Trends in Landcover Suitability for Sandhill Cranes Wintering in the Central Valley of California

Historic habitat conditions can affect contemporary communities and populations, but most studies of historic habitat are based on the reduction in habitat extent or connectivity. Little is known about the effects of historic habitat on contemporary species distributions when historic habitat has been nearly completely removed, but species persist in a highly altered landscape. More than 93% of the historic wetlands in the Central Valley of California, USA, have been drained and converted to agricultural and other uses, but agricultural wetlands, such as rice and its supporting infrastructure of canals, allow some species to persist. Little is known about the distribution of giant garter snakes Thamnophis gigas, a rare aquatic snake species inhabiting this predominantly agricultural landscape, or the variables that affect where this species occurs. We used occupancy modeling to examine the distribution of giant garter snakes at the landscape scale in the Sacramento Valley (northern portion of the Central Valley) of California, with an emphasis on the relative strength of historic and contemporary variables (landscape-scale habitat, local microhabitat, vegetation composition and relative prey counts) for predicting giant garter snake occurrence. Proximity to historic marsh best explained variation in the probability of occurrence of giant garter snakes at the landscape scale, with greater probability of occurrence near historic marsh. We suspect that the importance of distance to historic marsh represents dispersal limitations of giant garter snakes. These results suggest that preserving and restoring areas near historic marsh, and minimizing activities that reduce the extent of marsh or marsh-like (e.g. rice agriculture, canal) habitats near historic marsh may be advantageous to giant garter snakes.

Intensive surveys to locate greater sandhill cranes (Grus canadensis tabida) were conducted in Oregon in 1986 and California in 1988. We recorded 1223 pairs, 947 in Oregon, 276 in California and 765 nonbreeding cranes. Breeding pair numbers in Oregon indicated Oregon breeding pair numbers have remained mostly stable during the past 15 years, but some decreases were noted at localized areas. Breeding pairs increased 52So in California between 1971 and 1988. Seventy-two percent of the breeding pairs nested on private land, and 28So nested on federal and state lands. The Central Valley population of greater sandhill cranes (Grus canadensis tabida) breeds in southeast and southcentral Oregon, and northeast California. A few additional nesting pairs occur in northeast Oregon, Oregon Cascades, and southerrl Washington, while an undetermined rlumber breed in British Columbia (Littlefield and Thompson 1979). However, Pogson and Lindstedt (1991) estimated that between 2600-3600 cranes originate in British Columbia. The entire Central Valley population winters in the Central Valley of California. In the early 1970s, Littlefield and Thompson (1979) found 604 breeding pairs in Oregon and 122 in California. Inventories between 1980-1985 revealed an additional 103 breeding pairs in Oregon (C. Littlefield, unpubl. data) and 78 in California (Littlefield 1982). Recent declines in breeding crane pairs in portions of their breeding range, particularly at Malheur National Wildlife Refuge (NWR) in Oregon, and nesting habitat losses in Oregon and California, resulted in the population being classified a sensitive species by the U.S. Fish and Wildlife Service in 1982, a threatened species by the State of California in 1983, and a sensitive species by the State of Oregon in 1989. We conducted intensive surveys of greater sandhill cranes in Oregon in 1986 and California in 1988. In this report we summarize the number of nesting pairs and nonbreeding cranes, and compare the number of breeding pairs in selected areas with those recorded from earlier surveys to determine the status and trend of this breeding population.

Lesser snow geese (Anser c. caerulescens) from the Wrangel Island, Russia breeding colony spend the winter in two widely separated areas: the northern subpopulation in southern British Columbia and northern Washington and the southern subpopulation in the Central Valley of California. We examined 19 trace elements in the eggs and livers of geese from these two subpopulations to examine whether geese from the different wintering areas have similar trace element burdens. Eggs collected at the breeding colony from geese of the southern subpopulation had slightly higher levels of manganese, an element that can cause neurological damage and behavioral changes in chicks, than geese of the northern subpopulation. Livers from adult geese collected on the two wintering areas showed significant differences in trace elements including copper, iron, magnesium, molybdenum, and zinc. Copper concentrations in the livers of geese from the southern subpopulation were much higher than those from the northern subpopulation (&xmacr; = 116 vs. 46 ppm; dry weight). Elevated levels of copper may induce anemia in birds. The differences in trace element concentrations of these two subpopulations may be related to farming practices in their wintering areas. Geese from the northern subpopulation feed in pastures and coastal marshes and migrate along the coast, but geese from the southern subpopulation feed predominantly in rice fields and migrate over farm land. Copper and manganese are major components of fertilizers and fungicides commonly applied during rice cultivation.

