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Article

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

by
Gary L. Ivey
,
Andrew J. Caven
*,
Dorn M. Moore
and
Sara K. Gomez-Maier
International Crane Foundation, E11376 Shady Lane Road, Baraboo, WI 53913, USA
*
Author to whom correspondence should be addressed.
Birds 2025, 6(4), 56; https://doi.org/10.3390/birds6040056 (registering DOI)
Submission received: 9 September 2025 / Revised: 21 October 2025 / Accepted: 22 October 2025 / Published: 24 October 2025
(This article belongs to the Special Issue Resilience of Birds in Changing Environments)
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Simple Summary

The Central Valley of California is the most important wintering region for Sandhill Cranes along the Pacific Flyway. These large birds depend on wetlands, grasslands, and row crops like rice, corn, and alfalfa to feed and rest during the winter. However, agricultural landscapes in the region are changing quickly. Temporary row crops that cranes use are being replaced by permanent woody crops such as orchards and vineyards, which provide little habitat value for cranes. We studied land cover changes in key wintering areas from 2008 to 2023 to understand how this affects crane habitat availability, broadly speaking. Our analysis shows that suitable habitat declined from over 81% in 2008 to under 65% in 2023, with an average loss of just over 1% per year. At the same time, orchards and other woody crops increased across the region. These changes could reduce the Central Valley’s capacity to support Sandhill Cranes and make the population more vulnerable. Protecting wetlands and grasslands and working with farmers to maintain wildlife-friendly crops are important to sustaining this species and other regional birds.

Abstract

The Central Valley of California provides critical wintering habitat for Sandhill Cranes (Antigone canadensis), which rely on wetlands, grasslands, and grain crops to meet their energetic needs. However, temporary row crops that support Sandhill Cranes and other wintering birds are ostensibly being replaced by permanent woody crops, which offer little value for wetland and grassland-dependent species. To better understand how landcover changes may be affecting habitat availability for these wintering cranes, we analyzed landcover trends within priority crane wintering areas from 2008 to 2023. We employed a mixed-methods approach that allowed us to describe both linear and non-linear trends over time and across regions. Our findings indicate a significant decrease in landcover types suitable as crane habitat over the 16-year period (τ = −0.90, p < 0.001), with an average annual decline of approximately −1.15 ± 0.21% (B ± 95% CI). The best-fit trendline showed that habitat suitability in priority wintering areas decreased from over 81% in 2008 to under 65% in 2023. Specifically, grasslands, rice fields, and alfalfa acreage declined across priority wintering areas, while woody landcover—including orchards, vineyards, and riparian forest breaks—increased significantly (τ = 0.88, p < 0.001; B = 1.14 ± 0.20%). These landscape-level changes may constrain the regional carrying capacity for Sandhill Cranes and reduce their overall resilience.

1. Introduction

The Central Valley of California is of continental importance to wintering and migrating waterfowl, shorebirds, and other waterbirds, as well as grassland birds [1,2]. The Central Valley is over 650 km long, generally ranges from 65–100 km wide, and runs north to south through the heart of the state, where it is surrounded by mountains except at its drainage into the San Francisco Bay estuary. It is divided mainly into the Sacramento Valley, draining southward, the San Joaquin River Valley (hereafter San Joaquin Valley), draining northward, the Sacramento–San Joaquin River Delta (hereafter Delta), where these rivers converge, and Suisun Marsh, where land-locked wetlands merge with tidal-dominated habitats of the San Francisco Bay estuary. The characteristics of the soil, geography, and climate make the Central Valley of California the most agriculturally productive region in the United States [3,4].
In 1984, the Greater Sandhill Crane (Antigone canadensis tabida) was listed as state threatened, pursuant to Fish and Game Code Sections 2070–2080 and Title 14 of the California Code of Regulations (FGC §2070–2080 and 14 CCR 670.5). The Greater Sandhill Cranes that winter in the Central Valley are members of the Central Valley Population (CVP). The breeding range of the CVP encompasses northeastern California, central and eastern Oregon, south-central Washington and interior British Columbia [5]. Additionally, Lesser (A. c. canadensis) and putative “Canadian” Sandhill Cranes (A. c. rowani) that breed in Alaska and British Columbia winter in the Central Valley and are considered members of the Pacific Coast Population (PCP; see reference [6] for a taxonomic discussion). Approximately 50,000 Sandhill Cranes occur in the Pacific Flyway, which include an estimated 35,000 A. c. canadensis, 5000 A. c. rowani, and up to 10,000 A. c. tabida [7]. The Central Valley hosts 100% of the Central Valley Population (CVP) of Greater Sandhill Cranes and >95% of the Pacific Coast Population (PCP) of Lesser Sandhill Cranes (G. c. canadensis) during the winter [8]. Although Sandhill Crane numbers have increased significantly in California over the last century, current population and subspecies trends are uncertain. Considering available secondary data, Caven [9] suggested that the CVP was probably stable and that apparent regional growth in the abundance of Sandhill Cranes wintering in California likely reflected growth of the PCP.
The loss of foraging habitats for waterbirds in the Central Valley has been a major concern in recent years [10]. Over the past three decades, Central Valley grasslands and other agricultural lands have been urbanized at a rate higher than in any other region of the United States [11,12], in some cases eliminating Sandhill Crane foraging habitats. Traditional Central Valley crane wintering areas are also being degraded by habitat loss from conversion to incompatible crops (e.g., vineyards and orchards; [8]) and water development projects [13]. Orchards and vineyards represent the fastest growing land use type and recent estimates suggest they cover approximately 15% of the valley [14]. Pacific Flyway conservation plans, covering the CVP and the PCP, identify conversion of grasslands and grain crops to permanent woody crops such as orchards and vineyards as a habitat conservation issue [15,16]. As urbanization and habitat conversion to vineyards and orchards accelerates in the Central Valley, the enhancement and protection of crane roost sites close to wetland and agricultural foraging locations represents a key conservation objective [17]. Most of the current Sandhill Crane winter roosting sites are on conservation lands which will likely stay protected from long-term land use changes; however, most of their foraging occurs on unprotected private lands, which are adjacent to these protected roost sites [18,19]. Habitat losses within these landscapes surrounding roost sites could threaten the future welfare of wintering cranes in this region.
Much of the Sandhill Crane’s historic wintering landscape within the Central Valley is no longer available because of the lack of suitable night roost sites. Most available wetlands are used for waterfowl hunting at disturbance levels which generally preclude crane use; therefore, cranes have developed traditions to use wetlands protected from such disturbance (i.e., mostly on National Wildlife Refuges and habitat conservation sites). It is likely that wintering Sandhill Cranes traditionally depended on the vast floodplain wetlands and the acorn crops provided by the historically extensive valley oak (Quercus lobata) savannahs and grasslands, but Central Valley wetlands have been reduced by over 90% since European settlement [20], and oak savannahs and associated grasslands were similarly reduced. By the 1960s, over half of grasslands in the Central Valley were lost [14]. However, like some waterfowl species [21], Sandhill Cranes have adapted to increases in agriculture and commonly feed in specific row crops, especially grain fields [18,22,23,24,25,26,27,28]. They are now highly dependent on flood-irrigated row crops such as rice, corn, and other cereal grains in California [13,18,29].
Cranes only use a portion of the available foraging habitat because they focus their use around traditional night roosts and show strong interannual fidelity to these sites and their associated foraging landscapes [30]. The size and bounds of foraging areas are limited by crane energetics, for example, Greater Sandhill Cranes rarely fly more than five kilometers from roost sites to forage [30]. These specific landscapes, which we term “cranescapes”, are centered around undisturbed, secure roost sites, or complexes of neighboring roost sites, and include the surrounding agricultural foraging habitats [31]. Given that CVP and PCP Sandhill Cranes exhibit strong fidelity to wintering sites [30], continued loss of foraging habitats within key cranescapes may reduce carrying capacity, and continued habitat loss could ultimately threaten their long-term viability [32]. Therefore, it is important to understand the rate of habitat loss in these cranescapes in order to mitigate it through targeted conservation action. In this paper, we assess loss rates of landcover types that serve as suitable Sandhill Crane habitat in Central Valley cranescapes, such as grasslands, wetlands, and row crop agriculture, to further habitat conservation planning for the species. We hypothesize that landcover compatible with Sandhill Crane foraging has declined throughout their Central Valley wintering range as woody landcover has increased in recent decades.

