DISSERTATION PREDATORY AND ENERGETIC RELATIONS OF WOODPECKERS TO THE ENGELA~N SPRUCE BEETLE Submitted by James Ray Koplin In partial fulfillment of the requirements for the Degree of Doctor of Philosophy Colorado State University Fort Collins, Colorado June, 1967 COLORADO STATE UNIVERSITY June 1967 IT IS RECOMMENDED THAT THE DISSERTATION PREPARED BY ---- JAMES RAY KOPLIN ENTITLED PREDATORY AND ENERGETIC RELATIONS OF V\UODPECKERS TO THE ENGELMANN SPRUCE BEETLE BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIRE~ffiNT FOR THE DEGREE OF OOCTOR OF PHILOSOPHY. Committee £Q Graduate Work Major Professor Examination Satisfactory Chairman Permission to publish this dissertation or any part of it must be obtained from the Dean of the Graduate School. ii Abstract of Dissertation PREDATORY AND ENERGETIC RELATIONS OF WOODPECKERS TO THE ENGELMANN SPRUCE BEETLE A general theory of the population dynamics of predator­ prey systems was developed from a survey of pertinent literature. According to the theory, populations of simplified predator-prey systems fluctuate wildly and periodically. Complicating factors dampen the amplitude of the population fluctuations and thus exert a stabilizing influence on the systems. The predator-prey system between the Northern Three-toed, Hairy and Downy Woodpeckers, and the Engelmann spruce beetle was chosen for an investigation of the population dynamics of a natural predator-prey system. The population densities of several species of bark beetles attracted to trees killed and damaged by a fire on the study area in Northern Colorado, increased to levels that attracted the feeding attention of the woodpeckers. The numerical response of the woodpeckers to prey density was graded, that of the Northern Three-toed Woodpecker was the most pronounced and that of the Downy Woodpecker was the least pronounced. Spatial and temporal differences were noted in the foraging behavior of the three species of woodpeckers; similar but less apparent differences were also noted in the foraging behavior between the sexes of the Northern Three-toed and Hairy Woodpeckers. Both the interspecific and intersexual differences in foraging behavior were correlated with morphological and dietary iii differences. The metabolic demands of free-living woodpeckers were estimated by feeding diets of known caloric content to active woodpeckers in cages at several different ambient temperatures. Estimates were also made of the caloric content of Engelmann spruce beetle larvae and the rate at which they are digested by the woodpeckers. Combining these estimates with the estimates of the relative densities of woodpeckers, and the average number of spruce beetle larvae found per woodpecker stomach made it possible to calculate the number of larvae consumed by each species of woodpecker. This method gave results very similar to the usual method whereby the number of larvae surviving in bark protected from woodpeckers is compared with the number surviving in bark exposed to woodpeckers. Every aspect of the predator-prey system between woodpeckers and the Engelmann spruce beetle, except the number of larvae destroyed, conforms to general theory. The number of prey destroyed in this predator-prey system is higher than that known for any other sy·stem between vertebrate predators and invertebrate prey. James Ray Koplin Department of Zoology Colorado State University June, 1967 iv ACKNOWLEDGEMENTS This study was supported in part by cooperative aid from the u. s. Forest Service, through the auspices of Dr. Noel Wygant, principal Entomologist, of the Forest Insect Research Laboratory of the Rocky Mountain Forest and Range Experiment Station. The study was also supported by National Science Foundation Grants, GB-753 and G-2478, awarded to Dr. Paul H. Baldwin. I wish to thank Dr. Baldwin for his assistance and guidance throughout the study. I am grateful to Drs. 0. Wilford Olsen, David Pettus, Noel Wygant, and Harold Steinhoff for their services as committee members and for their many helpful comments and suggestions. Donald Beaver, Douglas Post, Gerald Lorentzson and James Gibson assisted in the field work and George M. Matthews assisted in the metabolic experiments. I had many helpful discussions of the subject of this dissertation with Douglas Post, Patrick Stallcup and Albert W. Spencer. A special note of thanks is due Mrs. Bernice M. George for her many acts of assistance during my tenure in the field on the Deadman study area. Finally, I am most grateful to my wife, Phyllis, for her patience and encouragement throughout the study, and for her help in preparing the manuscript. Most of the field equipment used in this study was supplied by the Forest Insect Research Laboratory, Rocky Mountain Forest and Range Experiment Station. v