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Movements, Habitat Use, Survival, and potential implications of Climate Change on Mottled Ducks (Anas fulvigula)
in the Texas Chenier Plain Region

Jena Moon, Ph.D. Student, Stephen F. Austin State University

Project Supervisors:
Dr. David Haukos
Dr. Warren Conway

U.S. Fish and Wildlife Service

Patrick Walther
Dr. Dan Collins

Jena Moon holding a female mottled duck outfitted with a satellite transmitter.

Location: Chenier Plain of the upper Texas and western Louisiana Gulf Coast

Completion: May 2014


(1) Determine movements of adult female mottled ducks during all major life stages, climatic events, high disturbance periods, and landscape habitat changes.
(2) Document course and fine scale habitat use during all major life stages.
(3) Model survival rates in relation to breeding periods, hunt periods, molting periods, and climatic events.
(4) Determine home range size for adult female mottled ducks.

Many studies and plans have outlined the importance of the Chenier Plain Region of the Western Gulf Coast (WGC) to resident mottled ducks (Anas fulvigula), including the Mottled Duck Conservation Plan and the Chenier Plain Initiative for the Gulf Coast Joint Venture. The Chenier Plain Region historically, and currently, has the greatest density of mottled ducks in the WGC Population. Loss and degradation of mottled duck coastal habitats is the leading cause for mottled duck decline in the Chenier Plain Region (Stutzenbaker 1988). Urbanization, erosion, subsidence, conversion to agriculture, saltwater intrusion, invasive plant and animal establishment, loss of natural disturbance, sea level rise, and heavy metal accumulation all have played a role in the decline of quantity and quality habitats available to mottled ducks (Stutzenbaker 1988, Wilson 2007). However, the over-riding limiting factor affecting the species recovery lies within altered hydrology of the Chenier Plain Region. The mottled duck (Anas fulgivula) has been established as an indicator species to coastal marsh health and function (Stutzenbaker 1988, USFWS 2011). Currently, biologists have a relatively poor understanding of mottled duck habitat use, regional movements, response to habitat management, and movements. This information is needed to assist in strategic habitat conservation planning and to inform conservation for the species.

We captured mottled ducks via night lighting from airboats during summer 2009, 2010, and 2011. Upon capture, we sorted mottled ducks based on sex, age, and mass. To each adult female >740 g, we fitted a Model 100 solar/satellite backpack PTT with a custom fitted Teflon ribbon harness. We attached satellite radio transmitters to 15, 30, and 45 adult female mottled ducks in 2009, 2010, and 2011, respectively. PTTs were deployed with a duty cycle of 10 hours active and 72 inactive. We used the Argos system to collect data on date, time, latitude, longitude, and location class of each tagged female. Mortalities were assessed through a series temperature and movement sensors in association with ARGOS collected data.

Factors limiting survival of WGC mottled ducks potentially include harvest, lead exposure, disturbance, habitat loss or degradation, predators, and variations in climate patterns (Stutzenbaker 1988, Wilson 2007). Several studies have attempted to measure annual and periodic survival rates of WGC mottled duck populations. Historical banding data from 1965-1971 suggested annual survival rates of mottled ducks at 57.5% (Stutzenbaker 1988). Wilson et al. (2003) estimated annual survival rates to be 55.9% for male and 50.2% for female mottled ducks in the WGC population. More recent studies have estimated breeding season survival rates range from 63.3%-87.2% on Anahuac National Wildlife Refuge. Preliminary analyses from a telemetry study conducted by the Gulf Coast Joint Venture estimated annual survival rates to be 41% for after hatch-year (AHY) females and 48% for hatch-year females in Texas and Louisiana (HY). Compared with common waterfowl species these estimates are low (Wilson 2007). Johnson (2009) also concluded that survival rates of mottled ducks estimated from band-recovery data were low compared to those of most dabbling ducks, and Florida populations of mottled ducks (Varner et al. 2014). We established the encounter interval for survival analyses as 1 week and the experimental unit for survival was each radio-tagged bird. We estimated cumulative weekly survival which allowed us to further define periods of relative high and low mortality, which will enabled us to compare our survival estimates to previous and ongoing studies.

We employed known fate modeling in program MARK to assess the influence of potential mortality factors affecting mottled duck survival. Models tested included the following predictors: (1) time, (2) hunting and non-hunting periods, (3) biological time periods; individual covariate of (4) mass at time of capture was also incorporated. We used adjusted Akaike's Information Criterion (AICc) scores and weights to rank and assess models. Analyses indicate that survival rates remain below average for mottled ducks (12-38% annual rate of survival), when compared with other waterfowl species inhabiting the Gulf Coast. Primary periods of mortality included all periods of hunting and the molt biological time period. Drought conditions during 2011 also had negative impacts on overall survival rates of transmittered females.

