Sediment accumulation threatens the viability and hydrologic functioning of many naturally formed... more Sediment accumulation threatens the viability and hydrologic functioning of many naturally formed depressional wetlands across the interior regions of North America. These wetlands provide many ecosystem services and vital habitats for diverse plant and animal communities. Climate change may further impact sediment accumulation rates in the context of current land use patterns. We estimated sediment accretion in wetlands within a region renowned for its large populations of breeding waterfowl and migrant shorebirds and examined the relative roles of precipitation and land use context in the sedimentation process. We modeled rates of sediment accumulation from 1971 through 2100 using the Revised Universal Soil Loss Equation (RUSLE) with a sediment delivery ratio and the Unit Stream Power Erosion Deposition model (USPED). These models predicted that by 2100, 21-33 % of wetlands filled completely with sediment and 27-46 % filled by half with sediments; estimates are consistent with measured sediment accumulation rates in the region reported by empirical studies. Sediment accumulation rates were strongly influenced by size of the catchment, greater coverage of tilled landscape within the catchment, and steeper slopes. Conservation efforts that incorporate the relative risk of infilling of wetlands with sediments, thus emphasizing areas of high topographic relief and large watersheds, may benefit wetland-dependent biota.
Climate change elevates conservation concerns worldwide because it is likely to exacerbate many i... more Climate change elevates conservation concerns worldwide because it is likely to exacerbate many identified threats to animal populations. In recent decades, grassland birds have declined faster than other North American bird species, a loss thought to be due to habitat loss and fragmentation and changing agricultural practices. Climate change poses additional threats of unknown magnitude to these already declining populations. We examined how seasonal and daily weather conditions over 10 years influenced nest survival of five species of insectivorous passerines native to the shortgrass prairie and evaluate our findings relative to future climate predictions for this region. Daily nest survival (n = 870) was best predicted by a combination of daily and seasonal weather variables, age of nest, time in season and bird habitat guild. Within a season, survival rates were lower on very hot days (temperatures ≥ 35°C), on dry days (with a lag of 1 day) and on stormy days (especially for those species nesting in shorter vegetation). Across years, survival rates were also lower during warmer and drier breeding seasons. Clutch sizes were larger when early spring temperatures were cool and the week prior to egg-laying was wetter and warming. Climate change is likely to exacerbate grassland bird population declines because projected climate conditions include rising temperatures, more prolonged drought and more intense storms as the hydrological cycle is altered. Under varying realistic scenarios, nest success estimates were halved compared to their current average value when models both increased the temperature (3°C) and decreased precipitation (two additional dry days during a nesting period), thus underscoring a sense of urgency in identifying and addressing the current causes of range-wide declines.
Disturbed xeric grasslands with short, sparse vegetation provide breeding habitat for mountain pl... more Disturbed xeric grasslands with short, sparse vegetation provide breeding habitat for mountain plovers (Charadrius montanus) across the western Great Plains. Maintaining local disturbance regimes through prairie dog conservation and prescribed fire may contribute to the sustainability of recently declining mountain plover populations, but these management approaches can be controversial. We estimated habitatspecific mountain plover densities and nest survival rates on black-tailed prairie dog (Cynomys ludovicianus) colonies and burns in the shortgrass steppe of northeastern Colorado. Mountain plover densities were similar on prairie dog colonies (5.9 birds/km 2 ; 95% CI ¼ 4.7-7.4) and sites burned during the preceding dormant season (6.7 birds/km 2 ; 95% CI ¼ 4.6-9.6), whereas the 29-day nest survival rate was greater on prairie dog colonies (0.81 in 2011 and 0.39 in 2012) compared to the burned sites (0.64 in 2011 and 0.17 in 2012). Reduced nest survival in 2012 compared to 2011 was associated with higher maximum daily temperatures in 2012, consistent with a previous weather-based model of mountain plover nest survival in the southern Great Plains. Measurements of mountain plover density relative to time since disturbance showed that removal of prairie dog disturbance by sylvatic plague reduced mountain plover density by 70% relative to active prairie dog colonies after 1 year. Plover densities declined at a similar rate (by 78%) at burned sites between the first and second post-burn growing season. Results indicate that black-tailed prairie dog colonies are a particularly important nesting habitat for mountain plovers in the southern Great Plains. In addition, findings suggest that prescribed burning can be a valuable means to create nesting habitat in landscapes where other types of disturbances (such as prairie dog colonies) are limited in distribution and size. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.
Playa wetlands on the west-central Great Plains of North America are vulnerable to sediment infil... more Playa wetlands on the west-central Great Plains of North America are vulnerable to sediment infilling from upland agriculture, putting at risk several important ecosystem services as well as essential habitats and food resources of diverse wetland-dependent biota. Climate predictions for this semi-arid area indicate reduced precipitation which may alter rates of erosion, runoff, and sedimentation of playas. We forecasted erosion rates, sediment depths, and resultant playa wetland depths across the west-central Great Plains and examined the relative roles of land use context and projected changes in precipitation in the sedimentation process. We estimated erosion with the Revised Universal Soil Loss Equation (RUSLE) using historic values and downscaled precipitation predictions from three general circulation models and three emissions scenarios. We calibrated RUSLE results using field sediment measurements. RUSLE is appealing for regional scale modeling because it uses climate forecasts with monthly resolution and other widely available values including soil texture, slope and land use. Sediment accumulation rates will continue near historic levels through 2070 and will be sufficient to cause most playas (if not already filled) to fill with sediment within the next 100 years in the absence of mitigation. Land use surrounding the playa, whether grassland or tilled cropland, is more influential in sediment accumulation than climate-driven precipitation change.
