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Understanding species–environment relationships is key to defining the spatial structure of species distributions and develop effective conservation plans. However, for many species, this baseline information does not exist. With reliable presence data, spatial models that predict geographic ranges and identify environmental processes regulating distribution are a cost‐effective and rapid method to achieve this. Yet these spatial models are lacking for many rare and threatened species, particularly in tropical regions. The harpy eagle (Harpia harpyja) is a Neotropical forest raptor of conservation concern with a continental distribution across lowland tropical forests in Central and South America. Currently, the harpy eagle faces threats from habitat loss and persecution and is categorized as Near‐Threatened by the International Union for the Conservation of Nature (IUCN). Within a point process modeling (PPM) framework, we use presence‐only occurrences with climatic and topographical predictors to estimate current and past distributions and define environmental requirements using Ecological Niche Factor Analysis. The current PPM prediction had high calibration accuracy (Continuous Boyce Index = 0.838) and was robust to null expectations (pROC ratio = 1.407). Three predictors contributed 96% to the PPM prediction, with Climatic Moisture Index the most important (72.1%), followed by minimum temperature of the warmest month (15.6%) and Terrain Roughness Index (8.3%). Assessing distribution in environmental space confirmed the same predictors explaining distribution, along with precipitation in the wettest month. Our reclassified binary model estimated a current range size 11% smaller than the current IUCN range polygon. Paleoclimatic projections combined with the current model predicted stable climatic refugia in the central Amazon, Guyana, eastern Colombia, and Panama. We propose a data‐driven geographic range to complement the current IUCN range estimate and that despite its continental distribution, this tropical forest raptor is highly specialized to specific environmental requirements., Understanding species–environment relationships is key to defining the spatial structure of species distributions and develop effective conservation plans. The harpy eagle (Harpia harpyja) is a large raptor with a continental distribution across the Neotropics, categorized as Near‐Threatened by the International Union for the Conservation of Nature (IUCN). We propose a data‐driven geographical range to complement the current IUCN range estimate and that despite its continental distribution, this tropical forest raptor is highly specialized to specific environmental requirements.

Most raptor populations are declining and nearly a fifth are threatened with extinction; thus there is a need to increase collaboration to ensure efficient and effective research, management, and conservation. Here, we introduce the Global Raptor Impact Network (GRIN; www.globalraptors.org), a tool to enhance collaboration and conservation impact of the raptor research community. We provide an overview of the history and current state of GRIN, including plans for expansion. Predecessors to GRIN include The African Raptor DataBank, which was launched in 2012 to ascertain the conservation status of raptors across Africa; and the Global Raptor Information Network, which was launched in the late 1990s as a website to provide information regarding diurnal raptors and facilitate communication among researchers. GRIN expands the data collection and storage capabilities of the African Raptor DataBank to a global scale via mobile application. We have implemented data-sharing rules to ensure the safety of sensitive species, and users of the GRIN mobile app can designate their records as confidential. GRIN staff and partners are developing analyses of species' population trends and geographic distributions to aid in conservation assessments. GRIN is also developing systematic reviews, detailed bibliographies, and online accounts that will summarize the state of knowledge for each raptor species. We hope that GRIN will benefit the entire raptor research community and aid in the collaboration necessary to help raptor populations thrive in the Anthropocene.

Understanding parasite-host ecology is increasingly important for conservation efforts in a changing world. Parasitic nest flies in the genus Philornis (Diptera: Muscidae) have been implicated in the decline of endemic island species and are also known to negatively impact breeding success of the Critically Endangered Ridgway’s hawk (Buteo ridgwayi) on the island of Hispaniola. Despite the importance of these effects on hosts, and extensive research of Philornis downsi in the Galápagos, the ecology of most species of philornid nest flies is poorly understood. We examined biotic factors related to Philornis pici infestations of nestling Ridgway’s hawks in the Dominican Republic, where both fly and hawk are native. We found grass-cover was negatively associated with P. pici infestations, while coverage and height of other vegetation classes (tree, shrub, herbaceous, and bare ground) had no association, which is interesting considering recent landscape-level changes to Ridgway’s hawk habitat. Anthropogenic activities in Los Haitises National Park, the last strong-hold of Ridgway’s hawk, have shifted the landscape from primary forest to a fragmented secondary forest with smallholder or subsistence farms and grassy patches. New information on the ecology of nest flies in their native habitat can inform conservation efforts and allow us to make recommendations for future research.

