Polk County Phosphate Mines - Manomet
Polk County Phosphate Mines
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Description: Polk County is located in interior central Florida between Tampa and Orlando. The active Polk Phosphate Mines are clay settling pits and reclaimed areas of southwestern Polk County. Five mining companies operate in the area. Phosphate mines are temporary in nature and locations change from year to year. Because of the nature of the mining operation, most of the pits that received heavy shorebird use are converted over time into thick stands of cattails or dry, bare fields, which receive less shorebird use. New pits are created each season and provide suitable habitat for enormous numbers of shorebirds for several years. Many impoundments containing approximately five to six square miles of water are in various stages of vegetative growth, which ranges from mudflats to cattails.
All mines are on private property. Permission must be obtained from the owner before entry. Chuck Geanangel had permits to enter some of these properties from IMC Global phosphate company, recently absorbed by Cargill; the negotiation of renewed access with Mosaic company is underway. The phosphate mines he monitors are located west of SR 17 and south of SR 60 all in Polk County, and the centralized location is the town of Bradley Junction.
Mr. Geanangel and Pete Timmer have monitored the area for 25 years, and more recently have been entering the counts into a database. The most numerous species for spring migration of 1995-2002 based on maximum counts from their surveys are: SEPL (115), KILL (45), GRYE (15), LEYE (1300), SPSA (5), SESA (14,525), LESA (3000), DUNL (21), SBDO (145). The most numerous species for fall migration of 1995-2002 based on maximum counts from their surveys are: SEPL (23), KILL (75), GRYE (10), LEYE (155), SOSA (1), SPSA (3), SESA (1500), LESA (5600), WILL (2) and SBDO (75).
Survey Method: Surveys are best conducted by vehicle on dike roads at stationary points with spotting scope early in the day. The roads are in rough condition and require a four-wheel drive vehicle. Note that the roads change as the location of the mines change. Visibility is excellent if little vegetation is present in the impoundments.
Selection Bias: Shorebirds may still be using impoundments that become obscured by tall, emergent vegetation and, in that case, are not visible from points along the road. If a long term trend in shorebird use exists in non-surveyable areas, a pilot study will be needed to determine the extent to which visibility problems are creating selection bias.
Measurement error: This is possible due to changes in land ownership and vegetation growth.
Measurement bias: This site consists entirely of private ownerships, which change frequently as mines are sold to other companies or developments. Access to certain areas may be forestalled and thus result in bias over time. Additionally, vantage points for counting shorebirds may have to be adjusted between surveys as viewing conditions change in response to vegetation growth.
To determine the extent of such bias, changes in ownership and obscuring vegetation from year to year should be documented.
Pilot Studies: A survey of the whole area, or the areas that are accessible, is necessary each year to determine current Type 1 habitat due to dramatically changing habitat conditions.
Local Contacts: Chuck Geanangel and Pete Timmer, Lake Region Audubon Society
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