Predatory Efficiency and Energetics of Belted Kingfishers

PREDATORY EFFICIENCY AND ENERGETICS OF BELTED KINGFISHERS

WINTERING ALONG THE MAD RIVER

Douglas J. Forsell

A Thesis

Presented to

The Faculty of Humboldt State University

In Partial Fulfillment

of the Requirements for the Degree

Master of Science

June, 1983 PREDATORY EFFICIENCY AND ENERGETICS

OF BELTED KINGFISHERS

WINTERING ALONG THE MAD RIVER

Douglas J. Forsell

Approved by the Master's Thesis Committee

James R. Koplin, Chairman

David W. Kitchen

Teri y Roelofs

Natural Resources Graduate Program

Approved by the Dean of Graduate Studies

Alba M. Gillespie ABSTRACT

Belted Kingfishers (Ceryle alcyon) were studied for two winters along the lower fad River, Humboldt County, California. Kingfishers spent 79.6 percent of daylight hours hunting, 12.2 percent inactively perched, 4.0 percent on intraspecific interactions, 2.3 percent handling prey, 1.6 percent preening and bathing, 0.18 percent in interspecific interactions, and 0.1 percent flying in response to human disturbances.

Kingfishers spent 11 percent more time hunting during the winter of

1975-76 than during the less severe winter of 1976-77.

Fish comprised 91 percent of the prey identified; salmonids

(Salmonidae), sculpins (Cottidae), and sticklebacks (Gasterosteidae) were the three major types of fish taken. Time spent subduing fish and the number of beats delivered to fish were positively correlated with length of fish. More time and a greater number of beats were needed to subdue sticklebacks and sculpins than salmonids of the same size class, possibly because more effort was required to disable the protective spines of sticklebacks and sculpins.

Over 50 percent of strikes from perches resulted in captures of prey, while only 20 percent of strikes from a hovering position were successful. Strike success was negatively correlated with the disturbance of the water's surface and was lowest when almost dark, highest at dusk, and decreased as light levels increased.

On the basis of 19 complete days of field data, kingfishers were observed to consume a mean of 70.2 kcal per day while an energetics model developed by Koplin et al. (1980) predicted 72.3 kcal would be

iii iv required daily assuming an assimilation efficiency of 0.821. From this model the population of 25 kingfishers wintering on the lower Mad River was predicted to have required 337,925 kcal or 84,481 fish of 4 g each, during an average winter. ACKNOWLEDGMENTS

I thank my advisor, Dr. James R. Koplin, for his guidance throughout this study and for his patience during the eight years it took me to finish the thesis. I am also grateful to Dr. Koplin and the members of my committee, Dr. David W. Kitchen, Dr. Terry D. Roelofs, and Dr. David G. Hankin, for editing earlier drafts of this thesis.

I also thank Dr. Patrick J. Gould and Colleen M. Handel for editorial comments and discussons with me on various aspects of my study.

Special thanks goes to Sherrilyn Diehl for typing the first draft and constructing many of the figures. I also thank Amy Zabloudil for her excellent drawings of kingfishers; Suzanne Miller and Debbie

Amos for their advice on statistics and help with computer programs; and Marlin Mixon and Greg Konkel for writing a program to analyze and portray data on prey handling.

I am grateful to the California Department of Fish and Game and the staff of the fish hatchery near Blue Lake, California, for allowing me access to the river near the hatchery.

Finally, I am very grateful to my supervisors with the U. S.

Fish and Wildlife Service, Dr. Calvin J. Lensink and Dr. Patrick J.

Gould, and to my many co—workers and friends with the Fish and Wildlife

Service for their constant encouragement and support.

TABLE OF CONTENTS

Page

ABSTRACT...... iii

ACKNOWLEDGMENTS...... v

LISTOF TABLES ...... ix

LISTOF FIGURES ...... x

INTRODUCTION...... 1

STUDYAREA ...... 3

METHODS...... 7

Time Budget...... 7

Perched Hunting ...... ....8

Perched-Inactive or Opportunistic Hunting 12

Prey Handling 12

Prey Holding ...... 12

Preening 13

Roosting ...... 13

Interspecific Interactions ...... 13

Reaction to Humans...... 14

Intraspecific Interactions ...... 14

Bathing ...... 14

Miscellaneous Flight Movements ...... 15

Strikes From Perches ...... 15

Hover Hunting ...... 15

Predatory Efficiency ...... 15

Energy Budget 17

vii

RESULTS AND DISCUSSION ...... 20

Time And Activity Budget ...... 20

Foraging Activity ...... 20

Perched-Inactive ...... 20

Maintenance Activities ...... 24

Intraspecific Interactions ...... 24

Interspecific Interactions ...... 25

Human Disturbance 26

Food Habits ...... 27

Prey Handling Time ...... 31

Predatory Efficiency 37

Hunting Method ...... 38

Area of River ...... 38

Time of Day 41

Height of Dive 43

Turbidity ...... 45

Water Surface...... 45

Wind ...... 48

Available Light 50

Cloud Cover ...... 50

Precipitation 84.000411,00414,,O10 ,000.141,1108041O,0004•100.0410•008.0 52

Prey Abundance .4111•4414, 11911•1•04161460•0010104.0.411140.0441441OOOS 52

Energy Budget 54

CONCLUSIONS 00•••••••••00110104410041••••••••••••••••04.41001••••••060410 59

Time Prey were Exposed to Predators 000•••••••••••••••••004100146 59

Hunger • • • • OOOOO • • • • • OOOOO • • • • • • • • • • • • • • • . • . • • • • • • • • • • • • • • • OOOOO 60

Prey Handling 60

viii

Rate of Successful Search...... 61

Food Habits and Energetics ...... 67

REFERENCES CITED ...... 69 LIST OF TABLES

Table Page

1 Comparison of Weather Conditions during the Winter of 1975-76 and the Winter of 1976-77 ...... 5

2 Time and Activity Budget of Belted Kingfishers 21

3 Diurnal. Time and Activity Budget of Belted Kingfishers Wintering along the Mad River ...... 23

4 Prey Taken by Belted Kingfishers along the Lower Mad River ...... 2R

5 Number and Percent of Identified Prey Taken by Belted Kingfishers in Three Areas of the Mad River .... 29

6 Mean Amount of Time Three Types of Fish Were Handled by Belted Kingfishers in Relation to Length of Fish ...... 33

7 Amount of Battering Delivered by Belted Kingfishers to Three Types of Fish in Relation to Length of the Fish ...... 35

8 Hunting Effort and Predatory Efficiency of Belted Kingfishers in Relation to Time of Day ...... 42

9 Heights from which Belted Kingfishers Hunted in Relation to Turbidity of Water ...... 47

10 Inputs to Daily Energy Budget for Belted Kingfishers Observed along the Mad River ...... 55

11 Food Intake of Belted Kingfishers Observed for 19 Full Days on the Had River ...... 56

12 Caloric Intake of Belted Kingfishers Observed for 19 Full Days ...... 57

13 Comparison of Fish Captured and Energy Expended 62 by Kingfishers Utilizing Two Hunting Methods ......

14 Predatory Efficiency of Selected Avian Predators ..... 65

ix LIST OF FIGURES

Figure Page

1 Study Area 4

2 Variation in Crest Elevations and Method of Estimating the Angle of Crest Elevation 9

3 Postures.... of Perched Belted Kingfishers while Hunting 10

4 Crest Angles of Belted Kingfishers during Various Activities...... 11

5 Time and Activity Budget of Belted Kingfishers Observed for 323 Hours along the Mad River 22

6 Relative Proportions of Salmonids, Sculpins, and Sticklebacks Taken in the Estuary, Middle River, and Upper Mad River ...... 30