We combined several existing spatial layers of potential playa wetland locations and geometries (... more We combined several existing spatial layers of potential playa wetland locations and geometries (Kansas Data Access and Support Center [http://www.kansas.org]; M. McLachlan, D. Pavlacky unpublished data) to create a single dataset containing roughly 84,000 playa wetlands on the west-central Great Plains. We assumed the playa data to be the current best estimate of playa location and extent. Due to file size processing limitations and because few playas occurred east of 98.4°W, we truncated the playa dataset here. Not including this playasparse portion of the study area in our analyses resulted in a loss of about 0.33% (788 ha) of total playa wetland area and ca 1% (1049) of all playas.
The influence of recent climate change on the world's biota has manifested broadly, resulting in ... more The influence of recent climate change on the world's biota has manifested broadly, resulting in latitudinal range shifts, advancing dates of arrival of migrants and onset of breeding, and altered community relationships. Climate change elevates conservation concerns worldwide because it will likely exacerbate a broad range of identified threats to animal populations. In the past few decades, grassland birds have declined faster than other North American avifauna, largely due to habitat threats such as the intensification of agriculture. We examine the effects of local climatic variations on the breeding performance of a bird endemic to the shortgrass prairie, the Lark Bunting (Calamospiza melanocorys) and discuss the implications of our findings relative to future climate predictions. Clutch size, nest survival, and productivity all positively covaried with seasonal precipitation, yet relatively intense daily precipitation events temporarily depressed daily survival of nests. Nest survival was positively related to average temperatures during the breeding season. Declining summer precipitation may reduce the likelihood that Lark Buntings can maintain stable breeding populations in eastern Colorado although average temperature increases of up to 38C (within the range of this study) may ameliorate declines in survival expected with drier conditions. Historic climate variability in the Great Plains selects for a degree of vagility and opportunism rather than strong site fidelity and specific adaptation to local environments. These traits may lead to northerly shifts in distribution if climatic and habitat conditions become less favorable in the drying southern regions of the Great Plains. Distributional shifts in Lark Buntings could be constrained by future changes in land use, agricultural practices, or vegetative communities that result in further loss of shortgrass prairie habitats.
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.
Effective conservation metrics are needed to evaluate the success of management in a rapidly chan... more Effective conservation metrics are needed to evaluate the success of management in a rapidly changing world. Reproductive rates and densities of breeding birds (as a surrogate for reproductive rate) have been used to indicate the quality of avian breeding habitat, but the underlying assumptions of these metrics rarely have been examined. When birds are attracted to breeding areas in part by the presence of conspecifics and when breeding in groups influences predation rates, the effectiveness of density and reproductive rate as indicators of habitat quality is reduced. It is beneficial to clearly distinguish between individual-and population-level processes when evaluating habitat quality. We use the term reproductive rate to refer to both levels and further distinguish among levels by using the terms per capita fecundity (number of female offspring per female per year, individual level) and population growth rate (the product of density and per capita fecundity, population level). We predicted how density and reproductive rate interact over time under density-independent and density-dependent scenarios, assuming the ideal free distribution model of how birds settle in breeding habitats. We predicted population density of small populations would be correlated positively with both per capita fecundity and population growth rate due to the Allee effect. For populations in the density-dependent growth phase, we predicted no relation between density and per capita fecundity (because individuals in all patches will equilibrate to the same success rate) and a positive relation between density and population growth rate. Several ecological theories collectively suggest that positive correlations between density and per capita fecundity would be difficult to detect. We constructed a decision tree to guide interpretation of positive, neutral, nonlinear, and negative relations between density and reproductive rates at individual and population levels.
Resumen. La disponibilidad de alimento y la depredación son las fuerzas principales que moldean l... more Resumen. La disponibilidad de alimento y la depredación son las fuerzas principales que moldean las decisiones que incrementan la adecuación biológica de las aves en todas las etapas de sus ciclos de vida. Durante la estación reproductiva, las aves pueden minimizar la pérdida de los nidos debido a la depredación mediante la selección de sitios con una menor probabilidad de depredación. Para entender los aspectos ambientales y sociales y las consecuencias de la selección de los sitios de anidación en las aves de pradera, exploramos la variación en los patrones de supervivencia de los nidos de Calamospiza melanocorys en la región de pradera de pastos cortos de América del Norte. A lo largo de cuatro estaciones reproductivas, documentamos la supervivencia de 405 nidos, realizamos 60 muestreos para estimar las densidades de las aves y medimos varios aspectos de la vegetación para describir la estructura del hábitat en 24 parcelas de estudio seleccionadas al azar. La supervivencia del nido varió con la densidad de C. melanocorys siguiendo la forma de un polinomio cuadrático, incrementando con una densidad menor a 1.5 aves/ha y disminuyendo con una densidad de entre 1.5 y 3 aves/ha, sugiriendo que un rango óptimo de densidades favorece el éxito reproductivo de los individuos de C. melanocorys, los cuales nidifican de modo semi-colonial. La supervivencia del nido también incrementó con un aumento en la estructura de la vegetación de las parcelas de estudio y varió con la edad del nido, incrementando a principios de la incubación y al final del período de pichón y disminuyendo suavemente desde mediados de la incubación hasta la mitad del período de pichón. La existencia de un rango óptimo de densidades en esta especie semi-colonial puede ser entendida a través de la "hipótesis de selección de bienes de consumo" a bajas densidades y por denso dependencia a altas densidades.
