Brigham Young University BYU ScholarsArchive Theses and Dissertations 1972-08-01 Raptor predation on pocket gopher populations by the use of hunting perches Robert C. Christensen Brigham Young University - Provo Follow this and additional works at: https://scholarsarchive.byu.edu/etd Part of the Life Sciences Commons BYU ScholarsArchive Citation Christensen, Robert C., "Raptor predation on pocket gopher populations by the use of hunting perches" (1972). Theses and Dissertations. 7658. https://scholarsarchive.byu.edu/etd/7658 This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. /:"/ ./ RAPTORPREDATION ON POCKET GOPHER POPULATIONS BYTHE USE OF HUNTINGPERCHES A Thesis Presented to the Department of Zoology Brigham Young University In Partial Fulfillment of the Requirements for the Degree Master of Science by Robert c. Christensen August 1972 11 This thesis by Robert C, Christensen is accepted in its present form by the Department of Zoology of Brigham Young University as satis­ fying the thesis requirement for the degree of Master of Science, :;_� �f., /f?z_ ?/Date Typed by Ann L, Spears 111 ACKNOWLEDGMENTS Grateful acknowledgment is made for the valuable suggestions and help given by the chairman of my advisory committee, Dr, Joseph R. Murphy, and for his aid in acquiring research funds from the National Audubon Society. Deep appreciation is also made for the suggestions and advice of the other members of my committee, Dr. H. Duane Smith and Dr, Odell Julander, I wish to express my thanks tow. Frank Savage of the Uinta National Forest and Jim Kiml::al of the Wasatch National Forest for their help and concern in the initiation and carry-through of this research problem, I am grateful for the field assistance received from my three younger brothers and for the valuable assistance of my wife, Kathy, in both field work and manuscript preparation, The Department of Zoology, Brigham Young University, supplied laboratory space and equipment, iv TABIEOF CONTENTS Page ACKNOWLEDGMENTSe t a e I t • e e e a e • e I e e I I ■ I e I I I e 111 LIST OF TABIES t e I I t t t I I I t I I I t I I I I I e I I t e I V LIST OF FIGURESt I I I I t I 8 I I t t e I • • • • • • • • • • • • vi INTRODUCTION• • • • • • • • • • • • • • • • • • • • • • • • • • • 1 REVIEWOF LITERATURE• • • • • • • • • • • • • • • • • • • • • • • 4 DESCRIPTIONOF STUDYAREA • • • • • • • • • • • • • • • • • • • • • 8 Location • • , • , , • , • • • • • • • • • • • • • , , , , 8 Topography , , • , • , • • • , , • , , • • , , , • • , , , 12 Clima.te , , , , , , • , , , , , , , • , , , • , , • , , , , 14 Vegetation , , , , , , , , • , • • , , , • , • • • • • • • 15 Animal Influents • , , • , •• , , , •• , , •••••• , 18 Grazing and HumanUtilization •• , , •• , • • • • • • • • 22 METHODSAND PROCEDURES·., , , , , • • • • • , • , • , • , , • , • , 24 RESULTS• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • JO Raptor Nests , , • , , , • , , • • , • • , • , , , , • • • JO Seasonal Variation in Raptor Numbers and Occurrence, • • • Jl Raptor Interaction •••• , , , • , , , • , , , -. , • • • J4 Raptor Utilization of Perches and Telephone Peles. , •• , 35 Raptor Utilization of Tree Perches , , •• , , • , • • • • 41 Prey Analysis • • • • , , , • , , , • , , • , • , • • , , • 42 Summaryof Prey Species Occurrence , , • , • , , , •• , , 45 Trapping Results • , , , • , •• , , •• , , , ••• , • , 47 Gopher Population Analysis • , ••• , , , • , • , • • • , 50 DISCUSSIONAND CONCLUSIONSt I I ■ I I t t I t a · I I I t I I t I I 5? SUMMARY••• • • I a I ■ t t I • • • • • • • • • • • • • • • • • • 76 LITERATURECITED , • • • , , , , • • • • • • , , • • • • • • • • • ?9 V LIST OF TABLES Table Page 1, Vegetative analysis of Sink Hollow study area. • • • • • • • 16 2, Cumulative monthly signs of large raptor utilization of hunt- ing perches and telephone poles in Sink Hollow, 1970 and 1971 ■ I I • • I I I I I I I I I I I I I I I I I I I I I a 37 3• Comparison of prey occurrence under perches and telephone poles in Strawberry Valley, 1970 & 1971 • , •••• , • • 46 4, Semimonthly composition of prey individuals in pellets and prey remains found under the perches and telephone poles in Sink Hollow, 1970. , , ••• , • , , •• , , • • • • • 48 5. Semimonthly composition of prey individuals in pellets and prey remains found under the perches and telephone poles in Sink Hollow, 1971 • , , •• • • , , , , • ••• • • • • 49 6. Number of animals trapped per 300 trap-nights per acre • • • 52 7. Comparison of number of new gopher mounds per 0,10 acre for 1970 and 1971 • • • • • • • • • • • • • • • • • • • • • • 54 8. Regression analysis of the relationship of distance from hunting perches