2. Materials and Methods

2.1. Crane Locational Data

We used 7187 crane foraging locations from multiple previous survey efforts (1991–2013) to define our study area. We included data from radio telemetry locations (77 radio-marked cranes) and field observations from a 2008–2009 study in the Delta [30]. Additionally, we used data from winter foraging flock surveys conducted from December 2012 through February 2013 on private lands throughout the Central Valley. Finally, we included 2012–2013 reports of flocks on the ground from eBird [33] in our dataset, as described in Ivey et al. [32]. Location data served only to define the boundaries of the study area. Our focus was therefore on producing a relatively comprehensive delineation of priority wintering areas rather than correcting for potential locational bias. To that end, we adopted an inclusive approach and pooled all available location data. Location data primarily reflects the early portion of the study period, allowing us to define static areas of importance for cranes in which to assess change over time. While this approach does not capture spatial shifts in use through time, we believe it effectively delineates the most critical areas for cranes. Given ongoing habitat loss, these areas are unlikely to shift significantly but suitable landcover could become more restricted [2,20,34]. These survey efforts informed the four priority Central Valley wintering areas assessed in this study: (1) the Sacramento Valley between Marysville and Chico; (2) Sacramento–San Joaquin Delta; (3) Northern San Joaquin Valley (San Joaquin River NWR and Grasslands Region); and (4) Southern San Joaquin Valley (Pixley NWR area; Figure 1).
Sandhill Cranes forage in a wide range of habitats, including grasslands, wetlands, and a variety of row crops; however, use of orchards, vineyards, blueberries, or nursery areas was never documented in a study of crane foraging in the Delta [35]. Cranes likely avoid these habitats because trees and shrubs make it difficult to see approaching predators and offer limited food value. For the sake of simplicity, and based on crane foraging choices [35], we categorized landcover types, including crops, as compatible with Sandhill Crane habitat use (e.g., cereal grains and grasslands) or incompatible (e.g., woody crops and forests). We also assessed annual trends in demonstrably important foraging and roosting landcovers.

