Behavior and Energetics of Ospreys Nesting in Northern California

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BEHAVIOR AND ENERGETICS OF OSPREYS NESTING IN NORTHERN CALIFORNIA

Howard Levenson

A Thesis Presented to The Faculty of Humboldt State University

In Partial Fulfillment of the Requirements for the Degree Master of Science

December, 1976 BEHAVIOR AND ENERGETICS OF OSPREYS NESTING IN NORTHERN CALIFORNIA by Howard Levenson

Approved by the Master's Thesis Committee Chairman

Approved by the Graduate Dean

ACKNOWLEDGEMENTS

I wish to thank Drs. James R. Koplin and David W. Kitchen for their friendship, their constant interest in my studies, and for critically reviewing the manuscript. Their enthu- siasm for ecological research provided me an extremely stimulating atmosphere in which to work. Jim Koplin, my major professor, deserves special thanks for directing my research; he deserves additional praise for directing various studies that have increased our understanding of birds of prey in general and of Ospreys in particular. I am most grateful to Dr. William R. Sise for his invaluable criticisms and witticisms of the manuscript. Dr. Roger J. Ledderer, of California State University at Chico, kindly gave me permission to use the facilities of the Eagle Lake Biological Station during my stay at Eagle Lake. My research at Eagle Lake was supported by a grant from the Frank M. Chapman Memorial Fund of the American Museum of Natural History (Grant #24464). I am grateful to Steve Berman for showing me the Chinese poem and for drawing the Chinese characters. I also would like to thank Kathy McDonough for drawing the map of the study areas and for the English calligraphy in the frontispiece. TABLE OF CONTENTS Page INTRODUCTION 1 Study Area 3 Geographic Location 3 Climate 3 Vegetation 6 METHODS 8 Field Observations 8 Definition of Behavioral Activities Observed 8 Data Analysis 12 Categories of Behavioral Activities 12 Stratification of Data 13 Computer Program and Statistical Analysis 14 Energy Expenditure 17 Estimated Energy Expenditure 17 Predicted Energy Expenditure 18 RESULTS 20 Time and Activity Budget 20 Seasonal Trends in Behavioral Activities 29 Nest Activities and Tree Activities 29 Perch on Nest and Perch on Trees 34 Nest Material Flight 38 Nest-building 38 Mounting and Copulation 43 Incubation and Brooding 43 Fishing 49 Feeding Activities 55 Aggressive Interactions 56 Diurnal Variations in Behavioral Activities 57 Date of Departure from Nesting Area 58 Energy Expenditure 59 DISCUSSION 65 Energy Expenditure 65 Time and Activity Budget of Ospreys 66 Breeding Behavior of Other Falconiforms 67

ii Page Evolution of Division of Labor of • Breeding Falc oni forms 69 SUMMARY 72 LITERATURE CI TED 76 APPENDICES 83

iii LIST OF FIGURES

Page

1. Location of nest 1, Washington Gulch Creek, Humboldt County, California, and nests 2 and 3, Eagle Lake, Lassen County, California. 5 2. Composite time and activity budget of female Osprey at nest 1, Washington Gulch Creek, Humboldt County, California, in relation to phase of the 1974 breeding season. 22

3. Composite time and activity budget of male Osprey at nest 1, Washington Gulch Creek, Humboldt County, California, in relation to phase of 1974 breeding season. 22 4. Time and activity budgets of male and female Ospreys during the Pre-Incubation phase of the 1974 breeding season at nest 1, Humboldt County, California, compared to the time and activity budgets of male and female Ospreys during the Pre-Incubation phase of the 1975 breeding season at nests 2 and 3, Eagle Lake, Lassen County, California. 24 5. Percent of daylight time Ospreys engaged in Nest Activities in relation to phase of the breeding season, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 31 6. Percent of daylight time female Ospreys engaged in Nest Activities in relation to the number of days prior to egg-laying, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the 1975 breeding season. 33 7. Percent of daylight time male Ospreys engaged in Nest Activities in relation to the number of days prior to egg-laying, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the 1975 breeding season. 33

iv Page

8. Percent of daylight time Ospreys engaged in Nest Activities and Tree Activities in relation to phase of the breeding season, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre- Incubation phase of the 1975 breeding season. 36

9. Numbers of items of nest material delivered per hour by female and male Ospreys in relation to phase of the breeding season, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre- Incubation phase of the 1975 breeding season. 40 10. Numbers of mounts and copulations engaged in by Ospreys in relation to numbers of days prior to and after egg-laying at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season. 45 11. Numbers of mounts and copulations engaged in by Ospreys in relation to number of days prior to and after egg-laying at nests 2 and 3, Eagle Lake, Lassen County, California, during the 1975 breeding season. 45 12. Relative percentages of daylight time each sex of Ospreys engaged in Incubation and Brooding in relation to number of days prior to and after egg-laying at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season. 48 13. Relative percentages of daylight time sexes and different pairs of Ospreys engaged in Fishing in relation to phase of breeding season, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre- Incubation phase of the 1975 breeding season. 51 14. Relative rates sexes and different pairs of Ospreys delivered fish to nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and to nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 54 v Page 15. Number of fish delivered per hour to nest 1, Washington Gulch Creek, Humboldt County, California, in relation to segment of the day during the 1974 breeding season. 60

vi LIST OF TABLES

Page 1. Activities of foraging Ospreys while absent from nests located near Humboldt Bay, Humboldt County, California. 15 2. Relative percentages of the 24-hour day sexes and different pairs of Ospreys engaged in Flying and Non-flying activities at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre- Incubation phase of the 1975 breeding season. 25 3. Percent of daylight time Ospreys engaged in behavioral activities (including Unknown activities) at nest 1, Washington Gulch Creek, Humboldt County, California, during each phase of the 1974 breeding season. 26 4. Percent of daylight time Ospreys engaged in behavioral activities (including Unknown activities) at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre- Incubation phase of the 1975 breeding season. 27 5. Relative rates at which sexes and different pairs of Ospreys engaged in Nest Construction, Nest Alteration, and Digging at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 41 6. Comparison of estimated and predicted energy expenditure of Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County,. California, during the Pre-Incubation phase of the 1975 breeding season. 61 7. Predicted energy intake and predicted numbers of fish ingested (based upon predicted daily energy expenditure) by Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 63

vii LIST OF APPENDICES Page 1. Frequency of occurrence, percent frequency of occurrence, and mean elapsed time in minutes Ospreys were engaged in each behavioral activity at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season. 84 2. Frequency of occurrence, percent frequency of occurrence, and mean elapsed time in minutes Ospreys were engaged in each behavioral activity at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre- Incubation phase of the 1975 breeding season. 87 3. Calculation of the percent of the 24-hour day the female Osprey at nest 1, Washington Gulch Creek, Humboldt County, California, engaged in Flying and Non-flying activities during the Incubation phase of the 1974 breeding season. 89 4. Estimated energy expenditure (calculated on the basis of food intake assimilated) of Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, during each phase of the 1974 breeding season. 90 5. Estimated energy expenditure (calculated on the basis of food intake assimilated) of Ospreys at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 92 6. Percentage of fish delivered by and subsequently totally consumed by Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre- Incubation phase of the 1975 breeding season. 93 7. Details of Aggressive Interactions of Nesting Ospreys. 94

viii Page 8. Predicted number of fish ingested (based upon predicted daily energy expenditure) by Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 105 9. Roles of female and male falconiforms in Delivery of Nest Material, Incubation, Brooding, Feeding Nestlings, and Supplying Food. 106

ix INTRODUCTION

Determination of the relationship between behavioral activities and energetic requirements of a species aids in understanding the behavior of the species and the transfer of energy within ecosystems. Time and energy budgets provide quantitative descriptions of an organism's behavior and aid in assessing the role of species populations in energy transfer. Energy transfer has received considerable attention since the 1940's, when the basic concepts of ecological energetics were developed (Lindemann 1942). However, analyses of energy transfer often are inhibited by a lack of data on the free-living energy requirements of species in the systems. Time and activity budgets have been obtained for only a few species of birds (Pearson 1954, Orians 1961, Verbeek 1964 and 1972, Schartz and Zimmerman 1971, Stiles 1971, Wolf and Hainsworth 1971, Utter and LeFebvre 1973, and others). Birds of prey (raptors) comprise a substantial portion of the higher trophic levels of the food chain in many ecosystems; however, little research has been conducted on their behavior in relation to their energy requirements. Some time and activity data have been gathered on wintering White-tailed Kites (Elanus leucurus) (Stendell 1972, Bammann 1975) and breeding American Kestrels (Falco sparverius) (Balgooyen 1976). Collopy (1975) recently completed a detailed study on the time and energy patterns of wintering 2

American Kestrels.' Collopy predicted the energy expenditure of kestrels with a deterministic model developed by Koplin (1972; Koplin et al, in prep.), and Koplin et al (in prep.) predicted the energy expenditure of White-tailed Kites with the same model. Energy expenditure estimated on the basis of food intake was compared with predicted energy expenditure as a means of testing the utility of the model. Detailed studies have not been conducted on the relationship between behavior and energetic requirements of raptors during the breeding season. Ospreys (Pandion haliaetus) are well-suited for such a study because of their relatively restricted diets and their easily observed nest sites. Osprey populations generally are declining throughout the world (Peterson 1969). Most of the extensive studies documenting Osprey reproductive performance and population trends in the eastern United States were summarized by Henny and Ogden (1970). Other studies documented reproductive performance in the western United States (French 1972, Garber 1972, D.L. MacCarter 1972, and Melquist 1974). Brief descriptions of Osprey behavior are mentioned throughout the literature, but few studies go into detail. Ames (1964) and Ames and Mersereau (1964) provided short, non-quantitative descriptions of nesting behavior. Hunting efficiency, rates of food delivery to nests, and the incubation behavior of Ospreys have been quantified (Lambert 1943, French 1972, Garber 1972, Garber and Koplin 3

1972, D.S. MacCarter 1972, and Ueoka 1974). No other aspects of the behavior or energetic requirements of Ospreys have been quantified thoroughly. The objectives of this study were to describe and quantify the behavioral activities, time and activity budget, and energy expenditure of Ospreys nesting in northern California. Time and activity patterns were evaluated in relation to seasonal and diurnal changes. Energy expenditures of nesting Ospreys were predicted with Koplin's deterministic model and then were compared with energy expenditures estimated on the basis of food intake. This study was conducted from March to September, 1974, and from April to May, 1975.

