Report of Surveys for Gray Vireo at the New Mexico Army National Guard Camel Tracks Training Site

June 2012

June 2012

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SUMMARY

The New Mexico Army National Guard has established training regulations at the Camel Tracks Training Site (CTTS) to protect the gray vireo from disturbance during the breeding season. The gray vireo is listed by the state of New Mexico as threatened. In addition to these protections, NMARNG monitors gray vireo to ensure continued quality habitat at CTTS.

Gray vireo was first detected by NMARNG at CTTS in 1995. Annual surveys have been conducted from 2001 to 2012 with birds found every year. The areas consistently used by gray vireos include several drainages of the western hills and the drainage leading off CTTS to the northeast.

In June of 2012, surveys found six areas containing a singing male. These areas were not surveyed for females or nests but it is likely that many or all of these areas have mated pairs. All six areas have supported nesting pairs in the past. Within CTTS, no singing males were detected outside the (gray) Vireo Seasonal Restricted Area (VSRA).

As no pairs were detected outside the boundaries of the VSRA, the New Mexico Army National Guard has no need to adjust the VSRA boundaries. As up to six vireo pairs may be using habitat within the VSRA, there is no need to adjust training regulations for the VSRA. Introduction

The gray vireo, Vireo vicinior, is listed as threatened by the State of New Mexico. It was first detected at the Camel Tracks Training Site (CTTS) during an initial Natural Heritage New Mexico (NHNM) survey conducted for the New Mexico Army National Guard (NMARNG) in 1995. As part of the ongoing NMARNG ecosystem management program for CTTS, monitoring of gray vireo areas is conducted yearly. The results of these surveys are used to delineate the boundaries of the Vireo Seasonal Restriction Area (VSRA) and assess VSRA regulations. This report presents the results of monitoring conducted during June 2012.

Gray Vireo Nesting Habitat

The gray vireo breeds in semi-arid shrub habitats with either extensive shrubland or scattered shrubs among pinyon-juniper (Pinus edulis - Juniperus sp.) woodlands (Figure 1). A continuous layer of shrub twig growth 0.3 to 1.5 meters above the ground is a common aspect of gray vireo habitat (Grinnell and Miller 1944, cited in USDA Forest Service 1994) and shrublands that are mature or late in post-fire succession may be preferred (USDA Forest Service 1994). In San Juan and Rio Arriba Counties of northwestern New Mexico, gray vireos were found in pinyon-juniper woodlands between elevations of 5800 and 7200 ft (1768 and 2195 m) (Reeves 1998).

Figure 1. Gray vireo oneseed juniper habitat at the Camel Tracks Training Area.

In northwestern New Mexico, gray vireos begin first-nest construction in May or early June, with both sexes incubating and tending young. As incubation takes 13 to 14 days and young fledge in 13 to 14 days (Ehrlich et al. 1988), gray vireos are still feeding fledglings in July. In addition, gray vireos can attempt a second nest and, if successful, be feeding fledglings well into August. Vireos usually begin migrating south in September.

In California, gray vireos seem to avoid woodland edge and prefer unbroken chaparral (USDA Forest Service 1994). And given the size of breeding territories in Texas and Arizona, Barlow and Wauer (1971) suggest that large tracts of undisturbed habitat are required to support individual pairs.

An avoidance of edge and preference for larger tracts may be related to brood parasitism by brown-headed cowbirds (Molothrus ater), a species often associated with forest-field edge habitat and livestock. The fragmentation of forest habitat is an often-cited reason for increases in cowbird parasitism outside the Great Plains (Mayfield 1977, Kerlinger and Doremus 1981) and parasitism rates are highest near forest-field edges (Gates and Gysel 1978). Cowbirds are associated with livestock, often feeding in horse corrals and cattle rangelands (Verner and Ritter 1983). In the Sierras of California, Verner and Ritter (1983) found few cowbirds more than 10 km from such food sources. In addition, Wauer (1977) observed that with the cessation of grazing and an increase in woody plants, gray vireo numbers increased in Big Bend National Park, Texas.

Gray Vireo Status

The geographic breeding range of the gray vireo includes portions of California, Nevada, Utah, Colorado, New Mexico, Texas, Arizona, northwestern Baja Chihuahua, and northwestern Coahuila, where its NatureServe status varies from Apparently Secure (S4) to Imperiled (S2) (Figure 2). The most abundant breeding area is in northern Arizona and southern Utah (Sauer et al. 1997). NatureServe status ranks are independent of government status designations but often better reflect the current biological condition of a species. Species without population concerns are listed as Secure (G5). Globally this species is listed as Apparently Secure (G4). A species listed as G4 is uncommon, but not rare, and usually widespread. Typically more than 100 occurrences or more than 10,000 individuals exist globally, but there may be reasons to be concerned about the long-term prospects of G4 species. North American Breeding Bird Survey trend estimates demonstrate population declines from 1966 to 1996 (-3.9 percent average annual decline; P = 0.01; N = 273 survey routes) and from 1980 to 1996 (-1.1 percent average annual decline; P = 0.14; N = 236) in surveys across the vireo’s range (Sauer et al. 1997).

Natural Heritage New Mexico, as part of the NatureServe network, reviewed current work on the gray vireo, including efforts by NMARNG, and upgraded the gray vireo from Vulnerable (S3) to Apparently Secure (S4) in 2005. NatureServe ranks by state suggest that populations in Arizona and Texas are also Apparently Secure (S4). The gray vireo is not listed as Secure (S5) in any U.S. or Mexican state. In Colorado and California it is listed as S2, Imperiled. It is listed as Vulnerable (S3), in Utah and Nevada. The State of New Mexico, through the Conservation Services Division of the Department of Game and Fish, lists the gray vireo as threatened, thus “likely to become endangered within the foreseeable future throughout all or a significant portion of its range in New Mexico.” As a New Mexico threatened species it is also listed by the state as a “Species of Greatest Conservation Need” (SGCN). U.S. Forest Service Region 3, New Mexico and Arizona, lists the gray vireo as sensitive and a species of concern. In addition, North American Breeding Bird Survey trends for 1966 to 1996 indicate population declines in northwestern New Mexico, but population increases in southern New Mexico. However, Breeding Bird Survey sample sizes in New Mexico are inadequate for reliable population trend estimates (Sauer et al. 1997).