7 Relationship Between Handling Time and Length of Three Types of Fishes 34

8 Relationship Between the Extent of Battering and Length of Three Types of Fish ...... 36

9 Number of Dives and Percent of Successful, Unsuccessful, and Aborted Dives by Belted Kingfishers Using Two Modes of Hunting 39

10 Predatory Efficiency of Belted Kingfishers in Relation to Time of Day and Area of the Mad River 40

11 Predatory Efficiency of Belted Kingfishers in Relation to Height of Dive and Turbidity of Water 44

12 Variability of Heights of Perches used by Hunting Belted Kingfishers in Relation to Turbidity of Water 46

13 Predatory Efficiency of Belted Kingfishers in Relation to Windspeed and Surface Conditions of Water 49

14 Predatory Efficiency of Belted Kingfishers in Relation to Available Light and Cloud Cover 51

15 Predatoryinn Relation Efficiency to Rain...... of Belted Kingfishers 53

x INTRODUCTION

A great deal of interest and research in recent years has focused on ecosystem modelling and energetics (Odum, 1968; Wiens and

Innis, 1974; Wiens and Scott, 1975). A basic requirement of an energetically-based ecosystem model is the prediction of energy requirements of free-living animals. Such predictions are especially useful in assessing the impact of predation on commercially important species, in this case the foraging of Belted Kingfishers (Ceryle alcyon) on salmonids.

Lagler (1939), White (1953), and others attempted to assess food requirements of kingfishers by using only observational and poorly quantified data. Vessel (1977) estimated energy requirements of kingfishers and developed an energetics model by measuring the food intake of caged birds. The present study was initiated to predict the average winter daily energy expenditure of free-ranging kingfishers by using a model developed by Koplin et al. (1980) and to test the model by comparing predicted energy requirements with the observed energy intake of free-ranging kingfishers.

Certain key factors that determine the rate at which predation takes place can be identified through analysis of predator-prey models, which attempt to quantify the numerical and functional responses of predators to prey density (Holling, 1959, 1965, 1966; Salt, 1967).

Functional responses of predators to prey, especially strike success and foraging success, are complex and an be understood only by looking at each component separately. Several researchers have attempted to evaluate environmental factors affecting predatory efficiency of pi iv- orous birds (Recher and Recher, 1969; Orians, 1969; Salt and Willard,

1971; Dunn, 1973; Ueoka and Koplin, 1973; Grubb, 1977). Most of these studies demonstrated that predatory efficiency was affected by conditions of the water surface, wind, tide, cloud cover, turbidity, and prey activity. The second facet of this study was to investigate the interaction of kingfishers and their prey, especially how predatory efficiency was affected by weather, water conditions, and prey abundance. STUDY AREA

Belted Kingfishers were studied along the lower Mad River,

Humboldt County, California, from the mouth of the river to the waters adjacent to the California Department of Fish and Game Hatchery near

Blue Lake (Figure 1). This area supported at least 19 and perhaps as many as 25 to 30 kingfishers during the winter of 1975-76. Observations were divided among three areas: the estuarine area, which extended about 2 km upstream from the mouth of the river; the middle river area which was near the Arcata Water District wells; and the upper river area, which was adjacent to the fish hatchery (Figure 1). This coastal region has a moist maritime climate with moderate winter temperatures.

Of the two winters of this study, that of 1975-76 was the colder and wetter (Table 1).

The Mad River drains a watershed of approximately 805 km2. The dominant vegetation of the watershed is second growth redwood (Sequoia sempervirens) and Douglas fir (Pseudotsuga menziesii). The water flow measured at a U.S. Geological Survey gauging station near Highway 101 has ranged from 0.48 m3/sec to over 1,416 m3/sec (Ridenbour et al.,

1961; Healey and Gilman, 1968).

The shores of the lower river consist of cut hanks or gravel bars which support a variety of vegetation including willows (Salix spp.), black cottonwood (Populus trichocarpa), tan oak (Lithocarpus densi- flora), Douglas fir, and redwoods. A large variety of small freshwater fish occur in the Mad River (Healey and Gilman, 1969; Ridenhour et al.,

1961). Since the river mouth is affected by tidal action, estuarine

3 Figure 1. Study Area and Territories (A) of Belted Kingfishers on the Lower Mad River, humboldt County, California, during the Winter of 1975-76. 5

Table 1. Comparison of Weather Conditions Between the Winter of 1975- 76 and the Winter of 1976-77 at the National Weather Service Office, Eureka, California (U. S. Department of Commerce, 1975-1977). 6 waters may also contain a variety of estuarine and saltwater fishes; however, winter runoff was usually great enough to preclude common occurrence of most saltwater fishes.

During this study the area was subjected to much human disturbance, including dairy farming, sportfishing, gravel quarrying, and automobile traffic. Extensive logging in the headwaters of the river in combination with highly erosive soils produced extremely turbid waters during heavy rains. A Secchi disk may be visible only 2-3 cm below the surface in periods of heavy runoff. Numerous man—made structures, including bridges, power lines, and cables, crossed the river. These structures provided hunting perches for kingfishers over areas which otherwise would have been accessible only to hovering birds. METHODS

A total of 87 hours was spent in 1974 and 1975 developing the techniques necessary to construct a time and activity budget and to obtain information on energetics and predatory efficiency of Belted

Kingfishers. Of particular relevance was the study and interpretation of crest angles and the delineation of basic behavioral sequences.

Kingfishers were observed along the lower Mad River for 343 hours on 45 days from October 1975 through March 1976 and from October

1976 through March 1977. The Focal—Animal method was used to make observations (Altmann, 1974). Additionally, Josh Washburn, a fellow student, and I observed kingfishers foraging in the raceways of the

Mad River Hatchery for 89 hours (Washburn, 1977 and this study). Most observations were made from an automobile with a 20x spotting scope or 10 x 50 binoculars. Kingfishers were relatively undisturbed by the stationary vehicle and regularly hunted as close as 30 m from me.

Field notes were recorded on cassette tape.

Time Budget

During each observation period, the behavior of the bird being watched was recorded along with the duration of each behavior to the nearest second. In order to moderate bias produced by conspicuous activities, only observation periods of over 200 continuous minutes were used to construct the time and activity budget. Observations were limited in October and March by much intraspecific flight activity,

which made it difficult to follow the birds. Since February 1977 was an especially rainy month, the river became rather turbid and kingfishers 8 fished in less turbid side streams; consequently for that month I was unable to observe the birds for long periods.

Thirteen behavioral categories were defined: six activities occurred from perches, five involved only flight, and responses to both intraspecific and interspecific intruders involved both stationary and flight behavior.

In this study, crest angles were used to determine the behavioral predisposition of kingfishers and to define some behavioral acts.

Brown (1964) demonstrated that crest elevations of Steller's Jays

(Cyonocitta stelleri) were positively correlated with the degree of agonistic arousal. I estimated the elevation of each kingfisher's crest in a manner similar to Brown's; that is, "The elevation of the crest was estimated as the acute angle which the upper two-thirds of the anterior edge of the crest made with the long axis of the bill"

(Figure 2). The following behavioral categories were used to construct the time budget:

Perched-Hunting

Kingfishers hunted by scanning the water from a variety of natural and man-made perches including trees, cut-banks, large rocks, power lines, cables, and bridges. Stationary birds were assumed to he hunting when the bill was oriented toward the water (Figure 3). Crest angles when perch hunting were usually 20 to 45 degrees (Figure 4) and the long axis of the back was usually oriented on a 20 to 30 degree angle to the water. 9

Figure 2. Variation in Crest Elevations of Belted Kingfishers and Method of Estimating the Angle of Crest Elevation. OP POR TUN 1ST IC HUNTING HUNT ING INTENSIVE HUNTING

Figure 3. Postures of Perched Relied Kingfishers while Hunting. 10 11

Degree of crest elevation

Figure 4. Crest Angles of Belted Kingfishers during Various Activities. 12

Perched-Inactive or Opportunistic Hunting

Kingfishers were categorized as inactive when they were not

watching the water. Opportunistic hunting usually occurred after large

amounts of food (e.g., 2-3 fish about 10 cm long) had been consumed;

the birds perched over the water but spent very little time watching

the water. If a prey item was sighted the birds assumed an intensive

hunting posture (Figure 3) and were classified as perched-hunting. In

nonhunting periods the elevation of the crest was usually 10 to 30

degrees (Figure 4) and the long axis of the back was oriented at about

a 50 degree angle with the surface of the water.