Conservation of quality coastal habitats remains a high priority to potentially offset current survival rates of mottled ducks. Because of recent tropical climatic events and continual saltwater intrusion, current estimates of habitat use and selection by mottled ducks are unavailable for Texas and Louisiana Gulf Coast. Previous studies of habitat use by mottled ducks focused on specific biological time periods, did not consider effects of numerous anthropogenic alterations in the region, and occurred prior to the recent tropical events that caused major alterations in mottled duck habitats within the Texas Chenier Plain Region. Mottled duck habitat use has been documented to be highly variable by past studies, with varied wetland types, land management practices and salinity regimes being documented (Stutzenbaker 1988). Managers need to have a better understanding of the role of habitat selection by mottled ducks to improve population management. We measured use and habitat selection based on habitat availability within the Texas Chenier Plain Region at fine, intermediate, and landscape scales. Our specific objectives include: 1) quantifying habitat use based on year and biological period (pairing, breeding, brood rearing, molt); 2) determining habitat selection for the Texas Chenier Plain Region; 3) comparing site- specific habitat metrics among locations across biological time periods; and 4) evaluating the effect of scale on habitat selection.

Habitat use was measured by taking values for land cover and salinity from within the buffered areas (250 m) surrounding used points. Habitat use data were analyzed using an analysis of variance to assess differences among marsh type for year, time of day, and month. Habitat selection analyses were completed using a generalized linear mixed modeling approach in R. Habitats considered locally available were limited to a 95% kernel density estimate for each individual, and landscape scale availability was merged home ranges for all individuals. Habitat use was closely tied to marsh type, with intermediate and brackish marsh being selected for the majority of locations (fresh marsh < 3%, intermediate marsh 29%, brackish marsh 46%, and 22% saline marsh. Mottled ducks also selected for grass dominated marshes with some use of emergent marsh. Freshwater habitats were available on the landscape; however, with drought conditions more freshwater wetlands were located farther inland than during normal or above average rainfall years. Habitat use was tied to salinity regime and water availability on the landscape with coastal marshes being selected for over adjacent ephemeral waters (e.g., stock tanks). Seasonal habitat selection varied based on average salinity and vegetative class within home ranges, with greatest sensitivity to salinity during breeding and brooding periods. Within season habitat use was extrapolated to identify potential high quality habitats based on local-scale selection patterns in the Texas Chenier Plain Region.

Habitat quality/quantity and disturbance were hypothesized to be important factors dictating mottled duck movements both spatially and temporally. Distance traveled, habitats used, and timing of movements by mottled ducks are widely unknown. Response to disturbance by mottled ducks inhabiting the upper Texas coast is also unknown. Because information on mottled duck movements is still widely unavailable, we documented weekly and seasonal movements of mottled ducks. In addition, we related variation in movement timing and distance with landscape habitat conditions (i.e., wetland availability), and disturbance. Specific study objectives were to 1) assess movement patterns among years, weeks, and biological time periods (fall, pairing, breeding, brood rearing, molt); 2) evaluate movements in relation to available habitat at the landscape level; 3) quantify movement patterns in association with high disturbance periods (e.g., periods of hunting); and 4) determine if changes in salinity regime or other habitat quality measure dictates movement patterns. To assess mottled duck movements, ArcGIS was employed to measure distances traveled weekly. Distances traveled were assessed using analysis of variance comparing among models containing independent variables of year, month, time of day, biological time period, season, and their respective interactions. Home range for each individual was also estimated and plotted using ArcGIS. Minimum convex polygons (95%) and kernel density estimators (50% and 90%) home ranges were also estimated. Analyses indicate that distances traveled by mottled ducks are short relative to other waterfowl <5,000 m on average. Movement occurrence, duration, and distance were linked to biological season, salinity regime, and habitat conditions on the landscape (i.e., available wetlands). Home ranges were small with an average size of 1516 ha and 6566 hectares for 50% and 95% KDE home ranges, respectively.

To project the potential implications of climate change to the WGC population of mottled ducks. Home ranges were then overlaid by the Sea Level Affecting Marshes Model (SLAMM; USFWS 2011b), which predicts availability of future habitat types based on predicted sea level rise. We compared composition of habitat types within home ranges of individual mottled ducks (i.e., 2005) to expected available habitat types in 2050 and 2100. Overall, proportion of habitat classes differed among years, and there are substantive changes in available habitat projected. Under current SLAMM predictions mottled ducks are poised to lose over one half of their preferred habitat type, which will likely result in further population declines for this species by the 22nd Century.

