Habitat requirements and restoration targets for secretive marshbirds in southeastern Wisconsin

Background/Question/Methods

Secretive marshbirds (SMBs) are cryptic, non-colonial, wetland-dependent waterbirds, such as rails, bitterns, grebes, and coots. Several SMB species are declining, making this a group of high conservation concern. But SMBs are difficult to monitor, and key gaps remain in our understanding of their ecology. This has led to uncertainty regarding the effects of wetland degradation on SMBs and the efficacy of standard wetland-restoration practices for SMB conservation. Our goals were to: (1) determine environmental and vegetation conditions indicative of suitable SMB habitat, and (2) assess whether wetlands restored under the federal Wetland Reserve Program (WRP) met these targets. As part of a larger, statewide SMB-monitoring program, in 2011 we sampled habitat characteristics in 20 natural wetland sites. We used three years (2009-2011) of bird-monitoring data to model SMB occupancy using the program PRESENCE. Occupancy was modeled as a function of measured local and landscape habitat variables to determine the attributes important for SMB habitat at different spatial scales. In 2011, we performed the same wetland sampling and bird monitoring in 10 WRP sites restored in the 1990s and tested whether their habitat characteristics were similar to those of natural wetlands that supported SMBs.

Results/Conclusions

SMB detections were low, with sufficient numbers to enable modeling for Virginia Rail (Rallus limicola) and Sora (Porzana carolina). At the local scale, Virginia rail was positively correlated with water cover and depth, cover of Typha spp. (cattails), and vegetation quality (mean coefficient of conservatism) and negatively correlated with litter cover and cover of Phalaris arundinacea (reed canarygrass). Sora was again associated with water cover/depth and cattails and was negatively associated with cover of woody vegetation. Landscape-level characteristics had little explanatory power for occupancy by either species. While WRP sites generally had hydrology, cattail abundance, and woody cover similar to natural sites, they had greater Phalaris cover and lower mean coefficients of conservatism. WRP sites may provide suitable habitat for species such as Sora but high Phalaris abundance and low vegetation quality indicate they may be unsuitable for Virginia Rail. Wetlands in Wisconsin have been heavily invaded by Phalaris, thus it is likely that functional wetland area for Virginia Rail and perhaps other SMBs is substantially lower than actual wetland area.