Southern Bald Eagle Population

Explanation of Indicator
Florida supports more breeding southern bald eagles (Haliaeetus leucocephalus leucocephalus) than any other state in the U.S.¹ These eagles are “dependent upon mature trees in which to nest and roost and perch.”² In addition, because eagles are at the top of the food chain and therefore susceptible to the bioaccumulation of pollutants, these animals will be among the first to respond to the changes that result from development of Florida’s wild lands.³ The southern bald eagle is therefore important as an indicator of the state’s coastal environmental health and the declining abundance of coastal habitat.

Little is known about post-fledging survival of young eagles and post-nesting behavior of adult eagles. The survey effort focuses on nesting eagle populations. An active territory is defined as an area where there has been a nest and adult eagles are in attendance (either in a tree or simply within the territory); within a given territory, only one nest is active at a time. A successful nest is one which has produced at least one chick that has survived to fledging. Young are defined as chicks that are big enough to survive and fledge and fly off, not as chicks that have merely hatched.⁴

Data Characteristics
SOURCE
Annual reports are maintained by the Florida Game and Fresh Water Fish Commission, Bureau of Wildlife Research. They are available from Dr. Brad Gruver at 620 South Meridian Street, Tallahassee, Florida 32399-1600, or at (904) 488-3831. The raw data can be obtained from Steve Nesbitt at the Florida Game and Fresh Water Fish Commission, Wildlife Research Laboratory, 4005 South Main Street, Gainesville, Florida 32601, or at (904) 955-2230.

ACQUISITION
Data can be obtained in hard copy or on floppy disk in dBase format at no charge.

COLLECTION
The Florida Game and Fresh Water Fish Commission has been collecting southern bald eagle data for the state since 1973. Known territories are surveyed at least twice each nesting season using fixed-wing aircraft. Data are displayed for each Florida coun ty that has ever contained a known bald eagle territory. Nesting population figures for each year represent periods that span from July 1 of one year to June 30 of the next year.

Data Limitations
The data are consistently collected over time, at intervals specific to this species’ breeding behavior, and should provide an excellent measure of the health of Florida’s coastal environment. However, since data are collected via aerial survey, the figures reflect the inherent limitations of all aerial surveys as well as occasional species-specific responses to the presence of aircraft (e.g., some eagles assume an incubation posture in response to the presence of the survey plane). In addition, since the methodology employed involves the search of known eagle territories (i.e., it is not a systematic statewide search), the data represent a conservative estimate of nesting bald eagle populations.⁵

Data Analysis
Florida’s southern bald eagle population levels have increased to the point where, in August 1995, this sub-species was re-classified as threatened (as opposed to the former classification of endangered) by the federal government. The eagles’ reproducti ve productivity, however, has been consistently higher in Florida’s non-coastal counties than in the coastal areas; from 1988 to 1995, the average number of active territories was 27% higher in non-coastal counties and the average number of successful nes ts was 35% higher than in the coastal counties. The average number of young per successful nest has remained close to 1.5 for both coastal and non-coastal counties. Between 1988 and 1995, the number of active bald eagle territories in the coastal counti es increased 96% and the number of successful nests increased 106%. Escambia, Nassau and Walton counties are the only coastal counties in Florida that have never documented the existence of an active bald eagle nest.

Southern Bald Eagle Reproductive Productivity in Florida

	Number of 	  		      Number of 		    Young per
    Active Territories		           Successful Nests	         Successful Nest

Year*	 Coastal    Non-    State      Coastal	  Non-	 State	   Coastal     Non	State
		  Coastal   Total	        Coastal	 Total		     Coastal	Total
1988	   190	    249	     439	 132	  174	  306	    1.46      1.67	1.58
1989	   231	    248	     479	 154	  186	  340	    1.42      1.56	1.50
1990	   230	    306	     536	 156	  210	  366	    1.61      1.59	1.60
1991	   254	    347	     601	 159	  229	  388	    1.49      1.55	1.52
1992	   275	    377	     652	 180	  288	  468	    1.60      1.53	1.56
1993	   300	    368	     668	 191	  257	  448	    1.46      1.55	1.51
1994	   347	    432	     779	 260	  331	  591	    1.63      1.59	1.61
1995	   373	    458	     831	 272	  349	  621	    1.59      1.62	1.61

¹Nesbitt, Stephen A. Personal Communication. Florida Game and Fresh Water Fish Commission. Gainesville, FL: September, 1995.
²ibid.
³Florida Game and Fresh Water Fish Commission. Unpublished Annual Report. 1 July 1994 - 30 June 1995.
⁴Nesbitt, Stephen A. Personal Communication. September, 1995.
⁵Florida Game and Fresh Water Fish Commission. Unpublished Annual Report. 1 July 1987 - 30 June 1988.
⁶Nesbitt, Stephen A. Personal Communication. September, 1995.
⁷ibid.