Papers by Victoria Dreitz
Animal Biodiversity and Conservation
Reintroduction is a powerful tool in our conservation toolbox. However, the necessary follow-up, ... more Reintroduction is a powerful tool in our conservation toolbox. However, the necessary follow-up, i.e. long-term monitoring, is not commonplace and if instituted may lack rigor. We contend that valid monitoring is possible, even with sparse data. We present a means to monitor based on demographic data and a projection model using the Wyoming toad (Bufo baxteri) as an example. Using an iterative process, existing data is built upon gradually such that demographic estimates and subsequent inferences increase in reliability. Reintroduction and defensible monitoring may become increasingly relevant as the outlook for amphibians, especially in tropical regions, continues to deteriorate and emergency collection, captive breeding, and reintroduction become necessary. Rigorous use of appropriate modeling and an adaptive approach can validate the use of reintroduction and substantially increase its value to recovery programs.
Because of continental-scale declines of grassland birds over the past century, conservation agen... more Because of continental-scale declines of grassland birds over the past century, conservation agendas are focused on increasing understanding of grassland bird ecology and habitat associations. Shortgrass prairie is a unique grassland ecosystem maintained, in part, by Black-tailed Prairie Dogs (Cynomys ludovicianus). The Mountain Plover (Charadrius montanus) and western Burrowing Owl (Athene cunicularia hypugaea) are species of conservation concern known to be associated with prairie dog colonies. We estimated abundance of Mountain Plovers and Burrowing Owls in three habitats within the Colorado shortgrass prairie ecosystem— prairie dog colonies, grassland not occupied by prairie dogs, and dryland agriculture. Further, we investigated habitat associations of Mountain Plovers and Burrowing Owls at multiple landscape scales. We estimated 8,577 Mountain Plovers (95% CI: 7,511–35,130) and 3,554 Burrowing Owls (95% CI: 3,298–8,445) in eastern Colorado. Mountain Plover density on prairie d...
The Mountain Plover (Charadrius montanus) is a declining migratory shorebird that nests on shortg... more The Mountain Plover (Charadrius montanus) is a declining migratory shorebird that nests on shortgrass prairies across the western Great Plains. This ground-nesting species exhibits an uncommon split-clutch mating system, in which each member of a pair simultaneously incubates a nest and uniparental care continues throughout brood-rearing. We report on an observation of within-season nest reuse in this species. To our knowledge, this report includes the first documented occurrence of 2 different Mountain Plovers using the same nest cup in the same breeding season. Nest reuse could represent a time- and energy-saving strategy for renesting individuals
Monitoring, management, and conservation of grassland birds are topics of importance because of w... more Monitoring, management, and conservation of grassland birds are topics of importance because of widespread population declines. Annual estimates of survival are available for many species, however knowledge of how survival varies on a seasonal basis remains poor. Information on the relative effects of breeding, overwintering, and migratory periods on population dynamics is necessary for effective management. Mortality risks often vary with the stage of the breeding cycle. In precocial species, mortality risks of adult birds are often higher during post-hatching care than prehatching. Using a multistate modeling approach, I investigated the influence of both environmental characteristics, measured by habitat, and individual characteristics, measured by sex and body mass, on post-hatching parental mortality of a declining grassland species, the Mountain Plover (Charadrius montanus). I found minimal evidence to support the effect of habitat, sex, or body mass on post-hatching parental ...
The Wilson Journal of Ornithology
BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.
Reintroduction is a powerful tool in our conservation toolbox. However, the necessary follow-up, ... more Reintroduction is a powerful tool in our conservation toolbox. However, the necessary follow-up, i.e. long-term monitoring, is not commonplace and if instituted may lack rigor. We contend that valid monitoring is possible, even with sparse data. We present a means to monitor based on demographic data and a projection model using the Wyoming toad (Bufo baxteri) as an example. Using an iterative process, existing data is built upon gradually such that demographic estimates and subsequent inferences increase in reliability. Reintroduction and defensible monitoring may become increasingly relevant as the outlook for amphibians, especially in tropical regions, continues to deteriorate and emergency collection, captive breeding, and reintroduction become necessary. Rigorous use of appropriate modeling and an adaptive approach can validate the use of reintroduction and substantially increase its value to recovery programs. Key words: Reintroduction, Monitoring, Adaptive processes, Amphibia...
