Golden Eagles of the Milton Ranch and Vicinity
Summary Compiled by Beth Madden, April 2015
Golden Eagles breed throughout the prairies of central Montana, nesting and raising young where both nesting substrate (cliffs or trees) and adequate prey are available. In the prairies, suitable cliffs or trees for nesting are not always available, and can be a limiting factor for breeding golden eagles. The Big Wall cliff formation on the Milton Ranch provides high quality nesting habitat, while the nearby colonies of prairie dogs and local populations of jackrabbits and other wildlife provide the prey base necessary for productive golden eagles’ territories. Along with relatively limited human activity in the area, these raptor amenities all equal a winning combination for golden eagles.
The ranch has been included in several golden eagle studies in the past 15 years. A study of golden eagle mortality along power lines in the Roundup-Melstone oil fields during 1996-2001 found 198 golden eagle carcasses with cause of death attributed to electrocution (Schomburg et al. 2003). An additional 21 golden eagle mortalities were attributed to mid-span wire collisions. Northwestern Energy funded this study with the goal of identifying offending power poles for retrofitting, and identifying other high-risk poles. After this alarming number of eagle mortalities was documented, NorthWestern Energy aggressively retrofitted poles (e.g., applied Kaddis guards to insulators and wires, changed cross arms, shielded transformers), and the reported number of mortalities was subsequently markedly reduced. Schomburg’s thesis is available online. Use the link below.
Coincident with this electrocution study, a survey of golden
eagle nesting distribution, density, and productivity was conducted in the same
Roundup study area during 1999-2003 (Harmata and Flath 2003). Area surveyed included primarily northeastern
Musselshell and western Rosebud Counties but included small southern portions
of Petroleum and Garfield Counties. An
average of 26 nests were checked per year within a 1,600 sq. km area, of which
an average of 16 were occupied, producing an average of 17 eaglets per year
from 12 successful nests. Several of the
nests were located on the Milton Ranch.
In 2010 and 2011, Harmata re-surveyed nesting golden eagles in this same study area, as part of a range-wide population assessment funded by the U.S. Fish and Wildlife Service. Although occupancy of golden eagle territories was similar to the previous results a decade earlier, the percent of eagle pairs successfully fledging young was down markedly. Prairie golden eagle populations are thought to be somewhat cyclic in nature, and additionally, weather conditions in the Roundup area were notably extreme during summer 2011 (heavy rains). This population monitoring was not funded after 2012, so whether the observed productivity decrease was part of a temporary/cyclic decline or a more long-term trend is not known.
Milton ranch golden eagles were included in another research project in 2013. The non-profit research institute Craighead Beringia South conducted a study in eastern Montana to determine the distribution, abundance, and habitat use of sub-adult Golden Eagles to aid in the long-term conservation of this species (Bedrosian et al 2013). They are investigating annual movements of eagles and how they utilize the landscape, particularly during the winter. As part of this study, the research team tagged a nestling on the Milton ranch in summer 2013 with a satellite-tracking transmitter that is allowing them to follow the eagle for several years. Climbers descended from the top of the Big Wall into the nest and collected the nestling eagle, affixed the transmitter, and returned the youngster to the nest (Figures A and B).
In 2010 and 2011, Harmata re-surveyed nesting golden eagles in this same study area, as part of a range-wide population assessment funded by the U.S. Fish and Wildlife Service. Although occupancy of golden eagle territories was similar to the previous results a decade earlier, the percent of eagle pairs successfully fledging young was down markedly. Prairie golden eagle populations are thought to be somewhat cyclic in nature, and additionally, weather conditions in the Roundup area were notably extreme during summer 2011 (heavy rains). This population monitoring was not funded after 2012, so whether the observed productivity decrease was part of a temporary/cyclic decline or a more long-term trend is not known.
Milton ranch golden eagles were included in another research project in 2013. The non-profit research institute Craighead Beringia South conducted a study in eastern Montana to determine the distribution, abundance, and habitat use of sub-adult Golden Eagles to aid in the long-term conservation of this species (Bedrosian et al 2013). They are investigating annual movements of eagles and how they utilize the landscape, particularly during the winter. As part of this study, the research team tagged a nestling on the Milton ranch in summer 2013 with a satellite-tracking transmitter that is allowing them to follow the eagle for several years. Climbers descended from the top of the Big Wall into the nest and collected the nestling eagle, affixed the transmitter, and returned the youngster to the nest (Figures A and B).
Figure A: Collecting Nestling Golden Eagles
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Figure B: Transmitter
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Similar to many of the eaglets from eastern Montana, the
Milton Ranch eagle exhibited an easterly dispersal movement into the Dakotas
(Fig C Map). Data collected from this
bird over the next few years will help determine areas of conservation priority
for eagles in Montana. Use the link below.
Figure C
Healthy Golden Eagle populations in Montana rely on the
maintenance of large tracts of native prairie and shrub-steppe habitats (and
their associated prey populations). The management
of the Milton Ranch for cattle production and sustainable rangelands is highly
compatible with the needs of its resident golden eagles, particularly if
continued care is given to a tolerance for existing prairie dog colonies. The use of non-lead ammunition when managing
prairie dogs, and during hunting of other wildlife on the ranch is an important
consideration for preventing lead poisoning, a common cause of golden eagle
mortality.
The interagency Montana Golden Eagle Working Group was convened in 2010 to address concerns between golden eagle management and growing land use changes in the state. For information and the Draft Montana Golden Eagle Monitoring Strategy use the link below.
The interagency Montana Golden Eagle Working Group was convened in 2010 to address concerns between golden eagle management and growing land use changes in the state. For information and the Draft Montana Golden Eagle Monitoring Strategy use the link below.
BEDROSIAN, B., V. SLABE,R. CRANDALL, AND S.
WILSON. 2013. Golden Eagle Seasonal Abundance and Distribution in BCR 17
(eastern Montana and western Dakotas) Craighead Beringia South, 2013 Year-End
Report. December 2013. 10 pp.
HARMATA. A.R., E. MADDEN, AND D. FLATH. 2012. Status of nesting Golden Eagles in southwestern & central Montana, 2010-2012. Unpubl. Rept., Prepared for Nongame Migratory Bird Section, U.S. Fish & Wildlife Service, Reg. 6, Denver, Colorado, USA. 17 pp.
SCHOMBURG, J. W. Development and evaluation of predictive models for managing Golden Eagle electrocutions. 2003. M.S. thesis, Montana State University, Bozeman, MT U.S.A.
HARMATA. A.R., E. MADDEN, AND D. FLATH. 2012. Status of nesting Golden Eagles in southwestern & central Montana, 2010-2012. Unpubl. Rept., Prepared for Nongame Migratory Bird Section, U.S. Fish & Wildlife Service, Reg. 6, Denver, Colorado, USA. 17 pp.
SCHOMBURG, J. W. Development and evaluation of predictive models for managing Golden Eagle electrocutions. 2003. M.S. thesis, Montana State University, Bozeman, MT U.S.A.