The culmination of this research was development of a population demography model that spans the WGC Population of mottled ducks. An important concern in most ecological fields is determining factors singularly, concomitant, or synergistically operating as limiting factors constraining populations of interest (Peterson et al. 1998). The development of sophisticated system dynamics modeling software, has facilitated the use of this approach in ecological modeling (Faust et al. 2003a). Through the use of STELLA 10.0.0 a seasonal conceptual demographic model was constructed and parameterized with much of the data currently available on mottled ducks. The model was then evaluated based on available demographic rates (including data collected from this study). Following model validation, the relative importance/relatedness of various vital rates to the total population of WGC mottled ducks was assessed, and population persistence rates were calculated using IUCN criteria. Model simulations indicate that the probability of persistence to 100 years was 46%, with an average λ = 0.383. Eighty of the 140 simulations reached quasi-extinction rates of > 2500 individuals, and 77% of simulations met some IUCN criteria for the species to be listed as threatened, endangered or critically endangered. The model was sensitive to variation in all breeding parameters, which can be influenced by quality habitat management practices. As future population projections for the species are not improving and substantial habitat restoration efforts are needed to sustain and improve production for mottled ducks within the WGC Population. The model presented herein, assumes constant habitat conditions across time and does not incorporate future degradation of habitats. There are many additional exogenous factors that are not included in this model that should provide additional concern for the persistence of the WGC mottled duck population (e.g., sea-level rise, further declines in rice farming, declines in water available for habitat management.


Jena Moon (Ph.D. 2014; advisor Conway/Haukos) Mottled Duck (Anas fulvigula) ecology in the Texas Chenier Plain Region. Ph.D. Dissertation, Stephen F. Austin State University.

Moon, J.A., D.A. Haukos, and W.C. Conway. 2015. Mottled duck (Anas fulvigula) movements in the Texas Chenier Plain Region. Journal of the Southeastern Association of Fish and Game Agencies 2:255-261.

Professional Presentations:
Moon, J., S. DeMaso, M. Brasher, W. Conway, and D. Haukos. 2016. A stochastic model to simulate mottled duck population dynamics. Annual Meeting of the Texas Chapter of The Wildlife Society, San Antonio, TX.

Moon, J. A., S. J. DeMaso, M. G. Brasher, W. C. Conway and D. A. Haukos. 2016. A Stochastic Model to Simulate Mottled Duck Population Dynamics. North American Duck Symposium, Annapolis, MD.

Moon, J. A., S. Lehnen, K. Metzger, S. Sesnie, D. A. Haukos, and W. C. Conway. 2016. Integrating Sea-Level Rise and Anthropogenic Change into Mottled Duck Conservation. North American Duck Symposium, Annapolis, MD. (Poster)

Moon, J., D. Haukos, W. Conway, and S. Lehnen. 2014. Habitat selection of adult female mottled ducks in the Texas Chenier Plain Region. Annual meeting of the Texas Chapter of The Wildlife Society, Austin, TX.

Moon, J.A., D.A. Haukos, and W.C. Conway. 2014. Habitat selection by mottled ducks on the upper Texas Gulf Coast. Mottled Duck Symposium, Annual Conference of the Southeastern Association of Fish and Wildlife Agencies, Destin, Florida.

Moon, J.A., D.A. Haukos, and W.C. Conway. 2014. Movements by mottled ducks on the upper Texas Gulf Coast. Mottled Duck Symposium, Annual Conference of the Southeastern Association of Fish and Wildlife Agencies, Destin, Florida.

Haukos, D.A., J. Moon, and W. Conway. 2013. Survival of Mottled Ducks in the Texas Chenier Plain Region. 6th North American Duck Symposium, Memphis, Tennessee.

Moon, J.A., D.A. Haukos, W. Conway, and P. Walther. 2013. Movements of mottled ducks in the Texas Chenier Plain Region. 6th North American Duck Symposium, Memphis, Tennessee.

Moon, J.A., D.A. Haukos, W. Conway, and P. Walther.. 2013. Habitat selection of mottled ducks in the Texas Chenier Plain. 6th North American Duck Symposium, Memphis, Tennessee.

Moon, J.A., D.A. Haukos, W. Conway, and P. Walther. 2013. Potential implications of climate change on the mottled duck. 6th North American Duck Symposium, Memphis, Tennessee. Poster

Moon, J., D.A. Haukos, W. Conway, and P. Walther. 2011. Habitat use and movements of adult mottled ducks on the Texas Chenier Plain. Annual Meeting of The Texas Chapter of The Wildlife Society, San Antonio, Texas.

Moon, J.A., D.A. Haukos, and W. Conway. 2012. Potential climate change impacts to mottled ducks on the Chenier Plain Region of Texas. Texas Chapter of The Wildlife Society, Fort Worth, Texas.