Fort Irwin National Training Center Research Articles

Habitat selection and water dependency of feral burros in the Mojave Desert, California, USA

AbstractExpansion of feral burro (Equus asinus) populations across the southwestern United States is causing human–wildlife conflicts including rangeland degradation, competition with livestock and native species, and burro–vehicle collisions. On the Fort Irwin National Training Center (NTC) in California, feral burros interfere with military training and are involved in vehicle collisions and other conflicts (e.g., burros blocking access to buildings). Limited data on burro movements and resource use poses a challenge for the development of management plans and mitigation strategies. We estimated home range size, second‐ and third‐order seasonal resource selection, and water dependency of 10 adult female feral burros fitted with global positioning system (GPS) collars on the NTC from November 2015 to April 2017. Mean 95% autocorrelated kernel home range size of female burros (253.9 ± 30.7 km2 [SE]) did not differ among seasons or between burros that resided close to or far from urban areas. Burros selected areas closer to water in all seasons and at both spatial scales, but selection was stronger in the dry season and at the landscape scale. When available, burros strongly selected for areas closer to urban areas. Burros consistently selected for areas with green forage and at lower elevations, but selection for other topographical features was variable. Water use patterns were consistent with the resource selection results. Burros visited water sources twice as often (every 22.2 ± 6.3 hr) during the hot‐dry season (Apr–Oct) compared to the cool‐wet seasons (Nov–Mar; 2015: 45.9 ± 21.0; 2016: 39.7 ± 9.3 hr). Our results suggest that urban areas, and resources therein, and water sources have the biggest influence on burro resource selection, and management plans could focus mitigation programs on these areas.

Accounting for residual heterogeneity in double‐observer sightability models decreases bias in burro abundance estimates

AbstractFeral burros (Equus asinus) and horses (E. ferus caballus) inhabiting public land in the western United States are intended to be managed at population levels established to promote a thriving, natural ecological balance. Double‐observer sightability (MDS) models, which use detection records from multiple observers and sighting covariates, perform well for estimating feral horse abundances, but their effectiveness for use in burro populations is less understood. These MDS models help minimize detection bias, yet bias can be further reduced with models that account for unmodeled variation, or residual heterogeneity, in detection probability. In populations containing radio‐marked individuals, residual heterogeneity can be estimated with MDS models by including a covariate that corresponds to the marked status of a group (MH models). Another approach is to use information from detections missed by both observers to account for the characteristics that make groups more or less likely to be detected, or recaptured, by the second observer (MR models). We used aerial survey data from 3 burro populations (Sinbad Herd Management Area, UT [2016–2018], Lake Pleasant Herd Management Area, AZ [2017], and Fort Irwin National Training Center, CA [2016–2017]) to develop MDS models applicable for feral burros in the southwestern United States. Our objectives were to quantify precision and bias of standard MDS surveys for feral burros and to examine which model type for incorporating residual heterogeneity (MH or MR) would result in the least‐biased estimates of burro populations relative to the minimum number known alive (MNKA) within the Sinbad Herd Management Area. Standard MDS model estimates achieved a mean coefficient of variation of 0.08, while underestimating MNKA by an average of 27.1%. Accounting for residual heterogeneity through recapture probability in MR models resulted in estimates closer to MNKA than MH models (9.5% vs. 16.5% less than MNKA). Our results indicate that MDS models can achieve precise enough estimates to monitor feral burro populations, but they routinely produce negatively biased estimates. We encourage the use of radio‐collars to reduce bias in future burro surveys by accounting for residual heterogeneity through MR models.

