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Population Monitoring

Florida Fish and Wildlife Conservation Commission (FWC) biologists have conducted an aerial survey of Florida’s mottled ducks every March since 1985, to provide an estimate of the density of birds within a central area of their range.  The FWC uses this density estimate to monitor the status of the mottled duck population.  In 2003, the FWC began to redesign the survey to improve its efficiency and provide a more reliable density estimate, one that is representative of the entire mottled duck population. 

To obtain a more reliable density estimate the survey area was expanded to incorporate a much larger proportion of the mottled duck population and more diverse habitats including man-made wetlands that occur in urban/suburban areas.  FWC biologists felt it necessary to include urban/suburban habitats because a significant proportion of the mottled duck population inhabits these areas, and as urbanization continues, it will be critical to monitor developed areas to obtain the most accurate population data.  In order to sample the highly congested areas within cities and suburbs a new survey method was employed that involved hovering over sample points located within 200 meters of wetlands, and counting the number of mottled ducks visible from each point.  This differs from the old survey methods of flying along straight transect lines, which is impossible to do in urban areas, and counting ducks within a certain distance on either side of the line.

The primary evaluation of the new survey methods was completed in March 2006.  The new methods worked well and FWC biologists are contemplating using these methods and the expanded survey area in all future surveys,

From 1985-2006, density estimates for the central portion of the mottled duck’s range have varied.  However, there appears to be no trend to these estimates, indicating the population in this core area has been relatively stable over this period of time.

The 2007 survey was the fifth year we conducted the survey using point-transect methods and the first year we were able to cover the entire survey area (the shaded areas of Fig. 1).  The estimated mottled duck density for the survey area is 1.8 (CV = 22.8%) birds/km² of wetland habitat, which extrapolates to a breeding population size of 31,754 (SE = 7,244) birds.