Prey Handling

Kingfishers always returned to a sturdy perch with their quarry.

Very small prey were consumed immediately, but at least a few seconds

were spent subduing most prey. Prey handling time was measured from

when the bird landed until the prey was swallowed or obviously dead.

Fish were usually held anterior of the dorsal fin with the dorsal fin

oriented toward the bird. Kingfishers usually subdued small fish by

repeatedly squeezing and shaking them. Larger prey were beaten on a

branch or rock, usually striking the head to one side then the tail

or dorsal fin to the other side, stopping periodically to adjust the

fish with short tosses. The fish rarely left the bill when being

tossed. Crests were rarely erected while kingfishers were handling

prey (Figure 4).

Prey Holding

The few occasions on which kingfishers held large prey items

(10-18 cm) for long periods after the prey was obviously dead (17-108 13 min, n = 5) were classified as prey holding. On three of the five occasions the birds had been observed for the majority of the day during which time they had consumed large amounts of food. I presumed the birds were satiated and were holding the prey until they were able to swallow them. The approximate capacity of the gut appeared to be at least 60 g (one 11-cm sculpin and one 18-cm salmonid consumed by a kingfisher in a two-hour period).

Preening

Kingfishers preened at all times of the day, most often after bathing or consuming large prey. Preening was considered continuous if no pauses longer than about 10 sec occurred during the activity.

Crest angles during preening were usually 20 to 30 degrees.

Roosting

Wintering kingfishers roosted in trees at night. Most roosts were in well-protected forests high in the trees and away from the river. The birds were presumed to be roosting from the time they entered the trees in the evening until they emerged in the morning.

Birds that perched in trees away from the river during the afternoon were also classified as roosting.

Interspecific Interactions

Interspecific behavior included all cases when a kingfisher reacted to another species regardless of the behavior of the other species. Usually a perched interaction included elevation of the crest to 80 to 90 degrees (Figure 4) when an avian predator passed overhead.

Flight interactions always consisted of kingfishers fleeing from avian 14 predators even when not pursued. Their crests were always compressed

(0 degrees) during flight interactions.

Reaction to Humans

Kingfishers usually flew in front of human intruders until the intruders reached the edge of the birds' territories; then the kingfishers flew in a large half-circle back into their territories. As in response to nonhuman intruders, when perched, birds elevated their crests to 80 to 90 degrees and compressed their crests when flying away (Figure 4). Since disturbance by humans on the river was extensive, especially during the fishing season, I selected observation areas with the least amount of human activity, as birds often were lost from view when fleeing from human intruders.

Intraspecific Interactions

Intraspecific interactions often involved a perched bird closely watching a second kingfisher in or near its territory. Territorial establishment and defense included what was termed a "face off" in which two kingfishers would perch close to each other at a territorial boundary and call, occasionally breaking into a chase. Crest angles were usually 80 to 90 degrees during perched interactions (Figure 4).

Bathing

Kingfishers bathed daily, usually by diving from a perch and hitting the water breast first rather than head first. Often birds then rose above the water about 1 m, moved laterally up to 3 m, and hit the water with the side of the body. Bathing was always followed by preening and the crest was always compressed while bathing. 15

Miscellaneous Flight Movements

The majority of flight time consisted of flights to and from the roost, general flights around the territory, and most often movements between hunting perches. No attempt was made to separate hunting and nonhunting flight unless a strike was made.

Strikes from Perches

Only flights from perches which ended in strikes or aborted strikes were placed in this category. Flights between hunting perches were not included.

Hover-Hunting

Kingfishers hunted while bovering in one position 1 to 17 m above the water. Hover-hunting occurred sporadically and forays lasted from 10 sec to 7.5 min and included 0 to R dives. Hover-hunts were timed from when the bird left the perch until it landed. As in all flight activities, the crest was always compressed during hover-hunting.

Predatory Efficiency

A predatory attempt was defined as a dive to the water; it was classified successful if prey was captured, or unsuccessful if either the bird did not emerge with a prey item or the dive was aborted within about 1 m of the water's surface. Step hovers, which consisted of rapid changes of altitude between hovers, were not considered predatory attempts. Several predatory attempts or strikes may have occurred during one hover-hunt, thus predatory efficiency refers only to strike success and not to success of the overall hunting effort. 16

The following data were recorded for each predatory attempt:

1. Water surface condition: smooth, rippled, choppy, or wavy.

2. Height of bird above the water surface at onset of the strike.

3. Time (Pacific Daylight Savings Time), to the nearest minute.

4. Cloud cover: sunny, partly cloudy or if the water was shaded,

heavy overcast, or foggy.

5. Precipitation: rain, drizzle, or no rain.

6. Wind: measured with an electric anemometer after each hover-hunt.

Birds hunting from perches often were protected from wind by stream-

side vegetation; under these conditions, wind speed was estimated

visually using the Beaufort Scale.

7. Turbidity: A Secchi disk reading was made to the nearest centimeter

three times daily. Each predatory attempt was assigned the reading

nearest to it in time.

Light: measured in foot candles using a General Electric B-13 light

meter. The meter was held 20 cm above the white side of a Kodak

Neutral Test Card (80 percent reflectance) oriented in the same

plane as the water. In general the categories of light intensity

were equivalent to the following: 0-50 foot candles = dark to dusk

(hard to observe birds with optical equipment); 51-200 = dusk; 201-

1,000 = heavily shaded area; 1,001-2,500 = heavy overcast; 2,501-

4,999 = light overcast or indirect sunlight; 5,000+ = direct sun.

When prey were captured the following data were recorded:

1. Species of prey.

2. Number of times prey was battered on the perch.

3. Handling time from when bird landed with its quarry until the bird

either swallowed the prey or stopped battering the prey. 17

4. Size: The length of each prey item was estimated as a fractional

multiple (to the nearest eighth) of the exposed culmen length of

the bird. Culmen lengths of 21 kingfisher bills averaged 56.54 mm (+ 0.56 The accuracy of this method varied depending on the

angle of view, but generally was believed to be within 10 percent

of the prey size.

Energy Budget

An energetics model (Koplin, 1972; Koplin et al., 1980) was used to predict the average daily energy expenditure of free-living Belted

Kingfishers during winter. The model is based on existence metabolic rates, mean air temperature, and energy expenditure of flight. Inputs to the model are a time and activity budget, mean air temperature, and body weight of the bird. The model was first tested by comparing predicted energy expenditures with observed energy intake of kingfishers observed for 15 full days and 4 days with less than 10 minutes break in observation. Activity data for those 19 days were used, along with an average air temperature of 9.98°C (mean of high and low for each day at the Blue Lake weather station). After testing, the model was used to predict energy expenditures and consequent food requirements of kingfishers throughout the winter using the time and activity data for both winters and the mean temperature for both winters (9.4° C) as inputs.

For both calculations, the average body weight of 15 museum specimens of Belted Kingfishers (176 g + 3.9 SE; range = 149 - 198 g) was used. Mean body weight of the 15 specimens was near the 6 oz

(168 g) reported by Salyer and Lagler (1946). However, Vessel (1977) 18

measured the post-absorptive body weight of 12 kingfishers over a year-

long period and found the weights averaged only 130.19 g (+ 0.49 g SE)

and ranged from 104.3 to 188.8 g. While the museum birds may have been

weighed with food in their stomachs making the weights high, those

Vessel's birds may have been low due to restricted activity and a lack

of muscle development. Western Grebes (Aechmophorus occidentalis),

also piscivorous birds, weighed as much as 25 percent less in captivity

than in the wild (Ronald Garrett, pers. comm.). Therefore, the 176 g

weight was used in calculations of the energy budgets.

