Secretive marsh bird habitat associations in the Mississippi Flyway: a meta-analysis

Abstract

Secretive marsh birds, including rails and bitterns, have experienced widespread population declines due to the loss of wetland habitat on which they depend. Because of their cryptic behavior, secretive marsh birds are challenging to study and information on their habitat requirements is limited, especially across the full annual cycle. Quantifying habitat associations throughout the annual cycle and at broad geographic scales can advance a more comprehensive approach for secretive marsh bird conservation. The goal of this study was to quantitatively synthesize results from empirical studies that examined species-habitat relationships of secretive marsh birds in the North American Mississippi Flyway to identify general patterns and information gaps that can guide future management and conservation efforts. We performed a meta-analysis and incorporated results from 40 studies that quantitatively assessed habitat associations of American Bittern (Botaurus lentiginosus), Least Bittern (Ixobrychus exilis), King Rail (Rallus elegans), Sora (Porzana carolina), Virginia Rail (Rallus limicola), and Yellow Rail (Coturnicops noveboracensis). Most studies examined breeding season habitat, whereas only 13% reported on habitat use during migration and none during winter. At landscape scales, breeding marsh birds were positively associated with amount of wetlands, especially in the Great Lakes region, and negatively associated with amount of urban land cover, particularly for American Bittern. At the local scale, breeding marsh birds were positively associated with cattail coverage (Typha spp) and other robust emergent vegetation. Overall, marsh birds were negatively associated with woody wetland vegetation, although effects were weaker in the Prairie region and varied among species. During autumn migration, moistsoil vegetation coverage was important for rails in the lower Midwest. The habitat use patterns we identified across studies provide a general characterization of marsh bird breeding habitat to aid in landscape-level multi-species conservation efforts. Our study also highlights the immediate research needs for full annual cycle conservation of secretive marsh bird habitat in North America: specifically, information during winter and migration.

Secretive marsh bird habitat relationships at mid‐continent spring migration stopover sites

“…American bittern site colonization had a negative relationship with percent open water and no relationship with cover‐to‐water ratio, suggesting wetlands dominated by emergent vegetation may be preferable to American bittern. Other studies have reported negative relationships of marsh birds to open water areas, including sora during autumn migration in Missouri (Fournier et al 2018), and multiple species during the breeding season in the Prairie Pothole region (Malone et al 2021). Nevertheless, other research in the northern portion of the mid‐continent region shows inconsistent associations of SMBs to open water during the breeding season (Malone et al 2021).…”

“…Other studies have reported negative relationships of marsh birds to open water areas, including sora during autumn migration in Missouri (Fournier et al 2018), and multiple species during the breeding season in the Prairie Pothole region (Malone et al 2021). Nevertheless, other research in the northern portion of the mid‐continent region shows inconsistent associations of SMBs to open water during the breeding season (Malone et al 2021).…”

“…Although the overall average of percent agriculture in wetlands was approximately 5%, sites ranged from 0–95% agricultural cover. Other researchers reported a broad positive relationship between percent agriculture in the surrounding landscape and sora occupancy, primarily for nesting birds (Malone et al 2021). Sora are generally considered a habitat generalist (Zimmerman 1984, Melvin and Gibbs 2020) and previous research reported plant species composition was often less important in predicting sora habitat use compared to vegetative structure (Rundle and Fredrickson 1981, Sayre and Rundle 1984, Reid 1989).…”

“…The relative importance of habitat factors influencing site colonization by SMB varied by species, although we also identified several similarities in habitat associations across species. Given the conservation status of this group of birds, understanding how habitat conditions influence their site use during a critical and understudied life phase is relevant to future wetland management and conservation efforts (Malone et al 2021).…”

“…Secretive marsh birds (SMBs) encompass a group of wetland‐dependent migratory birds, including rallids, bitterns, and grebes, among which several species have experienced extensive population declines and been designated species of conservation concern by many state natural resource agencies (Timmermans et al 2008, Tozer 2016, Pickens and Meanley 2020). Despite growing interest and concern for SMB populations throughout the mid‐continent of North America (U.S. Geological Survey 2021), limited information on SMB distribution and habitat use within primary migratory corridors results in uncertainty regarding contributions of wetlands to meet SMB life‐history needs in mid‐latitude states (Malone et al 2021). Overall, restricted distributions combined with low detectability have resulted in SMBs being among the least studied avian groups (Valente et al 2011) and for most species there is inadequate information on population levels, migration patterns, and overall habitat requirements for effective conservation and management throughout the full annual cycle (Eddleman et al 1988, Malone et al 2021).…”