Reproductive Success and Survival of Grassland Passerines in an Agriculture Landscape: the Contribution of Alternate Grazing Systems to Bird Population Viability
A comparison of reproductive success of Savannah Sparrows in rotationally grazed and continuously grazed pastures in southeast Minnesota found no difference between treatments. However, there was a great deal of variability between pastures in the same treatment. Reproductive success was positively correlated with increasing vegetation density and increased percentage cover of downed litter. Pastures with an average vegetation density of 1 dm Visual Obstruction Reading (VOR) had more breeding territories and a greater number of successful nests, compared with pastures with < 1 dm VOR. Implications of this data on programs such as the Conservation Security Act will be explored.
Objectives for the project were initially both short- and long-term. Short-term objectives included:
Build a more trusting relationship between university researchers, resource managers, and farmers.
Share ideas about grazing and birds with a broad range of interested folks.
Identify how rotational and continuous grazing effect the nest success of grassland birds.
The long-term objectives were:
To provide information to farmers to fuel a powerful direct marketing campaign for bird-friendly farming products.
To improve the quality of life for farmers in the project as they learn more about the needs of birds on their pastures.
Our research team, lead by the graduate student PI, spent the time to build strong relationships between farmer cooperators, natural resource personnel, and university researchers. The PI lead four informal, multi-farm tours that included local residents, professors from the University of Minnesota, and DNR employees. Many morning chats instigated to ask a farmer where the cows would be ‘rotated’ next ended with philosophical discussions about the future of farming, or an explanation of why a specific farming practice was chosen. One farmer cooperator put the team to work identifying the species of birds utilizing his small manure lagoon, and another assisted the team with nest searching. In August 2003, the research team held a picnic at Whitewater State Park for all cooperators. We all grilled local vegetables and meats and had a turnout of 40 people. Some farmers leaving the picnic said that they would like to be informed about further opportunities to participate in on-farm research.
We are collaborating with the Beginning Farmer and Agricultural Lender programs of the Land Stewardship Project to put on a Birds and Grazing Field Day, scheduled for June 16th, 2004, at a cooperator’s farm.
Our invitation reads, “Can birds like Savannah Sparrows and Bobolinks successfully hatch and raise their broods on a cattle pasture? A recent study of six pastures in Southeast Minnesota indicates that pasture management is an important element in grassland bird reproductive success. Join farmers, ornithologists, consumers, and natural resource personnel as we tour an organic dairy farm in beautiful Southeast Minnesota. Learn how one farm family practices sustainable farming methods that provide them a good quality of life, provide good habitat for nesting grassland birds, protect water quality, and prevent soil erosion. Learn how you can support bird habitat through your grocery purchases and how sustainable farms contribute to tourism in Minnesota. Then put on your binoculars and travel with us out to the pasture to see the birds for yourself and learn about their nesting requirements. After we answer your questions we will wrap up our field day with a meal of delicious locally produced and prepared food. For more details please call Melissa at 612 721-6735, or Heidi or Caroline at 507-523-3366.”
In addition, our PI has made a number of presentations to diverse groups. These include:
Driscoll, Melissa A., John P. Loegering, and Vernon B. Cardwell. Reproductive Success of Grassland Passerines in an Agricultural Landscape: The Contribution of Alternate Grazing Systems to Bird Population Viability. Conservation Biology Seminar, University of Minnesota, St. Paul Campus. April 14, 2003. 60 Minutes.
Driscoll, Melissa A., John P. Loegering, and Vernon B. Cardwell. Reproductive Success of Grassland Passerines in an Agricultural Landscape: The Contribution of Alternate Grazing Systems to Bird Population Viability. Wildlife Extension Agents Annual Event, St. Paul Campus. April 24, 2003. 2 – 15 Minute presentations.
Driscoll, Melissa A., John P. Loegering, and Vernon B. Cardwell. Reproductive Success of Grassland Passerines in an Agricultural Landscape: The Contribution of Alternate Grazing Systems to Bird Population Viability. Society for Conservation Biology, Duluth, MN 28 June – 2 July 2003, 15 minutes.
Driscoll, Melissa A., John P. Loegering, and Vernon B. Cardwell. Reproductive Success of Grassland Passerines in an Agricultural Landscape: The Contribution of Alternate Grazing Systems to Bird Population Viability. Presentation to FW 5603W Habitats and Regulation of Wildlife. Instructor: Peter Jordan, University of Minnesota. November 4, 2003. 30 minutes.
Driscoll, Melissa A. Creating and Enhancing Natural Habitats on the Farm. Presentation to the tri-state Women in Sustainable Agriculture Annual Fall Gathering, Spring Valley, MN. November 7 – 9, 2003. 75 minutes.