To determine the actual energy intake and food requirements,

the amount of energy in each prey item had to be determined. For fish,

weights were estimated according to their lengths. Weights of salmonids

were obtained by applying appropriate length-weight relationships de-

rived from the formula, weight(g) = [Length(mm)]3 x condition factor.

A mean condition factor of 0.000009785 was obtained from values given

by Piper et al. (1975) for various wild salmonids. Length-weight

relationships for sticklebacks (Gasterosteidae) and Humboldt suckers

(Catostomus occidentalis humboldtianus) were not available; thus, weight

estimates for these two species were derived from the salmonid formula.

A length-weight table for sculpins (Cottus spp.) was developed from

preserved specimens. Two, frogs (Rana sp.) captured were considered to

be 4.6 g each (Collopy, 1973). Weights of other prey items, including

ammocetes larvae (Lampetra sp.), crayfish (Astacidae), snails, and

unidentified insects were estimated by visual comparison with other

prey items.

Dry weights of fish were then estimated from live weights using

the values from formulas developed by Vanstone and Markerk (1968) to 19 estimate the water content of coho salmon (Onchorhynchus kisutch): mg water = 78 + (790) (live weight in grams) for fish weighing less than 15 g; and, mg water = 1150 + (720) (live weight in grams) for fish over 15 g. Since neither formula was developed for fish less than 5 cm long, a value of 83.9 percent water derived for a fish 5.5 cm long was used.

The energy content of salmon fry was obtained by bomb calor- imetry. Energy content of other prey was obtained from Lagler (1956) and Collopy (1975).

Vessel (1977) found Belted Kingfishers had an assimilation efficiency (calories utilized/calories ingested) of 0.821 0.004 SE and a range of 0.820-0.880. Thus 82.1 percent of the observed food intake was considered to be metabolized. RESULTS AND DISCUSSION

Time and Activity Budget

Foraging Activity

Foraging activity, including perched hunts, hover-hunts, strikes from perches, and miscellaneous flights, comprised the majority of the daily winter activities of kingfishers (Table 2, Figure 5). In the more severe winter of 1975-76, 84.3 percent of the time was spent foraging compared to the less severe winter of 1976-77 when only 74.6 percent of the time was involved in foraging (Table 3). The difference between winters in percent time spent foraging is statistically significant

(p < 0.05, Mann-Whitney Ti Test) if the three months (October 1975,

March 1976, and February 1977) with less than 400 minutes observation time are not included. This suggests that either hunting was more efficient or less food was required during the less severe winter of

1976-77 than during the previous winter. Kingfishers along the river spent about 80 percent of their daily activity foraging, while those hunting in the hatchery, where food was plentiful, spent only 9 percent of their daily activity foraging.

Perched-Inactive

Overall, kingfishers spent approximately 12 percent of their time perched and not hunting (Table 2). The marked decrease in foraging activity during the winter of 1976-77 resulted in a doubling of time spent perched-inactive (Table 3). The milder winter probably allowed the birds to obtain needed foods in less time than during the more 20 21

Table 2. Time and Activity Budget of Belted Kingfishers Wintering along the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. 22

Figure 5. Time and Activity Budget of Belted Kingfishers Observed for 323 Hours Along the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. 23 California, during the Winters of 1975-76 and 1976-77. of 1975-76 and during the Winters California, Table 3. Diurnal Time and Activity Budget of Belted Kingfishers Wintering along the had River, Humboldt County, the had River, Humboldt Wintering along Belted Kingfishers Budget of Diurnal Time and Activity Table 3. 24

severe winter; thus, a greater percent of their time was spent perched-

inactive.

Maintenance Activities

Bathing and preening occurred each full day the birds were

observed. Less than three percent of the daily activity was devoted to

maintenance (Table 2) and these activities remained relatively constant

throughout both winters (Table 3).

Intraspecific Interactions

Intraspecific interactions were relatively minimal from November

through February, comprising less than two percent of the daily activi-

ties (Tables 2 and 3). Over 12 percent of the daily activities during

October and March involved intraspecific interactions. Those in October

-primarily involved establishment of winter territories. Two birds spent

four hours in almost continuous chasing and "face offs" before finally

establishing a territorial boundary. On five occasions one bird flew

toward a perched bird, the birds locked bills, and both fluttered

toward the water; they usually released each other before hitting the

water, but on one occasion both birds fell into the water. These

interactions were recorded between one male and female in October and

between a different male and female in November. These interactions

may have been attempts by former breeding pairs to divide their joint

breeding territory into separate winter territories, but I could not

be sure the birds had been a breeding. pair. Similar fighting behavior

occurred between male European Kingfishers (Accido atthis) (lunge and

Lutthen, 1974). By the end of October most winter territories appeared 25 to be well established and relatively little time was spent maintain boundaries. Birds on the river generally maintained territories of about 1000 m x 50 m; two birds within the hatchery maintained territories smaller than 50 m x 50 m. However, the birds in the hatchery spent 11.6 percent of their time in intraspecific interactions compared with only 4.1 percent for kingfishers along the river.

The increase in intraspecific interactions in March of both winters appeared to be related primarily to courtship, although establishment of breeding territories undoubtedly was also involved. Flight interactions consisted of chases involving courtship, "play behavior", and most often territorial defense. Courtship behavior involved con- siderable chasing and calling which sometimes culminated in copulation while perched on a branch. Chasing also occurred as "play behavior", in which one bird pursued another until the bird being chased dove into the water and the other passed over. Often the birds then switched roles with the pursuer being pursued. White (1953) believed "play behavior" served as practice in escaping from predators. Chasing of this type was observed in summer between mated adults and between fledglings. Some of the interactions interpreted as territorial dis- putes actually may have been such "play behavior".

Interspecific Interactions

Interspecific interactions were relatively rare, usually occur- ring less than once per day and accounting for less than one percent of daily activities (Tables 2 and 3). Interspecific interactions were most frequent in February, 1976, when a New Gull (Larus canus) repeatedly harassed a kingfisher that was holding a large salmonid. Most 26 interactions involved a kingfisher watching raptors or raptorlike birds, such as Turkey Vultures (Cathartes aura) or Common Ravens (Corvus corax), or moving when a raptor or raptorlike bird was in the vicinity.

I never observed a raptor attack a kingfisher. On two occasions a kingfisher was mobbed by Starlings (Sturnus vulgaris) which chased the kingfisher across the river until it dove into the water and the starlings passed by.

Kingfishers also reacted to birds of other species hunting below them. A Great Blue Heron (Ardea herodias) elicited a 90 degree crest angle from a kingfisher when it captured prey below the kingfisher.

On one occasion a Pied-billed Grebe (Podilymbus podiceps) was observed feeding below a perched kingfisher. The kingfisher captured a fish on two separate dives while the grebe was underwater, possibly taking advantage of prey escaping the grebe. Meyerriecks and Nellis (1967) reported kingfishers using Great Egrets (Casmerodius albus) and Snowy

Egrets (Egretta thula) as "beaters" to secure prey disturbed by foraging activities of the egrets.

Human Disturbance

Flight activity related to human disturbance was much less than one percent of the daily activity (Tables 2 and 3). Human disturbance occurred primarily during the fishing season from October through

December (Table 2). Because I actively avoided observing kingfishers in areas and at times of great human activity, this sampling design minimized the computed energetic expenditures associated with human disturbance. 27

Food Habits

Belted Kingfishers captured a variety of fish, primarily salmonids, sculpins, and sticklebacks in the lower Mad River (Table 4).