Ecosphere, 2021
Preserving avian flyway connectivity has long been challenged by our capacity to meaningfully qua... more Preserving avian flyway connectivity has long been challenged by our capacity to meaningfully quantify continental habitat dynamics and bird movements at temporal and spatial scales underlying long‐distance migrations. Waterbirds migrating hundreds or thousands of kilometers depend on networks of wetland stopover sites to rest and refuel. Entire populations may rely on discrete wetland habitats, particularly in arid landscapes where the loss of limited stopover options can have disproportionately high impacts on migratory cost. Here, we examine flyway connectivity in water‐limited ecosystems of western North America using 108 GPS tagged greater sandhill cranes. Bird movements were used to reconstruct wetland stopover networks across three geographically unique sub‐populations spanning 12 U.S.–Mexican states and Canadian provinces. Networks were monitored with remote sensing to identify long‐term (1988–2019) trends in wetland and agricultural resources supporting migration and evalua...
Ecosphere, 2019
In semi‐arid ecosystems, timing and availability of water is a key uncertainty associated with co... more In semi‐arid ecosystems, timing and availability of water is a key uncertainty associated with conservation planning for wetland‐dependent wildlife. Wetlands compose only 1–3% of these landscapes; however, large populations of migratory waterbirds rely on these wetlands to support energetically demanding life history events such as breeding and migration. Migration is considered a crucial period for birds associated with individual survival and reproductive success, yet our understanding of migration ecology remains limited. To better inform conservation planning supportive of these demands, we quantified synchrony of wetland flooding and waterbird migration by reconstructing bi‐monthly surface water patterns from 1984 to 2015 across 11.4 million ha of the semi‐arid Great Basin, USA. Results were then linked to seasonal migration chronologies for seven dabbling ducks species. Seasonal patterns were used in landscape planning simulations to assess efficiency in conservation strategie...
Ecology and Evolution, 2018
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Avian Conservation and Ecology, 2010
Effective conservation measures should target the most sensitive life history attributes of a spe... more Effective conservation measures should target the most sensitive life history attributes of a species, assuming they are responsive to potential management actions. The Mountain Plover (Charadrius montanus) is a species of conservation concern with a patchy breeding distribution in western North America. Plovers prefer areas with short vegetation, bare ground, and disturbance for nesting. Current management tools, including grazing and burning, have been used to attract plovers and enhance nesting success. We used a stage-specific matrix model to study the influence of vital rates, e.g., juvenile and adult annual survival, on population growth rate in the Mountain Plover at two breeding sites in Colorado, South Park and Eastern Colorado, and one breeding site in Montana, USA. Our analysis was motivated by a need to 1) better understand the relationship between demographic rates and population growth rate, 2) assess current management tools for the plover by exploring their effect on population growth rate, and 3) identify areas of the plover's population biology where additional demographic work is needed. Stochastic population growth rate was most influenced by adult survival, especially in Montana and South Park, Colorado (elasticities > 0.60), and was least influenced by first-year reproduction (all elasticities < 0.20). The modeled relationships between lambda and each demographic rate were generally weak (r 2 < 0.30) with the exception of number of eggs hatched per nest in Eastern Colorado (r 2 = 0.63), chick survival in South Park (r 2 = 0.40) and Montana (r 2 = 0.38), and adult survival in Montana (r 2 = 0.36). We examined the predicted increase in lambda that would result from increasing each demographic rate from its mean to the maximum value observed in our simulations. Chick and adult survival showed the greatest increase in lambda while eggs hatched per nest produced the smallest increase. Our results suggest that future conservation efforts should favor ways to increase adult or chick survival over efforts to increase nest success. In particular, adult survival rates during the stationary periods, i.e., summer and winter, are relatively high, implying that efforts to increase adult survival rates may need to focus on the migratory periods. Increasing chick survival should be a priority for efforts that are restricted to the breeding