BIRDS AND LIVESTOCK GRAZING-A REVIEW

by George Wuerthner

Introduction

Livestock production is a contributing factor in the decline of many western species, including birds (Wuerthner and Matteson 2002). This is not surprising given the amount of land utilized for animal agriculture, including public and private lands. Approximately 578 million out of 1.9 billion acres in the West are grassland pasture or range. An additional 140 million acres of forests are grazed. Almost half of grazed landscapes are publicly owned (USDA ERS 2002). Nearly 90 percent of federal lands administered by the Bureau of Land Management (BLM) and 69 percent managed by the Forest Service are leased for livestock grazing. Grazing also occurs on state lands, and a significant number of federal and state wildlife refuges, state and national parks, national conservation areas, national monuments and wilderness areas. In total, as much as 700 million acres, or slightly more than a third of the land area of the contiguous United States may be grazed by domestic animals (Wuerthner and Matteson 2002).

In addition to the vast amount of acreage devoted to livestock grazing, most of the nation’s cropland is also used to produce livestock forage. Cropland totaled 344 million acres in 1999. Determining how many acres of this land was used to feed domestic livestock is beyond the scope of this paper. However, it should be noted that four crops-feeder corn, soybeans, hay and wheat-accounted for 80 percent of this acreage (USDA ERS 2002). Of these crops, three-corn, soybeans, and hay-are largely used for livestock feed, particularly cattle. When these acres are added to the land used for grazing, as much as 900 million acres, or nearly half of the acreage in the contiguous United States, may be used for livestock production. Because of the huge geographical area affected by livestock production, there are many, significant impacts on native wildlife.

“Livestock production,” as opposed to mere “grazing,” involves more than the cropping of grass or shrubs by domestic livestock. Growing livestock in the West involves multiple activities with consequences for bird species. These include, but are not limited to, the destruction of predators and “pests” (e.g., grasshoppers and prairie dogs); degradation of riparian areas through grazing and withdrawal of water from streams for crop irrigation; ground water pumping that can negatively affect riparian habitat, seeps, and springs; the spread of exotic species (invasive weeds, and non-native grasses planted for forage); and alteration of natural fire regimes (Wuerthner and Matteson).

Grazing Impacts on Birds

Livestock grazing impacts on birds vary with the type of livestock operation, region of the country and other factors. Responses of individual bird species are often habitat and species specific (Bock 2002). Not all livestock related changes have negative consequences for all bird species. Also, because their mobility allows birds to move someplace else when habitat is degraded by grazing, the effects of grazing on many bird species may be negative up to a point, but not enough to cause measurable population declines or clear direct impacts. For some birds, the effects of livestock production are neutral or even positive. For example, mountain plover nest on nearly bare lands created by overgrazing-although it should be noted that prairie dogs create similar suitable habitat and the decline of prairie dogs from persecution on behalf of livestock interests may be contributing to the decline of mountain plovers (Knowles et al 1982). Also, cowbirds have expanded their numbers and range due to the presence of livestock in the West (Goguen and Mathews 2001). However, the increase in cowbirds-which are brood parasites-has had its own negative consequences on many species of song birds (Marvil and Cruz 1989).

Despite these reservations, there is ample evidence that livestock production negatively affects many western bird species in multiple ways. Increased grazing intensity can lead to population declines in birds (Kantrud 1981). Livestock trampling can destroy nests (Jensen et al 1990) and degrade riparian habitat. Grazing negatively affects some waterfowl species by reducing nesting success (Gilbert et al. 1996).

Grazing can reduce hiding cover, leading to greater losses from predation (Gregg et al. 1994). Even in areas where grass cover remains in “excellent” condition because plant community changes have not occurred may still have less cover than is necessary for the survival of some species like sharptail grouse (Kirby and Grosz 1995) and lesser prairie chicken (Jackson 1963).

Haying of fields also eliminates cover, leading to reduced nesting success. Haying negatively impacted nesting sandhill cranes (Littlefield and Paullin 1990) and rough-legged hawks in Malheur National Wildlife Refuge in Oregon (Littlefield et al. 1992). Haying and other forage production use the vast majority of water in the West (Wuerthner 2002), resulting in a decline in riparian habitat and aquatic foods for species as diverse as bald eagles and great blue heron.

The spread of exotic weeds like cheatgrass can lead to overall degradation in vegetative communities, destroying important food sources and cover. For instance, cheatgrass invasion and subsequent frequent fires is one factor in the decline of sage grouse (Fischer et al. 1996).

“Pest control” done in the name of livestock grazing can negatively affect some bird species, such as the elimination of prairie dogs and the resultant impacts on burrowing owls that depend upon the rodents for both food and nesting habitat (Desmond et al. 2000). The loss of prey species like prairie dogs and ground squirrels also negatively affect some birds of prey (Bock 2002).