We studied diet and habitat use of greater white‐fronted geese (Anser albifrons) from autumn through spring on their primary staging and wintering areas in the Pacific Flyway, 1979–1982. There have been few previous studies of resource use and forage quality of wintering greater white‐fronted geese in North America, and as a consequence there has been little empirical support for management practices pertaining to habitat conservation of this broadly distributed species. Observations of >2,500 flocks of geese and collections of foraging birds revealed seasonal and geographic variation in resource use reflective of changes in habitat availability, selection, and fluctuating physiological demands. Autumn migrants from Alaska arrived first in the Klamath Basin of California and southern Oregon, where they fed on barley, oats, wheat, and potatoes. Geese migrated from the Klamath Basin into the Central Valley of California in late autumn where they exploited agricultural crops rich in soluble carbohydrates, with geese in the Sacramento Valley feeding almost exclusively on rice and birds on the Sacramento–San Joaquin Delta primarily utilizing corn. White‐fronted geese began their northward migration in late winter, and by early spring most had returned to the Klamath Basin where 37% of flocks were found in fields of new growth cultivated and wild grasses. Cereal grains and potatoes ingested by geese were low in protein (7–14%) and high in soluble nutrients (17–47% neutral detergent fiber [NDF]), whereas grasses were low in available energy (47–49% NDF) but high in protein (26–42%). Greater white‐fronted geese are generalist herbivores and can exploit a variety of carbohydrate‐rich cultivated crops, likely making these geese less susceptible to winter food shortages than prior to the agriculturalization of the North American landscape. However, agricultural landscapes can be extremely dynamic and may be less predictable in the long‐term than the historic environments to which geese are adapted. Thus far greater white‐fronted geese have proved resilient to changes in land cover in the Pacific Flyway and by altering their migration regime have even been able to adapt to changes in the availability of suitable forage crops. © 2010 The Wildlife Society.

In arid and Mediterranean regions, landscape‐scale wetland conservation requires understanding how wildlife responds to dynamic freshwater availability and conservation actions to enhance wetland habitat. Taking advantage of Landsat satellite data and structured and community science bird survey data, we built species distribution models to describe how three duck species, the Northern Pintail (Anas acuta), Green‐winged Teal (Anas crecca), and Northern Shoveler (Anas clypeata), respond to freshwater supply and food resources on different flooded land cover types in the Central Valley of California. Specifically, our models compared duck habitat suitability between the wettest and driest conditions in each month from September through April. Using abundance‐weighted boosted regression trees, we created three sets of species occurrence models based on different covariates: (1) near real‐time (hereafter “real‐time”) covariates in which duck observations were matched to the water availability within the 16‐day window of a Landsat observation, (2) a combination of real‐time covariates and waterfowl food resource covariates describing annual corn and rice biomass and managed wetland moist soil seed yield estimates derived from Landsat data, and (3) long‐term average covariates—the most common approach to species distribution modeling—in which long‐term average surface water availability was used. We modeled the monthly occurrence of three duck species as a function of surface water availability, land cover type, road density, temperature, and bird data source. We found that dry conditions result in reduced habitat suitability, with the biggest reductions in November through January and in agricultural fields; in contrast, suitability of flooded wetland habitat was relatively robust to surface water availability. When models of habitat suitability based on long‐term average climate conditions were compared to models based on real‐time conditions, the highest long‐term suitability values occurred in areas where suitability was high regardless of whether it was a wet or a dry year. While all models performed well, the inclusion of crop and wetland plant yield covariates resulted in slightly higher model performance. Overall, species distribution models created using data on the environmental conditions present at the time of bird observations can aid conservation efforts under extreme conditions over large spatial scales.

We used satellite telemetry during 2011–2015 to identify and characterize wintering areas and migration patterns of Swainson's Hawks (Buteo swainsoni) that bred in California's Central Valley. Twenty tracked hawks wintered across 7500 km from western Mexico to central South America. Wintering areas in Mexico, Central America, and central South America were dominated by agriculture and in northern South America by shrub-scrub. All hawks followed similar migration routes, through the interior of California, Sonoran Desert, and western Mexico, with some continuing through Central America to South America. Compared to northerly wintering birds, birds wintering farther south spent more time in migration, flew greater distance per day during southward (but not northward) migration, spent less time in wintering areas, and arrived later at the breeding area. Central Valley birds substantially used stopover areas (x = 53 d/ individual) during southward migration but returned more directly from wintering to breeding areas (x=0.3 stopover d/individual). Most stopovers occurred in western Mexico and the San Joaquin Valley, California. Land cover in stopover areas was dominated by agriculture and shrub-scrub. Use of varied wintering areas that have been altered from native habitat may indicate that migratory and wintering patterns have changed for this population. Advantages of using northern wintering areas may include less time spent in migration and earlier arrival in breeding areas. The diversity of wintering areas may provide resilience from effects of human activities compared to collective wintering in one area. Central Valley Swainson's Hawks’ migration routes and wintering areas differ markedly from those of the rest of the species’ North American population.