grounds because this life history stage is relatively short (< 3 mo) and it offers opportunities for targeted short-term management activities in breeding areas. RÉSUMÉ. Pour être efficaces, les mesures de conservation devraient cibler les éléments les plus sensibles du cycle biologique d'une espèce, en supposant que les actions de gestion possibles peuvent avoir un effet sur eux. Le Pluvier montagnard (Charadrius montanus), espèce dont le statut est préoccupant, présente une aire de reproduction clairsemée dans l'ouest de l'Amérique du Nord. Ce pluvier préfère nicher dans les endroits pourvus de végétation courte et de sol à nu, et qui sont fréquemment perturbés. Le pâturage et le brûlage, deux outils actuels de gestion, ont été utilisés pour attirer les pluviers et améliorer leur succès de
Avian Conservation and Ecology, 2015
Skewed sex ratios can have negative implications for population growth if they do not match a spe... more Skewed sex ratios can have negative implications for population growth if they do not match a species' life history. A skewed tertiary sex ratio has been detected in a population of Mountain Plover (Charadrius montanus), a grassland shorebird experiencing population declines. To study the cause of the observed male skew, we examined three early life stages between egg and fledgling in eastern Colorado from 2010 to 2012. This allows us to distinguish between egg production and chick survival as an explanation for the observed skew. We examined the primary sex ratio in eggs produced and the secondary sex ratio in hatched chicks to see if the sex ratio bias occurs before hatching. We also determined the sex ratio at fledging to reveal sex-specific mortality of nestlings. The primary sex ratio was 1.01 (± 0.01) males per female. The secondary sex ratio consisted of 1.10 (± 0.02) males per female. The probability of a chick surviving to fledging differed between males (0.55 ± 0.13) and females (0.47 ± 0.15), but the precision of these survival estimates was low. Sex ratios in early life stages of the Mountain Plover do not explain the skewed sex ratio observed in adults in this breeding population. Sex-ratios de la production d'oeufs à l'envol chez le Pluvier montagnard RÉSUMÉ. Des sex-ratios déséquilibrées peuvent avoir des effets négatifs sur la croissance d'une population si elles sont trop éloignées de la biodémographie naturelle de l'espèce. Une sex-ratio tertiaire déséquilibrée a été détectée chez une population de Pluvier montagnard (Charadrius montanus), un oiseau de rivage qui se reproduit dans les prairies et dont les populations sont en baisse. Dans le but d'étudier la cause du déséquilibre observé favorisant les mâles, nous avons examiné trois stades précoces des oeufs à l'envol, dans l'est du Colorado de 2010 à 2012. Cet examen nous a permis d'établir si la production d'oeufs ou la survie des jeunes pouvait expliquer la sex-ratio déséquilibrée. Nous avons examiné la sex-ratio primaire des oeufs et la sex-ratio secondaire des poussins éclos afin de déterminer si le déséquilibre de la sex-ratio était présent avant l'éclosion. Nous avons aussi déterminé la sex-ratio des jeunes à l'envol pour obtenir la mortalité spécifique au sexe des oisillons. La sex-ratio primaire s'élevait à 1,01 (± 0,01) mâle par femelle. La sex-ratio secondaire était de 1,10 (± 0,02) mâle par femelle. La probabilité qu'un oisillon survive jusqu'à l'envol était différente entre les mâles (0,55 ± 0,13) et les femelles (0,47 ± 0,15), mais la précision de ces estimations de survie était faible. La sex-ratio observée aux stades précoces n'explique pas le déséquilibre de la sex-ratio chez les adultes de cette population nicheuse de Pluvier montagnard.
Ecology and evolution, 2015
Event-time or continuous-time statistical approaches have been applied throughout the biostatisti... more Event-time or continuous-time statistical approaches have been applied throughout the biostatistical literature and have led to numerous scientific advances. However, these techniques have traditionally relied on knowing failure times. This has limited application of these analyses, particularly, within the ecological field where fates of marked animals may be unknown. To address these limitations, we developed an integrated approach within a Bayesian framework to estimate hazard rates in the face of unknown fates. We combine failure/survival times from individuals whose fates are known and times of which are interval-censored with information from those whose fates are unknown, and model the process of detecting animals with unknown fates. This provides the foundation for our integrated model and permits necessary parameter estimation. We provide the Bayesian model, its derivation, and use simulation techniques to investigate the properties and performance of our approach under sev...
