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    Mottled duck closeup

    Mottled ducks
    Andy Reago & Chrissy McClarren via Flickr CC 2.0,

Using light-level geolocators to measure breeding propensity of mottled ducks in the Western Gulf Coast

Formal Title: Using light-level geolocators to measure breeding propensity of mottled ducks in the Western Gulf Coast

Research Focus:

Conservation & Management Challenges:

The Western Gulf Coast (WGC) is home to approximately 90% of the worldwide population of mottled ducks (Anas fulvigula), a non-migratory species that must satisfy its annual cycle needs within a small geographic range. Available population survey data suggest the WGC mottled duck population has experienced a long-term steep decline in Texas, is stable or slightly increasing in Louisiana, and is stable to declining across the entire WGC range. Because of its population status and reliance on a restricted geography, the mottled duck has been identified as a focal species for the U.S. Fish and Wildlife Service and Gulf Coast Prairie Landscape Conservation Cooperative, a priority species in the Texas and Louisiana Comprehensive Wildlife Conservation Plans, and the subject of targeted conservation efforts by other regional conservation partnerships (e.g., Gulf Coast Joint Venture). Conversion and degradation of wetland and upland habitats are believed largely responsible for historical declines in mottled duck abundance; hence, habitat conservation activities that have greatest impacts on influencing vital rates are priority strategies for Gulf Coast conservation partners. 

Research Overview:

Of the vital rates that determine recruitment, breeding propensity (i.e., the proportion of females that lay at least one egg) and nest success appear to have the greatest influence, but breeding propensity remains poorly studied. The few studies that have been conducted reveal it to be highly variable among years (15–77%), likely in response to environmental conditions (e.g., precipitation and wetland availability), and lower than estimates from other dabbling ducks. Thus, quantifying breeding propensity across the mottled duck range in the WGC and identifying factors responsible for its variation remain high priorities for future investigation.  Breeding propensity is also among the most difficult vital rates to study, as it typically relies on intensive data collection from individual birds.  However, recently light-level geolocators have revealed both regional movements of hen canvasbacks as well as their nesting activities, as evidenced by regular patterns of extended darkness during the day caused by the geolocator being obscured from sunlight during egg laying and incubation. (Light-level geolocators are devices that record data on the duration and timing of daylight as a means of calculating a geographic position.)

Geolocators provide an exciting new opportunity to study mottled duck breeding propensity using minimally invasive methods, while potentially uncovering patterns of regional movement. Moreover, certain geolocators are manufactured to incorporate salinity and temperature sensors, which could provide additional information on mottled duck use of different marsh vegetation types through space and time. This study will deploy 240 geolocators on female mottled ducks captured during banding operations in late summer in coastal Louisiana and Texas as a pilot study of this method to:

  • Measure geolocator recovery rates from hunter harvest
  • Measure geolocator recovery rates from subsequent year banding operations
  • Evaluate the effectiveness of geolocators for identifying mottled duck breeding propensity and movements within the Gulf Coast environment (i.e., do they effectively record light-level data, or are there physical challenges within this environment)
  • Provide insight on the potential feasibility of a longer duration study 



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