Study Area Geographic Location Three pairs of Ospreys were studied at their nests in Humboldt and Lassen Counties, California. Nest 1 was near Washington Gulch Creek, a tributary of Jacoby Creek, Humboldt County (Figure 1). Nests 2 and 3 were on the southeast and southwest sides, respectively, of a two-acre marsh 0.1 mile east of Eagle Lake, Lassen County (Figure 1).

Climate The climate of the coastal redwood region in Humboldt County is moderate. Summers are cool and dry, and winters are cool and wet. Average annual precipitation, predominant- ly in the form of rain, is about 150 cm, with 90 percent of

Figure 1: Location of nest 1, Washington Gulch Creek, Humboldt County, California, and nests 2 and 3, Eagle Lake, Lassen County, California. 5 6 the precipitation occurring from November through April (Ahlstrom 1968). Mean daily temperatures during the 1974 breeding season ranged from 9.8 to 15.1 C (U.S. Department of Commerce 1974). The climate at Eagle Lake is more extreme than that of coastal Humboldt County. Average annual precipitation at Eagle Lake ranges from 25 to 203 cm, a portion of which falls as snow. Daily temperatures during the period of study at Eagle Lake averaged approximately 2 C.

Vegetation Nest 1 was in the top of a 125-foot redwood (Sequoia sempervirens) snag, on a hillside above Washington Gulch Creek. The hillside was vegetated primarily with second- and third-growth redwood, with an understory of evergreen huckleberry (Vaccinium ovatum), salal (Gaultheria shallon), sword fern (Polystichum munitum), and rhododendron (Rhododendron macrophyllum). Red alder (Alnus rubra) grew alongside the creek. The entire area is privately owned, and the lowlands on either side of the creek were cleared and utilized for grazing. Nest 2 was located in the top of a 35-foot Jeffrey pine (Pinus jeffreyi) snag. Nest 3 was located on top of a powerline pole. Both nest sites were situated in large openings bounded by the marsh or by forest. The forest vegetation was dominated by western juniper (Juniperus occidentalis) and Jeffrey pine. The vegetation in the openings and in the understory of the forest was composed 7 primarily of rabbitbrush (Chrysothamnos nauseosus), big sagebrush (Artemesia tridentata), and gooseberry (Ribes spp.). Nests 2 and 3 were on public land administered by the Bureau of Land Management. Some grazing and camping take place in this area during the year. 8

METHODS

Field Observations A 20X wide-angle spotting scope and 8X binoculars were used to observe behavioral activities. Elapsed time of all activities was measured to the nearest second with a stop watch. The chronological time at the beginning of each activity and the elapsed time of each activity were recorded on a tape recorder. Time of day for all observations was recorded in Pacific Daylight Time. The distance at which observations could be conducted at nest 1, in combination with extremely rainy weather, precluded obtaining sufficient data during the early portion of the 1974 breeding season; therefore, additional data were collected at nests 2 and 3 during the early portion of the 1975 breeding season. Nesting Ospreys were observed primarily from dawn until dusk, with some half-day observations, for 397.0 hours during the entire 1974 breeding season and 146.1 hours during the early portion of the 1975 breeding season.

Definition of Behavioral Activities Observed The behavioral activities of nesting ospreys were categorized as follows: Change of Location. Osprey flew from one location near the nest to another location near the nest. Nest Material Flight. Osprey left nesting area and returned with nesting material. Ospreys usually procurred 9 nest material by picking it up from the ground or from standing water, such as a marsh, or by flying to an exposed dead branch, grasping the branch in the talons, and using body weight and/or momentum of flight to break the branch off. Courtship Flight. Osprey engaged in flight, apparently as a courtship display, in the presence of its mate. Four types of courtship flight were observed: 1) one bird hovering, 2) one bird circling and occasionally diving, 3) one bird hovering and occasionally diving, while its mate was perched, and 4) both birds circling each other. Miscellaneous Flight. Osprey circled near the nest for no readily apparent purpose. Fishing. Osprey flew towards a body of water (such as Humboldt Bay or Eagle Lake) and later returned with a fish, or flew towards a body of water and remained there sufficiently long that I assumed it foraged for fish, even though it returned without a fish. Mounting. Male Osprey landed on and remained on female Osprey's back, but did not attempt to copulate. The male appeared to bend his legs so that most of his weight was on his tarsometatarsi, instead of his talons. He also flapped his wings approximately one time per second during most mounts. Copulation. Copulation always was preceded by Mounting. Copulation occurred when the female raised her tail, the male leaned backward and lowered his tail to the side of and below 10 the female's tail, and cloacal contact was made. Nest-building. Osprey manipulated the material comprising the nest, including the placing of new material in the nest ("Nest Construction"), rearranging old material ("Nest Alteration"), and digging in the center of the nest ("Digging"). Nest Construction and Nest Alteration consisted of grasping material in the beak and placing or rearranging it in the nest. Digging consisted of partially spreading the wings for balance, lifting the tail, and scraping the bottom of the nest with the talons; this apparently resulted in redistribution of smaller pieces of nest material which accumulated on the bottom of the nest. Incubation. Osprey covered the eggs with its body, presumably to warm them and/or to protect them from ambient conditions. An Osprey about to incubate eggs stepped into the center of the nest and then lowered its body onto the eggs. Brooding. Osprey provided cover for nestlings with various parts of its body, presumably to warm and/or to protect recently-hatched nestlings from ambient conditions. Perch on Nest. Osprey perched on the nest, without engaging in other behavioral activities already described. Perch on Nest included preening, stretching, moving head to look at different objects, and taking steps which resulted only in a slight change of location on the nest. Perch on Trees. Osprey perched on a branch or top of a tree, without engaging in other behavioral activities already 11 described. Perch on Trees included preening, stretching, moving head to look at different objects, and taking steps which resulted only in a slight change of location on the tree. Intraspecific Vocalization. Osprey called at another Osprey, excluding its mate, from a perched position. Intraspecific Wing-Flap. Osprey on nest flapped its wings and called, apparently in an attempt to keep a strange Osprey from landing on the nest. Intraspecific Flight. Osprey chased ("Chase" - strong flight directly towards) or escorted ("Escort" - slow flapping or soaring flight near) a strange Osprey. Interspecific Vocalization. Osprey called at an individual of another species. Interspecific Wing-Flap. Osprey on nest flapped its wings and called, apparently in an attempt to keep an individual of another species from landing on the nest. Interspecific Flight. Osprey chased or escorted an individual of another species. Food Transfer. Food was delivered to the nest by one Osprey and taken by its mate. In most Food Transfers, food was taken by the mate soon after the food was brought to the nest; occasionally, the food was left in the nest for a short time before it was taken by the mate. At the end of the breeding season, some Food Transfers were made directly to the fledglings. Feeding Self. Osprey ingested pieces of food itself; 12 after feeding, Osprey often rubbed its bill back and forth on sticks or branches. Feeding Nestlings. Adult Osprey fed the nestlings by lowering its head, with a piece of fish in its bill, so that the young could grab the fish. Male Feeding Female. Female stretched her head towards the male and turned it upwards, so that it was directly below the male's bill; this position is termed "juvenile begging posture," because it was similar to postures of nestlings while they were being fed. The female then took or received a piece of fish from the male's bill. The male often moved his head towards the female during this activity. Bathing. Osprey stood in shallow water and preened. Osprey occasionally dipped portions of its wings and lower body into the water, and then shook its entire body., Unknown. Osprey was not near the nest nor was it Fishing; actual behavioral activities engaged in at the time were unknown.

Data Analysis Categories of Behavioral Activities To facilitate several of the analyses, related behavioral activities were grouped together in a single category; some behavioral activities were grouped into more than one category. Courtship activities included Courtship Flight, Mounting, and Copulation. Feeding activities included Food Transfer, Feeding Self, Feeding Nestlings, and Male Feeding Female. Aggressive interactions included all Interspecific 13 and Intraspecific interactions. Nest Activities included all behavioral activities which occurred on the nest. Tree Activities included all behavioral activities which occurred on trees. Flying activities included all behavioral activities involving flight: Change of Location, Miscellaneous Flight, Nest Material Flight, Courtship Flight, Fishing, Interspecific Flight, and Intraspecific Flight.