Recent changes in global climate have dramatically altered worldwide temperatures and the corresp... more Recent changes in global climate have dramatically altered worldwide temperatures and the corresponding timing of seasonal climate conditions. Recognizing the degree to which species respond to changing climates is therefore an area of increasing conservation concern as species that are unable to respond face increased risk of extinction. Here we examine spatial and temporal heterogeneity in the rate of climate change across western North America and discuss the potential for conditions to arise that may limit the ability of western migratory birds to adapt to changing climates. Based on 52 years of climate data, we show that changes in temperature and precipitation differ significantly between spring migration habitats in the desert southwest and breeding habitats throughout western North America. Such differences may ultimately increase costs to individual birds and thereby threaten the long-term population viability of many species.
Resumen. El conocimiento sobre el comportamiento de las aves durante el periodo no reproductivo a... more Resumen. El conocimiento sobre el comportamiento de las aves durante el periodo no reproductivo aún es menor que el del periodo reproductivo, a pesar de que durante la ultima década ha habido una proliferación considerable de investigaciones que han producido un progreso significativo en el entendimiento de los patrones de migración de las aves de Norteamérica. A pesar de que históricamente la gran mayoría de los estudios sobre migración se han realizado en la parte este del continente, recientemente ha habido bastante progreso en el conocimiento de aspectos de la migración de las aves en el oeste. En particular, el uso más extendido de técnicas como radares, metabolitos plasmáticos, captura con redes de neblina, conteos, isótopos estables, datos genéticos y radiotelemetría de los animales, además del aumento de colaboraciones entre investigadores, han contribuido en conjunto al crecimiento del conocimiento. Existe un aumento en el reconocimiento de que la migración es el momento más limitante del año para las aves migratorias, lo que aumenta la importancia de continuar descifrando los patrones en la ecología de paradas migratorias, identificando los hábitats más importantes para las paradas y documentando las rutas migratorias en el paisaje diverso y cambiante del oeste americano. Aquí, revisamos y sintetizamos brevemente los hallazgos y avances más recientes en el estudio de la migración de las aves y consideramos las necesidades para delinear investigaciones futuras sobre la migración en el oeste.
Depressional wetlands in agricultural landscapes are easily degraded by sediments and contaminant... more Depressional wetlands in agricultural landscapes are easily degraded by sediments and contaminants accumulated from their watersheds. Several best management practices can reduce transport of sediments into wetlands, including the establishment of vegetative buffers. We summarize the sources, transport dynamics, and effect of sediments, nutrients, and contaminants that threaten wetlands and the current knowledge of design and usefulness of grass buffers for protecting isolated wetlands. Buffer effectiveness is dependent on several factors, including vegetation structure, buffer width, attributes of the surrounding watershed (i.e., area, vegetative cover, slope and topography, soil type and structure, soil moisture, amount of herbicides and pesticides applied), and intensity and duration of rain events. To reduce dissolved contaminants from runoff, the water must infiltrate the soil where microbes or other processes can break down or sequester contaminants. But increasing infiltration also diminishes total water volume entering a wetland, which presents threats to wetland hydrology in semi-arid regions. Buffer effectiveness may be enhanced significantly by implementing other best management practices (e.g., conservation tillage, balancing input with nutrient requirements for livestock and crops, precision application of chemicals) in the surrounding watershed to diminish soil erosion and associated contaminant runoff. Buffers require regular maintenance to remove sediment build-up and replace damaged or over-mature vegetation. Further research is needed to establish guidelines for effective buffer width and structure, and such efforts should entail a coordinated, regional, multi-scale, multidisciplinary approach to evaluate buffer effectiveness and impacts. Direct measures in ''real-world'' systems and field validations of buffer-effectiveness models are crucial next steps in evaluating how grass buffers will impact the abiotic and biotic variables attributes that characterize small, isolated wetlands.
