Del Apache National Wildlife Refuge Research Articles

Impacts of a Prescribed Fire on Air Quality in Central New Mexico

A short-duration but high-impact air quality event occurred on 28 November 2018 along the Rio Grande Valley of New Mexico. This fire occurred outside the typical wildfire season, and greatly impacted the air quality in Socorro, NM, and the surroundings. Measurements were taken during the event using an aerosol light scattering technique (integrating nephelometer) and a particulate mass concentration monitor (DustTrak PM optical monitor). The instruments sampled the ambient air during the event on the campus of the New Mexico Institute of Mining and Technology in Socorro, New Mexico. The peak values on a 5-min basis of light scattering and the PM mass concentration reached 470 Mm−1 and 270 µg/m3, respectively. We examined the meteorological context of the event using local meteorological data and back trajectories using the NOAA HYSPLIT model to determine atmospheric transport and possible sources. Several fires, both prescribed and wildfires, occurred in the region including a prescribed burn at Bosque del Apache National Wildlife Refuge (17 km south-southeast of the receptor site). The data suggest that the prescribed burn at Bosque del Apache was the dominant contributor due to transport evidence and the event’s narrow spatiotemporal extent. The increasing importance of restoring ecosystem function using prescribed fire in wildland fire management will likely lead to more frequent air quality impacts and sets up policy tradeoffs that require a balance between these public goals. This study examines the evidence of the effects of a prescribed fire in a protected wildland area impacting the air quality in a nearby populated area.

Influence of Environmental Stress and Anthropogenic Disturbance on the Energy Expenditure of Wintering Northern Pintails (Anas acuta)

Winter conditions impose hardships on waterfowl, impacting how they apportion energy and time. Human disturbances may affect this energetic balance, influence lipid reserves, and potentially survival. Objectives of this study were to determine effects of environmental and anthropogenic factors on energetic expenditure (kcal/day) of Northern Pintails (Anas acuta) in behaviors commonly associated with a disturbance response (alert, locomotion, and flight) during winter 2008-2009 and 2009-2010 at Bosque del Apache National Wildlife Refuge in central New Mexico, USA. The refuge is a frequently visited ecotourism destination with over 170,000 visitors each winter. Thermoregulatory cost, time-of-winter, amount of natural and anthropogenic disturbances, and forage availability were examined to determine their influence on pintail energetic response (e.g., flight, locomotion, alert behavior). Average number of pintails ranged from 7,524-15,769. Using Akaike Information Criteria, the top-ranked model indicated that increased thermoregulatory cost, and by association decreased temperature, may cause a decline in energetic response of pintails to disturbances. Modeled values for energetic response had a mean (± SE) of 175 ± 11.5 kcal/day in year 1, and 111.7 ± 7.22 kcal/day in year 2. Neither the amount of disturbance nor forage availability strongly influenced energetic response. Results of this study raise questions about the efficacy of using behavior or energy expenditure data, alone, to assess anthropogenic disturbance effects on waterfowl.

Population Dynamics Model to Inform Harvest Management of a Small Elk Herd in Central New Mexico