2.2. Geospatial Data

Using the crane location data described above, we created a 2 km buffer around all confirmed crane observation points to capture nearby foraging and roosting habitat, consistent with daily dispersal patterns for Sandhill Cranes in this region (i.e., mean foraging flight distance for the greater subspecies; see reference [30]). The resulting shapefile defined the spatial extent of our study area. We did not modify the polygons to fill gaps or smooth the edges (see Figure 2).
Annual land cover data were obtained from the USDA Cropland Data Layer (CDL) for the years 2008 through 2023 [36]. The CDL is a 30 m-resolution, satellite-derived raster dataset that provides detailed crop classification across U.S. agricultural landscapes. Each year’s CDL raster was clipped to the 2 km-buffered crane use polygons. These steps reduced the spatial extent of analysis to only those portions of the landscape (cranescapes) likely to influence crane winter habitat availability. This resulted in a total study area of 4260 km2, which was divided into four aforementioned units including the Sacramento Valley (1827 km2), the Sacramento–San Joaquin Delta (1430 km2), the Northern San Joaquin Valley (738 km2), and the Southern San Joaquin Valley (265 km2).
Two classification crosswalks were developed to support habitat interpretation:
  • The first grouped CDL crop codes into ecologically meaningful landcover categories (e.g., “Alfalfa,” “Rice,” “Orchard and Vineyard”) based on similarities in crop taxonomy, structure, and phenology (Table A1).
  • The second assigned each CDL code as either compatible or incompatible with winter habitat use by cranes (i.e., “suitable” vs. “unsuitable”), informed by expert knowledge of crane behavior, foraging ecology, and prior regional studies (Table A2).
All geospatial processing and raster summarization steps were performed in Python (version 3.11.10, Beaverton, OR, USA) using the ArcPy site package from ArcGIS Pro (version 3.5.0; Esri, Redlands, CA, USA). Raster clips and reclassifications were created using the 2 km-buffered extent of observations from all years, and annual summaries of total area (in hectares) were extracted for each reclassified landcover type and habitat compatibility class. All spatial analyses were conducted using the CDL’s native projection: NAD 1983 Contiguous USA Albers Equal Area Conic (EPSG:5070). Retaining this projection ensured accurate area calculations based on 30 m × 30 m pixels (900 m2 each). Pixels containing “NoData” values or partial edge coverage were excluded from suitability assessment and area summaries.
CDL classification accuracy varies by class and region. In California CDL metadata, NASS reports 85–95% accuracy for major crop-specific classes in 2022 [37]. The accuracy for non-agricultural classes (e.g., wetlands, pasture) is more uncertain, as these depend on the NLCD for classification support [38]. Published work [39] shows that when CDL classes are aggregated (e.g., grouping all crops vs. non-crops), user-level accuracy often exceeds 97% [39]. Although we did not perform independent per-class accuracy validation for our study years, these external assessments justify our use of grouped categories.

2.3. Data Analysis

All analyses were conducted using the open-source statistical software program R version 4.4.2 [40]. We determined whether a trend in landcover suitability or the proportional cover of relevant classes was present from 2008 to 2023 with a Mann–Kendall Trend Test (τ) using the “Kendall” package in R [41,42,43]. Trend analyses were based on 16 (n) annual data points for each priority wintering area as well as the overall Central Valley wintering range. This test determines if there is a consistent monotonic upward or downward trend in a variable through time; it can accommodate non-linear trends and non-normal data and it is generally robust to temporal autocorrelation [42]. Nonetheless, we employed a variance correction approach for serially correlated data to ensure that our Mann–Kendall Trend Test results were robust using the “modifiedmk” package in R [44,45]. However, this analytical approach does not estimate periodic (e.g., annual) rates of change. Therefore, if a monotonic trend was detected per the Mann–Kendall Test, we subsequently estimated annual rates of change (B) with 95% confidence intervals using Generalized Linear Models with a Gaussian distribution and an “identity” link function (GLMs; [46,47]). Finally, to ensure we also had a strong non-linear interpretation of temporal trends in landcover we assessed trendlines using locally estimated scatterplot smoothing regression (LOESS, span = 0.75, degree = 2) [48]. Local regression, as the technique is often termed, allowed us to predict landcover values using LOESS trendlines based on our landcover data. A mixed methods approach to trend analysis is regularly employed as the various approaches provide differing products, are generally robust to different analytical assumptions, and ultimately provide validation and additional description of documented trends, e.g., [49]. Finally, we employed a Kruskal–Wallis H test including a Dunn post hoc test (Z) with a Benjamini–Hochberg p-value correction to discern differences in landcover composition across major CVP wintering regions using the “FSA” package [50,51,52]. All results are provided in absolute percentage points rather than as relative percent change.

3. Results

3.1. Cranescape Suitability

On average, about 75.7% of landcover was compatible with crane habitat (i.e., “suitable”) across priority wintering areas and years (range = 62.1% to 88.7%; n = 64). Suitability varied significantly across priority cranescapes (H = 18.05, p < 0.001; df = 3) from 2008 to 2023. Across years, suitability was highest in the Southern San Joaquin Valley (78.7 ± 4.3%; x ¯ ± 95% C.I.), closely followed by the Sacramento Valley (78.6 ± 1.9%). The Northern San Joaquin Valley (75.3 ± 3.3%) had slightly lower coverage of landcovers compatible with crane use than the aforementioned priority wintering areas, but had higher crane landcover suitability than the Delta (70.1 ± 2.1%). Ultimately, all other priority wintering areas had significantly higher cranescape habitat compatibility than the Delta (Z > 2.4 & p < 0.03 across Dunn post hoc tests), but these areas did not differ significantly from each other.
Landcover compatible with crane habitat declined from 2008 to 2023 (τ = −0.90, p < 0.001) across priority Sandhill Crane wintering areas at a rate of about −1.15 ± 0.21% annually (B ± 95% C.I.). On average, suitable landcover was >80.0% from 2008 to 2013, >73.0% from 2014 to 2019, and <68% since 2020 across priority wintering areas. The best fit LOESS trendline demonstrated that cranescape suitability for habitat use declined from >81% in 2008 to <65% in 2023 on average across priority wintering areas (Figure 3). This decline was present within individual priority crane wintering areas to varying degrees. In the Sacramento Valley (τ = −0.70, p = 0.006) habitat compatibility declined at an estimated rate of −0.69 ± 0.21% annually from about 80% in 2008 to about 71% in 2023. Landcover providing apparently suitable crane habitat in the Delta area declined (τ = −0.83, p < 0.001) at a rate of −0.84 ± 0.17% annually from about 75% to about 62% per LOESS trendline. The decline in habitat compatibility in the Northern San Joaquin Valley was comparatively steep (τ = −0.88, p < 0.001; −1.31 ± 0.26% annually) and declined from about 83% to about 63% from 2008 to 2023. Finally, cranescape suitability within the Southern San Joaquin Valley declined most steeply on an annual basis (τ = −0.88, p < 0.001; −1.77 ± 0.28%) from about 88% in 2008 to 62% in 2023 per LOESS trendline.