Although kingfishers captured prey from other taxonomic groups, fish accounted for 94.8 percent of the prey numbers identified and 96.9 percent of the estimated live weight of prey identified (Table 4).

The length of fish taken averaged 7.4 cm and ranged from 1.8-19.0 cm

(n = 197). Other animal prey were consumed occasionally, but contributed minimally to the overall diet (Table 4). The preference of

Belted Kingfishers for fish is well documented (White, 1936, 1937;

Salyer and Lagler, 1946; Eippler, 1956), Kingfishers were observed to pick up plant material, but were never observed to consume it.

The relative composition of prey species captured by kingfishers differed among the three areas of the river studied (Table 5 and Figure 6). Primarily sculpins and sticklebacks were taken in the estuarine area, all prey types were taken in the middle river area, and predominantly salmonids were taken in the upper river near the fish hatchery (Figure 6 and Table 5). The frequency of capture among the three major fish species differed significantly ( p < 0.01, X2 = 28.9, df 2) suggesting that diets of kingfishers may have reflected the relative availability of prey species in the three different areas; however, I have no quantitative information on relative abundance of these prey. Qualitatively, the hatchery area had large numbers of salmonids present some of which escaped from the hatchery; in contrast, the estuarine area probably only had salmonids present when they were moving to sea. The wide variety of prey taken in the middle 28

Table 4. Prey Taken by Belted Kingfishers along the Lower Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77.

a Unidentified fish were primarily small salmonids or sticklebacks which were hard to distinguish. Sculpins were more easily identified.

Unidentified items were probably very small fish or insects swallowed too quickly to identify. 29

Table 5. Number and Percent of Identified Prey Taken by Belted King- fishers in Three Areas of the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77.

Prey Estuarine Mid-river Upper River 30

Figure 6. Relative Proportions of Salmonids, Sculpins, and Sticklebacks Identified as Prey Items Taken by Belted Kingfishers in the Estuary, Middle River, and Upper Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. 31

river area probably best represented the foods of wintering kingfishers

along most of the lower Mad River because of the high proportion of

salmonids near the hatchery and low proportion of salmonids in the

estuarine area. White (1937) postulated that kingfishers along the

Margaree River of Nova Scotia fed upon fish they could obtain most

easily; along different segments of the Margaree River kingfishers

captured prey in the same relative proportions in which the prey species

occurred. White (1937) also found a predominance of sticklebacks in

the diet of birds in an estuarine area and almost exclusively salmonids

in the diet of birds in the upper parts of the river.

Prey Handling Time

From the time a kingfisher landed with its prey until tbe

animal was subdued or swallowed, the prey was handled from 1.5 sec to

over 10 min and battered from 0 to 110 times. For fish, handling time

(H, in sec) was positively correlated with the total fish length (L,

in mm): R = 0.373 L3'42 (r = 0.77). The number of times a fish was

battered (B) was also positively correlated with the length of the fish:

B = 0.098 L1'64 (r = 0.68). Two primary factors probably contributed

to the variability in both handling time and battering: 1) apparent

differences in hunger among individual birds and 2) differences in

handling effort necessary for various species of prey. Douthwaite

(1971) found that prior feeding significantly increased the amount of

battering fish received by Pied Kingfishers (Ceryle rudis). Belted

Kingfishers appeared to beat fish more if they had recently consumed

several fish than if they had not recently eaten; however, variability 32 in prey size and species, extent of prior feeding by the kingfisher, and small sample sizes make this suggestion impossible to substantiate.

Kingfishers expended more time subduing sculpins and sticklebacks than salmonids of the same size class (Table 6 and Figure 7).

They also battered sticklebacks and sculpins more than salmonids of the same size class before consuming them (Table 7 and Figure 8). The differences were statistically significant (p < 0.05) for most size classes. Several other researchers have found a positive correlation between size of the prey and handling time (Hailing, 1966; Salt and

Willard, 1971; Werner, 1974). Among Pied Kingfishers, the amount of battering a fish received was most strongly correlated with the cross- sectional area of the fish (Douthwaite, 1971). Among fish similar in length, sculpins have a larger cross-sectional area than salmonids but sticklebacks have a cross-sectional area the same as or smaller than that of a similar length salmonid. However, both sculpins and stickle-backs possess spines which a kingfisher may need to render harmless before swallowing. Werner (1974) found that blue gill sunfish (Lepomis macrochirus) also spent more time handling prey with protective spines than those without spines.

Spines were considered by Recher and Recher (1968) to be effective devices for escape from herons, which dropped fish when the spines punctured the soft parts of the beak. I did not observe any sculpins or sticklebacks to escape from kingfishers. Reimchen (1980) observed kingfishers to "occasionally" drop sticklebacks; whether or not the birds were punctured by the spines was unknown. Since kingfishers had to spend more time handling sculpins and sticklebacks thac salmonids, there was more time when spines could cause the bird to drop the fish. 33

Table 6. Mean Amount of Time Three Types of Fish Were Handled by King- fishers in Relation to Length of Fish Captured in the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77.

a Differences are significant at 0.05 level, Kruskal-Wallis one-way analysis of variance (Siegel, 1956). b Difference not significant at 0.05 level, but significant at the 0.1 level, Kruskal-Wallis one-way analysis of variance (Siegel, 1956).

Differences are not significant at 0.10 level, Kruskal-Wallis one-way analysis of variance (Siegel, 1956). Figure 7. Relationship Between Handling Time and Length of Three Types of Fishes Preyed on by Belted Kingfishers along the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. Sculpins =0 (r = 0.65, n = 17), sticklebacks = * = 0.90, n = 13), and salmonids = + (r = 0.86, n = 68). 35

Table 7. Amount of Battering Delivered by Belted Kingfishers to Three Types of Fish in Relation to Length of Fish Captured in the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77.

a Differences are significant at 0.05 level, Kruskal-Wallis one-way analysis of variance (Siegel, 1956). b Differences not significant at 0.05 level, but significant at 0.1 level, Kruskal-Wallis one-way analysis of variance (Siegel, 1956). 36

Figure 8. Relationship Between the Extent of Battering and Length of Three Types of Fish Preyed on by Belted Kingfishers along the Mad River, Humboldt County, California, during the winters of 1975-76 and 1976-77. Sculpins = 0 (r = 0.47, n = 21), sticklebacks = * (r = 0.76, n = 11), and salmonids • + (r = 0.73, n = 69). 37

The presence of spines did not appear to deter kingfishers from taking sculpins or sticklebacks and the increased time and energy reauired in making the spines ineffectual was probably not an important factor in their selection. It is unknown how spines may have aided in escape underwater.

All fish captured by kingfishers in this study attempted to escape using violent flexions, the escape mechanism used most commonly by fish captured by herons (Recher and Recher, 1968). I observed only one fish out of 155 captured that was successful in escaping. This salmonid was so large (about 19 cm) it threw the bird's head and body up and down with its violent movements until it slipped from the bird's bill. White (1936) observed kingfishers to drop fish that were too large to swallow and reported that "bird marks" or scars from being struck by kingfishers were "common" on salmon parr and smolts. Violent flexions may be more effective in allowing fish to escape under water, where the resistance of water would assist forward movement that could aid the fish to escape. Fish escaping under water may have accounted for the bird marks commonly observed by White (1936).

Predatory Efficiency

Predatory efficiency is governed by a complex of interactions among predators, prey, and the environment. Various environmental parameters and behavioral characteristics were examined to determine their effect on kingfishers' success in capturing prey. Anti—predator characteristics of prey were difficult to evaluate. I assumed the prey were mobile fish that could detect birds diving at them and would try 38 to escape; this was not an unreasonable assumption since most fish move quickly in response to sudden movements above them.

