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Ramona Grassland Raptor Monitoring
A 3-year raptor study was initiated by the County of San Diego Department of Parks and Recreation to collect baseline information on eagle and other raptor activity at the Ramona Grasslands Preserve (preserve). The purpose of this study is to conduct an eagle/raptor foraging study for the Preserve and golden eagle nest monitoring in Bandy Canyon. Baseline information will provide a better understanding of species abundance and distribution within the Preserve, and be useful in informing management decisions (e.g., trail feasibility and alignments, seasonal closures) and will provide a reference point for any future studies or assessments pertaining to public use.
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| File name | Lead Author | Year | Type |
|---|---|---|---|
| Appendices- Ramona Grassland Project Raptor Survey 2014 Summary | 2014 | report | |
| Ramona Grasslands Preserves Raptor Surveys Summary Report | 2014 | report |
Distribution is entirely within North America, including Canada, Alaska, and northwest Mexico [1].
Annual winter visitor to Lake Henshaw, Cuyamaca, Corte Madera, and Moreno [2].
BEPA/ FP [3].
Prefers habitats with low human disturbance, but will tolerate human activity when feeding availability is high [4, 8]. Nests are generally built on cliffs, the tops of very tall conifer or deciduous trees, and close by fishable waters, i.e. lakes, rivers, reservoirs, marshes, or coastal waters. Nesting habitats are generally located in dense forested areas adjacent to large bodies of water [1]. Winters in temperate zones and dry climates in western valleys [5].
Generally divided into two subspecies, H.l. alascanus, which is the larger northern species, and H.l. leucocephalus, the smaller southern species [6, 7].
Year-long, diurnal activity. Breeds from late January through August, with peak occurrences in March through July [9]. In winter eagles migrate to areas with large trees, easily accessible branches, and ice-free fishable waters away from human activity.
Known to build some of the largest nest, generally 5-6 feet in diameter and 2-4 feet tall [11]. Both sexes will build the nest, which can take up to 3 months to construct and will typically be used every year. They generally use tall, sturdy conifers or deciduous in southern regions that overlook the forest canopy, enabling them easy flight access and good visibility [11]. In areas lacking trees they will use ground sites or cliff faces. Nesting eagles clutch 1-3 eggs, with one brood per year. Incubation can last approximately 35 days and nest 60-100 days. Bald eagles become fully feathered at 10 weeks and will often be mistaken for golden eagles as their feathers are mostly dark brown. Once they mature and reach adult plumage, within 4-5 years they develop their iconic bald eagle characteristics. Can live 20-30 years in the wild and even longer in captivity [5].
Bald eagles eat fish, reptiles, birds, mammals, invertebrates, carrion, and may even eat garbage [12, 13].
Humans pose the greatest threat to bald eagles through habitat destruction, pesticide use, and poaching [14, 15].
[1] Buehler, D. A. 2000. Bald Eagle (Haliaeetus leucocephalus). In The Birds of North America, No. 564 (A. Poole and F. Gill, eds.). The Birds of North America Online, Ithaca, New York.
[2] Unitt, P. 1984. The birds of San Diego County. San Diego Soc. Nat. Hist. Mem. no. 13:1-276.
[3] California Department of Fish and Wildlife, Natural Diversity Database. July 2017. Special Animals List. Periodic publication. 51 pp.
[4] Livingston, S.A., C.S. Todd, W.B. Krohn and R.B. Owen, Jr. 1990. Habitat models for nesting bald eagles in Maine. J. Wildl. Manage. 54(4):644-653.
[5] Bailey, R. G. 1989. Explanatory supplement to ecoregions map of the continents. Environment. Conserve. no. 16:307-309.
[6] American Ornithologists' Union. 2004. The A.O.U. check-list of North American birds, 7th edition, [Online]. American Ornithologists Union. Available: http://www.aou.org/checklist/index.php3
[7] Johnsgard, Paul A. 1990. Hawks, eagles, and falcons. Washington, DC: Smithsonian Institution Press. 403 p.
[8]
[9] Steenhof, K. 1976. The ecology of wintering Bald Eagles in southeastern South Dakota. Master's Thesis, Univ. of Missouri, Columbia.
[10] Southern, W.E. 1963. Winter populations, behavior, and seasonal dispersal of bald eagles in northwestern Illinois. Wilson Bull. 75(1):42-55.
[11] Buehler, David A.; Fraser, James D.; Seegar, Janis K. D.; [and others]. 1991. Survival rates and population dynamics of bald eagles on Chesapeake Bay. Journal of Wildland Management. 55(4): 608-613.
[12]
[13] Herrick, F. H. 1932. Daily life of the American eagle: early phase. Auk no. 49:307-323.
[14] Stalmaster, M. V. 1987. The Bald Eagle. New York: Universe Books.
[15] Sherrod, S. K., C. M. White and F. S. L. Williamson. 1976. Biology of the Bald Eagle on Amchitka Island, Alaska. Living Bird no. 15:145-182.
[16] Nisbet, I. C. T. 1989a. "Organochlorines, reproductive impairment, and declines in Bald Eagle Haliaeetus leucocephalus populations: mechanisms and dose relationships." In Raptors in the modern world., edited by B. U. Meyburg and R. D. Chancellor, 483-489. Berlin, Germany: World Working Group for Birds of Prey.
[17] Wiemeyer, S. N., C. M. Burick and C. J. Stafford. 1993. Environmental contaminants in Bald Eagle eggs-1980-1984-and further interpretations of relationships to productivity and shell thickness. 24:213-227.