The peregrine falcon (Falco peregrinus) and the gyrfalcon (Falco rusticolus) are top avian predators of Arctic ecosystems. Although existing monitoring efforts are well established for both species, collaboration of activities among Arctic scientists actively involved in research of large falcons in the Nearctic and Palearctic has been poorly coordinated. Here we provide the first overview of Arctic falcon monitoring sites, present trends for long-term occupancy and productivity, and summarize information describing abundance, distribution, phenology, and health of the two species. We summarize data for 24 falcon monitoring sites across the Arctic, and identify gaps in coverage for eastern Russia, the Arctic Archipelago of Canada, and East Greenland. Our results indicate that peregrine falcon and gyrfalcon populations are generally stable, and assuming that these patterns hold beyond the temporal and spatial extents of the monitoring sites, it is reasonable to suggest that breeding populations at broader scales are similarly stable. We have highlighted several challenges that preclude direct comparisons of Focal Ecosystem Components (FEC) attributes among monitoring sites, and we acknowledge that methodological problems cannot be corrected retrospectively, but could be accounted for in future monitoring. Despite these drawbacks, ample opportunity exists to establish a coordinated monitoring program for Arctic-nesting raptor species that supports CBMP goals.

We know little regarding how specific aspects of habitat influence spatial variation in site occupancy by Arctic wildlife, yet this information is fundamental to effective conservation. To address this information gap, we assessed occupancy of 84 Gyrfalcon (Falco rusticolus Linnaeus, 1758) breeding territories observed annually between 2004 and 2013 in western Alaska. In line with the theory of population regulation by site dependence, we asked whether Gyrfalcons exhibited a nonrandom pattern of site selection and if heterogeneous landscape attributes correlated with observed occupancy patterns. We characterized high- and low-occupancy breeding territories as those occupied more or less often than expected by chance, and we evaluated land cover at 1 and 15 km circles centered around nesting territories to identify habitat variables associated with observed occupancy patterns. We tested 15 competing models to rank hypotheses reflecting prey and habitat variables important to nesting Gyrfalcons. We confirmed a nonrandom pattern of site selection but found only weak evidence that the distribution of prey habitat was responsible for this pattern. We reason that preferential habitat use by nesting Gyrfalcons may be determined by spatial scales other than those we measured or may be driven by landscape-level attributes at time periods other than during the brood rearing period.

Quantifying habitat use is important for understanding how animals meet their requirements for survival and provides useful information for conservation planning. Currently, assessments of range-wide habitat use that delimit species distributions are incomplete for many taxa. The harpy eagle (Harpia harpyja) is a raptor of conservation concern, widely distributed across Neotropical lowland forests, that currently faces threats from increasing habitat loss and fragmentation. Here, we use a logistic regression modelling framework to identify habitat resource selection and predict habitat suitability based on a new method developed from the International Union for the Conservation of Nature Area of Habitat range metric. From the habitat use model, we performed a gap analysis to identify areas of high habitat suitability in regions with limited coverage in the Key Biodiversity Area (KBA) network. Range-wide habitat use indicated that harpy eagles prefer areas of 70-75 % evergreen forest cover, low elevation, and high vegetation heterogeneity. Conversely, harpy eagles avoid areas of >10 % cultivated landcover and mosaic forest, and topographically complex areas. Our habitat use model identified a large continuous area across the pan-Amazonia region, and a habitat corridor from the Chocó-Darién ecoregion of Colombia running north along the Caribbean coast of Central America. Little habitat was predicted across the Atlantic Forest biome, which is now severely degraded. The current KBA network covered ∼18 % of medium to high suitability harpy eagle habitat exceeding the target representation (10 %). Four major areas of high suitability habitat lacking coverage in the KBA network were identified in the Chocó-Darién ecoregion of Colombia, western Guyana, and north-west Brazil. We recommend these multiple gaps of habitat as new KBAs for strengthening the current KBA network. Modelled area of habitat estimates as described here are a useful tool for large-scale conservation planning and can be readily applied to many taxa.