Hunting Methods

Kingfishers had an overall predatory efficiency, or strike success, of slightly less than 50 percent (Figure 9). Strikes from perches were more successful than strikes from hovering positions (p = 0.01 x2 = 30.5, df 1). Collopy (1973) found American Kestrels (Falco sparverius) hunting from perches were 52 percent successful at capturing prey and 23 percent successful hunting from hovering positions. Prey

he able to detect hovering birds more easily than motionless birds on perches and thus may be able to escape more readily at the initiation of attacks by hovering birds. Hovering birds are also more active than birds hunting from perches and may dive at prey that are in less than optimal positions, whereas perched birds can afford to wait for the prey to move into more vulnerable positions. In the following analysis of the factors affecting predatory efficiency, perched- and hover-hunts were analyzed separately and combined.

Area of River

Predatory efficiency did not differ significantly among birds hunting by either method in the estuarine, middle, and upper river areas. For hover-hunts alone there was a trend toward a higher success rate in the upper and middle river areas than in the estuarine area

(Figure 10). Hover-hunts occurred most often in the estuarine region, where they comprised 28 percent of all strikes compared with 15 percent of the strikes in other areas. Since the estuarine area was subjected to tidal influence and large portions of the river edge became mud 39

Figure 9. Number of Dives and Percent of Successful, Unsuccessful, and Aborted Dives by Belted Kingfishers Using Two Modes of Hunting along the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. Figure 10. Predatory Efficiency of Belted Kingfishers in Relation to Time of Day and Area of the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. 4

Sample sizes are indicated by numbers within the bars. 0 41 and gravel bars at low tides, few perches were available during low tide and birds had to hunt from a hovering position. Upstream the river bed was rather wide, but each territory had one vegetated bank near the water. In the upper river area many territories also contained a power line, cable, bridge, or other man-made object on which birds could perch above the entire width of the river, thus reducing the amount of hover-hunting necessary to obtain sufficient food. The apparent difference in success of hover-hunts among the three areas may have occurred because the presence of permanent perches along the upper river allowed the birds there a continous choice of hunting method while birds in the estuarine area may have been forced to hover-hunt under suboptimal conditions. In the summer of 1975, when the estuarine area had very low water levels and thus few perches during all tidal cycles, 50 percent of 138 strikes involved hover-hunts (Forsell, 1974).

Time of D

Considered within four daily time periods, foraging activity was relatively constant with somewhat less activity from noon until dark than earlier (Table 8). While foraging time decreased only slightly during the second half of day, the number of strikes per hour of hunting decreased markedly, suggesting that there was a possible difference in prey availability or that hunting effort was less intense later in the day as hunger subsided. A predator-prey model developed by Rolling

(1959) predicted that a decrease in hunger would be accompanied by decreases in rate of search, strike threshold, and size of the reactive field. Kingfishers usually consumed several fish in the morning and thus probably were less hungry in the afternoon than in the pre-noon period. 42

Table 8. Hunting Effort and Predatory Efficiency in Relation to Time of Day of Belted Kingfishers Wintering on the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. 43

The increase in number of strikes per hour during the last compared to the third quarter of the day is accounted for by a large number of strikes which occurred in the last half hour of daylight.

Predatory efficiency was similar for all quarters but slightly lower in the third than other quarters (Table 8 and Figure 10). Lower strike success during the third quarter may have been related to the greater proportion of hover-hunts during that quarter compared with other quarters, but more likely was related to decreased hunting effort of the birds during the third quarter.

Height of Dive

Predatory strikes were initiated from perches ranging from 1 to 21 m high and from hovering positions ranging from 1 to 17 m high.

When hover-hunts and perched hunts were combined, predatory efficiency significantly improved as heights decreased (p < 0.001, X2 = 23.6, df = 5) (Figure 11). While not statistically significant, the same trend is evident for strikes initiated from perches but not for those initiated from hovering positions. Predatory efficiency presumably should increase as the height at which strikes are initiated decreases because: 1) dive time is shorter from low than high perches, thus the prey has less time during the attack to escape; 2) as height of the dive decreases the bird is less likely to make a mistake identifying its intended prey or judging its depth; and 3) smaller prey items should be more visible lower than from higher perches and these small fish may be younger and less experienced at escape. Also, since swimming speed is proportional to length, smaller fish swim slower than larger fish and may be easier to capture. Figure 11. Predatory Efficiency of Belted Kingfishers in Relation to the Height of Dive and Turbidity of Water in the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. Sample sizes are indicated by numbers within the bars. 45

Turbidity

Predatory efficiency appeared to be inversely related to turbidity of the waters for strikes initiated from hovering positions, but sample sizes were too small to test for statistical significance

(Figure 11). Strikes from perched positions into waters in which a

Secchi disk was visible to depths of 21-40 cm were more successful than strikes into either clearer or more turbid waters, but the difference was not statistically significant (p = 0.106, X2 = 10.47, df = 6). Water in which a Secchi disk is visible at 21-40 cm may be the level of turbidity where fish are visible to the bird, but the bird is slightly obscured to the fish. Recher and Recher (1972) suggested that clear water and bright sun should decrease predatory efficiency by increasing detection of the predator by the fish. In very clear waters birds also may spot fish at greater depths than in turbid waters and attempt to capture them when the fish are at depths below the bird's effective ability to capture fish or the fish may have a greater amount of time to escape than fish in shallower waters. While turbid waters did not have a statistically significant influence on predatory efficiency, it did influence the bird's behavior. The mean heights from which kingfishers hunted decreased as the turbidity of the water increased (Figure 12, Table 9). When waters in the river were extremely turbid kingfishers often foraged in less turbid side streams and road- side ditches.

Water Surface

Variation in conditions of the water surface was largely caused by wind, but water currents disturbed some surfaces. Kingfishers 46

Figure 12. Variability in Heights of Perches Used by Belted Kingfishers Hunting along the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. Horizontal lines represent the mean height, vertical lines represent the range, and vertical belts represent + 1 standard error. 47

Table 9. Heights from which Belted Kingfishers Hunted in Relation to Turbidity of Water in the Mad River, Humboldt County, Calif- ornia, during the Winters of 1975-76 and 1976-77.

a The mean height is low due to the number of observations under clear water conditions in an area where no perches higher than 8 m were available. 48 appeared to avoid high winds and rough water by hunting on the leeward side of stream banks and trees. No hunts were observed in areas where waves occurred. Predatory efficiency decreased for both hover- and perched-hunts as the water surface became more disturbed (Figure 13).

The differences were statistically significant for hunts from perches

(p < 0.05, X2 = 6.8, df 2), but not for hover-hunts (p = 0.40,

X2 = 1.8, df = 2).

The highest predatory efficiencies of Ospreys (Pandion haliaetus) (Grubb, 1977) and two species of terns (Dunn, 1972), were associated with rippled surface water. These species are hover-hunting birds and Dunn (1972) postulated that either the rippled surface of the water made it harder for the prey to detect the hovering bird or the wind causing the rippled surface conditions allowed the birds to hover in less vigorous manner giving them a better view and making less movement for the prey to detect. The fact that kingfishers showed a less pro- nounced difference in predatory efficiency with increased water disturbance when hover-hunting than when hunting from perches, supports

Dunn's second hypothesis.

Wind

At low velocities (0 - 11 kph), predatory efficiency of birds hunting from perches decreased with increasing wind, but it appeared to increase at higher velocities (Figure 13). Predatory efficiency hover-hunting kingfishers changed little with higher wind velocities, indicating a balance between more disturbed surface waters and less movement of the bird in hovering as discussed above. Figure 13. Predatory Efficiency of Belted Kingfishers In Relation to Windspeed and Surface 4V

' Conditions of Water in the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. Sample sizes are indicated by numbers within the bars. 50

Available Light

Light intensities ranged from less than 0 to over 5,000 foot candles. Predatory efficiency of birds hunting from perches differed significantly at different levels of light y (p = 0.001, X2 =

19.7, df = 5) (Figure 14). Success was lowest when less than 50 foot candles of light was available, increased sharply to 77.5 percent success with 51-200 foot candles of light, and then decreased gradually as light increased in intensity. No hunts from a hovering position were observed n. light intensities below 50 foot candles; diffe in predatory efficiency of hover-hunts under various light conditions were not statistically significant (Figure 14).

