Grassland and farmland bird populations have been declining around the world and declines are primarily attributed to grassland habitat conversion to agricultural practices. Also, many of the historical drivers (i.e., fire and large grazing ungulates) that once maintained, floristically diversified, and ensured a mosaic of successional stages, are often no longer prevalent in our contemporary landscapes. However, governments have recognized the need for set-aside farmlands for multiple environmental benefits, which may include alleviating grassland bird declines. In the United States, the most popular set-aside private lands program is the Conservation Reserve Program (CRP) and as of 2004, enrolled landowners are required to manage their grassland conservation cover mid-way through their contract to promote early-successional habitat for wildlife. Because of this unique opportunity to conduct research directly linked to policy-based management and landowner decision making, we set out to understand how specific (i.e., light-strip discing, spraying, and spray/interseed) and broad management options to CRP landowners could influence nest survival of grasslands birds. Additionally, we aimed to understand how management in relation to multi-scale habitat affected nest survival of: (1) red-winged blackbirds (Agelaius phoeniceus); (2) dickcissels (Spiza americana); (3) ground-nesting; and (4) the above-ground nesting community from 2011-2014 (Illinois, USA).
Results/Conclusions
From a multi-scale perspective, finer-scale habitat characteristics and temporal variables often predicted grassland bird nest survival better than management or landscape context. Blackbird nests survived better in denser and taller vegetation and above-ground nesters had greater survival in fields with higher forb diversity, and both blackbird and dickcissel nests survived better earlier in the breeding season. However, management focused analyses revealed that above-ground nesters responded positively to light-strip discing [i.e., 3.7% increase in daily nest survival from discing management equated to an on average 30% increase in probability of surviving the nesting period (PSNP)]. Herbicidal spraying and spray/interseeding generally improved nest survival of above-ground nesters compared to reference conditions, and native-established fields and management, regardless of type, generally improved nest survival in top management models (~4.4% to ~15.4% PSNP increase). Policy-based management can indeed improve nest survival of grassland birds, which is likely explained by increased vegetation structural heterogeneity and floristic diversity, created by management, reducing predator search efficiency and improving arthropod food resources for birds. Although landscape composition was generally not important in these analyses, we still advocate focusing management in beneficial landscapes that supports positive meta-population dynamics, such as increased field colonization and persistence, of focal species.