Estimating Abundance and Simulating Fertility Control in a Feral Burro Population

ABSTRACTOverabundant populations of feral equids are negatively affecting rangelands in the western United States. To better manage these populations, robust estimates of abundance and demographic rates and cost‐effective methods of reducing abundance are necessary. From August 2015 to April 2017, we estimated the abundance of feral burros (Equus asinus) at the Fort Irwin National Training Center (NTC; California, USA) using a double‐observer‐sightability aerial survey method; captured, radio‐collared, and inoculated female burros with porcine zona pellucida (PZP), an immunocontraceptive control agent; estimated female demographic rates; and used matrix population models to simulate how changes in demographic and PZP delivery rates would influence burro abundance. We estimated there were 690 (95% CI = 618–752) feral burros within the surveyed area, but these are part of a much larger population that is not geographically isolated from those in the survey area. Sighting probabilities ranged from 0.19–0.98 and were most strongly influenced by distance from observer and group size. We estimated age‐specific demographic rates at the NTC and compiled mean rates across burro populations in arid environments from the literature. Mean fecundity varied from 0.17 to 0.58 foals/adult female with younger females having lower fecundity. Mean survival was 0.90 for foals, 0.98 for yearlings, and 0.96 for adults. The PZP vaccine treatment strategies that suppressed fertility for up to 10 years predicted that burro abundance would be reduced by 67–88% after 15 years (compared with no treatment), but none of these strategies resulted in population extirpation. Population growth rates shifted from increasing to decreasing at adult survival rates below 0.84 and the population was predicted to become extirpated when adult survival declined to <0.60. In the absence of other methods to reduce burro numbers, our findings indicate that current formulations of PZP immunocontraception, which require multiple doses, would be inadequate for controlling population growth rates at the NTC. Our fieldwork also highlighted the difficulty of administering PZP vaccination to large, free‐ranging animals. Development of longer‐term fertility reduction agents or more efficient vaccine delivery techniques would likely improve the efficacy of fertility control for overabundant ungulate populations. Lack of geographic closure (physical barriers to migration) further complicated efforts to reduce burro numbers. © 2021 The Wildlife Society.

Weaponizing Affect: A Film Phenomenology of 3D Military Training Simulations during the Iraq War

This article critically considers the relation between simulation design and human experience through the analysis of three-dimensional military training simulation scenarios developed between 2003 and 2012 at the Fort Irwin National Training Center in the Mojave Desert of California. Following news reports of torture at Abu Ghraib, the US military began to implement “cultural awareness” training for all troops set to deploy to the Middle East. The military contracted with Hollywood special-effects studios to develop a series of counterinsurgency warfare immersive-training simulations, including hiring Iraqi-American and Afghan-American citizens to play villagers, mayors, and insurgents in scenarios. My primary question centers on the military technoscience of treating human bodies as variables in a reiterative simulation scenario. I analyze interviews with soldiers and actors, my own experiences videotaping training simulations at the fort, and the accounts of many other visiting journalists and filmmakers across time. From this, I contend that the stories participants tell about simulation experiences constitute one key outcome of the simulation itself, blunting dissent and aiding the fort’s long-term efforts to retain clout and funding in the face of wars whose intensity fluctuates. I treat the ongoing cinematic performances on the fort as a kind of “simulation body” unbounded by skin, a theoretical framework drawn from Vivian Sobchack’s (1992) film phenomenological concept of the “film body” and affect theory grounded in the work of Kara Keeling (2007), as well as Eve Sedgwick (2003), Sedgwick and Adam Frank (1995), and Lisa Cartwright (2008), by way of American behavioral psychoanalyst Silvan Tomkins (2008).

Catching Large Groups of Ravens: A Note on Procedures using Rocket Nets

ABSTRACT Capturing Common Ravens (Corvus corax) is very difficult. Several methods are currently used, but none effectively catch large numbers (>25 birds) of ravens at one time. Efficient capture of large numbers of ravens is needed for some autecology studies. We describe and evaluate the effectiveness of using a prebaited rocket net trapping method for simultaneously capturing large numbers of ravens. The study sites were within 2 landfills in California's Mojave Desert, one at Edwards Air Force Base and the other at Fort Irwin National Training Center. We captured 283 ravens on 5 trapping occasions between 1995 and 1997, with an average of 57 birds per trapping occasion. We observed greater numbers of ravens at the bait sites with increasing bait duration, and these numbers appeared to level off after 25 to 30 days of baiting. Longer bait durations may habituate ravens to the resource and compensate for their wariness, which could increase capture success. More than half of the ravens captured (55%) w...