Predatory efficiency of Reef Herons (Demigretta secra) foraging in clear water and bright sunlight on the Great Barrier Reef of Austra- lia was 48 percent compared to 65 - 67 percent for Little Blue Herons

(Florida caerulea) foraging in less intense sunlight and more turbid waters in Florida (Recher and Recher, 1972). Bright light may cause reflections and distort the bird's view or increase the ability of fish to detect the diving bird. At very low light intensities, the bird may have trouble judging prey size and distance, and may then be less efficient than at intermediate light intensities.

Cloud Cover

No significant effect of cloud cover was discernible in separate analysis of either hunts from perches or hunts while hovering, but when the two types of hunting were analyzed together, sample sizes were larger and strike success was significantly lower in direct sunlight than other categories of cloud cover (p = 0.002, X2 = 15.25, df = 3) Figure 14. Predatory Efficiency of Belted Kingfishers in Relation to Available Light and Cloud Cover along the Mad River, Humboldt County, California, during the Winters of 1975-76

and 1976-77. Sample sizes are indicated by numbers within the bars. 5 1 52

(Figure 14). Cloud cover alone probably has little effect on strike success, but likely contributes to the more important influence of light intensity.

Precipitation

The effect of rain on predatory efficiency was not statistically significant (p 0.052, X2 = 1.29, df = 2), but predatory efficiency was highest when it was drizzling (Figure 15). The small sample sizes make this finding suspect, but it may be that slight disturbance of the water surface by light rain gives the kingfisher an advantage in not being as detectable by the fish as the bird would be through a less disturbed surface.

Prey Abundance

Predatory efficiency of 56 hunts from perches within the hatchery raceways was 59 percent, while predatory efficiency of birds hunting on the river near the hatchery was 54 percent. Since environmental conditions were better in the hatchery than on the river (e.g. smoother water surface, shaded water, and less turbid water) and the food source was more limited in the river than in the hatchery, the similarity in predatory efficiencies suggested that prey abundance and density played a relatively minor role in the ability of kingfishers to capture prey.

The increase in prey abundance and the better environmental conditions

the hatchery, compared with the river, appeared to affect only the overall time required for foraging (see time and activity budget above), not strike success itself. Page and Whitacre (1975) found that the success rate of Merlins (Falco columbarus) attacking shorebirds was

25.6 percent on single birds, 6.9 percent on groups of 2 to 10 birds, Figure 15. Predatory Efficiency of Belted Kingfishers in Relation to Rain along the Had River, Humboldt County, California, during the Winters of 1975-76 and 1976-77. Sample sizes are indicated by numbers within the bars. 53 54

8.3 percent on groups of 11 to 49 birds, and 21.4 percent on groups of

50 to several hundred. Overall they found the success rate of attacks on individual birds (25.6 percent) was higher than that of birds in flocks (17.2 percent). I never observed schools of fish in the river, and thus assumed kingfishers normally preyed on individuals. It would seem that kingfishers could hardly have missed fish in the hatchery because the prey were so concentrated, and visibility so good, but the effect of schooling may have affected strike success because of the kingfishers' inability to fix its vision on a single fish. Schooling fish react in a coordinated manner and derive the benefits of many sets of eyes able to detect an attacking predator and able to initiate avoidance reaction as a group (Radakov, 1972; Shaw, 1978). Schooling also may have lowered predatory efficiency by what Welty (1934) called a "confusion effect" in which a predator has difficulty following an individual prey fish when many fish are moving erratically in unison.

Predatory efficiency of kingfishers on the river and in the hatchery may have been similar because the better environmental conditions within the raceways may have compensated for the kingfishers' inefficiency at hunting fish in large schools.

Energy Budget

During the 19 days when kingfishers were observed essentially continuously from dawn until dusk, the birds spent slightly more than one percent of the 24-hour day in flight activity (Table 10). Com-

bining this information with the appropriate values for body weight and mean air temperature, the energetics model (Koplin, 1972; Koplin et al., 1980) predicted an energy expenditure of 59.4 kcal per bird 55

Table 10. Inputs to Daily Energy Budget for Belted Kingfishers Observed along the Mad River, Humboldt County, California, for 19 Full Days during the Winters of 1975-76 and 1976-77. Based a Model Developed by Koplin (Koplin, 1972; Koplin et al. 1980).

a Assumes 82.1 percent of food is assimilated (after Vessel, 1977). 56

Table 11. Food Intake of Belted Kingfishers Observed for 19 Full Days along the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77.

Estimated Estimated Date Live Weight (g) Dry Weight (g) Energy (kcal) 57

Table 12. Caloric Intake of Belted Kingfishers Observed for 19 Full Days along the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77.

a Assumes 82.1 percent of food assimilated (after Vessel, 1977). 58 per day (Table 10). The observed caloric intake during the 19 days ranged from 9.4 to 134.9 kcal, and averaged 70.2 kcal per bird per day

(Tables 11 and 12). The observed average caloric intake, adjusted for the 0.821 assimilation efficiency, was 57.6 kcal per day, only 3.0 percent lower than that predicted by the model, a difference which easily could be accounted for by inaccuracy of the technique used to estimate observed caloric intake. Thus, it would seem the model is an excellent predictor of a free-ranging kingfisher's energy budget.

Coupled with an assumed assimilation efficiency of 0.821, the model predicted the energy requirement of kingfishers during the winter of 1975-76 (1.55 percent flight activity per day; 9.0° C mean air temperature) to be 74.1 kcal per bird per day; during the less severe winter of 1976-77 (1.98 percent flight activity per day; 9.8° C mean air temperature) the model predicted each bird required 74.3 kcal per day. CONCLUSIONS

Belted Kingfishers wintering on the Mad River devoted the majority of their time to obtaining food. To examine the factors determining the effort that the birds had to expend foraging, it was useful to adapt Holling's (1966) approach and analyze four basic components of a predator's response to its prey: the time predator and prey were exposed to each other, the predator's hunger level the time the predator spent handling each prey item, and the rate of successful search.

Time Prey were Exposed to Predators

The time prey were exposed to predators was dependent on the time the predators spent foraging during a day. Kingfishers living along the river spent 80 percent of their daily activity foraging compared with birds living in the hatchery, which spent only 9 percent of their daily activity foraging. The cost of maintaining a territory in the hatchery, however, required an expenditure of 65 percent more time in intraspecific interactions than that of kingfishers defending territories along the river. The greater amount of time expended in order to maintain territories within the hatchery was consistent with

Holling's ( 966) predictions of a numerical response of predators to increased prey density. Two birds maintained territories within the hatchery about 5 to 10 percent the size of territories maintained by birds on the river, but spent 65 percent more time defending these small but rich territories.

59 60

Hunger

I have very little information on how a kingfisher's hunger

influenced its interaction with its prey. The first subcomponent of

hunger, the rate of food digestion and assimilation (Rolling, 1959),

could not be estimated from my observational data, but the decrease in

hunting effort and predatory efficiency observed during the early after-

noon may have been influenced by satiation after feeding in the morning.

T e second subcomponent, maximum capacity of the gut, was at least 60 g,

or one 11-cm sculpin and one 18-cm salmonid, which I observed a king-

fisher consume within a two-hour period.

Prey Handling

The time spent handling prey could be divided into time spent

pursuing and subduing prey, time spent eating prey, and time spent in

a "digestive pause" (Rolling, 1959). The pursuit time, handling time,

and eating time varied according to the prey species taken, but overall

comprised only 2.3 percent of the kingfisher's diurnal activity budget.