One of the defining features of the Anthropocene is eroding ecosystem services, decreases in biodiversity, and overall reductions in the abundance of once-common organisms, including many insects that play innumerable roles in natural communities and agricultural systems that support human society. It is now clear that the preservation of insects cannot rely solely on the legal protection of natural areas far removed from the densest areas of human habitation. Instead, a critical challenge moving forward is to intelligently manage areas that include intensively farmed landscapes, such as the Central Valley of California. Here we attempt to meet this challenge with a tool for modeling landscape connectivity for insects (with pollinators in particular in mind) that builds on available information including lethality of pesticides and expert opinion on insect movement. Despite the massive fragmentation of the Central Valley, we find that connectivity is possible, especially utilizing the restoration or improvement of agricultural margins, which (in their summed area) exceed natural areas. Our modeling approach is flexible and can be used to address a wide range of questions regarding both changes in land cover as well as changes in pesticide application rates. Finally, we highlight key steps that could be taken moving forward and the great many knowledge gaps that could be addressed in the field to improve future iterations of our modeling approach.

One of the defining features of the Anthropocene is eroding ecosystem services, decreases in biodiversity, and overall reductions in the abundance of once-common organisms, including many insects that play innumerable roles in natural communities and agricultural systems that support human society. It is now clear that the preservation of insects cannot rely solely on the legal protection of natural areas far removed from the densest areas of human habitation. Instead, a critical challenge moving forward is to intelligently manage areas that include intensively farmed landscapes, such as the Central Valley of California. Here we attempt to meet this challenge with a tool for modeling landscape connectivity for insects (with pollinators in particular in mind) that builds on available information including lethality of pesticides and expert opinion on insect movement. Despite the massive fragmentation of the Central Valley, we find that connectivity is possible, especially utilizing the restoration or improvement of agricultural margins, which (in their summed area) exceed natural areas. Our modeling approach is flexible and can be used to address a wide range of questions regarding both changes in land cover as well as changes in pesticide application rates. Finally, we highlight key steps that could be taken moving forward and the great many knowledge gaps that could be addressed in the field to improve future iterations of our modeling approach.

Understanding how different crops use water over time is essential for planning and managing water allocation, water rights, and agricultural production. The main objective of this paper is to characterize the spatiotemporal dynamics of crop water use in the Central Valley of California using Landsat-based annual actual evapotranspiration (ETa) from 2008 to 2018 derived from the Operational Simplified Surface Energy Balance (SSEBop) model. Crop water use for 10 crops is characterized at multiple scales. The Mann–Kendall trend analysis revealed a significant increase in area cultivated with almonds and their water use, with an annual rate of change of 16,327 ha in area and 13,488 ha-m in water use. Conversely, alfalfa showed a significant decline with 12,429 ha in area and 13,901 ha-m in water use per year during the same period. A pixel-based Mann–Kendall trend analysis showed the changing crop type and water use at the level of individual fields for all of Kern County in the Central Valley. This study demonstrates the useful application of historical Landsat ET to produce relevant water management information. Similar studies can be conducted at regional and global scales to understand and quantify the relationships between land cover change and its impact on water use.

This study aims to assess the relative importance of natural and anthropogenic variables on the change of the red-crowned crane habitat in the Yellow River Nature Reserve, East China using multitempopral remote sensing and geographic information system. Satellite images were used to detect the change in potential crane habitat, from which suitable crane habitat was determined by excluding fragmented habitat. In this study, a principal component analysis (PCA) with seven variables (channel flow, rainfall, temperature, sediment discharge, number of oil wells, total length of roads, and area of settlements) and linear regression analyses of potential and suitable habitat against the retained principal components were applied to explore the influences of natural and anthropogenic factors on the change of the red-crowned crane habitat. The experimental results indicate that suitable habitat decreased by 5,935ha despite an increase of 1,409ha in potential habitat from 1992 to 2008. The area of crane habitat changed caused by natural drivers such as progressive succession, retrogressive succession, and physical fragmentation is almost the same as that caused by anthropogenic forces such as land use change and behavioral fragmentation. The PCA and regression analyses revealed that natural factors (e.g., channel flow, rainfall, temperature, and sediment discharge) play an important role in the crane potential habitat change and human disturbances (e.g., oil wells, roads, and settlements) jointly explain 51.8% of the variations in suitable habitat area, higher than 48.2% contributed by natural factors. Thus, it is vital to reduce anthropogenic influences within the reserve in order to reverse the decline in the suitable crane habitat.