We performed two nesting seasons of field work on six pastures in southeast Minnesota during 2002 and 2003. We located a total of 76 nests, including 61 Savannah Sparrow nests, eight Bobolink nests, two Eastern Meadowlark nests, one Western Meadowlark nest, and one Mallard nest. We found no difference in Savannah Sparrow daily survival rate between continuous and rotational grazing systems. We compared survival between all pastures regardless of treatment and found no differences (P > 0.01), except the DI pasture that contained no nests and therefore had zero reproductive success. Although the daily survival was not different between treatments, there was a broad range of daily survival exhibited within treatments.
Rotationally grazed sites had 8.33 +/- 1.33 (SE) species per pasture and 4.33 +/- 0.88 (SE) of those were grassland nesters. Continuously grazed sites had 9.00 +/- 2.65 (SE) species per pasture, and 4.67 +/- 1.45 (SE) of those were grassland nesters. No single species was more prevalent in one treatment than another (all P > 0.10).
Successful nests had lower percentage cover of bare soil (t = 2.41, 22 df, P = 0.02), lower percentage cover of cow pies (t = 3.29, 22 df, P < 0.01), higher vegetation densities (t = 4.94, 22 df, P < 0.01), and higher vegetation heights (t = 3.29, 22 df, P < 0.01) than failed nests. The best stepwise logistic regression model predicting whether a nest successfully fledged at least one chick (nest success) included vegetation density, distance to nearest shrub, percentage of cover of downed litter, and percentage cover of cow pies. Vegetation density was the best predictor of nest success; nests were 58 times more likely to fledge at least one chick with a one decimeter increase in vegetation density. Distance to shrubs, percentage cover of downed litter, and percentage cover of cow pies involved smaller odds ratios. For every 10 meter decrease in distance from a shrub, a nest was 9.7 times more likely to succeed. For a 10% increase in percentage cover of downed litter or 10% decrease in percentage cover of cow pies a nest was 1.01, and 0.87 times more likely to succeed, respectively. Our observations seem to indicate that the farmers who depend on vegetation for 90 – 100% of their cattle’s nutrients keep a closer eye on vegetation condition and thus provide more productive habitat for grassland birds. Further analysis is ongoing. We are currently busy working toward finishing this long-term goal and publishing our work in peer-reviewed journals as well as presenting to local farming and natural resource groups. For a list of recent presentations see point 2 (above). Our PI has kept in touch with farmer cooperators through letters and phone calls throughout the data gathering phase and up to the present. Each farmer will receive a copy of the research findings as well as extra data that is not included in published research but that they might find interesting and helpful. It will be interesting to see if any change their practices after reading our research.
Impacts and Contributions/Outcomes
We contribute to the development of alternative labeling standards, farmer knowledge of grassland bird needs, and the ongoing debate about the Conservation Security Program rules.
At 8.7 million ha., pastures are the most abundant grassland habitat in the Midwest, and most are privately owned. Our research quantifies how good land stewardship, profitable grassland farming, and good passerine nesting habitat can be accomplished on these pastures. With the recent Bovine Spongiform Encephalopathy scare in Washington, demand for grass-fed beef is rising along with renewed interest in knowing the origin of the food Americans eat. Our work to determine minimum vegetation densities, cattle densities, and rotation schedules for good grassland bird reproductive success dovetails well with current ‘natural beef’ marketing campaigns. This, in turn, may give consumers an additional reason to buy sustainably-raised beef, and give farmers an additional incentive to protect bird nesting habitat.
All farmers, University researchers, and agency personnel involved in the project have gained an appreciation for each others’ work, and the complexities inherent in farming with grassland birds in mind. Our next challenge is to write and publish articles sharing the results of our project with both ecological and farming audiences.
The soon-to-be-implemented Conservation Security Program (CSP) lists rotational grazing as a sponsored practice. Rotational grazing can be practiced in ways that are detrimental to birds and that is why we recommend that monitoring must be included in the CSP rules. Monitoring could include counting singing birds during the nesting season, measuring overall pasture vegetation density, keeping annual logs of bird activity in pastures, and working with neighboring farms to assess bird populations on a larger scale. Farmers reimbursed through CSP for providing bird habitat (among other benefits) should assure that their rotation of cattle gives birds enough time to choose a building site (two days), build a nest (two days), lay eggs (five days), incubate (12 days), and feed the young until they are free-flying (nine days) = 28 days, or about a month. Rotations shorter than 28 days in May and August are acceptable as this will not severely effect the reproductive success rates of ground nesting birds; however, June and July are periods of peak nesting intensity.
Our final report, to be completed during summer 2004, will outline further contributions.