Figure 2. Gray vireo geographic range. As a threatened species listed by the New Mexico Department of Game and Fish (NMDGF), the gray vireo is protected under sections 17-2-37 through 17-2-46 of the Wildlife Conservation Act (NMDGF 1988). Even without threatened status, it is protected under New Mexico state law and cannot be shot, injured, ensnared, trapped, or destroyed (NMDGF 1988). It is also protected by the Migratory Bird Treaty Act which “prohibits the attempt or actual pursuit, hunt, capture, or kill of any migratory bird, or any part, nest, egg, or products without proper authority” (MBTA 1918).

Gray Vireo at the Camel Tracks Training Area

Previous NMARNG/NHNM surveys for gray vireo (DeBruin 1996, Arbetan et. al. 2002, Arbetan and Muldavin 2003, 2004, 2005, and Johnson et al. 2011) found birds nesting and foraging in the far northwest and far northeast corners of the training area. These areas are dominated by juniper (Juniperus monosperma) with little pinyon (Pinus edulis). These surveys were used by NMARNG to construct and modify the VSRA.

Training Area Description

The training area lies within a semi-arid watershed with ephemeral arroyos draining predominantly northwest to south and southeast into the Santa Fe River. The vegetation in the northern half of CTTS is characterized by open woodlands dominated by oneseed juniper (Juniperus monosperma) with scattered pinyon pine (Pinus edulis) and interspersed with grama (Bouteloua spp.) grasslands that can have rabbitbrush (Chrysothamnus nauseosus), snakeweed (Gutierrezia sarothrae), or tree cholla (Opuntia imbricata) components. Grasslands predominate on the southern half of CTTS with blue grama (Bouteloua gracilis) grasslands heavily interspersed with patches of galleta (Hilaria jamesii), purple three-awn (Aristida purpurea), and sand dropseed (Sporabolus cryptandrus). The ephemeral drainages and valley bottoms are variable and distinctive in their high diversity of forbs and grasses.

Methods

Monitoring surveys were conducted from May 30, 2012 to June 3, 2012. The surveys began at dawn and ended three or four hours later. Surveys consisted of walking various routes and stopping approximately every 40 m to listen for bird vocalizations (Figure 3). All birds observed by sight or vocalization were recorded (spot-mapped). Some birds were followed for a time to improve spot-mapping. Use area (spot-mapped area) should be considered simply a sample of the greater area a bird is using as it is likely that gray vireos at CTTS use a larger area than depicted in the use areas.

Figure 3. Routes taken to survey for gray vireo at CTTS. Results

General Bird Surveys

Twenty-one bird species were detected at CTTS during the 2012 monitoring surveys, including female and male brown-headed cowbirds (Table 1).

Family Species Name Common Name Accipitridae Buteo jamaicensis red-tailed hawk Alaudidae Eremophila alpestris horned lark Caprimulgidae Chordeiles minor common nighthawk Cathartidae Cathartes aura turkey vulture Columbidae Zenaida macroura mourning dove Corvus brachyrhynchos American crow Corvidae Gymnorhinus cyanocephalus pinyon jay Chondestes grammacus lark sparrow Emberizidae Pipilo maculatus spotted towhee Spizella passerina chipping sparrow Falconidae Falco sparverius American kestrel Fringillidae Carpodacus mexicanus house finch Molothrus ater brown-headed cowbird Icteridae Icterus parisorum Scott's oriole Mimidae Mimus polyglottos northern mockingbird Paridae Baeolophus ridgwayi juniper titmouse Troglodytidae Salpinctes obsoletus rock wren Contopus sordidulus western wood peewee Tyrannidae Tyrannus verticalis western kingbird Vireo vicinior gray vireo Vireonidae Vireo plumbeus plumbeous vireo

Table 1. Bird species detected at CTTS in 2012.

Gray Vireo

Surveys found six areas containing a singing male (Figure 4). These areas were not surveyed for females or nests but it is likely that many or all of these areas have mated pairs. All six areas have supported nesting pairs in the past. Within CTTS, no singing males were detected outside the Vireo Seasonal Restricted Area (VSRA).

Figure 4. Areas used by gray vireos at CTTS in 2012. Conclusions and Recommendations

General Bird Surveys

Other than gray vireo, none of the species detected at the CTTS are species with conservation status at this time. However, periodic bird surveys are still recommended to track trends in biodiversity and detect unusual species occurrences.

Although the use areas detected with spot-mapping are similar in size to that reported for gray vireo territories, the authors experience with gray vireo at CTTS suggests these may be portions of a larger area used by a breeding pair. Previous experience with playback songs at CTTS found vireos to move quite a distance to investigate playback. Playback results suggest a more fluid nature of a pair’s territory, with vireos moving nest areas and current core territory across a larger home range (Anich et al. 2009). This shifting of nesting around a large area may be related to avoidance of cowbirds. Spot-mapping was used in this survey as the purpose of the work was to simply check if gray vireos are using CTTS habitat and the VSRA in particular.

The current VSRA (Figures 3 and 4) adequately covers current and historic gray vireo habitat at CTTS. No changes are recommended for the VSRA boundaries or regulations.

LITERATURE CITED

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