Stratification of Data The time and activity data were analyzed by calculating the relative frequency of occurrence and mean duration of each behavioral activity. Analyses of these data were stratified by sex, phase of breeding season, and time of day. The breeding season was divided into five sequential phases: Pre-Incubation, Incubation, Nestling, Fledging, and Post-Fledging. Ospreys at nest 1 were observed during all phases of the 1974 breeding season, while Ospreys at nests 2 and 3 were observed only during the Pre-Incubation phase of the 1975 breeding season. The Pre-Incubation phase began when Ospreys arrived in a nesting area (late March, 1974, at nest 1; early April, 1975, at nests 2 and 3) and ended when the first egg was laid (April 27, 1974, at nest 1; early May, 1975, at nests 2 and 3). The Incubation phase began when the first egg was laid (April 27, 1974) and terminated when the first egg hatched (June 3, 1974), The Nestling phase included the period during which nestlings were present, but not yet exercising their wings (June 4 until mid-July, 1974). The Fledging phase included the 14

period during which nestlings were exercising their wings, but not yet flying (mid-July until early August, 1974). The Post-Fledging phase began when the young took their first flights (early August, 1974) and terminated when all Ospreys left the nesting area (mid-September, 1974). To assess diurnal variations in the occurrence of behavioral activities, each day was divided into four equal time segments. The Early-morning segment lasted from dawn until mid-morning. The Late-morning segment lasted from mid-morning until mid-day. The Early-afternoon segment lasted from mid-day until mid-afternoon. The Late-afternoon segment lasted from mid-afternoon until dusk.

Computer Program and Statistical Analysis Tape-recorded data were transcribed and keypunched onto computer cards. Analyses of data were conducted on the Control Date Corporation 3150 computer at Humboldt State University. Program TIMACT (Collopy 1975) was modified and used to sum the time and activity data. For each category stratified (sex, phase of breeding season, or segment of day), the program summed the frequency of occurrence and elapsed time of each behavioral activity. Studies by Ueoka (1974) on foraging Ospreys (Table 1), and observations that fish delivered to nesting areas by male Ospreys usually are decapitated (Ames 1964, Ueoka 1974, this study), indicate that males perch and feed before re- turning to nesting areas. Until further studies are conducted, it is assumed that one-half of the 18.4 minutes unaccounted 15

Table 1. Activities of foraging Ospreys while absent from nests located near Humboldt Bay, Humboldt County, California.

Mean duration of Activity activity (minutes) A. Absent from nesta 67.3 B.Foraging a 11.9 C.Perched at sites adjacent to 27.0 foraging site on Humboldt Baya

D.Travelling time between nests 10.0 and Humboldt Bayb E.Unaccounted time (A - B - C - D) 18.4 F.Total time perched (C + E/2) 36.2 a Ueoka (1974) b Estimated 16 for during absences from the nest (Table 1) was spent perched and that the total amount of time perched, 36.2 minutes by these considerations, approximated fifty percent of the elapsed time included in Fishing. The assumed time spent perching was included in the behavioral activity, Perch on Trees. It was not necessary to apply this assumption to Fishing at Eagle Lake, where Ospreys flew directly to the lake from the nesting area and returned directly to the nesting area. Because unequal hours of observation were conducted during the different phases of the breeding season and during the different segments of the day, some bias may have occurred if absolute frequencies of occurrence or total elapsed times of a behavioral activity were compared. Therefore, the data were made comparable by expressing the frequency of occurrence as frequency of occurrence per hour of observation, and by calculating the percent of observation time a behavioral activity occurred. The absolute frequency of occurrence, percentage of the frequency of all activities, and the mean elapsed time were calculated for each activity engaged in by Ospreys at nest 1 (Appendix 1) and at nests 2 and 3 (Appendix 2). An exemplary calculation of the percent of a 24-hour day that flying and non-flying activities were engaged in by Ospreys is presented in Appendix 3. Chi-square tests (Zar 1974) were used to test for significant differences in the frequencies of occurrence per hour of behavioral activities in different strata. A test 17 based upon the arcsine transformation was used to test the equality of the percentages of time Ospreys engaged in different behavioral activities (Sokal and Rohlf 1969). In all statistical analyses, differences equal to or less than 5.0 percent (p ≤ 0.05) were considered significant.

Energy Expenditure Estimated Energy Expenditure Daily energy expenditure was estimated on the basis of food intake by recording the number of fish ingested per day by adults during each phase of the breeding season. Many fish delivered to the nesting areas were eaten by adults as well as nestlings. The fraction of these fish consumed by a specific adult was determined by dividing the total number of minutes that the adult fed on a fish by the total number of minutes all Ospreys fed on that fish; this assumes that all Ospreys fed upon fish at the same rate. To obtain the estimated daily energy expenditure, the number of fish ingested per day was multiplied by the average weight per fish, the fraction of dry weight per fish, the number of kilocalories per dry weight gram of fish, and the digestive and assimilation coefficients of fish-eating birds (Appendices 4 and 5) . Food intake by the female at nest 1 during the Post- Fledging phase and by the male at nest 1 during the entire season were not estimated; lack of data on feeding activities of these birds when they were absent from the nesting area precluded such estimates. Estimates were possible for the 18 female at nest 1 during the first four phases of the breeding season because she spent very little time away from the nesting area during these phases.

Predicted Energy Expenditure Koplin (1972) and Koplin et al (in prep.) developed a generalized model to predict energy expenditure of free- living birds. The data base for this model is average ambient temperature and a time and activity budget. Different levels of flying and non-flying behavioral activities were assigned different energetic costs. Ospreys engaged in non- flying activities were assumed to expend energy at the existence metabolic rate (Kendeigh 1970) for a given average daily temperature. Justification for this assumption is from ongoing studies in which various species of captive falconiforms expended energy at a rate similar to that predicted from equations for existence metabolic rate (Kendeigh 1970, Koplin et al in prep.). Flying Ospreys were assumed to expend thirteen times the "resting phase" of basal metabolic rate (BMR) (Aschoff and Pohl 1970). Justification for this assumption is based upon Koplin's analysis of studies on the energetics of flight of non-passerine birds (Lasiewski 1963, LeFebvre 1964, Raveling and LeFebvre 1967, Tucker 1968 and 1969, and Gessaman 1973a). Koplin found that the energetics of flight were approximately 12-fold higher than BMR of non-passerines ranging from 3 to 384 grams when BMR of these birds was calculated from equations developed by Lasiewski and Dawson (1967), and 13-fold higher than BMR of 19 these same birds when using equations for the " resting phase" of BMR developed by Aschoff and Pohl (1970). The time and activity parameters in Koplin's model are based upon both daytime and night-time activities. Nesting Ospreys were assumed to remain inactive (either on the nest or on a perch tree) for the entire night. Justification for this assumption is based upon several short night-time observation periods during which no movements by Ospreys were observed. If some flight activity did occur at night, it probably had relatively little impact on the overall energy budget. A reasonable approximation of the numbers of fish consumed by Ospreys during those phases of the breeding season for which data were lacking is to calculate the numbers of fish consumed on the basis of Koplin's model for predicting daily energy expenditure. That is, if daily energy expenditures predicted by the model are similar to those estimated on the basis of food consumption, then it seems reasonable to reverse the process -- to calculate on the basis of daily energy expenditure predicted from Koplin's model the number of fish ingested by Ospreys per phase of the breeding season. RESULTS

Time and Activity Budget Behavioral activities of breeding Ospreys differed in relation to sex and phase of breeding season (Figures 2, 3, and 4). Females engaged in Flying activities for less than 4 percent of the 24-hour day, during each phase of the breeding season except during the Post-Fledging phase (Table 2). During the Post-Fledging phase, the female at nest 1 engaged in Flying activities for almost 17 percent of the 24-hour day, a significantly greater amount of Flying activities than during earlier phases of the breeding season (ts=4.79, p<0.001). The increase in Flying activities of the female at nest 1 during the Post-Fledging phase resulted from an increase in the percentage of daylight time she engaged in Fishing (Table 3). Females at nests 2 and 3 spent a greater percentage of time during the Pre-Incubation phase engaged in Flying activities than did the female at nest 1 (Table 2), although the difference was not significant (ts=1.133, p> 0.25). Females spent between 1.4 and 3.7 percent of the 24-hour day engaged in Flying activities. However, females at nests 2 and 3 spent more time engaged in Miscellaneous Flight than did the female at nest 1. Females at nests 2 and 3 spent an average of 2.41 percent of daylight time, while the female at nest 1 spent 0.30 percent of daylight time, engaged in Miscellaneous Flight (Tables 3 and 4). 21

Figure 2. Composite time and activity budget of female Osprey at nest 1, Washington Gulch Creek, Humboldt County, California, in relation to phase of 1974 breeding season. The amount of daylight time expended in each behavioral category is expressed in percent.

