Florida Mottled Duck Research Project - Methods

Objectives of DU's Florida Mottled Duck Research Project

Objective 1: Identify habitat use patterns on a seasonal and annual basis.

Radio telemetry will be used to monitor habitat use by female mottled ducks throughout their annual cycle. Each year during August and September in and around the Everglades Agricultural Area (EAA), Lake Okeechobee, the lower Kissimmee River Basin (KRB), and the suburban areas to the east, a total of 100 adult female mottled ducks will be captured using night-lighting techniques. After capture, birds will be taken to a processing site where morphological measurements will be taken, standard U.S. Fish and Wildlife Service leg bands will be affixed, and a VHF radio transmitter implanted abdominally. The radios will have an expected life of 13 months. After a recovery and observation period (12-18 hours), birds will be released at their capture site.

Immediately after release, birds will be monitored daily from trucks equipped with dual 4-element null-peak detection systems and at least weekly from an aircraft (Cessna or similar) equipped with two 4-element Yagi antennas. For as many locations as possible, the habitat being used will be determined and recorded, that is, a visual will be made of the radio-marked bird. Examples of habitats to be categorized include 1) natural marsh, 2) intensively managed marsh, 3) flooded pasture, 4) flooded EAA field, 5) prairie pond, 6) flooded prairie, 7) flooded cattle pond, 8) flooded citrus impoundment, 9) flooded management area impoundment, 10) flooded ditch, 11) flooded canal 12) flooded rice, 13) other flooded agriculture, 14) upland habitat, 15) everglades marsh, 16) river, 17) lake, 18) lake Okeechobee marsh, or 19) AHRES project wetland. Additional categories will be added as necessary to describe habitats used by radio-marked birds. These data will be analyzed to determine which habitats are used most often (based on the proportion of individual bird's locations that occur within the different habitats), and if habitat use patterns vary by period of the annual cycle, year, and bird catch location. Habitat use patterns of birds from this study also will be compared to birds tracked during an earlier study of mottled duck habitat use in the SJRB.

Objective 2: Describe/characterize, in detail, wetlands used heavily by dabbling ducks.

Radio-marked mottled ducks will be used to obtain an unbiased sample of wetlands/wetland complexes being used heavily by dabbling ducks throughout the year. These wetland areas will be characterized by collecting data on average depth, mean percent vegetative cover, predominant vegetation types, bottom make-up, water level variability, water chemistry, distance to nearest human activity, distance to other water source, as well as other parameters. These data will be used to build a profiles for highly productive wetlands.

Objective 3: Compare heavily used wetlands to random and AHRES wetlands to Identify wetland characteristics that influence use by dabbling ducks.

Data collected to meet objective two will be compared to similar data collected from random wetlands and wetlands restored by the AHRES. These comparisons will be made to elucidate which parameters influence use of wetlands by mottled ducks and other dabbling ducks. Moreover, these comparisons will us to evaluate the effectiveness of current AHRES wetland enhancement practices with regard to their creating preferred habitat for dabbling ducks.

Objective 4: Determine if surface water availability influences habitat use, movement, and survival patterns of mottled ducks and habitat use patterns of other dabbling ducks.

Fifteen to 20 water bodies (5 each with hydrologic permanency classes of temporary, semi-permanent, and permanent) will be randomly selected from those within the study area. These wetlands will be monitored on a weekly basis to determine if surface water is present and to what extent the area of surface water has changed from the previous week. These data will be included as a predictor in the analysis of habitat use, movement, and survival data to determine if surface water availability influences these aspects of mottled duck and dabbling duck ecology.

Objective 5: Calculate annual and season-specific survival rates and determine if female survival differs among years, periods of the annual cycle and catch location.

Radios will be equipped with a 12-hour mortality sensor. Females will be monitored daily throughout the annual cycle to determine their status (i.e., dead or alive). Proportional hazards regression will be used to test for differences in survival in relation to period of annual cycle, year, and catch location.

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Objective 6: Identify causes of female mortality and determine if they differ by year, periods of the annual cycle and catch location.