3.2. Key Landcover Trends

Alfalfa declined across priority cranescapes (τ = −0.72, p < 0.001) at a rate of about −0.51 ± 0.12% annually from 2008 to 2023. The decline was detected at all priority wintering areas with the exception of the Delta, where there was no monotonic trend over time. The decline in alfalfa landcover was steepest in the South San Joaquin Valley (τ = −0.90, p < 0.001) where it disappeared at a rate of −1.10 ± 0.24% annually. The LOESS trendline demonstrated that alfalfa declined from nearly 20% landcover in 2008 to <3% landcover in 2023 in the Southern San Joaquin Valley (Figure 4).
The decline in corn rotations was only marginally significant across priority wintering areas (τ = −0.37, p = 0.053) with a predicted annualized trend of −0.25 ± 0.24%. A declining trend was significant but modest in the Sacramento Valley (τ = −0.58, p = 0.002; B= −0.06 ± 0.03%). A declining trend in corn rotations was most apparent in priority wintering areas in the Delta (τ = −0.70, p < 0.001; B= −0.76 ± 0.24%) where the corn landcover declined from >23% in 2008 to <12% in 2023 per LOESS trendline (Figure 5). There was no significant trend in corn rotation landcover in the Northern or Southern San Joaquin Valley.
Overall, there was no trend in developed landcover across priority Sandhill Crane wintering areas. However, trends were significant within particular priority areas. For instance, developed landcover increased (τ = 0.57, p = 0.031; B = 0.16 ± 0.06%) in the Southern San Joaquin Valley wintering area and actually decreased modestly in the Sacramento Valley (τ = −0.53, p = 0.005; B = −0.05 ± 0.02%) and the Northern San Joaquin Valley (τ = −0.53, p = 0.012; B = −0.06 ± 0.03%). There was no significant trend in the Delta. Developed landcover in the Southern San Joaquin Valley increased from <4% in 2008 to >6% in 2023.
The decline in grassland landcovers, including hay meadow and pasture, was significant across priority wintering areas (τ = −0.70, p < 0.001; B = −0.36 ± 0.16%). This declining trend was pronounced and significant in the Delta (τ = −0.90, p < 0.001; B = −0.46 ± 0.15%) and the Northern San Joaquin Valley (τ = −0.82, p < 0.001; B = −0.54 ± 0.11%; Figure 6). However, the negative trend was only marginally significant and more modest in the Sacramento Valley (τ = −0.35, p = 0.065; B = −0.13 ± 0.07) and the Southern San Joaquin Valley (τ = −0.32, p = 0.096; B = −0.30 ± 0.47).
Rice landcover declined across priority wintering areas (τ = −0.43, p = 0.022; B = −0.20 ± 0.15%). However, trends varied across specific regions. For instance, rice landcover increased marginally in the Southern San Joaquin Valley (τ = 0.41, p = 0.061; B = 5.8 × 10−5 ± 5.5 × 10−5%) but declined significantly in the Sacramento Valley (τ = −0.48, p = 0.010; B = −0.88 ± 0.58%). There was no apparent trend in the Delta or the Northern San Joaquin Valley.
There was a significant increase in the proportional landcover of woody species across priority crane wintering areas (τ = 0.88, p < 0.001; B = 1.14 ± 0.20%) including natural forests and shrublands (e.g., deciduous forest) as well as cultivated analogs (e.g., almonds, olives, grapes, etc.). The increasing trend was relatively consistent across priority wintering areas (τ = 0.72–0.93) with a predicted value of about 12% woody landcover in 2008 and 29% across sites in 2023 per LOESS trendline (Figure 7).
Wetland landcover, including open water, emergent wetlands, and aquicultural systems, generally increased across priority wintering areas for Sandhill Cranes in California (τ = 0.55, p = 0.003; B = 0.11 ± 0.04%; Figure 8). Looking at specific priority areas, the North (τ = 0.57, p = 0.003; B = 0.31 ± 0.10%) and South (τ = 0.48, p = 0.010; B = 0.03 ± 0.02%) San Joaquin Valley sites saw significant increases in wetland landcover, as did the Sacramento Valley (τ = 0.32, p = 0.018; B = 0.08 ± 0.07%). There was no trend in wetland landcover in the Delta.

