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 data suggest the WGC mottled duck population has experienced a slight to moderate decline across its range since 1985 (Gulf Coast Joint Venture [GCJV] Mottled Duck Working Group, Unpublished report). 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, a priority species in Texas and Louisiana Comprehensive Wildlife Conservation Plans, and the subject of targeted conservation efforts by other regional conservation partnerships (e.g., GCJV).
The GCJV Mottled Duck Conservation Plan (Wilson 2007) was developed to provide objective guidance on conservation strategies and research needs for WGC mottled ducks. Recent scientific investigations have bolstered our understanding of mottled duck ecology and enabled progress in identifying vital rates responsible for driving population growth (Johnson 2009, Rigby and Haukos 2014). While our understanding of annual and seasonal survival has improved in recent years (Wehland 2012, Haukos 2015), breeding propensity remains poorly studied. Breeding propensity is among the most difficult vital rates to study, as it typically relies on intensive data collection from individual birds.
Geolocators provide an exciting new opportunity to study mottled duck breeding propensity using minimally invasive methods, while potentially uncovering patterns of regional movement. This project was a 2.5-year pilot study to investigate the feasibility of using geolocators to measure breeding propensity of mottled ducks in the WGC. While not a primary objective, the potential exists to also document large-scale longitudinal movements of WGC mottled ducks. We deployed 240 geolocators on female mottled ducks captured during banding operations in late summer in coastal Louisiana and Texas. Specific objectives of this pilot study were 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 their physical challenges within this environment)
- Provide insight on the potential feasibility of a longer duration study