Abstract Crop depredation by wildlife is a frequent concern for natural resource managers and mitigation of this issue is often an important task for wildlife agencies. Elk Cervus elaphus and other ungulate species have depredated corn Zea mays at Bosque del Apache National Wildlife Refuge, New Mexico, USA, interfering with the ability of the Refuge to provide sufficient supplemental nutrition to overwintering sandhill cranes Antigone canadensis and geese (Anatidae). We estimated annual adult survival and calf recruitment rates of elk from 2011 to 2013 at Bosque del Apache National Wildlife Refuge. Natural adult survival (excludes human-related mortalities) was high (mean = 98.3%; 95% CI = 95.0–100.0%). Calf recruitment was lower than in some populations, and ranged from 13.0 to 36.7 calves : 100 cows at time of recruitment (March and April) with a mean of 21.9 (SD =12.9). Using this information, we constructed a harvest management model to determine annual harvest quotas required to stabilize the growth of the elk herd on the Refuge. The female segment of the herd is growing at an annual rate of 9.0% (95% CI = −1.1–24.1%). To stabilize the growth rate of the female elk population, 8.0% (95% CI = −1.1–19.4%) of the cows would need to be harvested annually. We estimated an adult elk abundance of 40.0 (SE = 4.57; 95% CI = 33.8–52.6) in 2012 and 61.1 (SE = 7.21; 95% CI = 49.9–78.8) in 2013. Our harvest management model provides Refuge staff, who ultimately intend to improve corn yield, with valuable information needed to stabilize the elk herd. Further, our approach outlines a simple, easily implemented modeling technique that can be used for the management of other ungulate herds.

Elk resource selection patterns in a semiarid riparian corridor

Elk (Cervus elaphus) have depredated corn at Bosque del Apache National Wildlife Refuge (BDANWR), New Mexico, USA, which has interfered with the refuge's ability to provide supplemental nutrition to overwintering sandhill cranes (Grus canadensis) and other waterbirds. To identify management options for minimizing cropland depredation, we examined elk resource selection patterns using negative binomial generalized linear mixed models. We used 8,244 global positioning system (GPS) locations collected from 9 adult female elk to model fine-scale resource use (sampling units were 100 × 100-m cells; n = 3,646) and corn field use (sampling units were corn fields; n = 18) by a resident herd along the Rio Grande River in central New Mexico, USA. The fine-scale model suggested that elk use in cropland areas increased when alfalfa and corn were present and elk use was greatest 0.14 km from uncultivated areas. Elk use in uncultivated areas increased as canopy cover increased. Elk use exhibited a quadratic relationship with hiding cover, which varied with distance to cropland. We validated the fine-scale model with an independent sample of radio-marked adult female elk (n = 12; 1,106 locations). The fine-scale model was successful in predicting elk use; 84.1% (SE = 1.1) of radio-marked elk locations fell within high or medium-high use cells. Corn field use models indicated that elk use increased as the proportion of the corn field perimeter adjacent to alfalfa increased. Elk use of corn fields declined as distance to uncultivated areas and the proportion of other corn fields at the same growth stage increased. Probability of elk use peaked when corn reached heights of 1.4 m to 1.7 m and use varied with distance to uncultivated areas. Corn fields at these heights were in the late vegetative or tassel-milk growth stage, which are the stages at which damage to corn plants is most detrimental to yield. The average distance each elk moved per day during the corn growing season was 5,013 m (SD = 957) and varied among individuals (3,251–6,317 m). This is relatively large in relation to the size of the managed floodplain at BDANWR. Our results, couched in elk daily movements, can help direct crop management, vegetation manipulation, and timing of hazing efforts aimed at reducing elk use of crops. © 2016 The Authors. Journal of Wildlife Management Published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.

Variation in phenology of hibernation and reproduction in the endangered New Mexico meadow jumping mouse (Zapus hudsonius luteus).

Hibernation is a key life history feature that can impact many other crucial aspects of a species’ biology, such as its survival and reproduction. I examined the timing of hibernation and reproduction in the federally endangered New Mexico meadow jumping mouse (Zapus hudsonius luteus), which occurs across a broad range of latitudes and elevations in the American Southwest. Data from museum specimens and field studies supported predictions for later emergence and shorter active intervals in montane populations relative to lower elevation valley populations. A low-elevation population located at Bosque del Apache National Wildlife Refuge (BANWR) in the Rio Grande valley was most similar to other subspecies of Z. hudsonius: the first emergence date was in mid-May and there was an active interval of 162 days. In montane populations of Z. h. luteus, the date of first emergence was delayed until mid-June and the active interval was reduced to ca 124–135 days, similar to some populations of the western jumping mouse (Z. princeps). Last date of immergence into hibernation occurred at about the same time in all populations (mid to late October). In montane populations pregnant females are known from July to late August and evidence suggests that they have a single litter per year. At BANWR two peaks in reproduction were expected based on similarity of active season to Z. h. preblei. However, only one peak was clearly evident, possibly due to later first reproduction and possible torpor during late summer. At BANWR pregnant females are known from June and July. Due to the short activity season and geographic variation in phenology of key life history events of Z. h. luteus, recommendations are made for the appropriate timing for surveys for this endangered species.