Avian Conservation and Ecology, 2012
Native grasslands have been altered to a greater extent than any other biome in North America. Th... more Native grasslands have been altered to a greater extent than any other biome in North America. The habitats and resources needed to support breeding performance of grassland birds endemic to prairie ecosystems are currently threatened by land management practices and impending climate change. Climate models for the Great Plains prairie region predict a future of hotter and drier summers with strong multiyear droughts and more frequent and severe precipitation events. We examined how fluctuations in weather conditions in eastern Colorado influenced nest survival of an avian species that has experienced recent population declines, the Mountain Plover (Charadrius montanus). Nest survival averaged 27.2% over a 7-yr period (n = 936 nests) and declined as the breeding season progressed. Nest survival was favored by dry conditions and cooler temperatures. Projected changes in regional precipitation patterns will likely influence nest survival, with positive influences of predicted declines in summer rainfall yet negative effects of more intense rain events. The interplay of climate change and land use practices within prairie ecosystems may result in Mountain Plovers shifting their distribution, changing local abundance, and adjusting fecundity to adapt to their changing environment. RÉSUMÉ. Les prairies naturelles ont été plus grandement modifiées que tout autre biome en Amérique du Nord. L'habitat et les ressources nécessaires pour favoriser la performance reproductrice des oiseaux de prairie endémiques de ces écosystèmes sont actuellement menacés par les pratiques de gestion des terres et les changements climatiques imminents. Les modèles climatiques pour les prairies des Grandes Plaines prévoient des étés plus chauds et plus secs, des sécheresses sévères durant plusieurs années et des évènements de précipitation plus fréquents et intenses que ce qu'on observe présentement. Nous avons examiné les effets des fluctuations des conditions météorologiques dans l'est du Colorado sur la survie des nids chez une espèce aviaire ayant subi un récent déclin des populations, le Pluvier montagnard (Charadrius montanus). Le taux de survie des nids s'élevait à 27,2 % en moyenne sur une période de 7 ans (n = 936 nids) et diminuait à mesure que progressait la saison de reproduction. La survie des nids était supérieure quand les conditions étaient sèches et les températures fraîches. Les changements prévus dans les tendances régionales des précipitations influenceront vraisemblablement la survie des nids : tandis que la diminution des précipitations estivales prévue entraînera un effet positif sur la survie, les évènements de précipitation plus intenses prévus auront, quant à eux, un effet négatif. L'interaction des changements climatiques et des pratiques d'utilisation des sols dans les écosystèmes de prairie amènera peut-être le Pluvier montagnard à modifier sa répartition, son abondance locale et sa fécondité pour s'adapter à l'environnement changeant.
Transactions of the American Fisheries Society, 2001
The Suwannee River, Florida, population of the Gulf of Mexico sturgeon Acipenser oxyrinchus desot... more The Suwannee River, Florida, population of the Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi, a subspecies of Atlantic sturgeon A. oxyrinchus oxyrinchus, was evaluated using a capture-recapture approach and an age-structured model to examine population trends from 1986 through 1995. The capture-recapture analysis revealed a positive rate of change () in the adult population, indicating that it was slowly increasing from the mid-1980s through the mid-1990s. The age-structured model revealed that the population was highly sensitive to changes in egg-toage-1 mortality, the percentage of females that spawn annually, and adult mortality. The model predicted that even slight increases in annual adult mortality (from 16% to 20%) would result in a decline in the Suwannee River Gulf sturgeon population. Population trends were consistent for both modeling procedures and were similar to those in published reports. Although this population is currently expanding, care should be taken to protect adult fish from any fishing or bycatch mortality. Given the particular attributes of Gulf sturgeon (such as late sexual maturation, the fact that few mature females spawn each year, and high early life mortality), managers should be patient and willing to monitor populations for extended periods of time (ϳ20 years) to detect changes in the adult population.
The Wilson Bulletin, 2005
We report movements and home-range sizes of adult Mountain Plovers (Charadrius montanus) with bro... more We report movements and home-range sizes of adult Mountain Plovers (Charadrius montanus) with broods on rangeland, agricultural fields, and prairie dog habitats in eastern Colorado. Estimates of home range size (95% fixed kernel) were similar across the three habitats: rangeland (146.1 ha ? 101.5), agricultural fields (131.6 ha ? 74.4), and prairie dog towns (243.3 ha ? 366.3). Our minimum convex polygon estimates of home-range size were comparable to those on rangeland reported by Knopf and Rupert (1996). In addition,
The Southwestern Naturalist, 2006
We monitored nest success of mountain plovers (Charadrius montanus) relative to distance from the... more We monitored nest success of mountain plovers (Charadrius montanus) relative to distance from the nearest anthropogenic edges, such as fence lines, roads, and perimeters of crop fields, in 2003 and 2004. We located and observed 163 mountain plover nests in eastern Colorado (USA). At least one egg hatched in 81 of 163 nests. Successful nests occurred at a mean distance of 93.94 m Ϯ 8.87 SE, whereas unsuccessful nests were located 84.39 m Ϯ 8.95 SE from the nearest edge. Based on our model selection criteria (AIC c), nests farther from edges were not necessarily more successful than those closer to edges. The logistic regression coefficient for edge effects (0.13 Ϯ 0.12 SE) suggests that nests farther from edges are more successful. However, the standard error for the edge coefficient was large and the 95% confidence interval (Ϫ0.08, 0.35) encompassed zero, suggesting nest success was independent of distance from an anthropomorphic edge. We conclude that phenomena determining nest success of mountain plovers cannot be attributed to the single factor of anthropogenic edges in this fragmented landscape.