Conservation challenges enhance the need for quantitative information on dispersed bird populatio... more Conservation challenges enhance the need for quantitative information on dispersed bird populations in extensive landscapes, for techniques to monitor populations and assess environmental effects, and for conservation strategies at appropriate temporal and spatial scales. By estimating population sizes of shorebirds in the U.S. portion of the prairie pothole landscape in central North America, where most migrating shorebirds exhibit a highly dispersed spatial pattern, we determined that the region may play a vital role in the conservation of shorebirds. During northward and southward migration, 7.3 million shorebirds (95% CI: 4.3-10.3 million) and 3.9 million shorebirds (95% CI: 1.7-6.0 million) stopped to rest and refuel in the study area; inclusion of locally breeding species increases the estimates by 0.1 million and 0.07 million shorebirds, respectively. Seven species of calidridine sandpipers, including Semipalmated Sandpipers (Calidris pusilla), White-rumped Sandpipers (C. fuscicollis), and Stilt Sandpipers (C. himantopus), constituted 50% of northbound migrants in our study area. We present an approach to population estimation and monitoring, based on stratified random selection of townships as sample units, that is well suited to 11 migratory shorebird species. For extensive and dynamic wetland systems, we strongly caution against a monitoring program based solely on repeated counts of known stopover sites with historically high numbers of shorebirds. We recommend refinements in methodology to address sample-size requirements and potential sources of bias so that our approach may form the basis of a rigorous migration monitoring program in this and other prairie wetland regions.
Many North American prairie bird populations have recently declined, and the causes of these decl... more Many North American prairie bird populations have recently declined, and the causes of these declines remain largely unknown. To determine whether population limitation occurs during breeding, we evaluated the stability of a population of prairie birds using population-specifi c values for fecundity and postfl edging survival. During 2001-2003, we radiomarked 67 female Lark Buntings (Calamospiza melanocorys) to determine annual fecundity and evaluate contributing factors such as nest survival and breeding response (number of breeding att empts and dispersal). Collectively, 67 females built 112 nests (1.67 ± 0.07 nests female -1 season -1 ; range: 1-3); 34 were second nests and 11 were third nests. Daily nest survival estimates were similar for initial and later nests with overall nest survival (DSR 19 ) of 30.7% and 31.7%, respectively. Nest predation was the most common cause of failure (92%). Capture and radiomarking of females did not aff ect nest survival. Lark Bunting dispersal probabilities increased among females that fl edged young from initial nests and females that lost their original nests late in the season. Conservative and liberal estimates of mean annual fecundity were 0.96 ± 0.11 and 1.24 ± 0.09 female off spring per female, respectively. Given the fecundity and juvenile-survival estimates for this population, annual adult survival values of 71-77% are necessary to achieve a stable population. Because adult survival of prairie passerines ranges between 55% and 65%, this study area may not be capable of sustaining a stable population in the absence of immigration. We contrast our population assessment with one that assumes indirect values of fecundity and juvenile survival. To elucidate limiting factors, estimation of population-specifi c demographic parameters is desirable. We present an approach for selecting species and areas for evaluation of population stability.
Determining population size and long-term trends in population size for species of high concern i... more Determining population size and long-term trends in population size for species of high concern is a priority of international, national, and regional conservation plans. Long-billed curlews (Numenius americanus) are a species of special concern in North America due to apparent declines in their population. Because long-billed curlews are not adequately monitored by existing programs, we undertook a 2-year study with the goals of 1) determining present long-billed curlew distribution and breeding population size in the United States and 2) providing recommendations for a long-term long-billed curlew monitoring protocol. We selected a stratified random sample of survey routes in 16 western states for sampling in 2004 and 2005, and we analyzed count data from these routes to estimate detection probabilities and abundance. In addition, we evaluated habitat along roadsides to determine how well roadsides represented habitat throughout the sampling units. We estimated there were 164,515 (SE ¼ 42,047) breeding long-billed curlews in 2004, and 109,533 (SE ¼ 31,060) breeding individuals in 2005. These estimates far exceed currently accepted estimates based on expert opinion. We found that habitat along roadsides was representative of long-billed curlew habitat in general. We make recommendations for improving sampling methodology, and we present power curves to provide guidance on minimum sample sizes required to detect trends in abundance.
We evaluated the influences of several ecological, biological, and methodological factors on post... more We evaluated the influences of several ecological, biological, and methodological factors on post-fledging survival of a shortgrass prairie bird, the Lark Bunting (Calamospiza melanocorys). We estimated daily post-fledging survival (n ϭ 206, 82 broods) using radiotelemetry and color bands to track fledglings. Daily survival probabilities were best explained by drought intensity, time in season (quadratic trend), ages Յ3 d post-fledging, and rank given drought intensity. Drought intensity had a strong negative effect on survival. Rank was an important predictor of fledgling survival only during the severe drought of 2002 when the smallest fledglings had lower survival. Recently fledged young (ages Յ3 d postfledging) undergoing the transition from nest to surrounding habitat experienced markedly lower survival, demonstrating the vulnerable nature of this time period. Survival was greater in mid and late season than early season, corresponding to our assumptions of food availability. Neither mark type nor sex of attending parent influenced survival. The model-averaged product of the 22-d survival calculated using mean rank and median value of time in season was 0.360 Ϯ 0.08 in 2001 and 0.276 Ϯ 0.08 in 2002. Survival estimates that account for age, condition of young, ecological conditions, and other factors are important for parameterization of realistic population models. Biologists using population growth models to elucidate mechanisms of population declines should attempt to estimate species-specific of postfledging survival rather than use generalized estimates.