Habitat Selection by the Endangered New Mexico Meadow Jumping Mouse on an Irrigated Floodplain

Abstract The New Mexico meadow jumping mouse Zapus hudsonius luteus is endemic to the American Southwest. It has undergone severe declines in distribution over the past century and it has been listed as endangered under the Endangered Species Act. The goal of this study was to determine current status and habitat selection by the New Mexico meadow jumping mouse at three spatial scales (landscape, macrohabitat, microhabitat) on a managed high-order floodplain. We hypothesized that the New Mexico meadow jumping mouse is a habitat specialist that might rely on specific habitat components at multiple spatial scales. The study occurred at Bosque del Apache National Wildlife Refuge, New Mexico. In comparison with the status of the species 2 decades ago, the New Mexico meadow jumping mouse was rare, with only 29 individuals captured. Trapping results and radiotelemetry of 20 individuals revealed that the current population existed along 2.7 km of a single irrigation canal. At the landscape scale, the distribution of the New Mexico meadow jumping mouse was determined by selection of canals, water, foxtail barley Hordeum jubatum herbaceous temporarily flooded association, and narrowleaf willow Salix exigua mesic graminoids shrubland association. At the macrohabitat scale, jumping mice selected canals and Hordeum jubatum herbaceous temporarily flooded association. At the microhabitat scale, jumping mice selected areas that were near water and contained moist soils, dense herbaceous canopy cover, dogbane Apocynum cannabinum, foxtail barley, and common threesquare Schoenoplectus pungens; jumping mice avoided habitats represented by eight plant species, including mule-fat Baccharis salicifolia, kochia Bassia scoparia, and saltcedar Tamarix ramosissima. Jumping mice only occurred where there is an overlap of the required habitats at all three scales and this may be a key limiting factor for the New Mexico meadow jumping mice at Bosque del Apache National Wildlife Refuge. Habitats used by jumping mice during maternal nesting and hibernation contained more woody plants and woody debris than at other times of their life cycle. Information gained from this study can help land managers protect and create habitat conditions required by the New Mexico meadow jumping mouse.

Herbeal Feeding Behavior of the New Mexico Meadow Jumping Mouse (Zapus hudsonius luteus)

Abstract. We report the first observations of feeding behavior by free-ranging New Mexico meadow jumping mice (Zapus hudsonius luteus). We made observations during a radiotelemetry study of Z. h. luteus in the floodplain of the Rio Grande at Bosque del Apache National Wildlife Refuge, Socorro Co., New Mexico, in 2009 and 2010. We observed Z. h. luteus eat the achenes or seeds of the order Cyperales: common threesquare (Schoenoplectus pungens), spikerush (Eleocharis spp.), saltgrass (Distichlis spicata), foxtail barley (Hordeum jubatum), Saunder's wildrye (Elymus saundersii), Japanese brome (Bromus japonicus), slender wheatgrass (Elymus trachycaulus), and knotgrass (Paspalum distichum). Mice frequently foraged 0.5–1 m above the ground in the canopy of herbaceous vegetation. Seed heads for consumption were harvested in several ways.