Alternative grazing regimes do little to reduce impacts on bird species. For instance, short duration grazing where livestock are concentrated in pastures and moved frequently from pasture to pasture leads to a greater reduction in hiding cover that exposes ground nesting birds to predators and contributes to greater trampling effects (Paine et al. 1996). Individual studies sometimes demonstrate changes in species abundance due to livestock production. A comparison study of grazed and ungrazed lands on the Audubon Ranch in southeast Arizona showed an increase in some bird species on grazed lands that were habitat generalists, but it also exposed declines in grassland species like the Botteri’s sparrow and Cassin’s sparrows in the same area (Bock and Bock 1993).

Literature Reviews on Grazing Impacts on Birds

Literature reviews and studies on livestock grazing impacts support the view that livestock production has a detrimental effect on many bird species (Fleischner 1994). Wilcove et al. (1998) reported that livestock grazing (as opposed to all-inclusive livestock production) was found to be one of the major factors of species endangerment in the United States, surpassing logging and other land uses. Flather et al. (1994) looked at various causes for species endangerment and reported that grazing was the most frequent reason cited for species decline in the Southwest.

Another review by former BLM biologist Elaine Rees found that livestock production contributed to the decline of 192 animal species with threatened, endangered or sensitive status in ten western states (Rees 1993). Among the diverse species of birds that Rees found negatively impacted by livestock production were sandhill crane, western yellow-billed cuckoo, southwest willow flycatcher, sharptailed grouse, ferruginous hawk, burrowing owl, mountain quail, Leconte’s sparrow, and Bell’s vireo.

A review by Larry Walker, a former BLM range conservationist, found that, of 153 species of southwestern birds affected by livestock grazing, 17 species show variable responses, both positive and negative depending on the situation, another 18 benefit from grazing, and 118 bird species are negatively affected by livestock grazing. Walker’s review showed that 91 percent of state listed birds in the Southwest are negatively affected by livestock grazing, demonstrating livestock’s role in species endangerment.

Sabb et al. (1995) found that livestock grazing had a major negative impact on many migratory landbirds in the western United States. Of 68 species of neotropical migrants reviewed, 29 percent increased with livestock grazing, 25 percent showed no clear response, while 46 percent decreased.

Krueper et al. (in press) recently reported that population trends of neotropical migrants in the San Pedro Riparian National Conservation Area in Arizona have shown a marked response to the removal of livestock from the area in 1987. Only 8 percent of migrant species declined after the removal of livestock, 39 percent showed no clear response, and 53 percent increased in abundance.

Grazing Impacts on Riparian Habitat–Consequences for Birds

Riparian habitat, the thin green lines of vegetation along streams, seeps, and springs in the arid West, is vitally important to birds and other wildlife (Rich 2002; Kauffman et al. 1997; Ohmart 1996; Johnson 1989; Carothers et al. 1974). Studies show that 50-80 percent of all bird species utilize riparian habitat. For example, in western Montana 51 percent of land birds use riparian habitat (Masconi and Hutto 1981). According to Rich (2002), some 77 western land birds are obligate or dependent on riparian zones for breeding.

Although western riparian areas have suffered significant degradation due to a variety of factors, including dams, Bureau of Reclamation water projects, housing and highway construction, and other human activities, livestock grazing is considered one of the most pervasive factors responsible for the damage to riparian habitat, particularly on public lands. Indeed, according to a 1990 study done for the Environmental Protection Agency, despite 100 years of range management, riparian areas were in the worst condition in history (Chaney et al. 1990). And an exhaustive review of over 200 riparian studies by Belsky et al. (1999) found none reporting a benefit of cattle on riparian areas when those areas were compared with ungrazed controls.

As a consequence, species with a high dependence on riparian habitat have been particularly hard hit by livestock-induced habitat degradation. Even species that generally depend on upland habitat like the Gunnison sage grouse can suffer livestock-induced declines as a result of riparian damage or loss due to their dependency on wet meadows during parts of their life cycle (Webb 2000).

Studies that compare riparian areas where livestock were removed with areas under continued grazing have demonstrated positive recovery in riparian-dependent bird species in Oregon at Malheur National Wildlife Refuge (Taylor and Littlefield 1986) and at Hart Mountain National Wildlife Refuge (Dobkin et al. 1998).

Conclusion

Livestock production on western lands has significantly impacted many bird species, often leading to such severe declines in some species that they are proposed or listed as threatened or endangered in parts or all of their range. Reducing livestock production on public lands through voluntary federal grazing permit buyout permit and other mechanisms would likely lead to the restoration and recovery of many bird species, as well as greater positive ecosystem response.

Text by George Wuerthner; edited by Mark Salvo.

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