Category: Wildlife Research
Published: October 2006
Author(s): Michael A. Schroeder and W. Matthew Vander Haegen
The Conservation Reserve Program (CRP) is currently the largest-scale effort to restore grassland and shrubsteppe habitat in the Columbia River Basin. Administered by the Farm Service Agency (FSA) of the US Department of Agriculture, this voluntary program pays farmers to take agricultural lands out of production to achieve conservation objectives including reduced soil erosion and provision of wildlife habitat. In Washington, about 1.5 million acres (600,000 ha) of converted farmland has been planted to perennial grasses, forbs and shrubs under the CRP. Unlike CRP in the mid-west that largely occurs on land that was formerly prairie, much of the CRP in Washington occurs on land that was historically shrubsteppe. The current acreage of CRP land in eastern Washington is equal to about 10% of the stateâ€™s total agricultural lands.
Declines in the abundance and quality of shrubsteppe have coincided with declines in the populations of many species including greater sage-grouse (Centrocercus urophasianus), sage thrashers (Oreoscoptes montanus), and Brewerâ€™s sparrows (Spizella breweri). While not an ideal solution to the problem of declining native habitat, CRP has enormous potential to provide habitat for many grassland and shrubsteppe species. Despite this potential, no studies have examined use of these CRP lands by grassland and shrubsteppe-obligate wildlife in the Columbia River Basin. The purpose of this research was to examine the relationship between wildlife and CRP in Washington, focusing primarily on the species closely adapted to shrubsteppe habitat.
Between 1992 and 1997 we captured 89 female sage-grouse and monitored their nest site selection with the aid of radio telemetry. Although more nests were in shrubsteppe than CRP during the course of this study (59% vs. 41% of 203 nests), the proportion of nests significantly increased in CRP from 31% in 1992-1994 to 50% in 1995-1997. The increase appeared to be associated with maturation of CRP fields, which was characterized by increased height and cover of the perennial grasses and invasion by big sagebrush (Artemisia tridentata). The capability of CRP to successfully support nesting sage-grouse was further supported by the lack of differences in apparent success for nests placed in the two habitat types (45% success in CRP, 39% success in shrubsteppe). These observations were further supported with comparison of long-term rates of population change in sage-grouse in north-central Washington (approximately 17% of occupied area with CRP) and south-central Washington (approximately 2% of occupied area with CRP). Pre-treatment (prior to CRP) and treatment (following implementation of CRP) data revealed a slight reversal of a population decline in the north-central Washington population following implementation of CRP while the south-central population continued a long-term decline.
PASSERINE BIRDS AND OTHER WILDLIFE
From 2003 to 2005 we surveyed for wildlife on 48 study areas in agricultural/shrubsteppe landscapes of eastern Washington. We compared wildlife communities in 3 vegetation communities (old CRP, new CRP, and extant native shrubsteppe), each represented in landscapes dominated by agriculture and in landscapes dominated by shrubsteppe. We surveyed for passerine birds using point-count methods and for greater sage-grouse, mule deer (Odocoileus hemionus), jackrabbits (Lepus spp.), and cottontail rabbits (Sylvilagusspp.) using pellet-counts. We also examined nesting success of selected passerines in shrubsteppe landscapes by locating and tracking the fate of nests. We examined species abundance with models that included habitat type, landscape, and site-specific vegetation variables.
We counted 6710 birds during our point-count surveys. Numbers of birds counted in CRP fields were comparable to those counted in native habitat though the dominant species differed. Savannah sparrows (Passerculus sandwichensis), horned larks (Eremophila alpestris), and grasshopper sparrows (Ammodramus savannarum) generally dominated CRP fields; Brewerâ€™s sparrows, vesper sparrows (Pooecetes gramineus), and western meadowlarks (Sturnella neglecta) dominated shrubsteppe habitats. Grassland birds as a group were more abundant in CRP and also were more abundant in croplanddominated landscapes. Shrubsteppe birds were most associated with extant shrubsteppe habitats and were more abundant in old CRP than in new CRP. Shrubsteppe birds used CRP fields only when sagebrush was present.
We were limited in our assessment of new CRP in that sagebrush had been planted on these study areas only since 1996. As the vegetation on these areas matures and shrub height increases they likely will see increased use by shrubsteppe passerines and sagegrouse. Old CRP fields with well-established sagebrush cover had numbers of Brewerâ€™s sparrows and sage thrashers comparable to that observed in native shrubsteppe. It is likely new CRP will support equivalent numbers of birds given an equal cover of mature sagebrush.
Nesting success of passerines in CRP was comparable to that of birds nesting in native shrubsteppe. Brewerâ€™s sparrows and vesper sparrows both showed similar rates of daily nest survival in new CRP, old CRP, and shrubsteppe, whereas savannah sparrows had greater rates of daily nest survival in CRP compared with native shrubsteppe.
Pellet surveys suggest that mule deer and jackrabbits are using CRP in fair numbers, with deer using New CRP and native shrubsteppe more than Old CRP and Jackrabbits using CRP in shrubsteppe landscapes more than in cropland landscapes. Cottontail rabbits appear to be using native shrubsteppe more than CRP regardless of landscape.
- Shrubsteppe passerines are benefiting from CRP both through creation of suitable nesting habitat and development of a more contiguous â€�"non-croplandâ€ landscape where CRP adjoins fragments of native shrubsteppe.
- CRP was of most benefit to shrubsteppe-obligate passerines and to greater sagegrouse when it contained sagebrush and was located in a shrubsteppe landscape.
- CRP is providing suitable nesting habitat for some passerine birds and for sagegrouseâ€" those species examined were equally successful at nesting in CRP fields compared to native shrubsteppe.
- CRP appears to be gaining in importance as nesting, brood-rearing, and wintering habitat for sage-grouse in Washington as the sagebrush matures.
- The greater sage-grouse population in north-central Washington, an area with abundant CRP, was the only population that demonstrated an average rate of increase. This increase corresponds with the development of CRP fields into habitat with abundant sagebrush.