DoD Biodiversity Conservation Handbook
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Chapter 5 Case Studies

Multiple Uses: Fort Hood

Balancing Critical Species Protection and Armored Military Training

Fort Hood is an 88,000 ha U.S. Army installation situated in central Texas. Mixed juniper-oak woodlands, shrublands, and grasslands characterize the vegetation. Military training includes brigade combat team (bct) live fire and maneuvers with rotary-wing and combat service support. Tactical weapon systems training includes heavy armor (Abrams Main Battle Tank), artillery (Paladin and Multiple Launch Rocket Systems), light armor (Bradley Infantry Fighting Vehicles), rotary wing (Apache and Blackhawk helicopters), unmanned aerial vehicles, and small unit arms. bct units train to maintain a high state of readiness for decisive victory on the battlefield.

Two federally listed migrant songbirds, the golden-cheeked warbler (Dendroica chrysoparia) and the black-capped vireo (Vireo atricapilla), nest on Fort Hood. The installation, which has the largest populations of both species under a single management authority, is considered a crucial site for species recovery. Recovery efforts, e.g. habitat and population protection, have the potential to conflict with the military mission at Fort Hood, but thanks to adaptive management techniques, diligence, patience, observation of military training/ecosystem response dynamics, and informed decisions, Fort Hood managed to greatly reduce training restrictions on the installation from 29 percent or ca 27,000 ha in 1993 to 4.3 percent or 3,846 ha in 2007. Restriction reduction does not indicate the habitat is nonexistent and no longer protected; birds still use the habitats and their populations are monitored. However, rather than being “off limits” to training, military units are allowed to conduct crucial battle skills training in the habitat all year long. The result: unit commanders have contiguous, realistic battlefields to plan and conduct bct operations, and the birds have contiguous, managed habitats to maintain viable population growth.

Geologically, Fort Hood is a karst landscape characterized by roughly sculpted limestone hills and mesas dotted with caves, sinkholes, rock shelters, and springs. At least 19 endemic, troglobitic (adapted for cave life) invertebrates are found in karst ecosystems on Fort Hood. Additionally, 244 invertebrate species and 23 vertebrate species have been recorded from the 250+ caves, sinkholes, and springs on Fort Hood. None of the recorded species is federally endangered; however, one bat species is considered a species of concern. Fort Hood proactively protects and manages these unique ecosystems.


  • Protect, manage, maintain, and monitor sensitive and unique fauna:
  • Populations and habitat of the federally listed black-capped vireo and golden-cheeked warbler
  • Cave-dwelling populations in 550+ karst ecosystems including 13 named and 6 unnamed endemic karst invertebrates
  • Populations of a possibly endemic, karst dependent sub-species of slimy salamander (Plethodon albagula)
  • Cave myotis bat (Myotis velifer incautus) maternal colony and bat caves.
  • Populations of a globally rare shrub, Texabama croton (Croton alabamensis texensis)
  • Support and conduct leading, innovative scientific research
  • Support and maintain the mission of the largest armored force in the U.S. Army by limiting natural resources encroachments and by providing quality, realistic training lands


Consultation with U.S. Fish and Wildlife Service (USFWS)

  • Prepared biological assessment
  • Biological opinion rendered by usfws: Based on the direct and indirect impacts of military training on the vireo and warbler populations and the conservation measures undertaken by III Corps to maintain and enhance Fort Hood's populations, the USFWS issued a "no jeopardy" opinion.

Development of an Endangered Species Management Plan (ESMP)

Fort Hood's ESMP is based on the concept of adaptive management. This approach recognizes that protection and management actions are implemented with imperfect knowledge. As research and monitoring progresses, the knowledge gaps are filled which allows improved management and decision making. Serves as primary guidance to protect, manage, inventory, monitor, and research threatened, endangered, and sensitive species and their habitats.

Habitat Assessment

Before protecting bird habitat, we needed to know the location, extent, and configuration (contiguous or not). This area in particular required flexibility on the part of the trainers and the natural resources land managers because it constantly evolved based on the data and survey effort. We used aerial photography and satellite imagery along with ground truthing; this method proved 100 percent accurate in identifying bird habitat. For karst features, we used Cultural Resources Branch archives, historic community karst accounts, and on-the-ground field searches to locate, map, inventory, study, and monitor features.

Population Monitoring

Once we established where habitat areas were situated, occupancy assessment and population monitoring became crucial parts of the inventory process.

  • We capture, band, and monitor birds to obtain valuable demographic data that provide a detailed account of population parameters. We use these data to document and update population baseline and demographic trends over time; both of which we use to assess the impacts of military training on the warbler and vireo populations. Adaptive management and flexibility are very useful tools as data are gathered and analyzed.
  • We manage populations of the brown-headed cowbird (Molothrus ater), an obligate nest brood parasite. Unmanaged cowbird populations are a serious threat to warbler and vireo reproductive success and population growth.
  • We monitor and index cave myotis bat maternal population monthly to document population trends across time. All other bat caves are also monitored for bat activity and roosting.
  • We sample karst invertebrates and monitor cave microclimate to obtain an index of occupancy and health of the ecosystem across time.

Establishment of Endangered Species Survey Areas (ESSA)

We needed to know if training is having a negative impact on warbler and vireo populations. This is easy enough to accomplish in the maneuver areas via demographic study areas and point count routes, but in the impact area the investigation is more difficult. A conflict exists because it is crucial for units to maintain weapons systems proficiency and wildlife surveys ultimately result in range shutdown. To minimize training time loss and to gather valuable demographic data, we established essas. Training managers schedule one day every two weeks (usually on weekends) for bird survey crews to gather demographic data on and near weapons firing ranges. This approach reduces training time loss by providing predictability in terms of access for both survey crews and for military units, plus it is scheduled on a day of the week when most ranges are not utilized.