Figure 3. Composite time and activity budget of male Osprey at nest 1, Washington Gulch Creek, Humboldt County, California, in relation to phase of 1974 breeding season. The amount of daylight time expended in each behavioral category is expressed in percent. 22 23

Figure 4. Time and activity budgets of male and female Ospreys during the Pre-Incubation phase of the 1974 breeding season at nest 1, Humboldt County, California, compared to the time and activity budgets of male and female Ospreys during the Pre-Incubation phase of the 1975 breeding season at nests 2 and 3, Eagle Lake, Lassen County, California. 24 25

Table 2. Relative percentages of the 24-hour day sexes and different pairs of Ospreys engaged in Flying and Non-flying activities at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season.a

PERCENT ELAPSED TIME Flying Activities Non-flying Activitiesb Nest and Phase of Breeding Season Female Male Female Male

Nest 1 Pre-Incubation 1.41 12.54 98.71 87.44 Incubation 0.74 14.82 99.24 85.21 Nestling 1.17 18.14 98.81 81.85 Fledging 2.56 13.83 97.45 86.17 Post-Fledging 16.93 17.77 83.08 82.16 Entire Season 3.56 15.81 96.44 84.19

Nest 2

Pre-Incubation 3.70 11.07 96.32 88.92

Nest 3 Pre-Incubation 3.03 12.24 96.96 87.85 a Based upon 397.0 hours of observation at nest 1, 95.1 hours at nest 2, and 51.0 hours at nest 3. b Assumes Ospreys did not engage in any Flying activities at night. Note: The sum of Percent Elapsed Time of Flying activities and Non- flying activities for a particular bird during a particular phase may differ slightly from 100.00 percent because of rounding errors in calculations. 26

a at nest 1, Washington Gulch Creek, Humboldt County, California, during each phase of the 1974 of the phase each during California, County, Humboldt Creek, Gulch 1, Washington at nest breeding season. breeding Table 3. Percent of daylight time Ospreys engaged in behavioral activities (including Unknown activities) activities) Unknown (including activities in behavioral engaged Ospreys time daylight of 3. Percent Table 27

a breeding season. breeding at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the of the phase Pre-Incubation the during California, County, Lassen Lake, Eagle and 3, 2 at nests Percent of daylight time Ospreys engaged in behavioral activities (including Unknown activities) activities) Unknown (including activities behavioral in engaged Ospreys time daylight of Percent 1975 4. Table Table 28

The male at nest 1 spent 12 to 18 percent of the 24-hour day engaged in Flying activities during the various phases of the 1974 breeding season (Table 2). Differences in percentages of the 24-hour day the male engaged in Flying activities during the Pre-Incubation, Incubation, and Fledging phases were not significant (ts=0.723, p> 0.45). During these phases, he spent an average of 13.70 percent of the 24-hour day engaged in Flying activities. Differences in percentages of the 24-hour day the male at nest 1 engaged in Flying activities during the Nestling and Post-Fledging phases also were not significant (ts=0.095, p > 0.90) . During these phases, he spent an average of 17.98 percent of the 24-hour day engaged in Flying activities. However, the difference in the percentage of time spent Flying between the Pre-Incubation, Incubation, and Fledging phases on the one hand and the Nestling and Post-Fledging phases on the other was almost significant (ts=1.953, p=0.051). The difference in Flying time between these two groups of phases of the breeding season was due to the greater percentage of daylight time the male engaged in Fishing during the Nestling and Post- Fledging phases (Table 3). There were no significant differences (ts=0.327, p >0.70) in the percentages of the 24-hour day males at all three nests engaged in Flying activities during the Pre-Incubation phase. Males spent between 11.0 and 12.6 percent of the 24-hour day engaged in Flying activities (Table 2). However, males at nests 2 and 3 spent less time Fishing and more time engaged in Miscellaneous Flight than did the male at nest 1 29

(Figure 4). Males at nests 2 and 3 spent an average of 6.35 percent, while the male at nest 1 spent only 0.89 percent, of daylight time engaged in Miscellaneous Flight (Tables 3 and 4). Males at nests 2 and 3 spent an average of 8.15 percent, while the male at nest 1 spent 13.65 percent, of daylight time engaged in Fishing (Tables 3 and 4).

Seasonal Trends in Behavioral Activities Nest Activities and Tree Activities Female Ospreys engaged in Nest Activities to a larger extent than males (Figure 5). During the first four phases of the 1974 breeding season, the female at nest 1 engaged in Nest Activities at least 80 percent of the daylight time. During the Incubation and Nestling phases, she spent over •91 percent of daylight hours on the nest. During the Post- Fledging phase, she was on the nest only 20 percent of the time, mostly perched on the rim. In contrast, the male at nest 1 spent less than 40 percent of daylight time during the first three phases, and less than 3 percent of daylight time during the last two phases of the breeding season, engaged in Nest Activities. Ospreys at nests 2 and 3 did not spend as much time engaged in Nest Activities during the Pre-Incubation phase as did Ospreys at nest 1; however, females still spent more time engaged in Nest Activities on nests 2 and 3 than did males (Figure 5). The amount of time female Ospreys engaged in Nest Activities varied greatly from day to day during the Pre- Incubation phase (Figure 6). Females generally spent the 30

Figure 5. Percent of daylight time Ospreys engaged in Nest Activities in relation to phase of the breeding season, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 31

PHASE OF BREEDING SEASON 32

Figure 6. Percent of daylight time female Ospreys engaged in Nest Activities in relation to the number of days prior to egg-laying, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the 1975 breeding season. Day first egg was laid is designated as day 0.

Figure 7. Percent of daylight time male Ospreys engaged in Nest Activities in relation to the number of days pri0r to egg-laying, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the 1975 breeding season. Day first egg was laid is designated as day O. 33 34 least time on the nest early in the Pre-Incubation phase, and most of the daylight time on the nest during the latter part of the phase. Male Ospreys did not exhibit as much variability or an increase in the amount of time engaged in Nest Activities during the Pre-Incubation phase (Figure 7). Males generally spent less than one-third of daylight hours during the Pre- Incubation phase engaged in Nest Activities. When not engaged in Nest Activities, female Ospreys usually perched on snags near their nests. The female at nest 1 spent more than 94 percent of the daylight hours during the first four phases of the breeding season engaged in Nest Activities and Tree Activities (Figure 8). During the Post-Fledging phase, though, she spent less than 45 percent of the daylight time engaged in Nest Activities and Tree Activities. Females at nests 2 and 3 spent 90 percent of daylight hours during the Pre-Incubation phase engaged in Nest or Tree Activities. Male Ospreys spent about two-thirds of daylight hours during the Pre-Incubation phase engaged in Nest Activities and Tree Activities (Figure 8). The male at nest 1 spent decreasing amounts of daylight time on the nest and on trees as the breeding season progressed, except for a slight increase in the percentage of daylight time Perched on Trees during the Fledging phase (Table 3).

Perch on Nest and Perch on Trees Males at nests 2 and 3 spent significantly less time Perched on the Nest (ts=3.79, p< 0.001) and insignificantly 35

Figure 8. Percent of daylight time Ospreys engaged in Nest Activities and Tree Activities in relation to phase of the breeding season, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 36

PHASE OF BREEDING SEASON 37 more time Perched on Trees (ts=0.731, p >0.40) during the Pre-Incubation phase than did the male at nest 1 (Figure 4). Males at nests 2 and 3 Perched on the Nest for an average of 13.92 percent of daylight time, while the male at nest 1 Perched on the Nest for 30.09 percent of daylight time (Tables 3 and 4). All three males spent between 38.5 and 43.1 percent of daylight time Perched on Trees (Tables 3 and 4). Differences in the total percentage of daylight time males at all three nests Perched on the Nest and Perched on Trees were significant (ts=2.54, p <0.05). The male at nest 1 spent 68.7 percent, and males at nests 2 and 3 spent an average of 57.0 percent, of the daylight time Perched on the Nest and Perched on Trees (Tables 3 and 4). Females at nests 2 and 3 spent significantly less time Perched on the Nest (ts=5.91, p <0.001) and significantly more time Perched on Trees (ts=4.67, p <0.001) during the Pre-Incubation phase than did the female at nest 1 (Figure 4). Females at nests 2 and 3 Perched on the Nest for an average of 39.21 percent of daylight time and Perched on Trees for an average of 44.87 percent of daylight time (Table 4). The female at nest 1 Perched on the Nest for 75.78 percent of daylight time and Perched on Trees for 11.65 percent of daylight time (Table 3). Differences in the total percentage of daylight time females at all three nests Perched on the Nest and Perched on Trees during the Pre-Incubation phase were not significantly different (ts=1.06, p> 0.25) . Females spent between 84.1 and 87.4 percent of daylight time Perched 38 on the Nest and Perched on Trees (Tables 3 and 4).

Nest Material Flight Nest Materials (Nest Material Flight) were delivered to nests throughout the entire breeding season (Figure 9). Males at all three nests delivered most of the nest material prior to the date eggs were laid. After the eggs hatched in nest 1, the female brought most of the additional material to the nest. The combined rate of Nest Material Flights by both sexes at nest 1 during the Pre-Incubation, Nestling, and Fledging phases ranged from 0.37 to 0.48 flights per hour (Figure 9). During the Incubation phase, while eggs were in the nest, and during the Post-Fledging phase, when fledglings spent little time in the nest (Levenson, unpublished data), significantly less nest material was delivered to nest 1 than during the other three phases of the breeding season (e=55.4, 1 d.f, p <0.001). The combined rate of Nest Material Flights by both sexes at nest 1 during the Incubation and Post-Fledging phases ranged from 0.06 to 0.11 flights per hour (Figure 9).

