Chihuahuan Desert Grassland

Chihuahuan Desert Grassland covers roughly the southern third of New Mexico and is found only in the Chihuahuan Desert Physiographic Area. This habitat extends along the southern border of the state; north to Hobbs and Roswell in the Pecos Valley; Carrizozo, and White Sands Missile Range in the Tularosa Basin; and San Acacia in the Middle Rio Grande Valley. It occurs north to Hillsboro (excluding the Plains of San Agustin) and west to the Gila River on the Arizona border. Elevations range from 2800 to 5500 feet.

Little of this habitat remains intact in the United States, due to persistent, large-scale impacts, primarily due to grazing. It may be the most endangered biome type in North America (W. Whitford pers.comm.). Small fragments of this habitat may exist on military reservations, such as Fort Bliss in southern New Mexico, but are unlike the major expanses of this habitat that existed before the advent of grazing (W. Whitford pers. comm.).

Continuous grazing has altered the historical composition of this habitat from primarily perennial bunch grasses to low-growing sod grasses in many areas, or where summer rainfall is low, to annuals (Brown 1982). Historically, black grama (Bouteloua eriopoda) was the dominant grass of this habitat, but it is probable that blue grama (B. gracilis) is currently more prevalent (W. Whitford pers. comm.). Other grasses include dropseeds and other Sporobolus spp., gyp grasses, and vine mesquite (Panicum obtusum). Major grass species include tobosa (Hilaria mutica), bushmuhly (Muhlenbergia porteri), burrograss (Scleropogon brevifolius), and side-oats grama (B. curtipendula).

Most major shrub species in Chihuahuan Desert Grassland are also major species of the Montane and Chihuahuan Desert Shrub types. Some of the more common shrubs include Acacia spp., Agave spp., false mesquite (Callianndra eriophylla), feather peabush (Dalea formosa), sotol (Dasylirion wheeleri), broom snakeweed (Gutierrezia sarothrae), longleaf jointfir (Ephedra trifurca), chollas (Opuntia spp.), and littleleaf sumac (Rhus microphylla). Associations of black grama and side-oats grama (B. curtipendula) with Chihuahuan Desert or Montane Shrub species, as shrub dominants, may be examples of climax desert grassland type (Dick-Peddie 1993).

The condition of these grasslands is a result of the combined effects of several forces. Soil, topography, drought, fire, and grazing history are the main factors. Shrubs tend to occur on sites where the soil is calcareous, where grazing history has been relatively intense, and/or where there has not been an intensive fire regime. Sites that are in good condition contain more grass and fewer shrubs (Dick-Peddie 1993).

Shrubby habitat (usually mesquite or yucca) is now extensive due to grazing. A combination of over-utilization, lack of fire, and poor soil has led to the current abundance of shrub habitat.

These grasslands were an important breeding area for the Aplomado Falcon prior to the 1930's. The last recorded breeding of this species in the southwestern United States was at Deming in 1952 (Clark 1987, Hubbard 1978). There have been a number of recent sightings in the Chihuahuan Desert Grasslands; this species may recolonize areas in southern New Mexico. Management for this species may be most appropriate in the Tularosa Basin.

During migration and in winter, these grasslands are used by large numbers of birds, particularly sparrows, meadowlarks, and mourning doves, but also raptors and other species. Three wintering species have been identified as a high priority: Sprague's Pipit, Baird's Sparrow, and McCown's Longspur.

Urban areas exist within this habitat and are considered to be a subhabitat. This section is being developed and will appear in a later version of this Bird Conservation Plan.

Impacts to this habitat include: 1) overgrazing, 2) shrub invasion, 3) fire and fire suppression, 4) drought, 5) fragmentation, 6) oil and gas development, and 7) prairie dog control.

This habitat is comprised of government-managed and privately-held lands. Most of the habitat east of the Guadalupe Mountains is privately owned in the north and managed by the BLM or the Department of Energy in the south. Much of the land in the south is leased to private oil and gas companies. The Tularosa Basin, west of the Guadalupe Mountains, is primarily under military management. In the Rio Grande Valley, most of the land north of Elephant Butte Lake is BLM-managed. The Hatch, Mesilla, and Las Uvas Valleys, and the Deming-Columbus corridor are predominantly private agricultural lands. Lands west of there, and along the Mexican border, are primarily BLM lands.

Physiographic Areas covered: Chihuahuan Desert and Mexican Highlands.

Associated priority species from Appendices B and C:

Table 1. Chihuahuan Desert Grassland Priority Species

Bird Habitat Requirements, Population and/or Habitat Objectives:
(in taxonomic order)

• open yucca grasslands with scattered tall yuccas, often reaching heights greater than 9ft (3m)
• dense grasses preferred, grasslands often have tobosa swales.
• lowest nests are approximately 6ft above ground in yuccas; largely uses nests constructed by ravens or other raptors
• dominant grasses are Hilaria mutica, Bouteloua gracilis, B. eriopoda and B. curtipendula
• dominant shrubs are Ephedra trifurca, Yucca Elata, Prosopis glanulosus, and Opuntia macrocentra
• In northern Chihuahua, the minimum mix of shrubs/ha is 13, while the maximum is 330
• large amount of avian biomass may be important to sustaining a breeding population (B. Locke pers. comm.)
• prey items in N. Chihuahua include meadowlarks, nighthawks, mockingbirds, western kingbird, cowbirds, mourning dove, pyrrhuloxia, cactus wren and canyon towhee
• home area for breeding may be over 6.6 mi5 (17 km5) (B. Locke pers. comm.)