Habitat suitability for breeding birds is defined at scales ranging from the landscape to individual nesting sites. Nesting site characteristics that govern exposure to inclement weather may affect breeding success, although attempts to understand this effect for Arctic breeding raptors have yielded ambiguous results. Further, breeding adults incur substantial costs from incubating eggs and brooding nestlings, and it is possible that greater site exposure results in increased nest attendance rates, increasing their cost of breeding. We quantified nesting site characteristics of Gyrfalcons (Falco rusticolus) and assessed how breeding parameters and nest attendance rates varied by protective site qualities on Alaska's Seward Peninsula, 2014–2019. The degree of physical exposure in the horizontal plane correlated negatively with the probability of hatching and fledging (provided hatch occurred), as well as overall productivity. The negative effect of horizontal exposure on the probability of fledging and productivity was greatest at nesting sites that were also more exposed in the vertical plane, although this interaction did not affect the probability of hatching. Early breeding pairs had higher productivity and tended to select more protected nesting sites. Additionally, nest attendance rates were higher in more horizontally exposed nesting sites, particularly when nestlings were approximately 2 wk old. The increased nest attendance and concurrent decreased productivity associated with greater nesting site exposure demonstrated that nesting site characteristics can have direct and indirect effects on Arctic breeding raptors and also highlight the importance of small-scale variables when evaluating habitat suitability.

Conservation of predators requires a comprehensive understanding of their life history and ecology, including the delineation of temporal and spatial dietary habits. Gyrfalcons (Falco rusticolus), Willow Ptarmigan (Lagopus lagopus), and Rock Ptarmigan (L. muta) are Arctic specialists, strongly linked in a dynamic predator-prey relationship, and facing similar conservation threats. We studied Gyrfalcon predation of ptarmigan on Alaska's Seward Peninsula and investigated whether species-specific contributions to diet reflected preferential selection or exploitation of the more abundant prey species. Additionally, we examined how the sex ratios of ptarmigan in Gyrfalcon diet varied throughout the breeding season. We collected ptarmigan prey remains from in and around occupied Gyrfalcon nesting sites in 2017, and identified species and sex by molecular techniques. We compared proportions of the two ptarmigan species in Gyrfalcon diet to proportions of the Rock and Willow Ptarmigans' preferred habitat around Gyrfalcon nesting sites (n = 205 skeletal remains from 12 nests), and compared sex ratios of ptarmigan prey remains temporally (n = 252 skeletal remains from 12 nests). We found that prey remains were more likely to be Rock Ptarmigan when areas around Gyrfalcon sites had greater slope and higher elevation (i.e., they better matched the habitat preferences of Rock Ptarmigan), which may suggest Gyrfalcon diet tracked ptarmigan availability without preference for species. Ptarmigan remains were biased toward male birds during June, when most female ptarmigan are incubating on concealed nests. Although we recommend additional analysis of these topics, our findings further our understanding of Gyrfalcon and ptarmigan ecology as the Arctic faces rapid changes to its climate and landscape.

La identificacion del habitat reproductivo es esencial para la implementacion de esfuerzos de conservacion en especies amenazadas. Usando siete variables naturales y antropogenicas y basados en 27 intentos de anidacion a lo largo de 17 anos, creamos un modelo de distribucion de especies para el habitat de cria de Harpia harpyja a traves de 5636 km2 en la Region del Pacifico de la Provincia de Darien, Panama. El habitat mas adecuado tuvo una alta cobertura de bosque, una baja altitud y una proximidad relativamente cercana a rios. Identificamos asociaciones de habitat reproductivo especificas para H. harpyja y encontramos que el 34% del area analizada incluyo habitat reproductivo muy adecuado. A escala regional, el habitat mas adecuado fue encontrado predominantemente en las cuatro cuencas presentes en la porcion norte del area de estudio y tambien a lo largo de la costa del Pacifico. La cuenca del Jurado, en el sur, presento relativamente poco habitat adecuado, debido a una alta cantidad de terreno montanoso. De las tres areas protegidas en la region, el Parque Nacional Darien incluyo una cantidad similar de habitat comparada con las vecinas y relativamente menores Reserva Forestal Chepigana y Corredor Biologico Serrania de Bagre. Esto resalta la importancia de los bosques del norte para la conservacion de H. harpyja en Darien. En terminos generales, las areas con mayor cantidad de influencia humana estuvieron asociadas con mayor perdida de bosque y menos habitat adecuado. Por ende, proponemos la necesidad de estrategias comunitarias para la gestion sostenible de los recursos y mitigar los niveles de disturbios forestales en areas donde H. harpyja coexiste con humanos. Considerando la gran importancia del habitat reproductivo para H. harpyja en el Corredor Biologico Serrania de Bagre y la Reserva Forestal Chepigana, recomendamos una revision de la legislacion que gobierna el uso extractivo de los recursos naturales en estas dos areas protegidas. [Traduccion de los autores editada]