Sediment accumulation threatens the viability and hydrologic functioning of many naturally formed... more Sediment accumulation threatens the viability and hydrologic functioning of many naturally formed depressional wetlands across the interior regions of North America. These wetlands provide many ecosystem services and vital habitats for diverse plant and animal communities. Climate change may further impact sediment accumulation rates in the context of current land use patterns. We estimated sediment accretion in wetlands within a region renowned for its large populations of breeding waterfowl and migrant shorebirds and examined the relative roles of precipitation and land use context in the sedimentation process. We modeled rates of sediment accumulation from 1971 through 2100 using the Revised Universal Soil Loss Equation (RUSLE) with a sediment delivery ratio and the Unit Stream Power Erosion Deposition model (USPED). These models predicted that by 2100, 21-33 % of wetlands filled completely with sediment and 27-46 % filled by half with sediments; estimates are consistent with measured sediment accumulation rates in the region reported by empirical studies. Sediment accumulation rates were strongly influenced by size of the catchment, greater coverage of tilled landscape within the catchment, and steeper slopes. Conservation efforts that incorporate the relative risk of infilling of wetlands with sediments, thus emphasizing areas of high topographic relief and large watersheds, may benefit wetland-dependent biota.
Climate change elevates conservation concerns worldwide because it is likely to exacerbate many i... more Climate change elevates conservation concerns worldwide because it is likely to exacerbate many identified threats to animal populations. In recent decades, grassland birds have declined faster than other North American bird species, a loss thought to be due to habitat loss and fragmentation and changing agricultural practices. Climate change poses additional threats of unknown magnitude to these already declining populations. We examined how seasonal and daily weather conditions over 10 years influenced nest survival of five species of insectivorous passerines native to the shortgrass prairie and evaluate our findings relative to future climate predictions for this region. Daily nest survival (n = 870) was best predicted by a combination of daily and seasonal weather variables, age of nest, time in season and bird habitat guild. Within a season, survival rates were lower on very hot days (temperatures ≥ 35°C), on dry days (with a lag of 1 day) and on stormy days (especially for those species nesting in shorter vegetation). Across years, survival rates were also lower during warmer and drier breeding seasons. Clutch sizes were larger when early spring temperatures were cool and the week prior to egg-laying was wetter and warming. Climate change is likely to exacerbate grassland bird population declines because projected climate conditions include rising temperatures, more prolonged drought and more intense storms as the hydrological cycle is altered. Under varying realistic scenarios, nest success estimates were halved compared to their current average value when models both increased the temperature (3°C) and decreased precipitation (two additional dry days during a nesting period), thus underscoring a sense of urgency in identifying and addressing the current causes of range-wide declines.
Disturbed xeric grasslands with short, sparse vegetation provide breeding habitat for mountain pl... more Disturbed xeric grasslands with short, sparse vegetation provide breeding habitat for mountain plovers (Charadrius montanus) across the western Great Plains. Maintaining local disturbance regimes through prairie dog conservation and prescribed fire may contribute to the sustainability of recently declining mountain plover populations, but these management approaches can be controversial. We estimated habitatspecific mountain plover densities and nest survival rates on black-tailed prairie dog (Cynomys ludovicianus) colonies and burns in the shortgrass steppe of northeastern Colorado. Mountain plover densities were similar on prairie dog colonies (5.9 birds/km 2 ; 95% CI ¼ 4.7-7.4) and sites burned during the preceding dormant season (6.7 birds/km 2 ; 95% CI ¼ 4.6-9.6), whereas the 29-day nest survival rate was greater on prairie dog colonies (0.81 in 2011 and 0.39 in 2012) compared to the burned sites (0.64 in 2011 and 0.17 in 2012). Reduced nest survival in 2012 compared to 2011 was associated with higher maximum daily temperatures in 2012, consistent with a previous weather-based model of mountain plover nest survival in the southern Great Plains. Measurements of mountain plover density relative to time since disturbance showed that removal of prairie dog disturbance by sylvatic plague reduced mountain plover density by 70% relative to active prairie dog colonies after 1 year. Plover densities declined at a similar rate (by 78%) at burned sites between the first and second post-burn growing season. Results indicate that black-tailed prairie dog colonies are a particularly important nesting habitat for mountain plovers in the southern Great Plains. In addition, findings suggest that prescribed burning can be a valuable means to create nesting habitat in landscapes where other types of disturbances (such as prairie dog colonies) are limited in distribution and size. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.
Playa wetlands on the west-central Great Plains of North America are vulnerable to sediment infil... more Playa wetlands on the west-central Great Plains of North America are vulnerable to sediment infilling from upland agriculture, putting at risk several important ecosystem services as well as essential habitats and food resources of diverse wetland-dependent biota. Climate predictions for this semi-arid area indicate reduced precipitation which may alter rates of erosion, runoff, and sedimentation of playas. We forecasted erosion rates, sediment depths, and resultant playa wetland depths across the west-central Great Plains and examined the relative roles of land use context and projected changes in precipitation in the sedimentation process. We estimated erosion with the Revised Universal Soil Loss Equation (RUSLE) using historic values and downscaled precipitation predictions from three general circulation models and three emissions scenarios. We calibrated RUSLE results using field sediment measurements. RUSLE is appealing for regional scale modeling because it uses climate forecasts with monthly resolution and other widely available values including soil texture, slope and land use. Sediment accumulation rates will continue near historic levels through 2070 and will be sufficient to cause most playas (if not already filled) to fill with sediment within the next 100 years in the absence of mitigation. Land use surrounding the playa, whether grassland or tilled cropland, is more influential in sediment accumulation than climate-driven precipitation change.