TABLE OF CONTENTS Page INTRODUCTION • • • • • • • • • • • • • • • • • • • • • • • • 1 Statement of Problem • • • • • • • • • • • • • • • • • • 2 Development of a General Theory • • • • • • • • • • • • 3 The Need for a General Theory • • • • • • • • • • • • 3 Models of Predator-Pr~y Interactions • • • • • • • • 5 Field Studies of Interactions Between Vertebrate Predators and Vertebrate Prey • • • • • • • • • • 16 Field Studies of Interactions Between Invertebrate Predators and Invertebrate Prey • • • • • • • • • 18 Field Studies of Interactions Between Vertebrate Predators and Invertebrate Prey • • • • • • • • • 20 Efficacy of Predators and Ecological Efficiency • •. • 21 Competition and Niche • • • • • • • • • • • • • • • • 23 Summary Statement of the General Theory • • • • • • • 29 METHODS • • • • • • • • • • • • • • • • • • • • • • • • • • 31 Study Area • • • • • • • • • • • • • • • • • • • • • • • 31 Measurement of Forest Composition and Stand Density • • • 31 Temperature Records • • • • • • • • • • • • • • • • • • • 34 Techniques for Manipulating the Spruce Beetle Population • • • • • • • • • • • • • • • • • • • • • 34 Spruce Beetle Census Technique • • • • • • • • • • • • • 35 Woodpecker Census Techniques • • • • • • • • • • • • • • 36 Measurement of Realized Niche • • • • • • • • • • • • • • 38 Metabolic Techniques • • • • • • • • • • • • • • • • • • 40 RESULTS ••• • • • • • • . • • • • • • . • • • • • • 44 Forest Composition and Stand Density • • • • • • • • • • 44 Temperature • • • • • • • • • • • • • • • • • • • • • • • 49 Wind Thrown Trees • • • • • • • • • • • • • • • • • • 49 Bark-Beetle Populations • • • • • • • • • • • • • • • 54 Woodpecker Populations • • • • • • • • • • • • • • • • • 59 Foraging Behavior • • • • • • • • • • • • • • • • • • 64 Food Habits • • • • • • • • • • • • • • • • • • • • • • • 86 Linear Measurements of Morphological Characters • • • • • 95 Energetics • • • • • • • • • • • • • • • • • • • • • • • 99 vi TABLE OF CONTENTS (Continued) Page DISCUSSION • • • • • • • • • • • • • • • • • • • • • . • • • 116 Components of Character Displacement • • • • • • • • • • • 116 Spatial and Temporal Differences ••••••••••• 117 Dietary Differences ••••••••••••••••• 129 Morphological Differences • • • • • • • • • • • • • • 136 Components of Predation • • • • • • • • • • • • • • • 145 Spruce Beetle Densities ••••••••••••••• 145 Numerical Response of Woodpeckers to Prey Density •• 151 Functional Response of Woodpeckers to Prey Density •• 155 Spruce Beetle Mortality from Woodpecker Predation •• 156 Factors Regulating the Effectiveness of Predation by Woodpeckers • • • • • • • • • • • • • • • • • • • • • 166 Nesting Territoriality •••••••••••• . 168 Differential Selections of Prey ••••••••• 169 CX>NCLUSIONS • • • • • • • • • • • • • • • • • • • • • • • • • 174 SUMMARY . 177 LITERATURE CITED • . • • • . 179 vii LIST OF TABLES Table Page 1 Density and basal area of Engelmann spruce in each two-inch diameter class on the Deadman study area • • • • • • • • • • • • • • • • • • • 45 2 Density and basal area of subalpine fir in each two-inch diameter class on the Deadman study area • • • • • • • • • • • • • • • • • • • • • • 47 3 Density and basal area of lodgepole pine in each two-inch diameter class on the Deadman study area • • • • • • • • • • • • • • • • • • • • • • 48 4 Relative location and year of initial invasion by bark beetles of blowdowns discovered on the Deadman study area •. • • • • • • • • • • • • • • 55 5 Number of acres censused and woodpeckers observed per census period on the Deadman study area • • 60 6 Number of acres censused and woodpeckers observed per census period outside the area of the 1962 burn • • • • • • • • • • • • • • • • • • • • • • 61 7 Number of acres censused and woodpeckers observed per census period within the area of the 1962 burn • • • • • • • • • • • • • • ~ • • • • • . 62 8 Comparisons of relative use of tree types and of foraging positions within trees for Northern Three-toed and Hairy Woodpeckers for the period July 16 to October 15, 1962 to 1965 •••• 68 9 Comparisons of relative use of tree types and of foraging positions within trees for Northern Three-toed and Hairy Woodpeckers for the period October 16 to May 10, 1962 to 1965 ••••••• 69 10 Comparisons of relative use of tree types and foraging positions within trees for Northern Three-toed and Downy Woodpeckers for the period October 16 to May 10, 1964 to 1965 ••••••• 70 viii LIST OF TABLES (Continued) Table Page 11 Comparisons of relative use of tree types and foraging positions within trees for Hairy and Downy Woodpeckers for the period October 16 to May 10, 1964 to 1965 ••••••• 71 12 Comparisons of total amount of time, in minutes, each tree type and foraging position was occupied by Northern Three-toed and