1 Fall 2016 Golden Eagle Migration S urvey Big Belt Mountains, Montana Photo by Ronan Dugan Montana Audubon, Helena, Montana March 2017 2 Fall 2016 Golden Eagle Migration Survey Big Belt Mountains, Montana Report submitted to: Helena - Lewis & Clark National Forest ATTN: Denise Pengeroth, Forest Biologist 3425 Skyway Drive, Helena, MT 59602 Report prepared by: Jeff Grayum, Ronan Dugan, & Steve Hoffman Counts conducted by: Ronan Dugan & Jeff Grayum Project coordinated by : Montana Audubon, Inc. Project Coordinator: Steve Hoffman P.O. Box 595, Helena, MT 59624 (406) 443 - 3949 March 2017 3 Table of Contents List of Tables ................................ ................................ ................................ .............................. 3 List of Figures ................................ ................................ ................................ ............................. 4 Introduction ................................ ................................ ................................ ................................ 5 Study Site ................................ ................................ ................................ ................................ .... 6 Methods ................................ ................................ ................................ ................................ ...... 8 Results and Discussion ................................ ................................ ................................ ................ 9 Observ ation Effort and Weather Summary ................................ ................................ ............... 9 Flight Summary ................................ ................................ ................................ ....................... 9 Species Accounts ................................ ................................ ................................ ................... 10 Age Ratios ................................ ................................ ................................ ............................. 12 Seasonal Timing ................................ ................................ ................................ .................... 14 The Big Belt Count: 2015 vs. 2016 Season ................................ ................................ ............ 15 A Comparison of the Big Belts and other Relevant Raptor Migration Sites ............................ 17 Wing - tagged Golden Eagles ................................ ................................ ................................ .. 18 Resident Raptors ................................ ................................ ................................ .................... 19 Other Wildli fe ................................ ................................ ................................ ....................... 20 Visitation ................................ ................................ ................................ ............................... 21 Recommendations ................................ ................................ ................................ ................. 21 Closing Remarks ................................ ................................ ................................ ................... 22 Acknowledgments ................................ ................................ ................................ ..................... 23 Literature C ited ................................ ................................ ................................ ......................... 24 Appendices ................................ ................................ ................................ ............................... 25 L ist of Tables Table 1. Inclement weather days, Fall 2016 season............................................................ ..9 Table 2. Flight summary for all migrating diurnal raptor species observed in the Big Belt Mountains, Fall 2016. ............................................................................................ 12 Table 3. A summary of all age data for Golden Eagles (GE) and Sharp - shinned Hawks (SS) for the 2016 season in the Big Belts ...................................... ........................ 13 Table 4. A comparison of species - specific totals between the 2015 and 2016 seasons in the Big Belts ..... ......... ........... .............................. ......................................................... 15 4 Table 5. Golden Eagles per 100 hours of observation in the Big Belts ............................... 16 Table 6. A comparison of 2016 raptor migration count totals for Montana hawk count sites and Mt Lorette (located in Alberta, Canada) ............................... ............ ..............17 Table 7. S ightings of wing - tagged Golden Eagles in the Big Belt Mountains by date, Fall 2 016 .......................................................................................... ..............................19 Table 8. Agi ng/sexing criteria for migrant raptors, relevant to the fall 2016 season ...........27 Table 9. Common names, scientific names, species abbreviation codes, and applicable age, sex, and color - morph classifications for all diurnal raptor species observed during fall migrat ion in the Big Belt Mountains............................................................... 28 Table 10. Daily count totals for eagles and accipiters........................................................... 30 Table 11. Daily count total s for buteos.................................................................................. 32 Table 12. Daily count totals for falcons................................................................................. 34 Table 13. Daily count totals for ot her raptors........................................................................ 36 List of Figures Figure 1. Location of the Big Belt and Bridger Raptor Migration Surveys............................ 7 Figure 2. Proportion of Flight by Taxa – Fall 2016.................................. ..............................10 Figure 3. 5 - day passage periods of all non - adult and adult Golden Eagles ...........................14 Figure 4. 5 - day passage periods for Immature and Adult Sharp - shinned Hawks ......... .........15 Figure 5. Effort - adjusted Golden Eagle passage rates at migration sites in Montana ............18 Figure 6. Effort - adjusted 5 - day passage rates for Golden Eagles. ............ ..............................24 Figure 7. Effo rt - adjusted 5 - day passag e rates for Bald Eagles............................................. 24 Figure 8. Effort - adjusted 5 - day passage rates for Accipiter species. .................................... 25 Figure 9. Effo rt - adjusted 5 - day passage rates for Rough - legged, Red - tailed, and Broad - winged Hawks. ......................................................................... ..............................25 Figure 10. Effort - adjusted 5 - day passage rates for small falcons .................................... ....... 26 Figure 11. Effort - adjusted 5 - day passage rates for large falcons. ........................................... 26 Figure 12. Effort - adjusted 5 - day passage rates for Northern Harriers and Ospreys. .............. 27 Figure 13. Approximate location of ha wk - count sites in Montana, with the addition of Mt. Lorette in Alberta, Canada ..................................................................................... 28 5 Introduction The majority of North American diurnal raptor species migrate bi - annually between their breeding and wintering grounds, instinctively following predictable migration routes. During migration raptors often concentrate along specific geographic features (especially high mountain ridges and coastlines) associated with optimal flyin g conditions, providing excellent opportunities for researchers to quantify long - term trends in migrant raptor populations, and, for some species, assess year - to - year demographic changes. It has been well established that standardized scientific annual cou nts at established hawk - watch sites are a cost - effective method for tracking long - term raptor population trends ( Zalles and Bildstein 2000, Farmer et al. 2007). Diurnal raptors are also key biological indicators, since trends in their populations can serve as useful barometers of the overall health of ecosystem function within their preferred habitat (Bildstein 2001). The monitoring of migratory Golden Eagles in western North America is especially critical because migrant populations passing through the Roc ky Mountain West have been in steady decline since the late 1990s (Smith et al. 2008, Sherrington 2016 a & b ). Migration counts in the Bridger Mountains, a historically significant site for censusing migrant Golden Eagles located approximately 60 miles sout h - southeast of the Big Belts (near Bozeman), have documented statistically significant declines of 35 - 40% in counts of Golden Eagles using this flyway (Smith et al. 2008, Davis et al. 2017). As the changing global climate is rapidly a ffecting northern lat itudes, monitoring population s of North American Golden Eagles breeding in far north ern latitudes (many of which migrate via the Rocky Mountain Flyway) has become increasingly important. The Big Belt Mountains were first recognized as a significant migration flyway for Golden Eagles in 2007 by Tim Pitz and Vince Slabe of Raptor View Research Institute (RVRI), based out of Missoula, Montana. Steve Hoffman, founder of Hawk Watch Internationa l and former Executive Director