Effects of anthropogenic and environmental stress on the corticosterone levels of wintering Northern Pintails (Anas acuta)

Winter-specific survival rates for female Northern Pintails (Anas acuta L., 1758; hereafter “Pintails”) at the Bosque del Apache National Wildlife Refuge were found in a previous study to be low relative to other wintering areas, raising concerns that tourism could be impacting the health of the population. Measurements of corticosterone levels enable the assessment and quantification of human-induced stressors that can ultimately affect fitness. We analyzed corticosterone concentrations and the relationship between body condition and maximum stress-induced corticosterone in areas with and without tourism access. Female Pintails were captured in winters of 2008–2009 and 2009–2010. The corticosterone response was similar between areas with and without tourism, but different between winters. In mid-January 2010, levels were 73% greater after 60 min compared with those in 2009. A greater stress response in mid-January 2010 may have been due to colder temperatures and arriving later and in poorer condition. Also in 2009–2010, there was a negative correlation between carcass fat and maximum corticosterone, possibly in response to colder temperatures, arriving in poorer condition, or a combination of both. Our study indicates that in mid- to late winter, activity of the hypothalamic–pituitary–adrenal axis may be higher during winters with comparatively greater environmental hardships, emphasizing the importance of carefully managing waterfowl during periods when they are most sensitive.

Infilling Missing Daily Evapotranspiration Data Using Neural Networks

This study used artificial neural networks (ANNs) computing technique for infilling missing daily saltcedar evapotranspiration (ET) as measured by the eddy-covariance method. The study site was at Bosque del Apache National Wildlife Refuge in the Middle Rio Grande Valley, New Mexico. Data was collected from 2001 to 2003. Several ANN models were evaluated for infilling of different combinations of missing data percentages and different gap sizes. The ANN model using daily maximum and minimum temperature, daily solar radiation, day of the year, and the calendar year as inputs showed the best estimation performance. Results showed coefficient of determination ( R2 ) of 0.96, root-mean-square error (RMSE) of 0.4 mm/day for 10% missing data and a maximum of half-month gap size data set. Missing data greater than 30% and maximum data gap size greater than 3 months resulted in R2 less than 0.90 and RMSE greater than 0.6 mm/day. The results from this study suggest that infilling of daily saltcedar ET using ANN an...

Seedling competition between native cottonwood and exotic saltcedar: implications for restoration

Altered hydrology of southwestern United States rivers has led to a decline in native cottonwood (Populus deltoides). Areas historically dominated by cottonwood have been replaced by invasive saltcedar (Tamarix chinensis). Restoration of historic hydrology through periodic flooding of riparian areas has been a means of restoring native species. However, due to similarity in germination requirements of cottonwoods and saltcedars, flooding may create an unwanted increase in the number of saltcedar seedlings. Therefore, we evaluated competitive aspects of these co-occurring species in an extant riparian habitat in the arid southwestern US. We measured effects of competition between cottonwood and saltcedar seedlings and among cottonwood seedlings during the first growing season following seedling establishment in 360, 0.5 × 0.5-m plots at the Bosque del Apache National Wildlife Refuge, New Mexico. We used five interspecific density treatments and five intraspecific density treatments. Cottonwood seedling biomass and height were twice that of saltcedar seedlings across all density treatments. As density of cottonwood increased, intraspecific competition increased in severity and biomass of cottonwood seedlings decreased. At 4 plants/0.25 m2, cottonwood seedlings had the greatest biomass; whereas, survival was highest at 10 plants/0.25 m2. Our results support greenhouse studies and suggest that if favorable germination conditions are established for cottonwood in floodplains, saltcedar seedlings that cogerminate could be outcompeted by native cottonwood seedlings.

