Fig 1.
Marsh bird survey sites for two regions of Illinois categorized by average maximum temperatures in May from the PRISM Climate Group at Oregon State University (Conway 2011).
Sites consisting of National Wetland Inventory (NWI; grey), wetlands managed for waterfowl (white), and Critical Trends Assessment Program (CTAP; black) wetlands.
Fig 2.
Example wetland management regimes (Y axis) and the range of waterfowl management intensity values (X axis) typically encountered based a visual index of management activities and capabilities present (1 [low intensity or passive management]– 8 [intensive/active management]).
Table 1.
List of factors and the corresponding units used as possible predictors of marsh bird detection and abundance in Illinois during late spring and early summer 2015–2017.
Fig 3.
Model-estimated marsh bird detection probability (black line) for all three marsh bird groups (± 95% confidence limits [grey lines]) by adjusted date.
Surveys were conducted from day 0 (April 15 or May 1, depending on latitude stratification) to day 48 across Illinois during late spring and early summer 2015–2017.
Table 2.
Model rankings for variables predicting detection probability by species groupings of marsh birds based on Akaike’s Information Criterion (AIC), difference in AIC relative to the highest-ranked model (ΔAIC), relative model weight (wi), and number of parameters (K) from surveys conducted at wetlands throughout Illinois during late spring and early summer 2015–2017.
Fig 4.
Predicted probability (95% confidence limits) of site occupancy across wetland complexity levels in Illinois during late spring and early summer 2015–2017.
Site type (National Wetland Inventory) was held constant. Each box represents one grouping of species, labeled at the top, with comprehensive being all the species in open water and emergent combined.
Fig 5.
Predicted probability (95% confidence limits) of site occupancy for the comprehensive group across wetlands managed for waterfowl, Critical Trends Assessment Program (CTAP), and National Wetland Inventory (NWI) site types in Illinois during late spring and early summer 2015–2017.
Each box represents one grouping of species, labeled at the top, all species in open water are in comprehensive.
Table 3.
Model rankings for variables predicting occupancy probability by species groupings of marsh birds based on Akaike’s Information Criterion (AIC), difference in AIC relative to the highest-ranked model (ΔAIC), relative model weight (wi), and number of parameters (K) from surveys conducted at wetlands throughout Illinois during late spring and early summer 2015–2017.
Fig 6.
Predicted probability (95% confidence limits) of site occupancy for the emergent marsh bird group (American bittern, Botaurus lentiginosus; least bittern, Ixobrychus exilis; sora, Porzana Carolina; king rail, Rallus elegans; virginia rail Rallus limicola, and yellow rail, Coturnicops noveboracensis) across survey rounds in Illinois during late spring and early summer 2015–2017.
Fig 7.
Predicted probability (95% confidence limits) of site occupancy for the emergent marsh bird group (American bittern, Botaurus lentiginosus; least bittern, Ixobrychus exilis; sora, Porzana Carolina; king rail, Rallus elegans; virginia rail Rallus limicola, and yellow rail, Coturnicops noveboracensis) across percent surface water inundation in Illinois during late spring and early summer 2015–2017.
Fig 8.
Predicted probability (95% confidence limits) of site occupancy for the emergent marsh bird group (American bittern, Botaurus lentiginosus; least bittern, Ixobrychus exilis; sora, Porzana Carolina; king rail, Rallus elegans; virginia rail Rallus limicola, and yellow rail, Coturnicops noveboracensis) across dense persistent emergent vegetation coverage in Illinois during late spring and early summer 2015–2017.
Fig 9.
Predicted probability (95% confidence limits) of site occupancy for the emergent marsh bird group (American bittern, Botaurus lentiginosus; least bittern, Ixobrychus exilis; sora, Porzana Carolina; king rail, Rallus elegans; virginia rail Rallus limicola, and yellow rail, Coturnicops noveboracensis) across wetland management intensity in Illinois during late spring and early summer 2015–2017.