Establishment of "Core" and "Non-core" Habitat Areas

Once we delineated habitat, established a population monitoring program, and assessed military training intensity/tactics; we needed to protect bird habitat. During the early nesting period, training restrictions in habitat were unnecessarily restrictive due to imperfect knowledge about how much habitat was needed for viable populations, how much habitat existed, population size and demographic trends over time, and how the population responded to training. By adhering to adaptive management principles and collecting reliable data, we were able to reduce training restrictions in areas highly used by units for multiscale operations, areas we refer to as “non-core” habitat. The small percentage of habitat currently under restrictions are rarely used by units for large-scale operations, we refer to these areas as “core” habitat. By leveraging protection to rarely used habitat areas and by lifting restrictions in highly used areas, we were able to greatly reduce military training and endangered species protection conflicts.

  • "Core" habitat areas are those areas needed for long-term population maintenance and in which training is highly restricted. We delineated these areas with highly visual signs for troops in the field. Most of these areas receive very low amounts of training, so there is little conflict with mission readiness.
  • "Non-core" habitat areas are also needed for long-term population maintenance, but training is not restricted in these areas. “Non-core” areas receive the same amount of protection and monitoring as “core” areas, except that units are allowed to plan and execute operations with minimal damage to the habitat. Current doctrine of bct battle drills usually result in ephemeral, temporally-spaced habitat occupation so bird populations are rarely exposed to long-term stressors. As contradictory as it seems, moderate amounts of bct maneuver training help create and maintain vireo habitat. Similarly, wildfire ignited by weapon systems firing assists in maintaining and creating open shrubland, a crucial habitat component for vireos.

Support and Conduct Leading, Innovative Research

Fort Hood is the leader in warbler and vireo research and the installation is often the reference location for such investigations. With respect to warbler and vireo management, Fort Hood has developed many innovative studies and monitoring techniques. Some examples include:

  • Light Detection and Ranging (LiDAR), which is very useful for remotely determining shrubland vertical structure (an important component of vireo habitat) and mature forest canopy structure (an important component of warbler habitat).
  • Remote Acoustic Monitoring. Fixed Autonomous Recording Units (arus) are deployed in remote and inaccessible habitat areas (e.g. impact area); the units automatically record bird vocalizations over a period of many weeks, data reveal density and breeding activity. Airborne arus are deployed on an aerial platform (much like weather balloons) and are launched over target areas; data give a quick, limited time-frame indication of occupancy and density.
  • Infrared (IR) Nest Cameras. ir camera systems are used to identify and quantify predators at vireo and warbler nests. Data reveal that Texas rat snakes (Elaphe obsoleta lindheimeri) are the primary predators of both species. Data also reveal predator behavior at the nests, warbler and vireo response to predators, and predator activity shifts and timing as the breeding season progressed. ir camera studies revealed that red imported fire ants (Solenopsis invicta) are a major predator of vireos. Small, organic pellets and strips (sustained release devices) with internal micropores charged with volatile ant repellant compounds were deployed at vireo nest sites. The devices slowly allow a miniscule repellant vapor "curtain" to develop, thereby providing protection from ants during the vireo nest cycle.
  • Stress Hormone Study. Vireos and similar shrubland nesting birds were subjected to various levels of stress which simulates military training. Hormone response analyses revealed that vireos tolerate moderate levels of simulated military stressors. An expanded hormone and heart telemetry study using warblers and vireos and various levels and types of simulated military stressors are currently under investigation.
  • Texas Rat Snake Study. Using implanted transmitters and 24-hour, autonomous transmitter tracking arrays, analysis and study are currently conducted on snake habitat use, territory size, prey availability, seasonal movement patterns, and local life history traits. Ultimately, predator-prey dynamics, especially with relation to warbler and vireo habitat, will be better understood.
  • Off-post Buffers. III Corps is working with several partners to establish conservation easements, safe harbor agreements, and wildlife management plans on private lands surrounding Fort Hood. The functions of this initiative are to relieve the warbler and vireo recovery burden placed onto Fort Hood and to preserve metapopulation dynamics between Fort Hood and the surrounding landscape.


Within the range of the warbler and vireo, Fort Hood is the only land manager with completely recovered populations. Fort Hood has greatly exceeded population and habitat goals.

  • Fort Hood has located, surveyed, and mapped many karst features; installed specially designed gates on caves with endemic cave-dwelling species that are near commonly used areas, and established karst management areas and buffer zones.
  • Currently studying population, distribution, and genetics of the karst dependent slimy salamander.
  • Protected the cave myotis bat maternity colony site with a buffer zone delineated by rock barriers and installed two Bat Conservation International-approved bat gates on cave entrances.
  • Karst ecosystems and croton populations are found in warbler and vireo habitat, so protection of bird habitat also provides protection for other rare and sensitive species.
  • Helped maintain mission readiness by providing quality training lands and minimizing training time loss for several bcts as they prepare for operations in the Middle East.

Lessons Learned

Potentially conflicting land uses, such as armored military training and ecosystem protection, can be attained with careful planning, observation, research, plan implementation, and most importantly, stakeholder collaboration. Difficult management decisions and decision analyses, as well as stakeholder compromises, must be made to accomplish the delicate balance of training the Armed Forces and preserving wildlife and their habitats.

© Copyright 2008. NatureServe.

About This Case Study's Author
By Charles E. Pekins
Wildlife Biologist
Department of the Army
DPW Environmental Division
Natural Resources
III Corps and Fort Hood
4612 Engineer Drive, Room 76
Fort Hood, Texas 76544-5028
Phone: 254-287-2885

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