Application of a geomorphic and temporal perspective to wetland management in North America

The failure of managed wetlands to provide a broad suite of ecosystem services (e.g., carbon storage, wildlife habitat, ground-water recharge, storm-water retention) valuable to society is primarily the result of a lack of consideration of ecosystem processes that maintain productive wetland ecosystems or physical and social forces that restrict a manager’s ability to apply actions that allow those processes to occur. Therefore, we outline a course of action that considers restoration of ecosystem processes in those systems where off-site land use or physical alterations restrict local management. Upon considering a wetland system, or examining a particular management regime, there are several factors that will allow successful restoration of wetland services. An initial step is examination of the political/social factors that have structured the current ecological condition and whether those realities can be addressed. Most successful restorations of wetland ecosystem services involve cooperation among multiple agencies, acquisition of funds from non-traditional sources, seeking of scientific advice on ecosystem processes, and cultivation of good working relationships among biologists, managers, and maintenance staff. Beyond that, in on-site wetland situations, management should examine the existing hydrogeomorphic situation and processes (e.g., climatic variation, tides, riverine flood-pulse events) responsible for maintenance of ecosystem services within a given temporal framework appropriate for that wetland’s hydrologic pattern. We discuss these processes for five major wetland types (depressional, lacustrine, estuarine, riverine, and man-made impoundments) and then provide two case histories in which this approach was applied: Seney National Wildlife Refuge with a restored fen system and Bosque del Apache National Wildlife Refuge where riverine processes have been simulated to restore native habitat. With adequate partnerships and administrative and political support, managers faced with degraded and/or disconnected wetland processes will be able to restore ecosystem services for society in our highly altered landscape by considering wetlands in their given hydrogeomorphic setting and temporal stage.

Neoechinorhynchus emyditoides Fisher, 1960 (Acanthocephala: Neoechinorhynchidae) from the Mexican Plateau Slider, Trachemys gaigeae (Testudines: Emydidae), in New Mexico, U.S.A

Three of 5 (60%) Mexican Plateau sliders, Trachemys gaigeae, from Bosque del Apache National Wildlife Refuge, Socorro County, New Mexico, U.S.A., were found to be infected with the acanthocephalan, Neoechinorhynchus emyditoides Fisher, 1960. This is the first report of N. emyditoides from T. gaigeae and New Mexico, U.S.A., and only the third article reporting parasites from this host.

Stable Isotope Evidence Links Breeding Geography and Migration Timing in Wood Warblers (Parulidae)

AbstractTracking seasonal movements of songbirds is a key step in understanding the annual cycle of migrants. To better understand autumn migration of wood warblers, I analyzed stable-hydrogen isotope ratios of feathers collected from three species captured during stopover at the Bosque del Apache National Wildlife Refuge, New Mexico. To assess the form and strength of the relationship between timing of migration and breeding origins, I regressed stable-hydrogen isotope ratios of feathers against date of capture. These analyses indicated that Orange-crowned Warblers (Vermivora celata) and Common Yellowthroats (Geothlypis trichas) breeding in the southern portion of these species' ranges precede their northern conspecifics in autumn migration. By contrast, Yellow Warblers (Dendroica petechia) from northern breeding sites arrived before more southerly breeding conspecifics. This pattern is similar to that reported previously in Wilson's Warbler (Wilsonia pusilla). These findings suggest that, among wood warblers, (1) timing of autumn migration is often strongly related to breeding location and (2) interspecific variation in the direction of this relationship is large. The direction and strength of these patterns have implications for our understanding of inter- and intraspecific geographic variation in the life histories of migrants.Evidencia de Isótopos Estables Conecta la Geografía de Nidificación con el Momento de la Migración en Especies de Parulidae

Even Mountains Vanish: Searching for Solace in an Age of Extinction by SueEllen Campbell