4. Discussion

Suitable landcover is generally decreasing for Sandhill Crane populations that winter in California. However, the impacts are likely more pronounced for foraging than roosting sites based on our analysis. The data indicate that roosting options (i.e., wetlands and [shallow] standing water) may have increased marginally over time. By contrast, natural and agricultural foraging areas including row crop agriculture (e.g., corn, rice) and grassland habitats (e.g., pastures) have declined steadily since 2008. Such declines in suitable foraging habitats may eventually reduce the carrying capacity of these important Central Valley cranescapes. Wetland (>90%) and grassland (>60%) habitat loss in the Central Valley have been pronounced and are linked to proportional declines in regional wetland and grassland bird abundance [2,20,34]. The loss of natural habitats has resulted in an increased dependence of avifauna on agricultural systems which can effectively provision habitat if managed appropriately [53,54]. However, herbaceous row crops are now being replaced with woody crops that do not supply habitat for the grassland and wetland birds that depend on the Central Valley during migration and wintering periods [53,55]. Forage availability related to agricultural practices has been directly linked to carrying capacity for crane species during the non-breeding season [56,57]. Additionally, limited surface water availability, which is an important component of roost habitat, also influences wintering area habitat availability and ostensibly landscape carrying capacity for cranes and other waterbirds [58,59]. Our findings underscore that while several avian species, including some crane species, have shown resilience to landscape-level changes and adaptability to agricultural environments [60], only a subset of agricultural systems are likely suitable for specific taxa. This suitability can depend on various factors, including crop structure (i.e., woody versus herbaceous), height, and seasonal management regimes (e.g., harvest timing) [53,55]. Other avian species are also vulnerable to habitat declines in California. One study documented that 97% of 61 bird taxa studied in the region are threatened by habitat loss [61], while a similar study reported that 97% of 92 bird taxa are threatened by habitat loss in California [62]. Also, grassland bird abundance in California has been declining more rapidly than the net loss of grassland habitat [2].
Although Pacific Flyway populations of Sandhill Cranes have increased markedly from historic lows in the 1940s [7], their current population status and trends are relatively unknown [9]. The Mid-Winter Waterfowl Survey, conducted each January, is the only comprehensive annual survey of Sandhill Cranes in the Pacific Flyway [63]. However, that survey of the Central Valley historically focused on counting waterfowl, which causes the crane estimates to be highly variable and somewhat unreliable [7,9,63]. Given that California’s Central Valley serves as the primary wintering ground for both the CVP and PCP, our findings raise an important question: what alternative regions, if any, could support these western Sandhill Crane populations if the Central Valley becomes too altered to meet their energetic needs? Our analyses indicate the availability of suitable foraging habitat was variable across priority Sandhill Crane wintering areas. The percentage of suitable landcover was lowest in the two regions that support the highest numbers of wintering cranes: the Delta and Northern San Joaquin Valley [7], making cranes wintering in these two areas more vulnerable to continued foraging habitat losses. Habitat loss rates varied by region. From 2008–2023, the Sacramento Valley lost 9%, the Delta lost 13%, the Northern San Joaquin Valley lost 20%, and the Southern San Joaquin Valley lost 26% of suitable foraging habitat. Corn is among the most selected crops by foraging Sandhill Cranes and is particularly important in the Delta [35]. Our results show an approximate 11% decline in corn in the Delta. Our results indicate that the main conservation challenge for Sandhill Cranes in the Central Valley, at the current time, is ensuring sufficient foraging habitat within each cranescape to support wintering populations.
Grassland birds and shorebirds, which require shallow wetlands, are facing some of the steepest declines among all North American avian taxa [64]. The Central Valley of California represents a highly important wintering site for these taxa within the Pacific Flyway, and local habitat loss rates, projected forward, could have flyway- and population-level impacts on key species of concern, especially considering additional stressors related to climate change [59]. Cranes have the capacity to serve as a “flagship” or “umbrella” species as meeting their habitat needs will benefit a range of other wetland- and grassland-dependent species [65,66]. Developing robust goals for Sandhill Crane habitat conservation and clearly identifying the ancillary benefits of key actions for other taxa may present an effective conservation strategy for developing partnerships and administering priority conservation actions for the CVP and PCP. Our work highlights the vulnerability of the Greater Sandhill Cranes within the state of California and suggests that clear habitat objectives should be met before a change is made in the species’ protected status at the state level.
Our results do not reflect the state as a whole, but a limited area encompassing 4260 km2 that is important to Sandhill Cranes. We examined trends in landcover that represent appropriate (i.e., “suitable” or “compatible”) habitat for Sandhill Cranes and not trends in habitat quality or availability as estimated per models. Therefore, we provide a relatively direct assessment of change in landcover relevant to Sandhill Cranes. Habitat selection models provide an approximation of static habitat preferences at a point in time, yet Sandhill Cranes are very flexible and can adapt to a range of herbaceous agricultural landcovers [60]. Additionally, we already have a strong understanding of Sandhill Crane habitat use patterns in a variety of contexts [18,22,23,24,25,26,27,28]. Finally, measuring changes in landcover categories that provision Sandhill Crane roosting and foraging habitat, and those that are antithetical to it, more directly informs conservation actions for priority Sandhill Crane wintering areas. For instance, based on our analysis, grassland conservation efforts should likely be a key priority in the Sacramento–San Joaquin Delta, where grassland landcover has declined most steeply. However, supporting rice agriculture may be a higher priority in the Sacramento Valley where that crop type, which provides both roosting and foraging benefits when managed correctly, has declined most sharply. Given our contexts, we ultimately felt that the tracking of landcover change provided more pertinent information for Sandhill Crane conservation than a habitat modeling approach extrapolated through time.

