PEREGRINE FALCON BIOLOGY AND MANAGEMENT IN COLORADO 1973 - 2001 STATE OF COLORADO - DIVISION OF WILDLIFE PEREGRINE FALCON BIOLOGY AND MANAGEMENT IN COLORADO 1973 - 2001 Gerald R. Craig and James H. Enderson Technical Publication No. 43 COLORADO DIVISION OF WILDLIFE July 2004 DOW-R-T-43-04 ISSN 0084-8883 STATE OF COLORADO Bill Owens, Governor DEPARTMENT OF NATURAL RESOURCES Russell George, Executive Director WILDLIFE COMMISSION Philip James, Chairman, Fort Collins; Jeffrey Crawford, Vice Chairman, Denver; Brad Phelps, Secretary, Gunnison; Bernard Black, Denver; Tom Burke, Grand Junction; Rick Enstrom, Lakewood; Claire O’Neal, Holyoke; Robert Shoemaker, Canon City; Ken Torres, Weston; Don Ament (Ex Officio); Russell George (Ex-Officio). DIVISION OF WILDLIFE Bruce McCloskey, Director MANAGEMENT STAFF: Steve Cassin, Planning/Budgeting; Marilyn Salazar, Support Services; John Smeltzer, Public Services; Jeff Ver Steeg, Wildlife Programs REGIONAL MANAGERS: Ron Velarde, Northwest; Mark Konishi, Southeast; Scott Hoover Northeast; Tom Spezze, Southwest. Study funded by Colorado Division of Wildlife Edited by Federal Aid in Wildlife Restoration Project W-173-R Sandy Cochran 1 CONTENTS ACKNOWLEDGMENTS ....................................................................................................................9 ABSTRACT ....................................................................................................................................11 INTRODUCTION .............................................................................................................................13 Distribution ................................................................................................................................13 Inventories.................................................................................................................................13 RECOVERY PROGRAM .................................................................................................................14 Recovery Plan...........................................................................................................................14 Propagation...............................................................................................................................14 Falcon Management .................................................................................................................14 Recycling ...........................................................................................................................14 Fostering............................................................................................................................16 Hacking..............................................................................................................................17 Cross-fostering ..................................................................................................................19 Results of Fostering and Hacking.............................................................................................20 Size of the releases ...........................................................................................................20 Population increase ...........................................................................................................21 Discovery of eyries ............................................................................................................22 Increases in known pairs ...................................................................................................23 NATURAL HISTORY........................................................................................................................26 Breeding Chronology ................................................................................................................26 Nesting Habitat .........................................................................................................................26 Cliff prominence.................................................................................................................26 Settings of cliffs .................................................................................................................28 Cliff orientation...................................................................................................................30 Nest ledges........................................................................................................................32 Hunting Range..........................................................................................................................33 Prey...........................................................................................................................................34 REPRODUCTION............................................................................................................................36 Clutch size ................................................................................................................................36 Brood Size ................................................................................................................................37 Fledging Rate............................................................................................................................37 Nest Success............................................................................................................................38 Nestling Attrition........................................................................................................................38 Productivity ...............................................................................................................................39 Sex Ratio of Nestlings ..............................................................................................................40 SHELL THICKNESS, DDE, AND REPRODUCTION ......................................................................42 Eggshell Thickness ...................................................................................................................42 Whole shells ......................................................................................................................42 Shell fragments..................................................................................................................43 Shell thickness and hatching .............................................................................................43 3 DDE Relationships....................................................................................................................43 DDE in eggs, 1973-90 .......................................................................................................43 DDE and shell thickness....................................................................................................45 Regional comparison of DDE levels..................................................................................45 DDE Overview ..........................................................................................................................45 REPRODUCTIVITY AND MORTALITY ...........................................................................................47 Minimum Productivity to Sustain the Population.......................................................................47 Adult Tenure and Productivity on Territory ................................................................................47 Reproductive Performance by Females....................................................................................49 Reproductive Performance by Males........................................................................................50 The Effect of Adult Turnover on Productivity.............................................................................51 Biases of Reproductive Estimates ............................................................................................51 Success at historical eyries compared to recently found sites..........................................51 Potential for bias caused by using data from year of discovery ........................................52 MORTALITY ....................................................................................................................................53 Predation ...........................................................................................................................53 Collisions ...........................................................................................................................54 Starvation...........................................................................................................................55 Gunshot and poison ..........................................................................................................55 Rock climbing ....................................................................................................................55 Mortality Rates..........................................................................................................................55 Estimates from band recoveries ........................................................................................55 Estimates from adult turnover............................................................................................55 MOVEMENTS AND WINTERING AREAS ......................................................................................56