Nest-building The bird which delivered material to the nest usually placed it into the nest (Nest Construction); patterns of Nest Construction by male and female Ospreys thus paralleled patterns of Nest Material Flights (compare Figure 9 and Table 5). On three occasions (1.8 percent of all Nest Material Flights, n=171), males dropped material into the 39

Figure 9. Numbers of items of nest material delivered per hour by female and male Ospreys in relation to phase of the breeding season, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 40

PHASE OF BREEDING SEASON c

Table 5. Relative rates at which sexes and different pairs of Ospreys engaged in Nest Construction, Nest Alteration, and Digging at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season.a

Nest Nest Construction Alteration Digging Nest and Phase of Breeding Season Female Male Female Male Female Male Nest 1 Pre-Incubation 0.11b 0.39 0.61 0.55 0 0 (4)c (15) (22) (21)

Incubation 0.02 0.08 0.15 0.08 0 0 (2) (8) (15) (8) Nestling 0.34 0.03 0.30 0.15 0 0 (48) (5) (43) (21) Fledging 0.48 0 0.14 0.02 0 0 (21) (0) (6) (1) Post-Fledging 0.05 0.01 0 0.01 0 0 (3) (1) (0) (1)

Nest 2

Pre-Incubation 0.16 0.14 0.31 0.54 0 0.23 (15) (13) (29) (51) (22)

Nest 3 Pre-Incubation 0.12 0.59 0.38 1.08 0.16 (6) (30) (19) (55) (8)

a Based upon 397.0 hours of observation at nest 1, 95.1 hours at nest 2, and 51.0 hours at nest 3. b Frequency per hour. c Total number of observations of the behavioral act. 42 nest and females arranged the new material in it. Most Nest Alterations during the Pre-Incubation phase were performed by males at nests 2 and 3 (Table 5). Nest Alterations usually were performed by the female throughout the entire breeding season at nest 1. The rate of Nest Alteration at nest 1 was highest during the Pre-Incubation phase, intermediate during the Nestling phase, and low during the other phases of the breeding season. This pattern is similar to that of Nest Construction, except that the rate of Nest Construction during the Fledging phase was relatively high and the rate of Nest Alteration during the same phase was relatively low. The combined rates of Nest Construction and Nest Alter- ation during the Pre-Incubation phase averaged 1.66, 1.15, and 2.17 activities per hour at nests 1, 2, and 3, respectively (Table 5). These rates were inversely related to the qualitative condition of the nests when Ospreys first arrived in the nesting areas. Nest 2 appeared to be in the best initial condition of the three nests; Ospreys spent the least amount of time repairing it. Nest 3 appeared to be in the worst initial condition; Ospreys spent the most amount of time repairing this nest. Nest 1 was intermediate in qualitative condition and in the amount of Nest Construction and Nest Alteration Ospreys performed. Digging was performed only by males at nests 2 and 3 (Table 5); however, the distances from which observations at nest 1 were conducted may have precluded observation of 43 this activity at that nest.

Mounting and Copulation Mounting and Copulation did not occur when Ospreys first arrived at nest 1 and at other nests in Humboldt County (Figure 10; Levenson, unpublished data). Ospreys were utilizing nests 2 and 3 when observations at these nests commenced; mounting and copulatory patterns during the beginning of the Pre-Incubation phase at Eagle Lake thus were unobserved. The frequency of Mounting and Copulation at all three nests gradually increased as the Pre-Incubation progressed (Figures 10 and 11). The frequency of Mounting and Copulation reached a peak approximately two to six days -- the exact number of days depending upon the pair of birds involved -- prior to the initiation of egg-laying and then decreased. Ospreys at nest 1 spent approximately 0.4 percent, and Ospreys at nests 2 and 3 spent approximately 0.2 percent, of the daylight time during the Pre-Incubation phase engaged in Mounting and Copulation (Tables 3 and 4). During the Incubation phase, Ospreys at nest 1 engaged in Mounting and Copulation for less than 0.01 percent of the daylight time (Table 3). Mounting and Copulation were not observed after the Incubation phase.

Incubation and Brooding The eggs at nest 1 were incubated for 96.1 percent of the daylight time (Table 3); 73.2 percent of the incubation was performed by the female. The male generally incubated 44

Figure 10. Numbers of mounts and copulations engaged in by Ospreys in relation to number of days prior to and after egg-laying at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season. Day first egg was laid is designated as day O.

Figure 11. Numbers of mounts and copulations engaged in by Ospreys in relation to number of days prior to and after egg-laying at nests 2 and 3, Eagle Lake, Lassen County, California, during the 1975 breeding season. Day first egg was laid is designated as day O. 45 46 the eggs while the female was feeding. The female always was incubating the eggs at dawn (n=7) and at dusk (n=6). The percentage of daylight time each sex incubated the eggs did not fluctuate greatly from one observation period to the next (Figure 12). The female initiated incubation sessions 1.11 times per hour (n=112); the mean duration of each incubation session was 37.9 minutes (Appendix 1). The male initiated incubation sessions 0.69 times per hour (n=70); the mean duration of each incubating session was 22.3 minutes (Appendix 1). The number of incubation sessions initiated per hour and the mean duration of each session engaged in by the male were significantly less than the number of incubation sessions initiated per hour (X2= 9.69, 1 d.f., p <0.005) and the mean duration of each incubation session (t=4.23, p <0.001) by the female. Thus, an incubation session by the female was not necessarily followed with an incubation session by the male. The female often terminated an incubation session, performed one or more short activities, and then initiated another incubation session. After the eggs hatched, the female performed 96.3 percent of all Brooding. The male brooded nestlings for 11.4 percent of the daylight time of the first day after the eggs hatched, but he rarely brooded them during the rest of the Nestling phase (Figure 12). The female spent approximately the same percentage of daylight time during the first two weeks of the Nestling phase brooding nestlings, as she previously spent 47

Figure 12. Relative percentages of daylight time each sex of Ospreys engaged in Incubation and Brooding in relation to number of days prior to and after egg- laying at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season. Day first egg was laid is designated as day 0. 48 DAYS PRIOR TO AND AFTER EGG - LAYING DAYS PRIOR TO AND 49 incubating eggs. During the next ten days, the percentage of daylight time she spent brooding rapidly declined to zero (Figure 12). Because of this drop in time spent brooding by the female, brooding did not comprise the majority of her behavioral activities during the Nestling phase (Figure 2). The female initiated brooding sessions 1.32 times per hour (n=82) during the first two weeks of the Nestling phase; the mean duration of each brooding session was 33.1 minutes. The male initiated brooding sessions only 0.13 times per hour (n=8), and the mean duration of each session was only 13.2 minutes.

Fishing Females at nests 2 and 3 engaged in little or no Fishing during the Pre-Incubation phase (Figure 13). The female at nest 2 was the only female observed Fishing during the Pre- Incubation phase; she only engaged in Fishing twice, both times near the beginning of the phase. The female at nest 1 did not fish during the first three phases of the breeding season and only fished for 1.19 percent of daylight hours during the Fledging phase (Figure 13). During the first four phases of the breeding season the female at nest 1 spent most of the daylight hours engaged in Nest Activities or Tree Activities (Figure 8). During the Post-Fledging phase, however, she fished for 26.1 percent of daylight time. The pattern of Fishing by male Ospreys contrasted markedly with the pattern of Fishing by females. Males at nests 2 and 3 engaged in Fishing between 7.9 and 8.6 percent 50

Figure 13. Relative percentages of daylight time sexes and different pairs of Ospreys engaged in Fishing in relation to phase of, breeding season, at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 51

PHASE OF BREEDING SEASON 52

of the daylight time during the Pre-Incubation phase (Figure 13). The male at nest 1 engaged in Fishing no less than 13.6 percent and up to 26.4 percent of the daylight time during the various phases of the breeding season; he fished least during the first two phases, when no young were present (Figure 13). The pattern of fish deliveries to nesting area paralleled the pattern of Fishing (Figures 13 and 14). Differences in rates of delivery of fish by males to nests 1,2,and 3 during the Pre-Incubation phase were insignificant (X2=3.21, 2 d.f., 0.10

0.10) . The female at nest 2 delivered two fish during the entire Pre-Incubation phase, and the females at nests 1 and 3 were never observed delivering fish during this phase. The rate of delivery of fish by both sexes of Ospreys at nest 1 was relatively low during the Pre-Incubation and Incubation phases, 0.26 fish per hour and 0.22 fish per hour, respectively; intermediate during the Nestling and Fledging phases, 0.42 fish per hour and 0.49 fish per hour, respectively; and highest during the Post-Fledging phase, 0.68 fish per hour. Males delivered 100 percent of the fish brought to nests 1 and 3, and 85 percent of the fish brought to nest 2, during 53

Figure 14. Relative rates sexes and different pairs of Ospreys delivered fish to nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and to nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 54

PHASE OF BREEDING SEASON 55 the Pre-Incubation phase. Of fish delivered to nest 1, the male brought 100 percent during the Incubation and Nestling phases, 95.9 percent during the Fledging phase, and 70.5 percent during the Post-Fledging phase. Thus, the male provided all the fish consumed by the female at nest 1 (n=71) during the first three phases of the breeding season, and 95.2 percent of the fish she ate (n=21) during the Fledging phase. During the Post-Fledging phase, however, most of the fish delivered to nest 1 by the male were transferred directly to the young. The male was observed delivering fish to the female only four times during this phase; all of these deliveries took place during the first week of the Post-Fledging phase. During the Post-Fledging phase the female delivered 75.0 percent of the fish she consumed (n=16)0 The rate of delivery of fish by the male to nest 1 during the Post- Fledging phase was approximately the same as during the Fledging phase (Figure 14).

Feeding Activities Males and females completely consumed some of the fish they delivered to the nesting area during the breeding season (Appendix 6). During the Nestling and Fledging phases at nest 1, both adults also consumed a portion of every fish eventually transferred to the young. During the Post-Fledging phase, 57.1 percent of the fish transferred to the young by the male. (n=28) and 70.0 percent of the fish transferred to the young by the female (n=10) were partially consumed; the remainder of the fish transferred to the young had not been fed upon by 56 either adult. The female at nest 1 fed the nestlings 125 times and the male fed them four times during the Nestling and Fledging phases. The female and male at nest 1 spent averages of 10.3 and 0.2 percent, respectively, of daylight time during the Nestling and Fledging phases Feeding Nestlings. During the Post-Fledging phase, the female spent 3.03 percent and the male spent none of the daylight hours Feeding Nestlings. During the Post-Fledging phase, both adults usually provided food to the fledglings by leaving an entire or partially- consumed fish in the nest. The fledglings then took the fish and fed themselves. The male at nest 1 fed his mate (Male Feeding Female) 11 times, only during the Nestling phase. The mean duration of a Male Feeding Female session was 6.55 minutes; during this time, the male fed the female an average of 8.9 pieces of fish per minute (n=4). Males at nests 2 and 3 were not observed feeding their mates.