Over the past century, flow regulation and vegetation encroachment have reduced active channel widths along the central Platte River, Nebraska. During the last two decades, an annual program of in‐channel vegetation management has been implemented to stabilize or expand active channel widths. Vegetation management practices are intended to enhance riverine habitats which include nocturnal roosting habitat for sandhill cranes. Evaluating the success of other management treatments such as streamflow modification requires an understanding of how flow shapes the sandbars in the river and how sandbar morphology interacts with flow to create crane habitat. These linkages were investigated along a 1‐km managed river reach by comparing the spatial pattern of riverine roosts and emergent sandbars identified with aerial infrared imagery to variables computed with a two‐dimensional hydraulic model. Nocturnal observations made multiple years showed that the area and patterns of riverine roosts and emergent sandbars and the densities of cranes within roosts changed with stage. Despite sandbar vegetation management, low flows were concentrated into incised channels rather than spread out over broad sandbars. The flow model was used to compute hydraulic variables for identical streamflows through two sandbar morphologies; one following a period of relatively high flow and the other following the low‐flow period. Compared with the simulation using the morphology from the antecedent high flow, the simulation using the morphology from the antecedent low flow produced a smaller quantity of available wetted area. These remote‐sensing observations and hydraulic simulations illustrate the importance of considering flow history when designing streamflows to manage in‐channel habitat for cranes. Published in 2008 by John Wiley & Sons, Ltd.

Life history strategies and habitat needs of the northern pintail: L. H. Fredrickson & M. E. Heitmeyer, Fish & Wildlife Leaflet - US Fish & Wildlife Service, 13.1.3, 1991, 8 pp

The Florida sandhill crane Antigone canadensis pratensis is designated as threatened by the state of Florida, where there is an urgent need to map and quantify available habitat. First, we used habitat suitability index (HSI) modelling to map and assess potential nesting habitat for sandhill cranes in Florida. Second, we used spatial optimization approaches to calculate the maximum number of breeding pairs that can simultaneously occupy potential nests given that they both must be of some minimum quality and must be spaced some minimal distance apart. Mapping results reveal that nesting habitat is concentrated in the central portion of the state, with adequate brooding habitat appearing to be the most limiting factor affecting habitat suitability. Assuming nesting only occurs in habitat rated as high quality (HSI ≥ 0.7) and spacing between adjacent nests is ≥1,000 m, we conservatively estimate that 5,540 nesting pairs of Florida sandhill cranes can potentially be supported. Additional nesting pairs may be supported in habitats of marginal (HSI ≥ 0.3; 14,530) to moderate (HSI ≥ 0.5; 8,723) quality. The suitability maps and breeding pair estimates can be used to identify important habitat areas to focus crane conservation efforts, determine potentially limiting habitat features across the landscape, and potentially guide future population monitoring efforts. For example, grassland or prairie restoration could be used to potentially increase nesting pairs in the southern portion of the state where emergent wetlands are abundant but brooding habitat is lacking.

River ecosystems in semi-arid environments provide an array of resources that concentrate biodiversity, but also attract human settlement and support economic development. In the southwestern United States, land-use change, drought, and anthropogenic disturbance are compounding factors which have led to departures from historical conditions of river ecosystems, consequently affecting wildlife habitat, including important wintering areas for migratory birds. The Rio Grande (River) in central New Mexico is the lifeblood of the Middle Rio Grande Valley (MRGV), maintaining large urban and agricultural centers and riparian and wetland resources, which disproportionately support a diversity of wildlife. The MRGV has been identified as the most important wintering area for the Rocky Mountain Population of greater sandhill cranes (Antigone canadensis tabida). Presently, however, changes in the hydrogeomorphology of the Rio Grande and landscape modification by humans have reshaped the MRGV and winter habitat for sandhill cranes. To evaluate these impacts, we investigated how land-use practices, anthropogenic disturbance, and river morphology influenced patterns of diurnal and roosting habitat selection by sandhill cranes. During the diurnal period, sandhill cranes relied heavily on managed public lands selecting agriculture crops, such as corn fields, and wetlands for foraging and loafing while avoiding areas with increasing densities of human structures. Sandhill cranes selected areas for roosting in the Rio Grande characterized by shallower water interspersed with sandbars, wide channel width, low bank vegetation, and farther away from disturbances associated with bridges. Our results establish and identify the central processes driving patterns of diel habitat selection by wintering sandhill cranes. Land use and riverine trends have likely gradually reduced winter habitat to managed public lands and limited reaches of the Rio Grande, underscoring the importance of natural resources agencies in supporting migratory birds and challenges involved when managing for wildlife in highly pressured semi-arid environments.

Mercury cycling in agricultural and managed wetlands of California, USA: Seasonal influences of vegetation on mercury methylation, storage, and transport