We combined several existing spatial layers of potential playa wetland locations and geometries (... more We combined several existing spatial layers of potential playa wetland locations and geometries (Kansas Data Access and Support Center [http://www.kansas.org]; M. McLachlan, D. Pavlacky unpublished data) to create a single dataset containing roughly 84,000 playa wetlands on the west-central Great Plains. We assumed the playa data to be the current best estimate of playa location and extent. Due to file size processing limitations and because few playas occurred east of 98.4°W, we truncated the playa dataset here. Not including this playasparse portion of the study area in our analyses resulted in a loss of about 0.33% (788 ha) of total playa wetland area and ca 1% (1049) of all playas.
The influence of recent climate change on the world's biota has manifested broadly, resulting in ... more The influence of recent climate change on the world's biota has manifested broadly, resulting in latitudinal range shifts, advancing dates of arrival of migrants and onset of breeding, and altered community relationships. Climate change elevates conservation concerns worldwide because it will likely exacerbate a broad range of identified threats to animal populations. In the past few decades, grassland birds have declined faster than other North American avifauna, largely due to habitat threats such as the intensification of agriculture. We examine the effects of local climatic variations on the breeding performance of a bird endemic to the shortgrass prairie, the Lark Bunting (Calamospiza melanocorys) and discuss the implications of our findings relative to future climate predictions. Clutch size, nest survival, and productivity all positively covaried with seasonal precipitation, yet relatively intense daily precipitation events temporarily depressed daily survival of nests. Nest survival was positively related to average temperatures during the breeding season. Declining summer precipitation may reduce the likelihood that Lark Buntings can maintain stable breeding populations in eastern Colorado although average temperature increases of up to 38C (within the range of this study) may ameliorate declines in survival expected with drier conditions. Historic climate variability in the Great Plains selects for a degree of vagility and opportunism rather than strong site fidelity and specific adaptation to local environments. These traits may lead to northerly shifts in distribution if climatic and habitat conditions become less favorable in the drying southern regions of the Great Plains. Distributional shifts in Lark Buntings could be constrained by future changes in land use, agricultural practices, or vegetative communities that result in further loss of shortgrass prairie habitats.
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.
Effective conservation metrics are needed to evaluate the success of management in a rapidly chan... more Effective conservation metrics are needed to evaluate the success of management in a rapidly changing world. Reproductive rates and densities of breeding birds (as a surrogate for reproductive rate) have been used to indicate the quality of avian breeding habitat, but the underlying assumptions of these metrics rarely have been examined. When birds are attracted to breeding areas in part by the presence of conspecifics and when breeding in groups influences predation rates, the effectiveness of density and reproductive rate as indicators of habitat quality is reduced. It is beneficial to clearly distinguish between individual-and population-level processes when evaluating habitat quality. We use the term reproductive rate to refer to both levels and further distinguish among levels by using the terms per capita fecundity (number of female offspring per female per year, individual level) and population growth rate (the product of density and per capita fecundity, population level). We predicted how density and reproductive rate interact over time under density-independent and density-dependent scenarios, assuming the ideal free distribution model of how birds settle in breeding habitats. We predicted population density of small populations would be correlated positively with both per capita fecundity and population growth rate due to the Allee effect. For populations in the density-dependent growth phase, we predicted no relation between density and per capita fecundity (because individuals in all patches will equilibrate to the same success rate) and a positive relation between density and population growth rate. Several ecological theories collectively suggest that positive correlations between density and per capita fecundity would be difficult to detect. We constructed a decision tree to guide interpretation of positive, neutral, nonlinear, and negative relations between density and reproductive rates at individual and population levels.
Resumen. La disponibilidad de alimento y la depredación son las fuerzas principales que moldean l... more Resumen. La disponibilidad de alimento y la depredación son las fuerzas principales que moldean las decisiones que incrementan la adecuación biológica de las aves en todas las etapas de sus ciclos de vida. Durante la estación reproductiva, las aves pueden minimizar la pérdida de los nidos debido a la depredación mediante la selección de sitios con una menor probabilidad de depredación. Para entender los aspectos ambientales y sociales y las consecuencias de la selección de los sitios de anidación en las aves de pradera, exploramos la variación en los patrones de supervivencia de los nidos de Calamospiza melanocorys en la región de pradera de pastos cortos de América del Norte. A lo largo de cuatro estaciones reproductivas, documentamos la supervivencia de 405 nidos, realizamos 60 muestreos para estimar las densidades de las aves y medimos varios aspectos de la vegetación para describir la estructura del hábitat en 24 parcelas de estudio seleccionadas al azar. La supervivencia del nido varió con la densidad de C. melanocorys siguiendo la forma de un polinomio cuadrático, incrementando con una densidad menor a 1.5 aves/ha y disminuyendo con una densidad de entre 1.5 y 3 aves/ha, sugiriendo que un rango óptimo de densidades favorece el éxito reproductivo de los individuos de C. melanocorys, los cuales nidifican de modo semi-colonial. La supervivencia del nido también incrementó con un aumento en la estructura de la vegetación de las parcelas de estudio y varió con la edad del nido, incrementando a principios de la incubación y al final del período de pichón y disminuyendo suavemente desde mediados de la incubación hasta la mitad del período de pichón. La existencia de un rango óptimo de densidades en esta especie semi-colonial puede ser entendida a través de la "hipótesis de selección de bienes de consumo" a bajas densidades y por denso dependencia a altas densidades.