5. Conclusions

Our research documented a broad decline in the landcover of suitable habitats for Sandhill Cranes within their core wintering range in the Central Valley of California. Nonetheless, it is important to note that our results do not characterize landcover trends throughout the entire Central Valley but within the just under 10% of it deemed most important for Sandhill Cranes per our winter-use locations for the species. Our findings introduce the key question of how to combat these habitat losses for the benefit of Greater Sandhill Cranes and other wetland and grassland-dependent avifauna that utilize the region. Within the Central Valley, beyond our study area, there are more suitable Sandhill Crane foraging habitats, predominantly on private farms. However, due to the species’ energetic constraints and the limited availability of suitable roosting sites, many potential alternative foraging areas in the region are not functionally available to cranes [31,67,68]. Because cranes are so loyal to traditional winter roosting sites in the Central Valley, they generally do not readily pioneer into new areas [31,68]. Therefore, we suggest that an assessment of priorities for Sandhill Crane habitat conservation should first consider whether the roost site distribution is adequate within a given region, and secondly whether the associated foraging landscapes around those roosts are adequate to support cranes. Conservation strategies for each major crane wintering region should likely include: (1) conservation of existing unprotected roost sites through easements or perhaps fee-title acquisitions from willing sellers; (2) safeguarding foraging landscapes around these roosts, primarily via easements that restrict incompatible crops and development; (3) enhancing food availability within these landscapes by improving management on conservation lands and providing annual incentives for private land improvements; (4) establishing additional and secure roosting sites along the edges of the species’ current wintering range to expand access to foraging areas [30]. Several of these objectives are now being addressed through regional private-lands conservation initiatives, notably the BirdReturns program, a partnership including The Nature Conservancy, Audubon California, and Point Blue Conservation Science, which incentivizes landowners to flood fields and restore habitat for wetland-dependent species, including Sandhill Cranes [54]. However, solution-oriented programs will need to be well-funded to succeed in solving the ongoing problem of habitat loss at scale.

Author Contributions

Conceptualization, G.L.I., A.J.C. and D.M.M.; Methodology, A.J.C., D.M.M. and G.L.I.; Formal analysis, A.J.C. and D.M.M.; Investigation, A.J.C., D.M.M. and G.L.I.; Data curation, G.L.I., D.M.M. and A.J.C.; Writing—original draft, A.J.C., G.L.I., D.M.M. and S.K.G.-M.; Writing—review & editing, A.J.C., S.K.G.-M., D.M.M. and G.L.I.; Visualization, A.J.C. and D.M.M.; Funding acquisition, G.L.I. and A.J.C. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the International Crane Foundation’s Conservation Impact Fund, project number 1047.

Institutional Review Board Statement

Our manuscript is based on secondary data including a significant amount of visual survey data that would not require approval by an Animal Care and Use Committee, much of which was described in Ivey et al. [32]. However, we do include data from 77 tracked cranes, which was originally described by Ivey et al. [30]. Regarding this data, the “…handling of cranes was conducted under the guidelines of the Oregon State University Animal Care and Use Committee (project no. 3605) to ensure that methods were in compliance with the Animal Welfare Act and U.S. Government Principles for the Utilization and Care of Vertebrate Animals Used in Testing, Research, and Training policies” [30]. Cranes were captured under California Department of Fish and Wildlife permit no. SC-803070-02 and United States Geological Survey federal banding permit no. MB 21142 [30].

Informed Consent Statement

Not applicable.

Data Availability Statement

Available via Mendeley Data: Ivey, G.L.; Caven, A.J.; Moore, D.M. Central Valley of California landcover compatibility with Sandhill Crane habitat use from 2008 to 2023. Mendeley Data, 2025; https://doi.org/10.17632/ZVB4P2PJXW (accessed on 21 October 2025).

Acknowledgments

We extend our sincere thanks to the anonymous reviewers for their valuable edits, insightful suggestions, and thoughtful guidance. We want to thank the myriad of partners working on Sandhill Crane conservation issues in California including but not limited to the Friends of Stone Lakes, Sacramento Audubon, Audubon California, Sacramento Chapter of the Sierra Club, Sacramento Zoo, Motherlode Chapter of the Sierra Club, Save our Sandhill Cranes, Sacramento-Shasta Chapter of The Wildlife Society, the U.S. Fish and Wildlife Service, The Nature Conservancy, the California Department of Water Resources, California Department of Fish and Wildlife, the Bureau of Land Management, and the Central Valley Joint Venture.

Conflicts of Interest

The authors declare no conflicts of interest.