w e s t e r n A m e r ic a n L it e r a t u r e S p r in g 2 0 0 6 Even Mountains Vanish: Searching for Solace in an Age of Extinction. By SueEllen Campbell. Salt Lake City: University of Utah Press, 2003. 141 pages, $17.95. Reviewed by Angela Waldie University of Calgary In the final hours of a week-long trip to the Canadian Arctic, SueEllen Campbell watches an Inuit woman named Doris demonstrate traditional string games. With quick and subtle shifts of her fingers, Doris produces a series of ephemeral string figures: “man in a kayak, fox, loon on a nest” (109). Each appears, hovers, and then vanishes to make way for the next. As its title suggests, Even Mountains Vanish is filled with such references to evanescence. In the prologue, Campbell paints with water on gray paper, then watches each brushstroke evaporate. Hiking in the Colorado Rockies, she witnesses a ptarmigan’s shifting capacity for camouflage— its mottled body, white tail feathers, and white wings allowing it to vanish against a backdrop of rock and melting snow. And attending a mandala ceremony at Colorado State University, she watches as Tibetan monks sweep up the colored sand from a mandala created with painstaking concentration. Some of this sand will be distributed to the audience in small glass vials and the rest sprinkled in a nearby creek “to heal the invisible spirits who are everywhere” (126). Like this mandala, the four essays of Even Mountains Vanish convey a sense of both ephemerality and connectedness. While this essay collection is an eloquent reflection on the impermanence of art and life, it is also a tribute to the immense scope of geologic and evolu­ tionary time, as well as the importance of understanding the environmental history of a place. After a trip to the Pajarito Plateau, Campbell researches the geologic history of this landscape as well as the evolutionary history of Albert’s squirrels, ponderosa pines, horsetails, and sandhill cranes—the species that she most closely associates with her time there. Attempting to articulate the duration of geologic time, she leads the reader on a hypothetical walk along a bookcase stretching eight and a half miles. This imagined bookcase is filled with packages of printer paper, the thickness of each single sheet correspond­ ing to a century. As our guide on this epic tour, Campbell makes accessible the almost incomprehensible scope of Earth’s history, identifying reference points such as the big bang, the appearance of life on earth, the evolution of conti­ nents, periods of glaciation, and the six major waves of extinction. Although humans have been present for only a fraction of this geologic history, Campbell continually reminds the reader of our power and culpability in altering natural processes. Alongside the creation of the Bosque del Apache National Wildlife Refuge in 1939, for example, which offered shelter to endangered sandhill cranes, Campbell juxtaposes the opening of a secret laboratory in Los Alamos in 1943, where scientists would develop the capacity—in a single atomic explosion—to decimate landscapes and life. BO O K REVIEW S I find Even Mountains Vanish outstanding in its ability to capture simultane­ ously scope and essence. With its nuanced connections between personal, geo­ logic, and evolutionary details, this essay collection would be well suited to courses in ecocriticism, environmental history, and personal narrative. Demonstrating the value ofbeing attentive to natural processes, Campbell reveals unique ways in which the evolutionary adaptations of species can inform our lives. From lichens Campbell learns to “accept that the same thin skin that admits nourishment also makes you vulnerable” and to understand the importance of “shar[ing] pieces of yourself with the world.” From alpine forget-me-nots she learns to “put down deep roots. Be passionate. Make beauty. Bloom like mad” (58). Filled with such lyrical insights, Even Mountains Vanish reveals how research and meditation on the essence of place can provide awareness, enjoyment, and wisdom. Sam Peckinpah’s West: New Perspectives. Edited by Leonard Engel. Salt Lake City: University of Utah Press, 2003. 268 pages, $21.95. Reviewed by Brian McCuskey Utah State University, Logan...

STABLE ISOTOPE EVIDENCE LINKS BREEDING GEOGRAPHY AND MIGRATION TIMING IN WOOD WARBLERS (PARULIDAE)

Abstract Tracking seasonal movements of songbirds is a key step in understanding the annual cycle of migrants. To better understand autumn migration of wood warblers, I analyzed stable-hydrogen isotope ratios of feathers collected from three species captured during stopover at the Bosque del Apache National Wildlife Refuge, New Mexico. To assess the form and strength of the relationship between timing of migration and breeding origins, I regressed stable-hydrogen isotope ratios of feathers against date of capture. These analyses indicated that Orange-crowned Warblers (Vermivora celata) and Common Yellowthroats (Geothlypis trichas) breeding in the southern portion of these species' ranges precede their northern conspecifics in autumn migration. By contrast, Yellow Warblers (Dendroica petechia) from northern breeding sites arrived before more southerly breeding conspecifics. This pattern is similar to that reported previously in Wilson's Warbler (Wilsonia pusilla). These findings suggest that, among wood wa...