Recent changes in global climate have dramatically altered worldwide temperatures and the corresp... more Recent changes in global climate have dramatically altered worldwide temperatures and the corresponding timing of seasonal climate conditions. Recognizing the degree to which species respond to changing climates is therefore an area of increasing conservation concern as species that are unable to respond face increased risk of extinction. Here we examine spatial and temporal heterogeneity in the rate of climate change across western North America and discuss the potential for conditions to arise that may limit the ability of western migratory birds to adapt to changing climates. Based on 52 years of climate data, we show that changes in temperature and precipitation differ significantly between spring migration habitats in the desert southwest and breeding habitats throughout western North America. Such differences may ultimately increase costs to individual birds and thereby threaten the long-term population viability of many species.
Resumen. El conocimiento sobre el comportamiento de las aves durante el periodo no reproductivo a... more Resumen. El conocimiento sobre el comportamiento de las aves durante el periodo no reproductivo aún es menor que el del periodo reproductivo, a pesar de que durante la ultima década ha habido una proliferación considerable de investigaciones que han producido un progreso significativo en el entendimiento de los patrones de migración de las aves de Norteamérica. A pesar de que históricamente la gran mayoría de los estudios sobre migración se han realizado en la parte este del continente, recientemente ha habido bastante progreso en el conocimiento de aspectos de la migración de las aves en el oeste. En particular, el uso más extendido de técnicas como radares, metabolitos plasmáticos, captura con redes de neblina, conteos, isótopos estables, datos genéticos y radiotelemetría de los animales, además del aumento de colaboraciones entre investigadores, han contribuido en conjunto al crecimiento del conocimiento. Existe un aumento en el reconocimiento de que la migración es el momento más limitante del año para las aves migratorias, lo que aumenta la importancia de continuar descifrando los patrones en la ecología de paradas migratorias, identificando los hábitats más importantes para las paradas y documentando las rutas migratorias en el paisaje diverso y cambiante del oeste americano. Aquí, revisamos y sintetizamos brevemente los hallazgos y avances más recientes en el estudio de la migración de las aves y consideramos las necesidades para delinear investigaciones futuras sobre la migración en el oeste.
Depressional wetlands in agricultural landscapes are easily degraded by sediments and contaminant... more Depressional wetlands in agricultural landscapes are easily degraded by sediments and contaminants accumulated from their watersheds. Several best management practices can reduce transport of sediments into wetlands, including the establishment of vegetative buffers. We summarize the sources, transport dynamics, and effect of sediments, nutrients, and contaminants that threaten wetlands and the current knowledge of design and usefulness of grass buffers for protecting isolated wetlands. Buffer effectiveness is dependent on several factors, including vegetation structure, buffer width, attributes of the surrounding watershed (i.e., area, vegetative cover, slope and topography, soil type and structure, soil moisture, amount of herbicides and pesticides applied), and intensity and duration of rain events. To reduce dissolved contaminants from runoff, the water must infiltrate the soil where microbes or other processes can break down or sequester contaminants. But increasing infiltration also diminishes total water volume entering a wetland, which presents threats to wetland hydrology in semi-arid regions. Buffer effectiveness may be enhanced significantly by implementing other best management practices (e.g., conservation tillage, balancing input with nutrient requirements for livestock and crops, precision application of chemicals) in the surrounding watershed to diminish soil erosion and associated contaminant runoff. Buffers require regular maintenance to remove sediment build-up and replace damaged or over-mature vegetation. Further research is needed to establish guidelines for effective buffer width and structure, and such efforts should entail a coordinated, regional, multi-scale, multidisciplinary approach to evaluate buffer effectiveness and impacts. Direct measures in ''real-world'' systems and field validations of buffer-effectiveness models are crucial next steps in evaluating how grass buffers will impact the abiotic and biotic variables attributes that characterize small, isolated wetlands.
