and M.A. Colwell. 2004. Sex differences in space use of breeding Common Ravens in western Marin County, California. Condor 106:529-539.

Seaman, D. E., J. J. Millspaugh, B. J. Kernohan, G. C. Brundige, K. J. Raedeke, and R. A. Gitzen. 1999. Effects of sample size on kernel home range estimates. Journal of Wildlife Management 63:739–747.

Seidel, K. D. 1992. Statistical properties and applications of a new measure of joint space use for wildlife. Thesis, University of Washington, Seattle, USA.

Sherman, M. W. 1993. Activity patterns and foraging ecology of nesting Common Ravens in the Mojave Desert, California. Thesis. Colorado State University, Fort Collins, CO, USA.

Singer, S.W., N.L. Naslund, S.A. Singer, and C.J. Ralph. 1991. Discovery and observations of two tree nests of the Marbled Murrelet. Condor 93:330-339.

Swihart, R.K. and N.A. Slade. 1985. Testing for independence of observations in animal movements. Ecology 66:1176-1184.

[USFWS] United States Fish and Wildlife Service. 1992. Endangered and threatened wildlife and plants; determination of threatened status for the Washington, Oregon, and California population of the Marbled Murrelet. 57 Federal Register 45328.

[USFWS] United States Fish and Wildlife Service. 2009. Marbled Murrelet (Brachyramphous marmoratus) 5-year review. Unpublished report. U.S. Fish and Wildlife Service, Region 1, Lacey, WA.

Wand, M.P. and M.C. Jones. 1995. Kernel Smoothing. Chapman & Hall, London, UK.

TABLES

Table 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.

Birda 95% Home Range (ha) 50% Core-use Area (ha) C 118 25 E 353 46 G 152 36 H 163 37 H(2009) 131 29 K 98 17 K(2009) 119 27 P 113 14 W 381 71 Y 82 5 Y(2009) 114 16 2009 121.3 ± 5.0 24.0 ± 4.0 2010 182.5 ± 41.5 31.4 ± 7.4 a Home range and core-use area size were estimated for 2009 and 2010 for the three ravens captured in 2009.

31

32 Table 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.

Volume of Intersection Pair 3-dimensional overlap (%) Y_K 2 K_C 4 C_W 2 W_H 3 G_P 6 2010 Average 3.4 ± 0.8

33 Table 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 the utilization distributions and 2-dimensional overlap measures the area of overlap between years. Mean (±SE) of each variable are also provided.

Site Fidelity Bird 3-dimensional overlap (%) 2-dimensional overlap (%) Y 54 80 K 67 77 H 74 86 Average 65 ± 0.06 81 ± 0.03

34 Table 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.

AIC weight Model No. times Avg. Range Humana 3 0.26 0.00 - 0.61 Old-growthb 2 0.30 0.00 - 0.91 Habitatc 0 0.05 0.00 - 0.10 Globald 3 0.39 0.01 - 1.00 a Human model included distance to road and distance to human use area. b Old-growth model included a dummy variable for old-growth forest and distance to old-growth edge. c Habitat model included old-growth, bare ground, mixed hardwood, prairie, and a dummy variable for second-growth. d Global model included distance to human use area, distance to road, distance to old- growth edge, and all of the habitat variables.

FIGURES

Figure 1. Location of the study area within the southern portion of Redwood National and State Parks, Humboldt County, California.

35

36

Figure 2. Routes surveyed during area searches to locate breeding Common Ravens. Despite surveys in forest interior, ravens were only detected along roads and forest edges.

37

Figure 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.

38 Bird K Bird H

Bird Y

Figure 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.

Appendix A. Common Raven banding information and morphometric measurements, Redwood National and State Parks, California, 2009 and 2010.

Wing Culmen Tarsus Color Weight Date Band no. Trap Bait Ageb How agedc Sexd Howe sexed chord length length banda (g) (cm) (mm) (mm) 5/20/09 Y 1987-01001 Bow net Raw meat & Cheetos ASY I, P, MC, CP M CP, B - 43.5 47.2 66.4 6/1/09 H 1987-01002 Bow net Raw meat ASY I, P, MC, BP F BP, B 935 41 45 65 6/6/09 K 1987-01003 Bow net Raw meat ASY I, P, MC, BP F BP 891 40 48 64 3/10/10 W 1987-01004 Bow net Beef fat ASY I, P, MC F B 1055 - 56 73 3/17/10 J 1987-01005 Bow net Beef fat ASY I, P, MC F S 840 42 50 66 4/10/10 E 1987-01006 Bow net Beef fat ASY I, P, MC M S, B, V 1035 44 45 67 4/16/10 P 1987-01007 Bow net Beef fat & Cheetos ASY I, P, MC F S, V 970 - 47 - 4/30/10 S 1106-12051 Bow net Bread ASY I, P, MC F S, V 925 42 42 65 5/12/10 C 1987-01008 Bow net Carrion ASY I, P, MC F S, V 950 45 50 68 5/23/10 G 1987-01009 Bow net Cheeseburger & fries ASY I, P, MC F S, V 890 43 45 67 aColor bands were white with dark green lettering etched into each band. b After second year. c I = iris color, P = plumage, MC = mouth color. d M = male, F = female. e CP = cloacal protuberance, BP = brood patch, B = behavior, S = size, V = vocalization.