Saltcedar Recovery after Herbicide-Burn and Mechanical Clearing Practices

Mechanical clearing and herbicide-burn treatments were compared to evaluate saltcedar (Tamarix chinensis Lour.) control and recovery along the Rio Grande on the Bosque del Apache National Wildlife Refuge, Socorro, N.M. The herbicide-burn treatment included an aerial application of imazapyr (+)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid] + glyphosate [N-(phosphono-methyl)glycine] (0.6 + 0.6 kg ai ha-1 rate) followed 3 years later by a prescription broadcast fire that eliminated > 99% of the standing dead stems. Six years after initial herbicide application, saltcedar mortality was 93%. Mechanical saltcedar clearing entailed removing aerial (trunks and stems) growth by blading, stacking and burning debris, followed by removal of underground plant portions (root crowns) by plowing, raking, and burning stacked material. Saltcedar mortality 3 years after mechanical clearing averaged 70%, which was deemed unsatisfactory. Thus, root plowing, raking, and pile burning was repeated. Three years later, after the second mechanical clearing, saltcedar mortality was 97%. Costs for the herbicide-burn treatment averaged $283 ha-1, whereas mechanical control costs were $884 ha-1 for the first surface and root clearing and an additional $585 ha-1 for the second root clearing. Riparian managers should consider environmental conditions and restoration strategies prior to selecting a saltcedar control approach. Although control costs were significantly lower for the herbicide-burn treatment compared to mechanical clearing in this study, the choice of methods should always consider alternative control strategies for saltcedar. Frequently, combinations of methods result in more efficient, cost-effective results. DOI:10.2458/azu_jrm_v56i5_mcdaniel

Saltcedar recovery after herbicide-burn and mechanical clearing practices

Mechanical clearing and herbicide-burn treatments were compared to evaluate saltcedar (Tamarix chinensis Lour.) control and recovery along the Rio Grande on the Bosque del Apache National Wildlife Refuge, Socorro, N.M. The herbicide-burn treatment included an aerial application of imazapyr (+)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid] + glyphosate [N-(phosphono-methyl)glycine] (0.6 + 0.6 kg ai ha-1 rate) followed 3 years later by a prescription broadcast fire that eliminated > 99% of the standing dead stems. Six years after initial herbicide application, saltcedar mortality was 93%. Mechanical saltcedar clearing entailed removing aerial (trunks and stems) growth by blading, stacking and burning debris, followed by removal of underground plant portions (root crowns) by plowing, raking, and burning stacked material. Saltcedar mortality 3 years after mechanical clearing averaged 70%, which was deemed unsatisfactory. Thus, root plowing, raking, and pile burning was repeated. Three years later, after the second mechanical clearing, saltcedar mortality was 97%. Costs for the herbicide-burn treatment averaged 283 ha-1, whereas mechanical control costs were 884 ha-1 for the first surface and root clearing and an additional 585 ha-1 for the second root clearing. Riparian managers should consider environmental conditions and restoration strategies prior to selecting a saltcedar control approach. Although control costs were significantly lower for the herbicide-burn treatment compared to mechanical clearing in this study, the choice of methods should always consider alternative control strategies for saltcedar. Frequently, combinations of methods result in more efficient, cost-effective results.