Conservation challenges enhance the need for quantitative information on dispersed bird populatio... more Conservation challenges enhance the need for quantitative information on dispersed bird populations in extensive landscapes, for techniques to monitor populations and assess environmental effects, and for conservation strategies at appropriate temporal and spatial scales. By estimating population sizes of shorebirds in the U.S. portion of the prairie pothole landscape in central North America, where most migrating shorebirds exhibit a highly dispersed spatial pattern, we determined that the region may play a vital role in the conservation of shorebirds. During northward and southward migration, 7.3 million shorebirds (95% CI: 4.3-10.3 million) and 3.9 million shorebirds (95% CI: 1.7-6.0 million) stopped to rest and refuel in the study area; inclusion of locally breeding species increases the estimates by 0.1 million and 0.07 million shorebirds, respectively. Seven species of calidridine sandpipers, including Semipalmated Sandpipers (Calidris pusilla), White-rumped Sandpipers (C. fuscicollis), and Stilt Sandpipers (C. himantopus), constituted 50% of northbound migrants in our study area. We present an approach to population estimation and monitoring, based on stratified random selection of townships as sample units, that is well suited to 11 migratory shorebird species. For extensive and dynamic wetland systems, we strongly caution against a monitoring program based solely on repeated counts of known stopover sites with historically high numbers of shorebirds. We recommend refinements in methodology to address sample-size requirements and potential sources of bias so that our approach may form the basis of a rigorous migration monitoring program in this and other prairie wetland regions.
Many North American prairie bird populations have recently declined, and the causes of these decl... more Many North American prairie bird populations have recently declined, and the causes of these declines remain largely unknown. To determine whether population limitation occurs during breeding, we evaluated the stability of a population of prairie birds using population-specifi c values for fecundity and postfl edging survival. During 2001-2003, we radiomarked 67 female Lark Buntings (Calamospiza melanocorys) to determine annual fecundity and evaluate contributing factors such as nest survival and breeding response (number of breeding att empts and dispersal). Collectively, 67 females built 112 nests (1.67 ± 0.07 nests female -1 season -1 ; range: 1-3); 34 were second nests and 11 were third nests. Daily nest survival estimates were similar for initial and later nests with overall nest survival (DSR 19 ) of 30.7% and 31.7%, respectively. Nest predation was the most common cause of failure (92%). Capture and radiomarking of females did not aff ect nest survival. Lark Bunting dispersal probabilities increased among females that fl edged young from initial nests and females that lost their original nests late in the season. Conservative and liberal estimates of mean annual fecundity were 0.96 ± 0.11 and 1.24 ± 0.09 female off spring per female, respectively. Given the fecundity and juvenile-survival estimates for this population, annual adult survival values of 71-77% are necessary to achieve a stable population. Because adult survival of prairie passerines ranges between 55% and 65%, this study area may not be capable of sustaining a stable population in the absence of immigration. We contrast our population assessment with one that assumes indirect values of fecundity and juvenile survival. To elucidate limiting factors, estimation of population-specifi c demographic parameters is desirable. We present an approach for selecting species and areas for evaluation of population stability.
Determining population size and long-term trends in population size for species of high concern i... more Determining population size and long-term trends in population size for species of high concern is a priority of international, national, and regional conservation plans. Long-billed curlews (Numenius americanus) are a species of special concern in North America due to apparent declines in their population. Because long-billed curlews are not adequately monitored by existing programs, we undertook a 2-year study with the goals of 1) determining present long-billed curlew distribution and breeding population size in the United States and 2) providing recommendations for a long-term long-billed curlew monitoring protocol. We selected a stratified random sample of survey routes in 16 western states for sampling in 2004 and 2005, and we analyzed count data from these routes to estimate detection probabilities and abundance. In addition, we evaluated habitat along roadsides to determine how well roadsides represented habitat throughout the sampling units. We estimated there were 164,515 (SE ¼ 42,047) breeding long-billed curlews in 2004, and 109,533 (SE ¼ 31,060) breeding individuals in 2005. These estimates far exceed currently accepted estimates based on expert opinion. We found that habitat along roadsides was representative of long-billed curlew habitat in general. We make recommendations for improving sampling methodology, and we present power curves to provide guidance on minimum sample sizes required to detect trends in abundance.
We evaluated the influences of several ecological, biological, and methodological factors on post... more We evaluated the influences of several ecological, biological, and methodological factors on post-fledging survival of a shortgrass prairie bird, the Lark Bunting (Calamospiza melanocorys). We estimated daily post-fledging survival (n ϭ 206, 82 broods) using radiotelemetry and color bands to track fledglings. Daily survival probabilities were best explained by drought intensity, time in season (quadratic trend), ages Յ3 d post-fledging, and rank given drought intensity. Drought intensity had a strong negative effect on survival. Rank was an important predictor of fledgling survival only during the severe drought of 2002 when the smallest fledglings had lower survival. Recently fledged young (ages Յ3 d postfledging) undergoing the transition from nest to surrounding habitat experienced markedly lower survival, demonstrating the vulnerable nature of this time period. Survival was greater in mid and late season than early season, corresponding to our assumptions of food availability. Neither mark type nor sex of attending parent influenced survival. The model-averaged product of the 22-d survival calculated using mean rank and median value of time in season was 0.360 Ϯ 0.08 in 2001 and 0.276 Ϯ 0.08 in 2002. Survival estimates that account for age, condition of young, ecological conditions, and other factors are important for parameterization of realistic population models. Biologists using population growth models to elucidate mechanisms of population declines should attempt to estimate species-specific of postfledging survival rather than use generalized estimates.
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Papers by Susan Skagen