Faulting and Groundwater in Arid Environments: Airborne Electromagnetics in Support of Framework Hydrology in the northern Mojave Desert, southern California

Groundwater basins within the Mojave Desert of the south-western United States are often compartmentalized by faults. As part of an effort to understand and manage groundwater resources in arid environments, the U.S. Geological Survey is investigating a number of basins within the Fort Irwin National Training Center (NTC) using multiple geophysical methods. Gravity, aeromagnetic, ground-based and airborne time-domain electromagnetic (TEM) data were collected over Leach Basin, a geologically complex, internally-drained basin bisected and flanked by Quaternary faults including the Garlock and Death Valley fault zones. The airborne TEM data show abrupt changes in earth response across faulted boundaries, reflecting the strong resistivity contrast between igneous rocks and basin sediments. The distribution of faults throughout the basin can be directly obtained from the airborne data. A resistivity stratigraphy has been developed by integrating borehole geophysical logs, lab resistivity measurements, and ground-based gravity and TEM soundings. The results are applied to the airborne resistivity models and are used to trace aquifer hydrostratigraphy throughout the basin. Interpreted parameters include the depth to basement, the depth to water, and the thickness of the primary aquifer. Together with hydrologic investigations, these results are being used to estimate groundwater storage within the basin

Cyanobacteria in Soils from a Mojave Desert Ecosystem

The Fort Irwin National Training Center in the Mojave Desert of California contains soils that represent a diversity of disturbance regimes, including some soil sites that have been protected from anthropogenic disturbance for many years. Previous studies of the soils of this military installation discussed biogeography and ecology of the crusts but did not conduct detailed study of the species present. In this study, we selected 6 sites in and around the Fort Irwin Training Center to be the subject of intensive isolation efforts. These sites contained at least some development of microbiotic soil crust. Out of the more than 90 cyanobacterial isolates characterized, only 23 distinctive morphospecies were differentiated. Of these, only 13 were identified to a previously described species, the others being comparable to previously described aquatic species (cf.) or so dissimilar to described taxa that they were given numbers as identification. Leptolyngbya was the most species rich and also the most commonly isolated genus. Twelve filamentous genera were found; no coccoid representatives occurred in our samples. All taxa are described and illustrated. This study is significant as it is the first since the 1960s to examine cyanobacterial taxonomy of Mojave Desert soils in a systematic fashion. Our unidentified taxa are very likely new species but will require molecular sequence analysis before they can be named.

Development of immobilized cyanobacterial amendments for reclamation of microbiotic soil crusts

Cyanobacteria were immobilized on hemp cloth, which was subsequently cut into fine pieces for use as a soil amendment. The amendment is intended for speeding recovery of microbiotic soil crusts in semi-arid and arid lands where such crusts have been destroyed by anthropogenic activities. Microcoleus vaginatus, Schizothrix calcicola, and Nostoc were used to create amendments, but most of the experiments in this study utilized the Microcoleus amendment, as it is the most cosmopolitan and ecologically important cyanobacterial taxon in desert soil crusts. The amendment was found to retain its viability in storage for at least 18 months. M. vaginatus grew best in CT and Z8+ (plus vitamins) media with aeration and addition of KHCO 3 . A field test of Fort Irwin National Training Center, Mojave Desert, California, showed significant increases in phototrophic biomass 6 and 12 months after inoculation, but the stimulans was not evident at 18 months. Four other field tests did not show significant gains. We suspect the failure of the field tests is due to a loss of cyanobacterial viability after inoculation but before favorable growth conditions. Cyanobacteria were possibly killed by UV irradiation or photo-oxidation in the hot desert environment M. vaginatus is known to live below the surface in desert soils, and so likely is sensitive to full sunlight. Laboratory experiments in full sunlight verified this hypothesis.