Appendix A

Table A1. Grouped Crop Type Reclassification Table.
Table A1. Grouped Crop Type Reclassification Table.
Class_NameAttributeReclassified_Name
Alfalfa36Alfalfa
Corn1Corn_rotations
Sweet Corn12Corn_rotations
Pop or Orn Corn13Corn_rotations
Dbl Crop WinWht/Corn225Corn_rotations
Dbl Crop Oats/Corn226Corn_rotations
Dbl Crop Triticale/Corn228Corn_rotations
Dbl Crop Corn/Soybeans241Corn_rotations
Developed82Developed
Developed/Open Space121Developed
Developed/Low Intensity122Developed
Developed/Med Intensity123Developed
Developed/High Intensity124Developed
Sod/Grass Seed59Grass_hay
Switchgrass60Grass_hay
Pasture/Grass62Grass_hay
Grassland/Pasture176Grass_hay
Cotton2Other
Sunflower6Other
Peanuts10Other
Tobacco11Other
Mint14Other
Canola31Other
Flaxseed32Other
Safflower33Other
Brassica napus34Other
Mustard35Other
Other Hay/Non-Alfalfa37Other
Camelina38Other
Sugarbeets41Other
Dry Beans42Other
Potatoes43Other
Other Crops44Other
Sugarcane45Other
Sweet Potatoes46Other
Misc Vegs & Fruits47Other
Watermelons48Other
Onions49Other
Cucumbers50Other
Chickpeas51Other
Lentils52Other
Peas53Other
Tomatoes54Other
Caneberries55Other
Hops56Other
Herbs57Other
Clover/Wildflowers58Other
Fallow/Idle Cropland61Other
Barren65Other
Clouds/No Data81Other
Non-ag/Undefined88Other
Perennial Ice/Snow112Other
Barren131Other
Carrots206Other
Asparagus207Other
Garlic208Other
Cantaloupes209Other
Honeydew Melons213Other
Broccoli214Other
Greens219Other
Strawberries221Other
Squash222Other
Vetch224Other
Lettuce227Other
Pumpkins229Other
Dbl Crop Lettuce/Cantaloupe231Other
Dbl Crop Lettuce/Cotton232Other
Cabbage243Other
Cauliflower244Other
Celery245Other
Radishes246Other
Turnips247Other
Eggplants248Other
Gourds249Other
Cranberries250Other
Rice3Rice
Other Small Grains25Soy_Sorghum_SmallGrains
Oats28Soy_Sorghum_SmallGrains
Buckwheat39Soy_Sorghum_SmallGrains
Sorghum4Soy_Sorghum_SmallGrains
Millet29Soy_Sorghum_SmallGrains
Soybeans5Soy_Sorghum_SmallGrains
Dbl Crop WinWht/Soybeans26Soy_Sorghum_SmallGrains
Dbl Crop Soybeans/Cotton239Soy_Sorghum_SmallGrains
Dbl Crop Soybeans/Oats240Soy_Sorghum_SmallGrains
Water83Wetlands_water
Wetlands87Wetlands_water
Aquaculture92Wetlands_water
Open Water111Wetlands_water
Herbaceous Wetlands195Wetlands_water
Barley21Wheat_barley_relatives
Durum Wheat22Wheat_barley_relatives
Spring Wheat23Wheat_barley_relatives
Winter Wheat24Wheat_barley_relatives
Rye27Wheat_barley_relatives
Speltz30Wheat_barley_relatives
Triticale205Wheat_barley_relatives
Dbl Crop Lettuce/Durum Wht230Wheat_barley_relatives
Dbl Crop Lettuce/Barley233Wheat_barley_relatives
Dbl Crop Durum Wht/Sorghum234Wheat_barley_relatives
Dbl Crop Barley/Sorghum235Wheat_barley_relatives
Dbl Crop WinWht/Sorghum236Wheat_barley_relatives
Dbl Crop Barley/Corn237Wheat_barley_relatives
Dbl Crop WinWht/Cotton238Wheat_barley_relatives
Dbl Crop Barley/Soybeans254Wheat_barley_relatives
Forest63Woody
Shrubland64Woody
Cherries66Woody
Peaches67Woody
Apples68Woody
Grapes69Woody
Christmas Trees70Woody
Other Tree Crops71Woody
Citrus72Woody
Pecans74Woody
Almonds75Woody
Walnuts76Woody
Pears77Woody
Deciduous Forest141Woody
Evergreen Forest142Woody
Mixed Forest143Woody
Shrubland152Woody
Woody Wetlands190Woody
Pistachios204Woody
Prunes210Woody
Olives211Woody
Oranges212Woody
Avocados215Woody
Peppers216Woody
Pomegranates217Woody
Nectarines218Woody
Plums220Woody
Apricots223Woody
Blueberries242Woody
Table A2. Crop Compatibility Reclassification Table.
Table A2. Crop Compatibility Reclassification Table.
Class_NameAttributeReclassified_Name
Corn1compatible
Cotton2compatible
Rice3compatible
Sorghum4compatible
Soybeans5compatible
Sunflower6compatible
Peanuts10compatible
Tobacco11compatible
Sweet Corn12compatible
Pop or Orn Corn13compatible
Mint14compatible
Barley21compatible
Durum Wheat22compatible
Spring Wheat23compatible
Winter Wheat24compatible
Other Small Grains25compatible
Dbl Crop WinWht/Soybeans26compatible
Rye27compatible
Oats28compatible
Millet29compatible
Speltz30compatible
Canola31compatible
Flaxseed32compatible
Safflower33compatible
Brassica napus34compatible
Mustard35compatible
Alfalfa36compatible
Other Hay/Non-Alfalfa37compatible
Camelina38compatible
Buckwheat39compatible
Sugarbeets41compatible
Dry Beans42compatible
Potatoes43compatible
Other Crops44compatible
Sugarcane45incompatible
Sweet Potatoes46compatible
Misc Vegs & Fruits47compatible
Watermelons48compatible
Onions49compatible
Cucumbers50compatible
Chickpeas51compatible
Lentils52compatible
Peas53compatible
Tomatoes54compatible
Caneberries55incompatible
Hops56incompatible
Herbs57compatible
Clover/Wildflowers58compatible
Sod/Grass Seed59compatible
Switchgrass60compatible
Fallow/Idle Cropland61compatible
Pasture/Grass62compatible
Forest63incompatible
Shrubland64incompatible
Barren65compatible
Cherries66incompatible
Peaches67incompatible
Apples68incompatible
Grapes69incompatible
Christmas Trees70incompatible
Other Tree Crops71incompatible
Citrus72incompatible
Pecans74incompatible
Almonds75incompatible
Walnuts76incompatible
Pears77incompatible
Clouds/No Data81incompatible
Developed82incompatible
Water83compatible
Wetlands87compatible
Non-ag/Undefined88incompatible
Aquaculture92incompatible
Open Water111incompatible
Perennial Ice/Snow112incompatible
Developed/Open Space121incompatible
Developed/Low Intensity122incompatible
Developed/Med Intensity123incompatible
Developed/High Intensity124incompatible
Barren131incompatible
Deciduous Forest141incompatible
Evergreen Forest142incompatible
Mixed Forest143incompatible
Shrubland152incompatible
Grassland/Pasture176compatible
Woody Wetlands190incompatible
Herbaceous Wetlands195compatible
Pistachios204incompatible
Triticale205compatible
Carrots206compatible
Asparagus207compatible
Garlic208compatible
Cantaloupes209compatible
Prunes210incompatible
Olives211incompatible
Oranges212incompatible
Honeydew Melons213compatible
Broccoli214compatible
Avocados215incompatible
Peppers216compatible
Pomegranates217incompatible
Nectarines218incompatible
Greens219compatible
Plums220incompatible
Strawberries221compatible
Squash222compatible
Apricots223incompatible
Vetch224compatible
Dbl Crop WinWht/Corn225compatible
Dbl Crop Oats/Corn226compatible
Lettuce227compatible
Dbl Crop Triticale/Corn228compatible
Pumpkins229compatible
Dbl Crop Lettuce/Durum Wht230compatible
Dbl Crop Lettuce/Cantaloupe231compatible
Dbl Crop Lettuce/Cotton232compatible
Dbl Crop Lettuce/Barley233compatible
Dbl Crop Durum Wht/Sorghum234compatible
Dbl Crop Barley/Sorghum235compatible
Dbl Crop WinWht/Sorghum236compatible
Dbl Crop Barley/Corn237compatible
Dbl Crop WinWht/Cotton238compatible
Dbl Crop Soybeans/Cotton239compatible
Dbl Crop Soybeans/Oats240compatible
Dbl Crop Corn/Soybeans241compatible
Blueberries242incompatible
Cabbage243compatible
Cauliflower244compatible
Celery245compatible
Radishes246compatible
Turnips247compatible
Eggplants248compatible
Gourds249compatible
Cranberries250compatible
Dbl Crop Barley/Soybeans254compatible