Forest canopies contribute significantly to global forest biodiversity and ecosystem functioning, yet are declining and understudied. One reason for a knowledge gap is that accessing forest canopies can be difficult and dangerous. Thus, lack of relevant canopy access skills may compromise knowledge gain and personal safety. We assessed skill levels in canopy access methods and self-perception of skills amongst ecologists worldwide via a web-based survey, available in four languages. We obtained responses from expert arborists as a control group. From 191 respondents who said canopy access is relevant to their research (of 1,070 total responses), we found that ecologists are not attaining the full potential provided by existing methods of canopy access. Specifically, most respondents are unable to access much of the forest canopy, especially areas away from the trunk and between trees. The survey further revealed the common use of unsafe and inefficient practices among ecologists and that few are adequately equipped with aerial rescue skills. Importantly, ecologists with the lowest skill levels overestimate their expertise the most. Proper field techniques are key components of good science: they can improve study design, increase potential for data collection, and ultimately reveal greater knowledge on canopy organisms and processes. By safely allowing greater access to the forest canopy, proper techniques can reduce bias in our scientific understanding of forest ecology. To facilitate safe and effective canopy access for ecological research, we recommend increasing instruction and collaboration, implementing certification programs, and conducting audits of canopy research programs. With increased access to such opportunities, ecologists will acquire improved skills in accessing forest canopies, develop a greater appreciation for the full breadth of possibilities among methods of canopy access, and more safely and effectively gather the data needed to better understand forest ecosystems.

There are currently four world bird lists referenced by different stakeholders including governments, academic journals, museums and citizen scientists. Consolidation of these lists is a conservation and research priority. In reconciling lists, care must be taken to ensure agreement in taxonomic concepts—the actual groups of individual organisms circumscribed by a given scientific epithet. Here, we compare species-level taxonomic concepts for raptors across the four lists, highlighting areas of disagreement. Of the 665 species-level raptor taxa observed at least once among the four lists, only 453 (68%) were consistent across all four lists. The Howard and Moore Checklist of the Birds of the World contains the fewest raptor species (528), whereas the International Ornithological Community World Bird List contains the most (580) and these two lists are in the most disagreement. Of the disagreements, 67% involved owls, and Indonesia was the country containing the most disagreed upon species (169). Finally, we calculated the amount of species-level agreement across lists for each avian order and found raptor orders spread throughout the rankings of agreement. Our results emphasize the need to reconcile the four world bird lists for all avian orders, highlight broad disagreements across lists and identify hotspots of disagreement for raptors, in particular.

The peregrine falcon (Falco peregrinus) and the gyrfalcon (Falco rusticolus) are top avian predators of Arctic ecosystems. Although existing monitoring efforts are well established for both species, collaboration of activities among Arctic scientists actively involved in research of large falcons in the Nearctic and Palearctic has been poorly coordinated. Here we provide the first overview of Arctic falcon monitoring sites, present trends for long-term occupancy and productivity, and summarize information describing abundance, distribution, phenology, and health of the two species. We summarize data for 24 falcon monitoring sites across the Arctic, and identify gaps in coverage for eastern Russia, the Arctic Archipelago of Canada, and East Greenland. Our results indicate that peregrine falcon and gyrfalcon populations are generally stable, and assuming that these patterns hold beyond the temporal and spatial extents of the monitoring sites, it is reasonable to suggest that breeding populations at broader scales are similarly stable. We have highlighted several challenges that preclude direct comparisons of Focal Ecosystem Components (FEC) attributes among monitoring sites, and we acknowledge that methodological problems cannot be corrected retrospectively, but could be accounted for in future monitoring. Despite these drawbacks, ample opportunity exists to establish a coordinated monitoring program for Arctic-nesting raptor species that supports CBMP goals. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13280-019-01300-z) contains supplementary material, which is available to authorized users.