Responses of a Riparian Forest-Floor Arthropod Community to Wildfire in the Middle Rio Grande Valley, New Mexico

Abstract We documented patterns of species extirpation, shifts in species dominance, and rates of recolonization of litter-layer arthropod species following a catastrophic forest fire. The study site was located along the Rio Grande within the Bosque del Apache National Wildlife Refuge, Socorro County, NM, in a riparian forest dominated by cottonwood [Populus deltoides ssp. wislizenii (S. Watson) Eckenwalder] and salt cedar (Tamarix chinensis Loureiro). The forest-floor arthropod community was sampled with 18 pitfall traps during 1994–1997. The study site burned in June 1996, and the intense fire reduced the litter layer to mineral ash and killed all the above-ground portions of trees; salt cedar and some cottonwood trees began to stump-sprout shortly after the fire, and achieved heights of two m by October 1996. The prefire forest-floor arthropod community consisted of 80 species, dominated by spiders (Lycosidae, Gnaphosidae, Salticidae), beetles (Carabidae, Staphylinidae, Cryptophagidae, Tenebrionidae),...

Insights into Wilson's Warbler migration from analyses of hydrogen stable-isotope ratios.

Our ability to link the breeding locations of individual passerines to migration stopover sites and wintering locations is limited. Stable isotopes of hydrogen contained in bird feathers have recently shown potential in this regard. We measured hydrogen stable-isotope ratios (δD) of feathers from breeding, migrating, and wintering Wilson's Warblers. Analyses of feathers from museum specimens collected throughout the western portion of the breeding range indicate that δD values are significantly negatively related to latitude of collection (R 2=0.52), which is an indication that δD values are a good descriptor of breeding latitude. Analyses of feathers collected from birds migrating through the Bosque del Apache National Wildlife Refuge, New Mexico (USA), revealed a significantly positive relationship between δD values and the timing of autumn migration (R 2=0.34), but not the timing of spring migration. This pattern indicates that Wilson's Warblers that bred furthest north migrated earliest in the autumn. Finally, analysis of feathers collected on the wintering grounds indicate that the hydrogen isotope ratio is significantly positively related to wintering latitude (R 2=0.80), which indicates that birds that bred furthest north wintered furthest south. In combination, these patterns suggest that in the western portion of their range, Wilson's Warblers have a leapfrog migration system in which the northern-most breeding birds pass through New Mexico early in the autumn to arrive on the wintering grounds in southern Central America, the southern edge of the Wilson's Warblers winter range. We know of no other literature documenting or suggesting that Wilson's Warbler engage in leapfrog migration. We think the novelty of these results is a reflection of the potential for stable-isotope techniques to revise our understanding of bird migration.

Nutrient cycling at the landscape scale: The role of diel foraging migrations by geese at the Bosque del Apache National Wildlife Refuge, New Mexico

Wildlife refuges are sites of dense aggregations of wintering waterfowl. Refuge managers are concerned about local water‐quality effects and the amount of birdborne nutrient load that might cause eutrophication in roosting ponds and(or) be exported to downstream systems. We initiated this research effort to test the hypothesis that daily feeding migrations by geese represented a significant source of nutrients to wetland systems at the Bosque del Apache National Wildlife Refuge in the middle Rio Grande River valley of New Mexico. We documented the role of geese in translocating nutrients through a combination of time budget and mass balance models for birds, bioassays of phytoplankton growth, and stable isotope methods that trace the source of nitrogen to food webs. Geese increased the nutrient loading rates in some wetland ponds by up to 40% for total nitrogen and 75% for total phosphorus. Bioassays revealed that nitrogen was consistently limiting to primary production by algae in the ponds. Chlorophyll levels increased in proportion to bird densities. Fish and crayfish from the ponds intensively used by birds had very low stable nitrogen signatures relative to those from the Rio Grande River. This result derived from the low 15N in alfalfa and corn, which were the primary forage for birds, and accumulated through food webs in proportion to bird use of individual ponds as roosting areas. In general, the wetland ponds functioned efficiently in retaining the birdborne, allochthonous nutrient load and only modest amounts of the total nitrogen or phosphorus were exported downstream.