The mottled duck breeding population survey has been conducted every March since 1985 within a core area of their range in Florida.  The purpose of this survey is to provide a density estimate, and for this estimate to serve as an index to population status.  However, because we do not survey the entire mottled duck range, there is some question whether this density estimate is a good population index because of possible immigration and emigration of birds into and out of the surveyed area among years in response to various factors such as changing water availability.  In 2000, we began a redesign of the survey to address this and other concerns (e.g, annual changes in visibility bias), and to collect data that will allow us to calculate a statewide mottled duck population estimate.  As part of the redesign, we incorporated several changes and enhancements including expanding the surveyed area, the use of a moving map system for navigation and data entry, adding a second helicopter and crew, and adjustments of data analysis.  To allow direct comparison to previous survey results, data from new transects were not used in this analysis.  A separate report will be prepared specifically covering the survey redesign and analysis of the new data.       

We conducted a line-transect survey March 1-10, 2000 to determine breeding density estimates of mottled ducks within a 13,383 km² portion of their range.  Pilots and observers recorded a total of 369 ducks (173 and 196 respectively) from 101 observations (single, pairs, and groups).  Observers saw 66% of all observations and pairs represented 65% of observations.  The average group size was 2.93 ducks.  Program DISTANCE was used to estimate a mottled duck density of 0.85 birds/km² with a population estimate of 11,376 mottled ducks within the surveyed area.  Habitat was dry, relative to past years, with only 72% of the emergent wetlands holding water. The results of the survey suggest that the mottled duck population within the surveyed area did not changed significantly from 1999.   

We collected 1111 data points on habitat types.  Mottled ducks were observed using more emergent marshes and open water habitats this year similar to 1997 when habitat conditions also were very dry.  Wetland habitats comprised an estimated 23% of the surveyed area versus 24% in 1999, and 72% of emergent wetlands contained water compared to 75% in 1999.  Upland habitats were again nearly dry this year (0.7% wet) when compared to 1998 (15% wet). 

Data from 1985-2000 indicate that during years with wet habitat conditions mottled ducks tend to be more evenly distributed over the surveyed area than during dry years.  When relatively dry conditions prevail (2000, 1999, 1997, and 1990), mottled ducks tend to be grouped together on or near more permanent water bodies (lakes and rivers).   

Figure 1.  Range of Florida's mottled ducks, core breeding area is darker area.  

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