The digestive pause was more time-consuming than the other subcompon-

ents. Digestive pauses were hard to discern, but certainly included

the time a kingfisher spent holding fish prior to swallowing them

(1.6 percent) and probably included the inactive periods spent perched-

inactive (12.2 percent) which often followed consumption of large

amounts of prey. The time spent perched-inactive might be dedicated

to foraging in years with poor foraging success and may be considered

an indicator the ease with which a kingfisher was able to obtain 61 its needed food, and thus an indicator of the quality of its territory, the bird's ability to capture prey, or conditions of the environment.

Rate of Successful Search

The rate of successful search depended on the speed of movement of the predator relative to that of its prey, size of the predator's reactive perceptual field, and capture success (Honing, 1959). The search speed of an ambush predator such as a kingfisher relative to that of its prey was essentially zero, so the rate of successful search was mainly dependent on the speed at which prey passed below the bird.

Salt and Willard (1971) estimated that the perceptual field of a

Forster's Tern (Sterna forsteri) approximated a cone, with the bill as its axis and with an apical angle of about 17 degrees. The area of this perceptual field increased with the height from which the bird hunted. From a height of 6 m the projection of this cone would inter- sect a circle of about 1 m diameter at the water surface. The hunting height of a kingfisher varied considerably within a day depending on available light, turbidity of the water, and the number and heights of perches available. Therefore, those factors that affected the height from which a kingfisher hunted (i.e. available light and turbidity) affected the rate of search.

Predatory efficiency was most significantly affected by the method of hunting (Figure 9). The number of prey taken per hour of actual hunting averaged 9.74 by hover-hunting birds and 0.89 for birds hunting from perches (Table 13). Kingfishers expended 2.70 kcal per fish captured from a perched position but only 1.20 kcal per fish captured from a hovering position; thus hovering birds could have made 62

Table 13. Comparison of Fish Captured and Energy Expended by Belted Kingfishers Utilizing Two Hunting Methods on the Mad River, Humboldt County, California, during the Winters of 1975-76 and 1976-77.

a From Table 3. b Ratio of Energy Expenditure in Flight to BMR (FC) = 13.68; Table 10. c Basal Metabolic Rate (BMR) = 0.4616 W 0.734 = 20.54; Table 10. d Existence Metabolism at Ta = 56.44 kcal (Table 10). 63

2.2 times as many captures with the same amount of energy expended by a bird hunting from a perch (Table 13). Therefore, it would seem to have been energetically more efficient for a kingfisher to hover-hunt.

However, the birds hover-hunted only when perch sites were limited or when insufficient prey were obtained by hunting from perches. Why did they not hunt by hovering more often?

The energy expended in perched-hunting was essentially the same as that spent while perched-inactive, since less than one percent of the perched-hunting i e involved flight to capture prey (strikes from perches; Table 3). In contrast, all of the time spent hover-hunting was spent in flight; overall hover-hunting was more energy-efficient than perched-hunting only because less time was required to capture the same number of prey. If kingfishers had hunted only by hovering, each day after the needed food was obtained more time would have to be spent perched-inactive. The total energy required for hover-hunting plus the hidden cost of the surplus time spent perched-inactive, was actually 1.35 times greater than the energy required to capture an equal number of prey by hunting from a perch. Thus, a bird should have hunted from a perch as long as sufficient food was obtained.

Only if a bird could not obtain its food requirements in a given period of time should it have resorted to hover-hunting because the return per unit time was greater for hover-hunting than hunting from perches, although the overall cost was greater. Kingfishers were never observed to hunt from a hovering position at the hatchery raceways where food was unlimited. Additionally, during the summer of 1974, when kingfishers were feeding young and their energy requirements were greater than during the winter, 50 percent of the predatory attempts were from 64 a hovering position (Forsel 1974); in this winter study only 19 percent of the strikes were initiated from a hovering position. The amount of hover-hunting in which a bird engaged may have been inversely proportional to the food availability in a territory and directly proportional to the energy requirements of the bird.

The two most significant environmental factors that affected the predatory efficiency of kingfishers were the amount of light available and surface conditions of the water (Figures 13 and 14). Predatory efficiency decreased with increased disturbance of the water's surface and was lowest when almost dark, highest at dusk, and decreased at higher light levels. Characteristics of the habitat that affect these environmental conditions, and thus the predatory efficiency of kingfishers, could be used to evaluate the quality of territories used by different birds.

Predatory efficiency of kingfishers hunting from perches appeared to be similar regardless of prey abundance or geographic area and fell within the range of 48 to 76 percent efficiency found for numerous other avian predators attacking small prey from a stationary position (Table 14). Predatory efficiency of hover-hunting kingfishers

(20 percent) also fell within the range of 13 to 54 percent found for other hover-hunting predators (Table 14). The lower success of strikes from a hovering position compared with strikes from perches in general may be caused by a combination of the three factors surmised to be operating iT kingfishers: 1) prey have a longer time to detect a hovering bird since a sedentary predator does not move until the strike is made; 2) a hovering bird may have difficulty iudging the position of the intended prey, while a sedentary bird may be able to watch the prey 65 Table 14. Predatory Efficiency of Selected Avian Predators. Predators. Selected Avian Efficiency of Predatory Table 14. Table 14. (Continued). 67 longer; and 3) the hovering bird may be more likely to attack when the prey is in less than an optimal position, whereas a sedentary bird can afford to wait longer for the prey to move into a more vulnerable position.

Although Ospreys (Pandion haliaetus) and Brown Pelicans (Pel- ecanus occidentalis) are also aerial predators, their predatory efficiencies were much higher than other birds that hover-hunt and were instead similar to those of sedentary predators (Table 14). Ospreys take large fish which may have different escape abilities than smaller fish, but also use their talons rather than their bills to capture prey.

Two sets of talons can cover a larger area than a bill and may he more efficient than the bill. Brown Pelicans use a large pouch and bill to capture fish, which also may be more efficient than a small bill.

Food Habits and Energetics

The quantity and species of fish consumed by Belted Kingfishers has been of interest to biologists, sportsmen, "preservationists", and hatchery managers for many years. Salmonids, sculpins, and sticklebacks ranging in size from 1.8 - 19.0 cm and averaging 7.4 cm formed the bulk of the kingfishers' diet on the Mad River during the two winters they were studied by me, but the relative proportions of each species taken varied among the three major areas of the river studied. My findings suggested that kingfishers took fishes in proportion to their frequency of occurrence.

Previous estimates of the daily intake of a free-ranging kingfisher varied widely: De la Torre Brueno (1936, as cited in Salyer and

Lagler, 1946) concluded "three fingerling trout constituted a day's 68 ration"; White (1936) estimated that a nestling kingfisher consumed

100-200 g per day and that an adult consumed about 20 fish larger than

6 cm each day; Lagler (1939) estimated adults consumed three meals a day, each consisting of about 3.7 fish. Vessel (1977) found that caged kingfishers required 71vb kcal per day, or 9.2 fingerlings of

6 g each.

In this study the daily food intake of kingfishers on 19 full days of observations averaged 70.2 kcal which was equivalent to 17.4 salmonid fingerlings each of 7.4 cm in length, approximately 4.0 g live weight 81.0 percent water content, and approximately 4.0 kcal energy content. The energy intake predicted by Koplin's model (Koplin et al., 1980) closely approximated the observed intake: 72.33 kcal or

18.1 fingerlings per day for the same period. Using the time and activity budget for the two winters combined, the model predicted that during the 182 days from October through March, an individual kingfisher would require 13,517 kcal or 3,379 fish of 4 g each. Thus the 25 kingfishers estimated to have wintered on the lower Mad River would have consumed 337,925 kcal of fish or 84,418 fish of 4 g each during a

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