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Birds 06 00056 g001
Figure 1. Map of the Central Valley of California study area including four distinctly defined priority wintering areas for Sandhill Cranes (Antigone canadensis; red squares—main map) with an inset of the contiguous United States highlighting the state of California (black fill) and the overall study area (red square—inset).
Figure 1. Map of the Central Valley of California study area including four distinctly defined priority wintering areas for Sandhill Cranes (Antigone canadensis; red squares—main map) with an inset of the contiguous United States highlighting the state of California (black fill) and the overall study area (red square—inset).
Birds 06 00056 g001
Birds 06 00056 g002
Figure 2. Example of priority wintering area delineation using the 2 km buffering approach around Sandhill Crane (Antigone canadensis) use locations in the Sacramento Valley, which is situated within the larger “Central Valley,” of California, USA.
Figure 2. Example of priority wintering area delineation using the 2 km buffering approach around Sandhill Crane (Antigone canadensis) use locations in the Sacramento Valley, which is situated within the larger “Central Valley,” of California, USA.
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Figure 3. The proportion of landcover within priority areas of the Central Valley region of California that is suitable for Sandhill Crane (Antigone canadensis) winter habitat use. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
Figure 3. The proportion of landcover within priority areas of the Central Valley region of California that is suitable for Sandhill Crane (Antigone canadensis) winter habitat use. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
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Figure 4. Proportion of landcover as alfalfa (Medicago sativa) in the Southern San Joaquin Valley priority Sandhill Crane (Antigone canadensis) wintering area within the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
Figure 4. Proportion of landcover as alfalfa (Medicago sativa) in the Southern San Joaquin Valley priority Sandhill Crane (Antigone canadensis) wintering area within the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
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Figure 5. Proportion of landcover as corn (Zea mays) rotations in the Sacramento–San Joaquin River Delta priority Sandhill Crane (Antigone canadensis) wintering area within the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
Figure 5. Proportion of landcover as corn (Zea mays) rotations in the Sacramento–San Joaquin River Delta priority Sandhill Crane (Antigone canadensis) wintering area within the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
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Figure 6. Proportion of landcover as grass, hay, or pasture in the Northern San Joaquin Valley priority Sandhill Crane (Antigone canadensis) wintering area within the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
Figure 6. Proportion of landcover as grass, hay, or pasture in the Northern San Joaquin Valley priority Sandhill Crane (Antigone canadensis) wintering area within the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
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Figure 7. Proportion of landcover as woody species (natural and cultivated) across priority Sandhill Crane (Antigone canadensis) wintering areas in the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
Figure 7. Proportion of landcover as woody species (natural and cultivated) across priority Sandhill Crane (Antigone canadensis) wintering areas in the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
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Figure 8. Proportion of landcover as wetlands and open water across priority Sandhill Crane (Antigone canadensis) wintering areas in the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
Figure 8. Proportion of landcover as wetlands and open water across priority Sandhill Crane (Antigone canadensis) wintering areas in the Central Valley region of California. Blue dots represent observed data points and the red line is the best-fit LOESS (Locally Estimated Scatterplot Smoothing) regression curve.
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MDPI and ACS Style

Ivey, G.L.; Caven, A.J.; Moore, D.M.; Gomez-Maier, S.K. Trends in Landcover Suitability for Sandhill Cranes Wintering in the Central Valley of California. Birds 2025, 6, 56. https://doi.org/10.3390/birds6040056

AMA Style

Ivey GL, Caven AJ, Moore DM, Gomez-Maier SK. Trends in Landcover Suitability for Sandhill Cranes Wintering in the Central Valley of California. Birds. 2025; 6(4):56. https://doi.org/10.3390/birds6040056

Chicago/Turabian Style

Ivey, Gary L., Andrew J. Caven, Dorn M. Moore, and Sara K. Gomez-Maier. 2025. "Trends in Landcover Suitability for Sandhill Cranes Wintering in the Central Valley of California" Birds 6, no. 4: 56. https://doi.org/10.3390/birds6040056

APA Style

Ivey, G. L., Caven, A. J., Moore, D. M., & Gomez-Maier, S. K. (2025). Trends in Landcover Suitability for Sandhill Cranes Wintering in the Central Valley of California. Birds, 6(4), 56. https://doi.org/10.3390/birds6040056

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