A dickcissel in a CRP field in Henry County.
Managing Private Lands for Grassland Birds
Photos courtesy of the author.
Grassland Bird Decline Alleviated by Private Lands Farm Bill Conservation Programs
Grassland bird declines across North America have been a consistent theme in past decades. We know this due to the volunteer Breeding Bird Survey routes that are conducted each year across the U.S., Mexico and Canada. Thankfully, many Farm Bill conservation programs for private landowners do exist and have alleviated these declines. Declines do, however, still remain. The most popular private lands program, known as the Conservation Reserve Program (CRP), incentivizes agricultural producers to take marginal and environmentally sensitive ground out of production and plant forms of conservation cover – often grassland practices. This cover reduces erosion and improves air and water quality while also providing crucial wildlife habitat for many grassland species. Landowners can choose from multiple conservation practices based on their goals and the context/layout of their farming operation. At this time, approximately 23 million acres of active CRP exist across the U.S. which, if combined, would represent 62 percent of the land area of Illinois. CRP contracts typically last 10 to 15 years and the landowners are required to manage and maintain this cover as required by the program. The management practices they choose are meant to encourage early-successional habitat for species, such as northern bobwhite quail.
Challenges in Studying Grassland Bird Management
What is the best management practice for grassland birds within CRP? This was the focal question of my graduate research with Southern Illinois University Carbondale’s Cooperative Wildlife Research Laboratory. I was particularly excited about the applied nature of this research and how it was connected to the country’s largest private lands conservation program. After my studies, classes and four-plus years of intense data collection and analysis, I soon realized, as with most ecological field research, the answer is often, “it depends.”
- How birds are responding to management and habitat can be measured in multiple ways – some better than others – and research budgets often dictates the type of data that can feasibly be collected. An abundance of birds of a given species detected in a visual and auditory survey doesn’t necessarily mean the species are having successful nests and surviving well. It is most ideal to connect management practices to species productivity and survival.
- Different bird species have different habitat requirements. Management that benefits one species may come as a detriment to another. For example, if no maintenance or management is done on grassland CRP, trees and shrubs often encroach on these fields which could be beneficial for shrubland birds such as the Bell’s vireo, which is an Illinois Species of Greatest Conservation Need.
- The composition of surrounding landscape itself is habitat and can positively or negatively influence many grassland birds. Thus, getting at the true effects of management remains challenging in ecological field research without good study designs and statistical techniques to account for so much inherent variation that cannot be controlled as it could be in lab studies.
Working with my adviser, Dr. Clayton Nielsen, we addressed this focal management question in relation to grassland specialist and generalist species while simultaneously tending to these issues in a published study in Agriculture Ecosystems & Environment. Because prescribed fire is a management practice that requires a lot of skill, knowledge and trained personnel to be conducted safely, tractor-based management options seemed more feasible for use in CRP contracts. I specifically looked at light-strip disking, herbicidal strip spraying and strip spraying with forb interseeding. The study was also done on two different general CRP field types, native grass and non-native grass (smooth brome, Bromus inermis) dominated fields.
The goal of the conducted research was to provide informed decision-making spanning from the landowner to the land manager.
As suspected, different species responded in different ways to management techniques, and it remained challenging to pin-point a best management practice even for an individual species. I also chose to investigate how birds would respond to different grass types regardless of management type. The study found that more bird species (generalists and specialists) were found in native grass dominated fields that received more management, but more individuals were counted on native fields that received less management. Native grass CRP fields generally have more structural and plant species diversity that I suspected attract some of the more general grassland species that use taller vegetation structure such as red-winged blackbirds. If left unmanaged, non-native grass fields dominated by brome grass often had little vegetation structural and plant diversity. These non-native fields attracted a few key grassland specialist birds that are also Illinois Species of Greatest Conservation Need, including bobolinks, Henslow’s sparrows and eastern meadowlarks.
After several of the study brome fields were sprayed for management, a dramatic release of weedy forbs resulted, many of which were unwanted by the landowners (some backed out of the study after seeing the vegetation response). The most problematic culprits noticed included wild parsnip (Pastinaca sativa) and horseweed (Conyza canadensis), which also created more nesting opportunities for red-winged blackbirds. Some of these fields became overrun with red-winged blackbird flocks later in their breeding season during the later year of the surveys. This led to significantly more generalist birds found in sprayed treatments compared with control and disked brome fields.
The nesting analysis was heavily influence by red-winged blackbirds, the most common species and easiest nests to find, providing the opportunity to further study their nest defense behavior. When all nests were combined, survival was best in native grass fields. Native fields have more structural and plant diversity which likely helps confuse nesting predators by reducing their search efficiency and native field are more likely to have abundant arthropod resources for growing chicks that can also improve nest survival. Having nesting information should help improve management decisions, but, in the case of eastern meadowlark, a grassland specialist, it was not always clear. This species’ nests appeared to survive better in native grass CRP fields, yet meadowlark adult densities from count surveys was highest on unmanaged brome and these densities decreased on brome fields with increasing management.
Light Strip-disking: The Goldilocks of Management Practices?
This research suggests management appears to be most beneficial for native fields and spray treatment on non-native brome fields has the potential consequence of releasing many undesirable forbs from the seed bank that in turn could attract many red-winged blackbirds. Based on this and previous work looking specifically at nest survival, disking might be a good, conservative, tractor-based management practice for CRP landowners, which would be beneficial across both field types. Disking may have the most positive influence across the most species of birds as it appeared to have less of a potential to dramatically release forbs in brome fields but still diversified the plant community in both field types. This practice also creates bare ground patches, which improves brood-rearing habitat for popular game species such as pheasants, quail and wild turkey.
Dr. Justin J. Shew is the Conservation Program Manager for the National Great Rivers Research and Education Center (NGRREC) of Lewis and Clark Community College (Godfrey). He is past president of the Illinois Chapter of the Wildlife Society and holds and adjunct professor and research mentor position with Webster University (St. Louis, MO). He manages the NGRREC’s Land Conservation Specialist Program and Habitat Strike Team and has the privilege of mentoring students on research projects connected to restoration and wildlife ecology. Contact Shew with any questions at firstname.lastname@example.org and a pre-print version of the manuscript discussed in this story can be found here.