Reproductive Success and Survival of Grassland Passerines in an Agriculture Landscape: the Contribution of Alternate Grazing Systems to Bird Population Viability

Project Overview

GNC02-004
Project Type: Graduate Student
Funds awarded in 2002: $10,000.00
Projected End Date: 12/31/2004
Region: North Central
State: Minnesota
Graduate Student:
Faculty Advisor:

Annual Reports

Commodities

  • Agronomic: grass (misc. perennial), hay
  • Additional Plants: native plants
  • Animals: bovine
  • Animal Products: dairy

Practices

  • Animal Production: grazing - continuous, free-range, pasture fertility, grazing - rotational, feed/forage
  • Education and Training: on-farm/ranch research
  • Farm Business Management: marketing management
  • Natural Resources/Environment: habitat enhancement, indicators, wildlife
  • Sustainable Communities: partnerships

    Abstract:

    We compared the abundance and reproductive success of grassland birds in rotationally- and continuously-grazed cattle pastures in southeast Minnesota to determine if either grazing practice was more beneficial to grassland bird populations. Savannah sparrows (Passerculus sandwichensis) were the most abundant species, and we found no difference in savannah sparrow nest success between grazing systems (P > 0.1). Cattle stocking rate and vegetation density were the best predictors of nest success in all pastures. Nest survival rates trended downward with decreasing vegetation density. Intervals of <30 days between grazing events on rotationally-grazed paddocks contributed to low nest productivity.

    Introduction:

    Recent declines of grassland bird species in the Midwest (Knopf 1994, Herkert et al. 1996) correlate with a 6.5 million ha decline in the regional acreage of pastures and hay fields between 1966 and 1992 (Herkert et al. 1996). In the Eastern and Central United States, 60% of grassland species declined between 1980 and 1998 (Murphy 2003). The magnitude of these declines suggests that local and regional extinctions are likely if grasslands are not managed to minimize breeding season disturbances (Herkert 1994). Because native prairie exists in less than 5% of its original range in Minnesota (Samson and Knopf 1994), birds that traditionally nested on prairies have become largely dependent on privately held, non-native, agricultural grasslands for breeding habitat (Johnson 1996). Most grasslands in the Midwest are used to produce forage that is harvested either mechanically or by grazing animals, primarily cattle (Herkert et al. 1996).

    A growing number of farmers are practicing intensive rotational grazing (IRG) and finding it more cost effective than continuous grazing (U.S. Department of Agriculture 1996, Undersander et al. 1993). To practice IRG, a pasture is divided into small paddocks that support a herd for a half-day to two or thee days, depending on forage availability and quality, and animal condition (Blanchet et al. 2003). Ideally a 10-12.5 cm (4-5 inch) stubble remains after animals have been rotated to the next paddock, and the grass is rested for about a month before animals are allowed to graze it again (Blanchet et al. 2003). IRG is becoming increasingly popular on farms located in the unglaciated region of southeast Minnesota. Although statistics for Minnesota are not available, >10% and >15% of dairy farmers in Wisconsin (Paine et al. 1996) and Pennsylvania (U.S. Department of Agriculture 1996), respectively, are using IRG and its popularity is increasing (Paine et al. 1996). This grazing method is touted as bird-friendly (Undersander et al. 2000, but see Temple et al. 1999), although Johnson and Ward (1997:8) suggest that "if grassland birds are attracted to these fields under an IRG system, the question of their breeding success still needs to be addressed."

    Farmers who manage for increased reproductive success of birds nesting on their pastures should benefit through value-added product labels, and consumers who care about grassland birds should be given the information they need to support these farmers. A growing number of farmers in Minnesota and across the nation are marketing their products directly to consumers, and products with labels touting environmental and human health benefits are becoming popular nationwide (McLaughlin 2004). A recent U.S. Department of Agriculture (Payne 2002) survey found a 63% increase in the number of farmers markets between 1994 and 2002. In addition, bird watching increased by 155% between 1983 and 1995 nationwide (Iverson 2002), and participation in wildlife viewing in Minnesota increased 53% between 1996 and 2001 (U.S. Fish and Wildlife Service 2002b). Ecologically-sound, bird-friendly products such as shade-grown coffee, which represents 5% of sales in the United States gourmet coffee market (Griswold 1999), can help provide habitat for birds who winter in the tropics. However, Murphy (2003) has indicated that recent grassland bird declines in Midwestern and eastern states were linked to changes in agricultural land use regardless of a species' migratory behavior or nesting habits. Whether a bird uses a cavity or makes a cup nest on the ground, and whether it flies to Argentina or to Alabama, if it is a grassland bird it is more affected by land management practices on North American farms than habitat changes occurring in the southern hemisphere (Murphy 2003). North American farmers have become de facto managers of grassland bird habitat. They exert a great deal of control over the success of grassland bird populations, and could benefit financially through sales of certified 'bird-friendly' beef and milk.

    Savannah Sparrows were useful in our study because of their abundance, ubiquity, and habitat niche. They were abundant enough for us to find enough nests to make single-species statistical comparisons between treatments and farms. Because Savannah Sparrows prefer mid-range vegetation heights, soil moisture, grazing intensities and vegetation densities (Herkert et al. 1993) they can indicate ecological minimum needs for a number of rarer, tall-grass species such as the Bobolink, Sedge Wren, Eastern and Western Meadowlark, and Dickcissel. Providing good Savannah Sparrow nesting habitat is a starting point for any grassland farmer interested in providing habitat for other grassland nesters.

    Our objective was to determine if rotationally- or continuously-grazed pastures better supported stable grassland bird communities. We found and monitored nests to determine if pastures and treatments had reproductive success capable of supporting stable populations of birds. We also measured vegetation and other aspects of nest sites and pastures to explore how these variables were correlated with success. Broadly, our goal was to provide farmers with the information to make land management and marketing decisions that enhance their financial bottom line as well as the reproductive success for grassland birds on their pasture. We also aimed to provide resource managers with tools to design government programs that promote more bird friendly practices on pastures. Finally, we provided bird-watchers and scientists with data to inform a new eco-labeling program (Institute for Agriculture and Trade Policy 1998). In this way, consumers’ grocery purchases could support farmers who provide productive grassland bird habitat.

    Project objectives:

    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 affect 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 farm products.

    To improve the quality of life for farmers in the project as they learn more about the needs of birds on their pastures.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.