Aggressive Interactions The male at nest 1 spent 0.17 to 1.16 percent of daylight hours engaged in Aggressive interactions during the various phases of the 1974 breeding season (Table 3); most of the interactions were with other species, except during the Post- Fledging phase (Appendix 7). The female at nest 1 spent 0.16 to 0.87 percent of daylight hours engaged in Aggressive interactions during the various phases of the 1974 breeding season (Table 3). Most of her Aggressive interactions were with 57 other Ospreys, except during the Incubation and Fledging phases (Appendix 7). The males at nests 2 and 3 spent 2.31 and 1.29 percent, respectively, of daylight hours during the Pre-Incubation phase engaged in Aggressive interactions. Females at nests 2 and 3 spent 1.10 and 0.28 percent, respectively, of daylight hours during the Pre-Incubation phase engaged in Aggressive interactions (Table 4). Most of the interactions of both sexes were with other Ospreys (Appendix 7). Differences in percentages of daylight hours males at all three nests engaged in Aggressive interactions during the Pre-Incubation phase were insignificant (ts=0.376, p > 0.70) . Differences in percentages of daylight hours females at all three nests engaged in Aggressive interactions during the Pre- Incubation phase also were insignificant (ts=0.037, p > 0.95). For purposes of comparison with other studies -- such as Collopy (1975) and Bammann (1975) -- detailed information is presented in Appendix 7 on the frequencies and types of Agonistic interactions involving the Ospreys studied.

Diurnal Variations in Behavioral Activities Variations at all three nests were observed in the percentage of each daily time segment during which Perch on Nest, Perch on Trees, Mounting and Copulation, Nest Material. Flights, Incubation, Brooding, and Fishing occurred. However, the variations observed in the performance of each activity were not significantly different from one an0ther (Levenson, unpublished data). More data on the performance of these 58 activities by nesting Ospreys are needed before a refined analysis can be attempted. A pattern of fish deliveries at nest 1 was apparent when the total number of fish delivered per hour during each daily time segment was analyzed (Figure 15). The total number of fish delivered per hour was high in the Early-morning, decreased during the Late-morning, and then increased during the Early- afternoon and reached a peak during the Late-afternoon. This pattern was apparent both before and after the eggs hatched, although the frequency of fish deliveries was greater after the eggs hatched than before.

Date of Departure from Nesting Area The female at nest 1 was last seen in the nesting area on August 30, 1974. She was not observed during an entire day of observations at nest 1 on September 2, nor was she observed on subsequent dates. The male and the two fledglings were observed up to and including September 14, but they were not observed on September 18 or on subsequent dates. Whether the male and the two fledglings departed from the nesting area together or separately is unknown.

Energy Expenditure Prediction of daily energy expenditure of Ospreys using Koplin's model and a comparison of predicted values with values estimated on the basis of food intake assimilated are presented in Table 6. Differences between estimated and predicted energy expenditure did not exceed 12 percent and usually were less 59

Figure 15. Number of fish delivered per hour to nest 1, Washington Gulch Creek, Humboldt County, California, in relation to segment of the day during the 1974 breeding season. 60

SEGMENT OF DAY 6 1 Creek, Humboldt County, California, during the 1974 breedin3 season, and at nests 2 and 3, Eagle 3, Eagle 2 and at nests and season, breedin3 the 1974 during California, County, Humboldt Creek, Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season. 1975 breeding phase of the the Pre-Incubation during County, California, Lake, Lassen Table 6. Comparison of estimated' and predicted daily energy expenditure of Ospreys at nest 1, Washington Gulch Gulch 1, Washington at nest of Ospreys expenditure energy daily predicted and of estimated' 6. Comparison Table 62 than 10 percent. Females and males at nests 2 and 3 expended more energy per day during the Pre-Incubation phase than did the female and male, respectively, at nest 1 (Table 6). However, females and males at nests 2 and 3 ingested fewer fish during the entire Pre-Incubation phase than did the female and male at nest 1 (Table 7), because the Pre-Incubation phase at nests 2 and 3 was approximately thirteen days shorter than the Pre- Incubation phase at nest 1, and because fish captured in Eagle Lake were larger than fish captured in Humboldt Bay (Table 7). Adult Ospreys at nest 1 ingested a predicted total of 612.0 fish, or 1.57 x 105 Kilocalories, during the entire breeding season (Table 7). Two young were raised at this nest in 1974; the young ingested an estimated 118.0 fish (3.11 x 104 Kilocalories), 55.3 fish (1.17 x 104 Kilocalories), and 228.2 fish (5.60 x 104 Kilocalories) during the Nestling, Fledging, and Post-Fledging phases, respectively. Therefore, Ospreys at nest 1 ingested a predicted total of 1013.5 fish, or 2.56 x 105 Kilocalories, during the 1974 breeding season. The breeding success of Ospreys nesting east of Humboldt Bay in 1971 and 1972 averaged 1.11 fledglings per active nesting pair (French 1972). When my predictions of food consumption are applied to all Ospreys preying upon fish from Humboldt Bay and its tributaries, the average pair of active nesting Ospreys and their offspring would be expected to consume a predicted total of 834.8 fish (2.12 x 105 Kilocalories) during each breeding season. The predicted number of fish consumed 63

Table 7. Predicted energy intake and predicted numbers of fish ingested (based upon predicted daily energy expenditure) by Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season.a

a Refer to Appendix 8 for calculations of predicted energy intake and predicted }umbers of fish ingested. 64 may be overestimated, since it is based upon herring as a food source. The Ospreys at nest 1 utilized herring-like fish; however, most Ospreys foraging in Humboldt Bay prey upon various species of surfperch (Ueoka 1974), which weigh more than herring of the same length (based upon comparison of data in Carlander 1953, and Anderson and Bryan 1970). Therefore, an average pair of Ospreys and their young probably consume fewer than 834.8 fish during a breeding season. There are approximately 20 pairs of Ospreys nesting in Humboldt Bay. Based upon the above predictions, Ospreys and their offspring remove and consume 16,696 fish (4.24 x 106 Kilocalories) from Humboldt Bay during the course of one breeding season. The impact of Ospreys upon their prey cannot be assessed, because data are lacking on the sizes of fish populations in Humboldt Bay. DISCUSSION

Energy Expenditure Research has been conducted on methods of directly measuring free-living energy expenditure (LeFebvre 1964, Gessaman 1973a and 1973b), but most of these methods are difficult and costly to utilize under field conditions. Koplin's model is an indirect method of predicting energy expenditure of free-living falconiforms. Utilization of the model requires knowledge of the time and activity budget of the birds -- which is a quantitative description of their behavior -- and ambient temperature; these data are relatively easy to gather. Predicted energy expenditures based upon the model have been obtained for three species of raptors: wintering American Kestrels and White-tailed Kites (Koplin et al, in prep.), and breeding Ospreys (this study). Differences between predicted and estimated energy expenditures ranged from less than 1 percent to approximately 12 percent, indicating that Koplin's model is a useful method of approximating energy expenditure of free-living falconiforms. The model is useful in assessing the role of falconiform populations in energy transfer, if the densities of the falconiform populations are known. It also can be utilized in studies on predator-prey relationships to assess the impact of falconiforms on their prey, if data are available on the population sizes and caloric values of the prey. 66

Time and Activity Budget of Ospreys Species which migrate long distances and which have long breeding seasons must begin nest-building and egg-laying quickly, so that the young have sufficient time to complete their development (Matray 1974); little time is spent on pair formation or territorial disputes (Ames 1964). This study supports Matray's and Ames' hypotheses, since Ospreys at all three nests studied spent, little time engaged in Courtship activities or in Intraspecific Interactions, and began Nest- building shortly after their arrival in the nesting area. The members of a pair of Ospreys arrive in their nesting area within five days of each other (Allen 1892, Ames 1964, Garber 1972); Ospreys may mate for more than one breeding season and return to the nest site of the previous year, thereby reducing the need for extensive courtship. Minimizing courtship might be particularly critical in an area with climatic exremes such as those found at Eagle Lake, where the Pre- Incubation phase was approximately thirteen days shorter than the Pre-Incubation phase in climatically more moderate areas such as coastal Humboldt County. The Pre-Incubation phase of breeding seasons generally is shorter in areas with extreme weather conditions than in areas with more moderate climates (Cade 1960, Balgooyen 1976). Because ambient temperatures were lower at Eagle Lake than near Humboldt Bay, Ospreys at nests 2 and 3 may have engaged in more Miscellaneous Flight than Ospreys at nest 1 simply to thermoregulate; flight activities result in a higher 67 body temperature than do non-flight activities. The pattern of increased mounting and copulation prior to egg-laying fits well with the ideas that such a pattern aids in synchronization of the hormonal systems of the two sexes (Lehrman 1958, Lofts and Murton 1968) and in maintenance of the pair bond (Cade 1960). By delivering most nest material during the Pre-Incubation, Nestling, and Fledging phases, Ospreys at nest 1 were able to repair and maintain their nest without disturbing the eggs during the Incubation phase. There was little reason to maintain the nest during the Post-Fledging phase, since young and adults spent little time in the nest at that time. Young Ospreys can capture fish within a few days of their first flight (Brown and Amadon 1968). If they are proficient at capturing fish for themselves during the last few weeks of the Post-Fledging phase, one or both adults may be released from parental duties before the young migrate from the nesting area. If one parent usually leaves earlier than its mate and the young, intraspecific competition for prey would be reduced at a time when the local population of Ospreys reaches its peak. Competition also may be reduced on the southward migration, since adult Ospreys would pass through areas at different times and because young Ospreys tend to migrate along different routes than do adult (Worth 1936, Osterlof 1951).