39

40 Appendix 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.

Bird LSCVa 0.4refb 0.6refb 0.8refb REFc HPId Hpi.diagd Y 13 97 146 188 222 75 82 H 80 127 156 183 208 152 163 K 66 71 90 110 128 87 98 W 217 282 388 485 586 142 381 E 80 293 414 506 589 322 353 P 16 92 131 162 188 101 113 C 64 97 121 146 170 107 118 G 155 105 131 161 191 141 152 Average 86.4 145.5 197.1 242.6 285.3 140.9 182.5 a Least squares cross validation. b Proportion of reference bandwidth. c Reference bandwidth. d Plug-in method.

41 Appendix C. Fixed-kernel density estimates core-use area (50% kernel) size (ha) Estimates for seven bandwidth selection techniques of eight Common Ravens in Redwood National and State Parks, 2010.

Bird LSCVa 0.4refb 0.6refb 0.8refb REFc HPId Hpi.diagd Y 1 6 11 17 23 5 5 H 17 27 36 42 47 38 37 K 12 13 16 19 22 16 17 W 45 55 73 92 114 70 72 E 14 37 56 76 99 43 46 P 2 11 15 19 24 13 14 C 12 20 27 32 38 24 25 G 37 28 33 37 42 35 36 Average 17.5 24.6 33.4 41.8 51.1 30.5 31.5 a Least squares cross validation. b Proportion of reference bandwidth. c Reference bandwidth. d Plug-in method.

42 Appendix 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.

Bird Model k ΔAIC wi C Global 8 0.00 1.00 Old-growth 3 33.28 0.00 Human 3 181.19 0.00 Habitat 5 192.82 0.00 G Global 8 0.00 1.00 Habitat 5 108.57 0.00 Old-growth 3 175.88 0.00 Human 3 207.05 0.00 P Human 3 0.00 0.50 Old-growth 3 0.32 0.42 Habitat 5 3.79 0.07 Global 8 8.95 0.01 Y Old-growth 3 0.00 0.49 Human 3 0.38 0.41 Habitat 5 3.64 0.08 Global 8 6.34 0.02 H Human 3 0.00 0.56 Old-growth 3 1.14 0.32 Habitat 5 3.56 0.10 Global 8 6.28 0.02 K Human 3 0.00 0.61 Old-growth 3 1.52 0.29 Habitat 5 3.73 0.09 Global 8 7.90 0.01 E Global 7 0.00 1.00 Habitat 5 109.40 0.00 Old-growth 3 133.41 0.00 Human 2 138.33 0.00 W Old-growth 3 0.00 0.91 Global 8 3.50 0.06 Habitat 5 7.62 0.02 Human 3 8.09 0.01

43 Appendix 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.

Bird Covariate MLE SE Lower CI Upper CI C Intercept 9.574 0.023 9.529 9.618 Dist. to road -0.331 0.008 -0.348 -0.315 Dist. to human use 0.040 0.013 0.014 0.066 Dist. to old gr. edge -1.934 0.017 -1.967 -1.900 Bare ground 0.257 0.008 0.242 0.272 Mixed hardwood 0.034 0.007 0.021 0.047 Old-growth 0.159 0.008 0.143 0.176 Prairie 0.054 0.012 0.032 0.077 G Intercept 14.741 0.028 14.687 4.796 Dist. to road -0.529 0.009 -0.546 -0.512 Dist. to human use 0.115 0.012 0.092 0.138 Dist. to old gr. edge -1.589 0.018 -1.623 -1.554 Bare ground 1.687 0.016 1.656 1.719 Mixed hardwood 0.254 0.013 0.228 0.280 Old-growth -0.053 0.012 -0.077 -0.029 Prairie 0.835 0.017 0.803 0.868 Y Intercept -0.252 0.033 -0.316 -0.188 Dist. to road -0.034 0.003 -0.040 -0.029 Dist. to human use -0.035 0.006 -0.048 -0.022 Old-growth -0.032 0.003 -0.039 -0.025 Dist. to old gr. edge -0.066 0.005 -0.076 -0.057 K Intercept 0.724 0.012 0.701 0.746 Dist. to road 0.021 0.002 0.018 0.024 Dist. to human use -0.009 0.002 -0.013 -0.005 Old-growth 0.002 0.001 0.001 0.004 Dist. to old gr. edge -0.002 0.001 -0.003 0.000 H Intercept 0.219 0.012 0.195 0.243 Dist. to road -0.021 0.001 -0.023 -0.019 Dist. to human use 0.008 0.001 0.005 0.010 Old-growth 0.008 0.000 0.007 0.009 Dist. to old gr. edge -0.006 0.001 -0.009 -0.003 E Intercept 17.547 0.025 17.499 17.596 Dist. to road -1.017 0.013 -1.043 -0.991 Dist. to old gr. edge 0.589 0.010 0.570 0.608 Bare ground 0.728 0.011 0.706 0.750 Mixed hardwood 0.727 0.012 0.704 0.750 Old-growth -0.431 0.012 -0.455 -0.407 Prairie 0.457 0.009 0.440 0.474 W Intercept 0.804 0.009 0.786 0.822 Old-growth -0.005 0.001 -0.007 -0.003 Dist. to old gr. edge -0.029 0.001 -0.031 -0.027 P Intercept 0.69 0.017 0.657 0.722 Dist. to road -0.021 0.003 -0.027 -0.016 Dist. to human use 0.008 0.002 0.005 0.012 Old-growth -0.009 0.001 -0.012 -0.006 Dist. to old gr. edge -0.006 0.002 -0.01 -0.002