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12 GREAT BLUE HERON of chicks fledged per successful nest /mean dutch size) is 62.5% (n = 8 studies, Florida to Alberta). LIFE SPAN AND SURVIVORSHIP Mortality estimates from band recovery data: first year 69.0 %, second year 36.3%, subsequent years 21.9% (Henny 1972). Varies regionally (Bayer 1981b). Oldest banded heron 23 yr (RWB). Herons banded on refuges in U.S. appeared to live longer than herons banded off refuges (Bayer 1981b). MORTALITY AND DISEASE Diseases and body parasites. Giardia found in adult male in New York (Georgi et al. 1986). Also carries the nematode Eustrongylides ignotus, which can kill herons (Locke 1961). Transmission of fish pathogenic viruses may occur via the Grey Heron (A. cinerea, Peters and Neukirch 1986). RANGE Initial dispersal from natal site. Little information. Band recoveries suggest that few yearlings return to natal areas (Henny 1972). Fidelity to breeding and winter home range. No information, but some adults hold feeding territories through winter Bayer 1978, Butler 1991). Figure 5. Median number of Great Blue Herons per region in Christmas Bird Counts reporting L 1 heron, winter 1991, U.S. and Canada. A. Poole, P. Stettenheim, and F. Gill, Editors The Birds of North America, No. 25, 1992 Dispersal from breeding site or colony. Disperse away from colonies after breeding (Gill and Mewaldt 1979, Pratt 1970, Butler 1991), along coast and up rivers in Texas (Telfair and Swepston 1987). Band recoveries suggest dispersal in all directions 2 to 3 months post - breeding, then southward movement in autumn; one banded juvenile from U.S. found in Belize (Henny 1972). Home range. Little known outside breeding season. Breeding adults range within about 30 km of colony, most much closer (Parris 1979, Butler 1991). POPULATION STATUS Estimates or counts of density. Coastal breeding populations of Great Blue Heron on U.S. East Coast, Gulf Coast, and Great Lakes show highest densities in Texas, Mississippi delta, w. Florida, and Chesapeake Bay (Spendelow and Patton 1988). Stable or increasing in Tennessee (since 1974; Fleming et al. 1984) and Illinois (since 1982; Kleen 1987), probably stable on coast of British Columbia (since 1982; Butler 1989) and n. Washington (Murphy 1988), but many colonies abandoned after a :few years. Increasing in Michigan (since early .1980s; W. C. Scharf, unpubl. data) and probably in Louisiana (5 censuses over 37 yr; Ogden 1978). In New York, increased 1952 to 1962 (Bull 1964) and since 1962 (Andrle 1988). Decreased after dams built on Colorado River (Rosenberg et al. 1991), probably declined in Iowa (Dinsmore et a1.1984) and in Illinois (Robbins et al. 1986). Great White Heron have rebounded since the 1930s and may be stable or still increasing (Ogden 1978).Figure 5 shows winter density. Population numbers. About 32% of all breeding Great Blue Herons (36,248 birds) along coast from Texas to Maine and in U.S. Great Lakes were on Atlantic Coast, < 10% in Florida, 40% in Louisiana and Texas, and 18% along the Great Lakes (Spendelow and Patton 1988). About 12,211 herodias nests in 248 colonies and 34 isolates in Ontario in early 1980s (Peck and James 1983), minimum of 13,022 pairs in Ontario in 1980 to 1981 (Dunn et al. 1985). On Great Lakes in Michigan, 1,064 nests tallied in 32 colonies in 1987 (Scharf, unpubl. data). About 5,340 nesting pairs in 35 colonies in Illinois (IQeen 1987). Between 1967 to 1972, 4,000 nests counted in 56 colonies in Canadian Prairies (Vermeer 1973). Little information elsewhere in heron's range. About 1,500 individual Great White Herons estimated for Florida Bay in 1985 (Powell et a1.1989).