Breeding Behavior of Other Falconiforms The sexes of most nesting falconiforms, including Ospreys, differ in terms of their relative roles in the delivery of 68 nest materials, incubation, brooding, feeding nestlings, and procurement of food (Appendix 9). While nest material usually is brought to the nest by both sexes of falconiform species which build nests, females generally deliver most of this material. Male and female Ospreys showed seasonal differences in the delivery of nest material; similar differences previously were recorded only for the African Harrier Hawk (Polyboroides typus, Brown 1972). Incubation and brooding are. performed by both sexes, although females perform most of both activities. Males generally brood for only a small percentage of daylight hours, and they usually cease brooding several days before females. Nestlings usually are fed by females. However, males supply most or all of the food until the young no longer need the protection of brooding; females then begin hunting and supplying at least some food for themselves and the young. Patterns of mounting and copulation similar to the pattern recorded for Ospreys have been recorded for other falconiforms (Watson 1940, Hawbecker 1942, Cade 1955 and 1960, Liversidge 1961, Enderson 1964, Willoughby and Cade 1964, and Balgooyen 1976). Falconiforms frequently perch for long periods of time (Herrick 1924, Lawrence 1949, Liversidge 1961, Ames 1964, and Enderson 1964); a male White-tailed Kite observed for one day during the breeding season spent 75.8 percent of the day perched (Stendell 1972). With the exception of Stendell's observations and the data on Ospreys reported in this study, however, quantitative date are lacking on the precise amount 69 of time most falconiforms engage in perching during the breeding season. Ospreys and most falconiforms thus exhibit a distinct division of labor between sexes in care of the young and in obtaining food. On the basis of information available, it appears as if the primary role of females is to shelter eggs and young, and to feed the young; during the latter part of the breeding season females obtain a portion of the food consumed by themselves and the young. The primary role of males appears to be procurement of food for themselves, their mates, and the young; secondarily, males aid females in incubation and protection of eggs. Both sexes of Ospreys and probably both sexes of other falconiforms spend a large percentage of daylight hours during the breeding season engaged in relatively sedentary behavioral activities. The significance of reversed sexual dimorphism exhibited by falconiforms is beyond the scope of this study. Interested readers are referred to Amadon (1975) for a review of this topic.

Evolution of Division of Labor of Breeding Falconiforms Behavior of organisms presumably results in optimal allocation of time and energy devoted to reproduction (Orians 1961, King 1974). Three strategies of coping with the increased demands of reproduction include 1) maintaining relatively constant total energy expenditures, with different amounts of time and energy allocated to various activities during the 70 breeding and non-breeding seasons, and 2) increasing or 3) decreasing total energy expenditures during the breeding season (Orians 1961, Stiles 1971). Male passerines usually use the first strategy, while male Anna Hummingbirds (Calypte anna) utilize the second (Stiles 1971). Unfortunately, comparable studies on the time and activity budget of a falconiform during both the breeding and non- breeding seasons are not available. Until such studies are conducted during both seasons, the type of reproductive time and energy strategy that falconiforms utilize cannot be assessed. Factors responsible for the division of labor between the sexes of breeding falconiforms still are interesting. Altricial young are poikilothermic for several days after hatching and must be brooded by an adult until they are able to thermoregulate (Ricklefs 1974); therefore, in monogamous birds with altricial young, the male usually must help raise the young to independence. The division of labor exhibited by falconiforms frees the female to brood the young, while the male forages for food for the entire family. The altricial mode of growth of falconiform nestlings may be the ultimate factor (Baker 1938) responsible for the division of labor. The proximate factor involved in the division of labor may be related to the prey of falconiforms. Falconiforms consume foods high in nutrient quality and energy content (Colley 1961, Koplin unpublished data). Although the capture of such prey may involve considerable expenditure of energy, energy intake exceeds energy expended; male Ospreys captured 71 more fish than needed to fulfill their own energetic requirements. Energy content of falconiform prey apparently is sufficiently high that only one sex of a breeding pair needs to forage, at least until young fledge, in order to fulfill the energy requirements of the pair and their offspring. The two sexes of falconiforms still could share foraging and other activities equally, but do not do so for two possible reasons. First, egg production by females requires a large amount of energy (Ricklefs 1974); therefore, it would benefit the process of egg production for females to conserve energy by remaining relatively sedentary. Second, it probably is relatively advantageous for each sex to specialize in a relatively narrow repertoire of behavioral acts than to have to be adept at the full spectrum of behavioral acts associated with reproduction. When the young approach fledging, their energetic requirements probably exceed that which the male is capable of providing. At this time the young no longer need to be protected from ambient conditions. Therefore, during the latter part of the Fledging phase and the early part of the Post-Fledging phase, the division of labor between the sexes breaks down and both adults forage. SUMMARY

A study was conducted to describe the behavioral activities, time and activity budget, and energy expenditure of Ospreys nesting near Humboldt Bay, Humboldt County, California, during the 1974 breeding season, and of Ospreys nesting at Eagle Lake, Lassen County, California, during the early portion of the 1975 breeding season. Data on time and activity budgets and energy expenditures were stratified by different phases of the breeding season, chronological hour, and sex. During the first four phases of the breeding season at the nest near Humboldt Bay (nest 1), and during the Pre- Incubation phase at the nests at Eagle Lake (nests 2 and 3), females engaged in Flying activities for less than 4 percent of the 24-hour day; during the Post-Fledging phase, the female at nest 1 engaged in Flying activities for almost 17 percent of the 24-hour day. Males at all three nests spent 11 to 12.5 percent of the 24-hour day during the Pre-Incubation phase engaged in Flying activities. The male at nest 1 spent between 13.8 and 17.8 percent of the 24-hour day during the remaining phases of the breeding season engaged in Flying activities. During the first four phases at nest 1, and during the Pre-Incubation phase at nests 2 and 3, females spent over 90 percent of the daylight hours engaged in Nest or Tree Activities. Males at all three nests spent about two-thirds of the daylight time during the Pre-Incubation phase engaged in Nest Activities and Tree Activities. The male at nest 1 spent between 44 and 58 percent of the daylight time during the remaining phases of 73 the breeding season engaged in these activities. Males at all three nests obtained most of the nest material during the Pre-Incubation phase; after the eggs hatched at nest 1, the female obtained most nest material. The rate of delivery of nest material at nest 1 was relatively low during the Incubation phase, when eggs were in the nest, and during the Post-Fledging phase, when young and adults spent little time in the nest. The combined rates of Nest Construction and Nest Alteration at the three nests during the Pre-Incubation phase were inversely related to the qualitative condition of the nests when Ospreys first arrived in the nesting areas. Mounting and Copulation at all three nests gradually increased as the Pre-Incubation phase progressed, reached a peak just prior to egg-laying, and then decreased. The pattern of progressively increased rates of Mounting and Copulation may serve to synchronize the hormonal systems of the two sexes. The female at nest 1 performed 73.2 percent of the Incubation and 96.3 percent of all Brooding. The male generally incubated the eggs while the female was feeding. The male brooded the nestlings 11 percent of the first day after the eggs hatched, but he rarely brooded the eggs during the remainder of the Nestling phase. Females at nests 1 and 3 were not observed Fishing during the Pre-Incubation phase; the female at nest 2 Fished twice at the beginning of this phase. The female at nest 1 also was not observed. Fishing during the Incubation and Nestling phases, 74 and rarely fished during the Fledging phase; however, she engaged in Fishing for 26.1 percent of the daylight time during the Post-Fledging phase. Males at nests 2 and 3 fished between 7.9 and 8.6 percent of daylight time during the Pre-Incubation phase. The male at nest 1 engaged in Fishing between 13.6 and 26.4 percent of daylight time during the various phases of the breeding season. Males provided the majority of food for themselves, their mates, and the young up through the first four phases of the breeding season. During the Post-Fledging phase, the female at nest 1 captured three-fourths of the fish she consumed and approximately one-third of the total number of fish consumed by the pair and their young. Although the male at nest 1 obtained most of the food consumed by the young during the Nestling and Fledging phases, the female fed the young 97 percent of the time. During the Post-Fledging phase, the young usually fed themselves. The female at nest 1 left the nesting area two weeks before the male and the young. Early departure of one adult may reduce intraspecific competition for prey at a time when the local population of Ospreys reaches a peak and also during the southward migration. Energy expenditures predicted by the model on the one hand, and energy expenditures estimated on the basis of food consumption on the other, usually differed by less than 10 percent. Adult Ospreys and their two offspring at nest 1 ingested a predicted total of 1013.5 fish, or 2.56 x 105 Kilocalories, 75

during the 1974 breeding season. The breeding population of Ospreys utilizing fish from Humboldt Bay removes and consumes a predicted total of 16,696 fish, or 4.24 x 106 Kilocalories, from the bay during one breeding season. The usefulness of the model for predicting the energy expenditure of falconiforms is discussed. The breeding behavior of other falconiforms is compared with the breeding behavior of Ospreys. Falconiforms in general exhibit a division of labor between the sexes similar to that observed for Ospreys; females primarily take care of the eggs and young, and feed the young, while males primarily forage for the entire family. Factors involved in the evolution of the division of labor are discussed. LITERATURE CITED

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Appendix 2. Frequency of occurrence, percent frequency of occurrence, and mean elapsed time in minutes Ospreys engaged in each behavioral activity at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season.a 88

Appendix 2. (Continued) 89

Appendix 3. Calculation of the percent of the 24-hour day the female Osprey at nest 1, Washington Gulch Creek, Humboldt County, California, engaged in Flying and Non-flying activities during the Incubation phase of the 1974 breeding season.