Landscape Ecology, 2008
Sylvatic plague is a major factor influencing the dynamics of black-tailed prairie dog (Cynomys l... more Sylvatic plague is a major factor influencing the dynamics of black-tailed prairie dog (Cynomys ludovicianus) colonies in the western Great Plains. We studied the nesting response of the mountain plover (Charadrius montanus), a grassland bird that nests on prairie dog colonies, to plaguedriven dynamics of prairie dog colonies at three sites in the western Great Plains. First, we examined plover nest distribution on colonies that were previously affected by plague, but that had been recovering (expanding) for at least 6 years. Plovers consistently nested in both young (colonized in the past 1-2 years) and old (colonized for 6 or more years) portions of prairie dog colonies in proportion to their availability. Second, we examined changes in plover nest frequency at two sites following plague epizootics, and found that mountain plover nest numbers declined relatively rapidly (B2 years) on plague-affected colonies. Taken together, our findings indicate that available plover nesting habitat associated with prairie dog colonies closely tracks the area actively occupied by prairie dogs each year. Given the presence of plague throughout most of the mountain plover's breeding range in the western Great Plains, important factors affecting plover populations likely include landscape features that determine the scale of plague outbreaks, the distance that plovers move in response to changing breeding habitat conditions, and the availability and quality of alternate breeding habitat within the landscape.
Journal of Wildlife Management, 2008
Concern over the decline of grassland birds has spurred efforts to increase understanding of gras... more Concern over the decline of grassland birds has spurred efforts to increase understanding of grassland bird-habitat relationships. Previous studies have suggested that black-tailed prairie dogs (Cynomys ludovicianus) provide important habitat for shortgrass prairie avifauna, such as mountain plover (Charadrius montanus) and western burrowing owl (Athene cunicularia hypugaea), although such studies are lacking in Colorado (USA). We used methods to estimate occupancy (w) of mountain plover and burrowing owl on prairie dog colonies and other shortgrass prairie habitats in eastern Colorado. Mountain plover occupancy was higher on prairie dog colonies (w ¼ 0.50, 95% CI ¼ 0.36-0.64) than on grassland (w ¼ 0.07, 95% CI ¼ 0.03-0.15) and dryland agriculture (w ¼ 0.13, 95% CI ¼ 0.07-0.23). Burrowing owl occupancy was higher on active prairie dog colonies (w ¼ 0.80, 95% CI ¼ 0.66-0.89) compared with inactive colonies (w ¼ 0.23, 95% CI ¼ 0.07-0.53), which in turn was much higher than on grassland (w ¼ 0.01, 95% CI ¼ 0.00-0.07) and dryland agriculture (w ¼ 0.00, 95% CI ¼ 0.00-0.00). Mountain plover occupancy also was positively correlated with increasing amounts of prairie dog colony in the landscape. Burrowing owl occupancy was negatively correlated with increasing amounts of prairie dog colony in the surrounding landscape. Our results suggest that actions to conserve mountain plovers and burrowing owls should incorporate land management to benefit prairie dogs. Because managing for specific colony attributes is difficult, alternative management that promotes heterogeneity may ensure that suitable habitat is available for the guild of grassland inhabitants.
Journal of Applied Statistics, 2002
The rate of population growth (k) is an important demog raphic parameter used to assess the viabi... more The rate of population growth (k) is an important demog raphic parameter used to assess the viability of a population and to develop management and conser vation agendas. We examined the use of resighting data to estimate k for the snail kite population in Florida from 1997-2000. The analyses consisted of (1) a robust design approach that derives an estimate of k from estimates of population size and (2) the Pradel (1996) temporal symmetr y (T SM) approach that directly estimates k using an open-population capture-recapture model. B esides resighting data, both approaches required information on the number of unmarked individuals that were sighted during the sampling periods. The point estimates of k diþ ered between the robust design and TSM approaches, but the 95% con® dence inter vals overlapped substantially. We believe the diþ erences may be the result of sparse data and do not indicate the inappropriateness of either modelling technique. We focused on the results of the robust design because this approach provided estimates for all study years. Variation among these estimates was smaller than levels of variation among ad hoc estimates based on previously reported index statistics. We recommend that k of snail kites be estimated using capture-resighting methods rather than ad hoc counts. 1 Introduction Understanding the biological and physical factors that regulate a population is a fundam ental challenge in population ecology (H astings, 1997). In¯uctuating
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Papers by Victoria Dreitz