Species considered raptors are subjects of monitoring programs, textbooks, scientific societies, legislation, and multinational agreements. Yet no standard definition for the synonymous terms “raptor” or “bird of prey” exists. Groups, including owls, vultures, corvids, and shrikes are variably considered raptors based on morphological, ecological, and taxonomic criteria, depending on the authors. We review various criteria previously used to define raptors and we present an updated definition that incorporates current understanding of bird phylogeny. For example, hunting live vertebrates has been largely accepted as an ecological trait of raptorial birds, yet not all species considered raptors are raptorial (e.g., Palm-nut Vulture [Gypohierax angolensis]), and not all raptorial birds are considered raptors (e.g., skuas [Stercorariidae]). Acute vision, a hooked bill, and sharp talons are the most commonly used morphological characters for delineating raptors; however, using those characters as criteria may cause confusion because they can be vague and exceptions are sometimes made. Old World vultures, for example, are in the family Accipitridae along with hawks and eagles, and thus are usually considered raptors despite their lack of sharp talons. We define raptors as species within orders that evolved from raptorial landbirds (Telluraves) in which most species maintained raptorial lifestyles. Raptors are therefore all species within Accipitriformes, Cathartiformes, Falconiformes, and Strigiformes. Importantly, we believe that seriemas (Cariamiformes) should also be considered raptors. Our definition combines phylogeny with morphology and ecology, and avoids ambiguity associated with owls, vultures, and shrikes. Establishing a common definition of raptors should improve interpretability across studies and lessen ambiguity of research and management recommendations.

Perspectives on Rangeland Management Education and Research in Argentina DOI:10.2458/azu_rangelands_v33i1_anderson

SummaryThe Honduran Emerald Amazilia luciae is endemic to dry forests of Honduras and currently recognised as ‘Critically Endangered.’ Here we present the first modern assessment of its distribution, ecology, and conservation, based partly on our rediscovery of the species in western Honduras and on our observations in three Honduran departments. We found that dry forests inhabited by the emerald differed in structure and species composition between eastern and western Honduras, where we observed emeralds in open-canopied deciduous thorn forests and closed-canopied semi-deciduous woodlands, respectively. We interpret these differences in light of the geological and anthropogenic origins of dry forests in Honduras, and discuss the implications of such origins for the conservation of dry forests. Although our findings expand the known distribution and population size of the species, its status as ‘Critically Endangered’ is warranted due to its restricted distribution in dry forest fragments and increasing human pressures on this habitat.

Birds of the forest canopy are important components of tropical forest ecosystems, but difficulty of access or viewing into the canopy complicates their study. If ground methods are biased against canopy birds, as has been suggested, this bias could affect our understanding of forest ecology as well as biological monitoring and conservation practices. This study is the first to quantitatively compare results from ground- and canopy-based methods of censusing canopy birds. I used three methods to assess differences in ground-based and canopy-based methods for detecting forest birds in a 100-ha plot of lowland forest in northern Honduras: (1) point counts from the ground, (2) 22 repeat censuses from two canopy trees, and (3) single censuses from 22 canopy trees. I counted birds for a full annual cycle from April 2006 to April 2007 and recorded 157 species in over 4000 individual detections. Ground methods significantly underestimated species and familial richness as well as abundance of individual...

In the first comprehensive survey of tern colonies in the Honduras Bay Islands, 46 cays were surveyed in 2005 and 2006 and three species of terns were observed nesting in colonies on ten individual cays. Apparent colony turnover was high between years for Least (Sternula antillarum) and Roseate (Sterna dougallii) Terns, from 71% to 100%, respectively. The first nest records of Bridled Tern (Onychoprion anaethetus) for Honduras are documented.

I studied the relationship between diurnal raptor diversity, density, and richness, and landscape heterogeneity in continuous primary forests and forests farmed by native Amerindians in the Rio Platano Biosphere Reserve of northeastern Honduras from January to June 1996 and 1997. I estimated landscape heterogeneity—the variability in naturally occurring and/or anthropogenic habitat mosaics—by mapping the extent and distribution of five human-modified and natural habitats in 24 1 km2 survey plots. I used the Shannon index to calculate landscape heterogeneity values for the respective plots based on the proportion of total area of each habitat within each plot. Diurnal raptor surveys from canopy-emergent viewpoints in these plots resulted in 137 observations of 18 species of raptors. Four species (Coragyps atratus, Ictinia plumbea, Leucopternis albicollis, and Buteo magnirostris) differed significantly in abundance among heterogeneity classes. Raptor diversity, density, and richness all increased d...

