Grassland and breeding bird use of moist-soil wetlands managed for waterfowl

Grassland birds;moist-soil wetlands;nest success;avian density;conservation significance;Illinois

Finch, Kristen Marie ; Benson ; Thomas J. ; Hagy ; Heath M.

关键词: Grassland birds;    moist-soil wetlands;    nest success;    avian density;    conservation significance;    Illinois;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/92987/FINCH-THESIS-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Many species of breeding birds are declining in the United States, and grassland birds are among those experiencing the steepest declines. One of the most widely accepted reasons for decreasing populations is habitat loss. For grassland birds in the midwestern United States during the spring and summer, a major concern is the loss of breeding habitat. Illinois has retained less than 1% of native prairie from the early 1800s due to the expansion of agriculture and urban development. Birds that historically relied on prairies for breeding must use alternate vegetative communities to fulfill their needs. Seasonally dewatered wetlands (e.g., moist-soil wetlands) provide vegetation structure similar to grasslands and may provide breeding habitat for birds during the summer when dewatered. I quantified avian use of dewatered moist-soil wetlands in the Illinois River Valley and used environmental variables to predict measures of avian density, avian conservation significance (ACS), nest density, and nest success. Nest densities were greater in grasslands (0.13 nests/ha, SE = 0.02) than in moist-soil wetlands (0.09 nests/ha, SE = 0.01), but habitat did not have a strong effect on avian density (grassland= 13.5 birds/ha, SE = 3.5; moist-soil wetland= 10.2 birds/ha, SE = 1.1) or ACS (grassland= 218.6, SE = 27.8; moist-soil wetland= 214.2, SE = 15.9). The percent cover of woody vegetation had a positive relationship with ACS, and the percent cover of forbs had a negative relationship with avian density. Sites that were disconnected from the river had greater avian conservation significance than partially connected sites. Wetland size and the proximity to the Illinois River were poor predictors of nest density. I observed many grassland birds using moist-soil wetlands, including nesting dickcissels (Spiza americana, a generalist-grassland nester) and grasshopper sparrows (Ammodramus savannarum, an obligate-grassland nester). I also observed the state endangered northern harrier (Circus cyaneus), common gallinule (Gallinula galaeta), and Forster's tern (Sterna forsteri) in moist-soil wetlands. Dewatered moist-soil wetlands provide useful breeding habitat for grassland birds, but wetlands that are partially connected to the Illinois River pose a risk to nesting birds if they are flooded during the breeding season. I recommend that moist-soil managers conduct a mid-season or late drawdown of wetlands that are at a high risk of flooding to avoid creating an ecological trap for breeding birds. In moist-soil wetlands that are disconnected from the Illinois River and less likely to flood, I recommend an early drawdown to allow moist-soil vegetation to grow and provide habitat for grassland birds.