• ground cavities created by burrowing mammals, usually prairie dogs, critical for Western Burrowing Owl
• in variable areas with friable soils for excavation
• nest burrows generally in areas with other burrows, surrounded by bare ground or short grass, high perches nearby may be a critical factor
• in urban areas, concrete rubble or pipes going underground may be used but are not preferred
• tolerant of limited human presence or disturbance

• (summering) in the U.S., T = -1.0%, p = 0.81, N = 33, RA = 0.58 (Sauer et al. 1997)
• monitor for presence in the Chihuahuan Desert during the months of December, January and February
• maintain areas with taller grass, generally grama-dominated situations (not in swales) with high grass canopy cover Assumption: This will provide appropriate wintering habitat.

• ungrazed or lightly grazed taller grass areas without trees or shrubs
• in winter, found much more often in tobosa swales, possibly vine mesquite or other grasses, with denser grass than surrounding areas (NM PIF)
• enough thatch and ground cover without a mat of vegetation may be critical
• nearly absent from areas that receive more than moderate grazing
• may be found in areas containing Lehmann=s lovegrass or bluestem in migration
• wintering habitat needs are assumed to be the same as breeding habitat (AZ PIF)
• most productive breeding habitat in NW North Dakota contained native grasslands - average height of 9 in (23 cm) - with litter up to 0.8 in (2 cm) deep, <10% shrub cover, and a mosaic of forbs, grass, and bare ground (Winter 1994 in Jones and Green 1998).
• breeds more commonly in areas burned over twelve years than area burned only twice or not at all (Winter 1994 in Jones and Green 1998).

• (summering) in the U.S., T = 2.6%, p = 0.33, N = 39, RA = 2.2 (Sauer et al. 1997)
• maintain continued presence in the Chihuahuan Desert, Colorado Plateau, and Pecos and Staked Plains during the months of December, January and February
• reduce new plowed acreage in shortgrass areas
• manage for shortgrass vigor, either through light to moderate burning in healthy areas or rotation grazing techniques

Associated Species: Aplomado Falcon, Swainson's Hawk, Grasshopper Sparrow

Over time and a large landscape managers should address at the following issues:

Even in healthy grasslands, 100% grass canopy coverage does not occur. However, managers should try to achieve an overall 50-65% grass canopy cover. Bare ground should be kept to a minimum. Canopy cover is important for grass-utilizing species and lack of enough cover will not maintain these species. Bare ground is important for such birds as Horned Lark. While an important component of most grassland bird assemblages, this should not be the only dominant bird in Chihuahuan Desert grasslands .

Managers should strive to maintain grass heights averaging 9.8 in. (25cm) or more. Depending on soil conditions, grazing regimes and other factors, this is not always possible in every area, but can be maintained over an entire landscape. In particular, areas which are slightly more mesic, ie. drainages in grassland areas, swales, etc. grasses should be maintained at an average of 13.6 in. (35cm).

Chihuahuan Desert Grassland should have few shrubs. Healthy grasslands naturally allow only minimal shrub encroachment. Encroachment is an indication that grassland is not maintaining its integrity. Limited shrub cover is a natural part of grasslands but generally at considerably lower densities than found in most grasslands today. Managers should work toward maintaining no more than 20% shrubs in the overall landscape. Tall shrubs, especially yuccas over 9 ft (3 m) should be encouraged and maintained. Shrub habitat is used by many birds. The extreme xerification of grasslands has caused an increase in the abundance of birds utilizing shrubs at the expense of those species which require pure or primarily grass habitats.

Rest-rotation methods or the Savory method appear to be better methods for maintaining grassland integrity, as well as the health of the herd, than many historic grazing methods. Studies on the Jornada Experimental Range near Las Cruces, New Mexico have shown that areas that have been recently burned or affected by drought, and are grazed during the growing season, require two or more years to recover. This recovery period is a considerable increase for these areas when compared to dormant season grazing. (K. Havstaad pers. comm.)

Prairie dog control:

Burrowing Owls depend on burrows created by prairie dogs and they can be an important food source for wintering raptors such as Golden Eagles and Ferruginous Hawks. Managers should refrain from controlling prairie dog populations whenever possible.

Watering points are critical for the success of wintering grassland birds. Managers are encouraged to preserve or restore cienagas, natural playas, lakes, springs, or other water sources. Restoration or preservation of natural water areas is encouraged over the installation of water tanks.

Additional species for which monitoring is recommended:

• Scaled Quail
• Common Nighthawk
• Cassin's Sparrow