Linking wetland management decisions to secretive marsh bird habitat use during spring migration and summer breeding on public wetlands in Missouri
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The extent to which secretive marsh birds rely on wetlands in Missouri during spring migration is relatively unknown. My objective for chapter one was to determine how initial marsh bird occupancy and subsequent colonization and departure probabilities were influenced by wetland management practices, including the duration and initiation date of spring water-level drawdowns, and associated wetland habitat characteristics. We used dynamic occupancy modeling to evaluate factors that influence SMB occupancy and colonization/departure probabilities. Sora and American bittern occupancy models indicated a positive relationship between occupancy probability and duration of drawdown, however the top occupancy model for Virginia rail was the null model. The top colonization/departure model for sora included vegetation density and percent of a site containing emergent vegetation, with both variables having a positive relationship with colonization probability and a negative relationship with departure probability. The top colonization/departure model for Virginia rail included range of water depth and range of vegetation height, both of which had a negative relationship with colonization and departure probability. The top colonization/departure model for American bittern included vegetation interspersion, whereas the top model for least bittern included the percent site inundated and overall area inundated. My objective for chapter two was to determine effects of hydrologic management and habitat characteristics on habitat selection and the daily survival rate (DSR) of least bittern on public wetlands in Missouri at two scales: the entire wetland and the nest point. Least bittern populations have been in decline since the 1970s, most likely due to extensive loss of freshwater emergent wetlands, the primary nesting habitat of least bittern. The decline in nesting habitat emphasizes the need for effective wetland management within the nesting range of least bitterns. The extent to which least bittern rely on wetlands in Missouri during summer nesting efforts is poorly understood. The logistic exposure method was used to evaluate DSR as a function of covariates. At the wetland scale, logistic regression was used to evaluate models composed of combinations of covariates thought to influence least bittern nest site selection. The percent of a wetland covered in emergent vegetation and the average water depth were positively associated with probability of selection at the wetland scale. At the point scale, discrete choice was used to evaluate models composed of combinations of covariates thought to influence least bittern nest site selection. The relative probability of use was positively related with water depth, percent of a site in emergent vegetation, and negatively related with vegetation density. Daily Survival Rate was positively related with average water depth at nest points. These results are important to inform management decisions intended to create wetland conditions favorable to SMBs. Both migrants and breeders are more likely to use wetlands with emergent vegetation interspersed with patches of open water. Drawdown schedules will increase occupancy if they are timed to conform to the life history stage of the target species, providing water for migrants in April-May, and for breeders in June and July. A possible ecological trap will be avoided if drawdowns are complete before least bittern begin nest site selection in mid to late May.
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