to number of new gopher mounds ••• , • , 55 vi LIST OF FIGURES Figures Page 1. Map showing location of study areas in Wasatch County, Utah • • , , , , • • • • • • , , • • , • , , • • • • I I I 9 2. Map of Sink Hollow study area showing location of hunting perches, telephone lines, and Long-eared Owl nest , , , • 10 J, Map of Big Flat area showing location of hunting perch •• , 11 4. Aerial photograph of the Sink Hollow study area ••••• , • l) 5. Aerial photograph of the Big Flat study area , •• , , , , • l) 6. Camera detecting device set up by perch no, 1 with perch no, 2 and ma.in telephone line in l::a.ckground , •• , , , • 26 7, Assorted ra.ptor pellets found under perches and telephone poles • • • • • • • • • • • • , • • • • • • • • • , , , , .26 8, Assorted skulls and osseous remains found under perches and telephone poles ••••••• • • ••• , •••• , , • , 27 9. Dissected ra.ptor pellets showing fur and osseous remains , • 27 10, Occurrence of ra.ptor species in Sink Hollow area, 1970 & 1971 I I I I I I t I I I I I I I I I I I I I I I I I I I I '.32 11, Swainson's Ha.wkon hunting perch • • , • • • • , • • • • • , 39 12, Semimonthly occurrence of prey individuals in pellet and prey remains for 1970 and 1971 • • • , , • • • , • • • • , 50 lJ, Percent frequency, percent composition, and total numbers of gophers found in prey analysis, 1970 • • • • • • • , • 51 14, Percent frequency, percent composition, and total numbers of gophers found in prey analysis, 1971 • , • • • , • • • 51 15, Gopher winter casts on Big Flat, June 7, 1971 • • • • • • • • 53 INTRODUCTION The Northern Pocket Gopher (Thomomystalpoides) is commonon open range lands at high altitudes, and range management personnel have long been confronted with the problem of controlling gopher pop- ulations. Although some studies indicate that pocket gophers have little or no injurious effects on range in good condition, other stud- ies show that large populations of these animals can seriously damage seeded ranges and ranges in poor condition (Colorado State University Exp, Stat., 1960). Julander, Low, and Morris (1969) indicate that in areas where gophers have reached populations of 27-39 gophers per acre, forage removal by gophers may be from 4.75 to 7 pounds of fresh weight vegetation per acre per day. This converts to 435-670 pounds of air- dry plant material per acre per year. On depleted ranges this repre- sents a large percentage of the total annual growth. Hansen (1965) re- ported that in 1961 gophers numbered 52 per acre on Black Mesa, Colo- rado, Such a high density of gophers could have drastic effects on range soils and vegetation. Considerable research has been done by government agencies on various methods of controlling pocket gophers. Dixon (1922) and the Colorado State University Experiment Station (1960) outlined some of these methods. Indirect controls involve such practices as (1) the use of herbicides (2,4-D), (2) water manipulation (flood-irrigation), (3) crop rotation, and (4) the encouragement and protection of the 2 gopher's natural predators. Direct methods of control consist of (1) the use of poison 1:aits (hand-1:aiting, probing methods, mechanical dis- pensing, and mechanical burrow-building), (2) control trapping (good for small areas only), and (3) fumigating. The primary methods that have been used on a large scale 1:asis are those involving toxic baits. It is not known what adverse effects these substances may have on the environment. Even with their use, effective economical means of con- trolling pocket gophers on range lands still remain a problem (Kimbal, Poulson, and Savage, 1970). In 1968 it was noted by Uinta National Forest personnel that in a.n area of high gopher activity where a telephone line traversed Strawberry Valley, Wasatch County,· Utah, there was a distinct absence of gopher mounds around the base of each telephone pole. Closer ex- amination of the area under the poles revealed the presence of rodent hair and bones as well as fecal droppings of ra.ptorial birds. On Octo- ber 18, 1968~ a. 12 foot pole with a six foot cross-beam was erected in an area of high gopher activity. One hundred thirty-one active mounds were counted in a radius of 35 feet around the pole. One year later on October 15, 1969, there were no active gopher mounds within a 37 foot radius of the pole, although gopher activity had not decreased over the total area. Indications were that ra.ptors had effectively used the pole as a hunting perch, and in so4oing had reduced the num- ber of gophers in the immediate locality of the pole. (Kimbal, et al., 1970). Raptorial birds often use telephone poles, tree branches, and fence posts