Flying Non-flying Parameter Activities Activities

A. Percent of daylight hours 1.14 98.82 engaged in Activities

B. Total hours of daylight 589 589 during phase C. Total hours Activities 6.71 582.05 occurred during daylight hours of phase ( AB/100 ) D. Percent of night hours 0 100.00 engaged in Activities

E. Total hours of night 323 323 during phase

F. Total hours Activities 0 323 occurred during night hours of phase ( DE/100 ) G. Total hours Activities 6.71 905.05 occurred during phase ( C + F ) H. Percent of 24-hour day 0.74 99.24 Activities occurred ( G/ total hours in phase =[G/ (B + E)]x 100 ) 90

Appendix 4. Estimated energy expenditure (calculated. on the basis of food intake 'assimilated) of Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, during each phase of the 1974 breeding season.a 91

Appendix 4. (Continued) 92

Appendix 5. Estimated energy expenditure (calculated on the basis of food intake assimilated) of Ospreys at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the 1975 breeding season.a 93

Appendix 6. Percentage of fish delivered by and subsequently totally consumed by Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation Phase of the 1975 breeding season.a 94

Appendix 7 Details of Aggressive Interactions of Nesting Ospreys

The female at nest 1 engaged in 157 Aggressive interactions, out of 215 potential encounters, during the 1974 breeding season. Most of these interactions were with other Ospreys and with Ravens (Corvus corax) (Table A). The female responded to other Ospreys, usually by Vocalization, 98.2 percent (n=57) of the times they were in the vicinity of the nest (Table B). She responded to Ravens, usually by Chasing or Wing-Flapping, 81.2 percent (n=112) of the times they were in the vicinity of the nest (Table B). She failed to respond to Ravens only when they were flying quickly through the nesting area. During 30 potential encounters with Turkey Vultures (Cathartes aura), the female responded four times, twice by Vocalizing, once by Chasing, and once by Escorting (Table C). The female also Vocalized once at a Red-tailed Hawk (Buteo jamaicensis), Chased an unidentified falcon once, and Chased White-tailed Kites (Elanus leucurus) three times (Table C). The male at nest 1 engaged in 205 Aggressiveinteractions, out of 226 potential encounters, during the 1974 breeding season. Three-fourths of the interactions were with Ravens, and one-half of the remaining interactions were with Ospreys (Table A). The majority of interactions during the Pre-Incubation, Incubation, and Nestling phases involved Ravens, while the majority of interactions during the Fledging and Post-Fledging phases involved other Ospreys (Table A). The male responded to other Ospreys, by Vocalizing or Escorting, 96.7 percent (n=30) of the 95 California, during each phase of the 1974 breeding season.a breeding season.a phase of the 1974 during each California, Appendix 7. (Continued) (Continued) 7. Appendix Table A. Aggressive interactions engaged in by Ospreys at nest 1, Washington Gulch Creek, Humboldt County, Humboldt Gulch Creek, at nest 1, Washington in by Ospreys engaged Aggressive interactions Table A. 96

Appendix 7. (Continued)

Table B. Relative frequency of Aggressive responses of Ospreys at nest 1, Washington Gulch Creek, Humboldt County, California, to other Ospreys and to Ravens during the 1974 breeding season.a 97 (Continued) (Continued) Humboldt County, California, engaged in Aggressive interactions during the 1974 breeding season.a the 1974 breeding during Aggressive interactions engaged in County, California, Humboldt 7. Appendix Appendix Table C. Relative frequency and mean duration of time in minutes Ospreys at nest 1, Washington Gulch Creek, Gulch Creek, 1, Washington at nest Ospreys minutes in of time duration and mean frequency C. Relative Table 98

Appendix 7. (Continued) times they were in the vicinity of the nest (Table B). He responded to Ravens, usually by Chasing, 96.3 percent (n=160) of the times they were in the vicinity of the nest (Table B). Like the female, the male did not respond to Ravens quickly passing through the nesting area. The male responded to Turkey Vultures on six of fifteen potential encounters by Escorting and on one occasion by Vocalizing (Table C). He Chased White- tailed Kites, which were nesting nearby, during all ten interactions with them. During five potential interactions with Red-tailed Hawks, he responded three times, once by Vocalizing and twice by Chasing (Table C). Ravens were present in the vicinity of nest 1 throughout the entire breeding season, but seldom came near the nest except during the Incubation phase. During the Incubation phase, Ravens frequently tried to get into the nest, presumably to get the eggs, even when Ospreys were incubating the eggs (Figure A, Table A). During these encounters, the Osprey in the nest would not leave the nest, but Wing-Flapped at the Ravens; if the mate of the Osprey on the nest was in the vicinity of the nest, it usually Chased the Ravens. Females at nests 2 and 3 engaged in 61 Aggressive interactions, out of 74 potential encounters, during the Pre-Incu- bation phase (Table D). Most of the interactions were with other Ospreys. The female usually responded to other Ospreys by Escorting, Vocalizing at, or Chasing them. They failed to respond to other Ospreys on two occasions (Table E). Females 99

Appendix 7. (Continued) Figure A. Rates of non-vocal Aggressive interactions between Ravens and male and female Ospreys in relation to phase of the breeding season at nest 1, Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season. 100

PHASE OF BREEDING SEASON 101 breeding season.a breeding 1975 California, during the Pre-Incubation Phase of the Phase of Pre-Incubation during the California, 7. 7. Appendix Appendix Table D. Aggressive interactions engaged in by Ospreys at nests 2 and 3, Eagle Lake, Lassen County, County, Lake, Lassen Eagle 3, 2 and at nests in by Ospreys engaged interactions D. Aggressive Table 102 breeding season.a breeding at nests 2 and 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the phase during the Pre-Incubation California, Lake, Lassen County, 2 and 3, Eagle at nests 1975 Table E. Relative frequency and mean duration of time in minutes Ospreys engaged in Aggressive interactions Aggressive interactions engaged in in minutes Ospreys of time and mean duration Relative frequency Table E. Appendix 7. (Continued) (Continued) 7. Appendix 103

Appendix 7. (Continued) also interacted with Bald Eagles (Haliaeetus leucocephalus), Red-tailed Hawks, accipiters, and Turkey Vultures. Females did not respond to Turkey Vultures during eleven of twelve possible encounters, nor to Red-tailed Hawks once in six and accipiters once in four possible encounters. The females did not respond at all to Canada Geese (Branta canadensis), American Kestrels (Falco sparverius), or White Pelicans (Pelecanus erythrorhynchos) during twelve, two, and one possible encounters, respectively (Table D). Males at nests 2 and 3 were involved in 97 Aggressive interactions, out of 104 potential encounters, during the Pre- Incubation phase of the 1975 breeding season (Table D). Most of the interactions were with other Ospreys. Males responded to other Ospreys, usually by Vocalizing or Escorting, on 80 of 81 possible encounters. Males also interacted with Bald Eagles, Red-tailed Hawks, Turkey Vultures, Great Blue Herons (Ardea herodias), and an accipiter (Table D). Males did not respond to Turkey Vultures in five of eight possible encounters, nor to Red-tailed Hawks once in four and an accipiter once in two possible encounters. The males did not respond at all to Canada Geese during seven possible encounters nor to an American Kestrel during a single possible encounter. Ospreys carrying fish were chased by Bald Eagles on three occasions during the Pre-Incubation phase at Eagle Lake; the Ospreys lost the fish during each encounter. On April 23, at 1138 hours, the male from nest 2 was chased by an immature 104

Appendix 7. (Continued)

Bald Eagle. Both birds disappeared behind some trees; the Osprey soon emerged without the fish, which presumably was recovered by the Bald Eagle. On April 28, at 0635 hours, an immature and an adult Bald Eagle chased an Osprey carrying a fish. The Osprey dropped the fish, and the adult Bald Eagle flew to the ground, presumably to retrieve the fish. On April 28, at 0743 hours, an immature and an adult Bald Eagle chased another Osprey carrying a fish. The Osprey dropped the fish, which the adult Bald Eagle caught with its talons in the air, after the fish had fallen approximately twenty feet. Once the Osprey released the fish it was carrying, it no longer was harassed by the Eagles on all three occasions. 105 breeding season. breeding 1975 Washington Gulch Creek, Humboldt County, California, during the 1974 breeding season, and at nests 2 and 2 and at nests and season, breeding the 1974 during California, County, Humboldt Creek, Gulch Washington 3, Eagle Lake, Lassen County, California, during the Pre-Incubation phase of the phase during the Pre-Incubation California, Lake, Lassen County, 3, Eagle Predicted number of fish ingested (based upon predicted daily energy expenditure) by Ospreys at nest 1, nest 1, at by Ospreys expenditure) energy daily predicted upon (based fish ingested of number Predicted 8. Appendix Appendix 106 Nestlings, and Supplying Food. Food. Supplying and Nestlings, Appendix 9. Roles of female and male falconiforms in Delivery of Nest Material, Incubation, Brooding, Feeding Feeding Brooding, Incubation, Nest Material, of in Delivery falconiforms and male female Roles of 9. Appendix Appendix 9. (Continued) 10 7