When a mortality is indicated, efforts will be made to determine the cause. When possible, carcass and radio condition will be used to assess the cause of mortalities. If the cause of death is not obvious upon examination of the carcass, the carcass will be sent to the Southeast Cooperative Wildlife Disease Study (University of Georgia at Athens) for necropsy.

Objective 7: Determine relative importance of hunting mortality to annual survival of mottled ducks.

All sources of mortality identified during the study will be analyzed to determine the relative importance of each.

Objective 8: Determine home ranges of females and the influence of period of the annual cycle, year and catch location on movements.

Using ground and aerial techniques, point locations of females will be obtained at least twice per week throughout the annual cycle. The annual cycle will be divided into 4 periods (1) reproductive, (2) post-reproductive, (3) hunting season, and (4) late winter. On the ground, point locations will be estimated using Lenth's maximum-likelihood estimator (MLE; White and Garrott 1990). MLEs will be calculated on site from at least 3 azimuths on a notebook computer. From the air, point locations will be determined using a GPS.

Point locations will be used to determine if movement patterns vary among years and between catch locations.

Objective 9: Describe nesting and brood-rearing sites and identify characteristics that influence nest fate and female survival.

Beginning in February, monitoring will focus on the identification of nest sites and brood-rearing areas. At the time each nest is located, latitude and longitude of the site will be determined using a Global Positioning System (GPS). Also, nest initiation and hatch date will be estimated by candling eggs, and the number of eggs in the clutch will be recorded. If no eggs are present, another visit will be made several days later to determine the status of the nest, and if active, estimate hatch date. For each nest site, the major plant species immediately surrounding the nest bowl, density of nesting cover at the nest bowl and intervals of 1, 5, 10, and 20 meters from the nest bowl in the four cardinal directions will be recorded. These measurements also will be recorded at 5 random locations in close proximity to the nest. In addition, predominant land use within 100 meters and 1 km, distance to nearest water body, distance to brood-rearing area for successful nests, and distance to nearest human dwelling and paved road will be recorded.

Density of nesting cover at and near the nest bowl will be determined using a robel pole (Robel et al. 1970). Predominant land use within 100 meters of the nest site will be determined in the field and classified as (1) cattle production, (2) milk production, (3) citrus production, (4) sugarcane production, (5) rice production, (6) other agriculture, (7) transportation corridor, (8) urban development, (9) wildlife management, or (10) other. The predominant land use within 1 km will be determined using current Geographical Information System (GIS) data layers in the lab, and will be categorized as with the 100-meter data. Distance to nearest water body, brood-rearing area, and human dwelling, and paved road also will be determined on-site or from GIS data.

To determine characteristics of nest sites that influence female survival and whether a nest is successful, proportional hazards regression will be used to test for differences in nest fate and female survival in relation to nest site characters. To determine if females are selecting nest sites based on vegetation height and density, paired t-tests will be used to compare data taken at the nest bowl to those taken at the 5 random locations around the nest site. Logistic regression models will be developed to investigate predictive abilities using aforementioned parameters.

Brood-rearing habitats will be identified by monitoring wetland use of brood-leading, radio-marked females. Brood-rearing habitats will be characterized by recording (1) distance from nest site, (2) size of wetland, (3) predominant vegetative types, (4) percent cover of water and emergent vegetation, (5) permanency class (Stewart and Kantrud 1971) of wetland, (6) distance of wetland from nearest human dwelling and paved road, (7) distance to another wetland, and (8) predominant land use within 1 km of the area. These data will be obtained using a combination of GIS data and data collected at each site.

To determine characteristics of brood-rearing areas that influence female survival, proportional hazards regression will be used to test for differences in survival in relation to the aforementioned characters.

Objective 10: Determine if nest and female success differs between years and catch location.

All nests located as described in Objective 5, and believed still to be active based on female behavior, will be revisited shortly after the estimated hatch date to determine fate. Proportional hazards regression will be used to test for differences in nest and female success in relation to year and catch location.