Atmospheric samples were collected during warm and cold weather conditions at continental, coastal and marine sites. Source sampling was performed at a coal-fired power plant and several volcanic sites. Atmospheric gas-phase and particulate boron concentrations were determined by neutron capture prompt-gamma activation analysis and compared to measurements from other studies. Rain and snow samples collected at one continental site were analysed for soluble and insoluble B. Volcanic deposit and ash samples were also analysed for B. The tropospheric burdens for particulate and gas-phase B were estimated to be 0.6 × 1010 g and (6–11) × 1010 g, respectively, with the latter about a factor of 3 lower than previous estimates. Global anthropogenic particulate and gas-phase B source estimates were consistent with previous estimates, and natural particulate and gas-phase B source estimates agreed reasonably well with previously reported upper limits. About 65–85 % of total B source strength can be attributed to the oceans, and 8–20% to coal, agricultural, fuelwood and refuse burning. Volcanism may contribute 6–15% of the total, but accurate source estimates are difficult. Total global B removal from the atmosphere by wet and dry deposition was estimated to be (530–700) × 1010 g yr−1, a factor of 2 lower than previously reported but in fairly good agreement with the global total B source estimate of (200–530) × 1010 g yr−1.

Field experiments conducted between 1982 to 1988 compared 2,4-D [(2,4-dichlorophenoxy)acetic acid] and metsulfuron [2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino)carbonyl]amino]sulfonyl]benzoic acid) for control of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young) in northern New Mexico. Precipitation was near or above normal during years of herbicide applications. Broadcast sprays of 2,4-D at 2.2 kg/ha were most efficacious during rapid shoot elongation, but mortality averaged less than 38% from treatments applied over 4 separate years. Wyoming big sagebrush shoot growth was greatest in April and May compared to other months, but growth was highly variable among shrubs and probably reduced effectiveness of 2,4-D sprays. The optimum application timing for metsulfuron was during the late-flower growth and fruiting stages. Fall-applied metsulfuron at 0.035 kg/ha provided 65% Wyoming big sagebrush mortality compared to 27% when spring-applied. When metsulfuron was fall-applied at 0.07 kg/ha or higher, control averaged 88% following 3 annual applications. Combining metsulfuron at .0175 kg/ha plus 2,4-D at 1.1 kg/ha was comparable to or more effective than either herbicide applied alone in spring or fall. Total standing crop of grasses increased by nearly 300% after 1 or 2 growing seasons when Wyoming big sagebrush canopy cover was reduced by at least 75% following herbicide treatments.

Atmospheric particulate material collected from the stratosphere in the plume of the 18 May 1980 eruption of the Mount St. Helens volcano was quite similar in composition to that of ash that fell to the ground in western Washington. However, there were small but significant differences in concentrations of some elements with altitude, indicating that the stratospheric material was primarily produced from fresh magma, not fragments of the mountain.

The strong influence of colonial agrarian policies on the process of decolonization in Eastern Africa has been recognized by historians for some time. The Depression struck savagely at the economies of all the African colonies from 1929 until 1935, affecting both European settler agriculture and African production. The South African Soil Erosion Conference of 1929, and the creation of a Soil Erosion Council in the Union, resulted in the implementation of anti-erosion schemes by 1933. The issue of soil conservation had emerged as a central concern of government in East Africa by 1938. The droughts of 1927–29 and 1933–34 took a heavy toll of African livestock, but to the alarm of observers this did little to relieve the pressure on the parched grasslands. Awareness of an environmental threat to the land, and of a consequent threat to the future viability and profitability of farming, prompted more thorough research into the methods of arable and pastoral production in Africa.

Neutron-capture prompt γ-ray analysis (PGAA) is an exceptionally good method for the determination of the major and minor elements Na, Mg, Al, Si, K, Ca, Ti, Mn and Fe in most geological matrices. The trace elements H, B, S, Cl, Cd, Sm and Gd can often be readily measured in most geological materials. This technique was applied to volcanic ash samples collected in Washington and Montana by various groups following the May 18 eruption of the Mt. St. Helens volcano, as well as to several particulate samples collected at altitudes between 13 and 18 km by a NASA U-2 research aircraft. Groundfall ash samples show distinct elemental variations versus distance from the volcano. For example, Si/Al ratios vary from 2.85 near the volcano to about 3.70 at≽400 km to the east. Samples collected sequentially at a given location (Almira, Washington) also exhibit variations in the elemental ratios. These sequential samples were also subjected to leaching studies to determine soluble B, Cl and S. On the average, PGAA is able to account for 99.4±1.7% of the mass of each sample when the elements are considered to be in their common oxide forms. The stratospheric samples were collected May 19 on IPC cellulose filters on apparatus in a wing tank of the U-2. The PGAA results indicate that the sample from the greatest altitude resembles ashfall near the volcano, while those at lower altitudes somewhat resemble more distant ashfall.