Fecal corticoid monitoring in whooping cranes (Grus americana) undergoing reintroduction

We used radioimmunoassay to determine fecal corticoid concentrations and assess potential stress in 10 endangered whooping cranes (Grus americana) undergoing reintroduction to the wild. Fecal samples were collected shortly after hatching at a captive facility in Maryland, during field training in Wisconsin, and throughout a human‐led migration to Florida. After a 14‐day decline following hatching, fecal corticoid concentrations stabilized at baseline levels for the duration of the captive period, despite exposure to potentially stressful stimuli. Shipment of the cranes to the field training site was correlated with an eight‐ to 34‐fold increase in fecal corticoid concentrations, which returned to baseline levels within 1 week. Increases were positively correlated with age but not body weight at the time of shipping. Fecal corticoid concentrations during the training period increased slightly and exhibited greater variation than levels observed at the captive facility, but were well within expected norms based on previous studies. Fecal corticoid concentrations increased twofold following premigration physical examinations and placement of radiotransmitters, and persisted for up to 4 days before they returned to baseline levels. Though fecal corticoid concentrations and variation during the migration period were similar to training levels, there was an overall decline in fecal corticoid concentrations during the artificial migration. Acute stressors, such as capture, restraint, and severe storms, were associated with stress responses by the cranes that varied in accordance with lasting physical or psychological stimuli. The overall reintroduction process of costume‐rearing, ultralight aircraft habituation, training, and artificial migration was not associated with elevations in fecal corticoid concentrations suggestive of chronic stress. Zoo Biol 24:15–28, 2005. © 2005 Wiley‐Liss, Inc.     

Fecal corticosterone reflects serum corticosterone in Florida sandhill cranes

Florida sandhill cranes (Grus canadensis pratensis) were conditioned to confinement 6 hr/day for 7 days. On day 8, each bird's jugular vein was catheterized, blood samples were drawn, and each crane was confined for 6 hr. Using a randomized, restricted cross-over design, cranes were injected intravenously with either 0.9% NaCl solution or ACTH (cosyntropin; Cortrosyn; 0.25 mg). During the 6 hr of confinement, fecal samples (feces and urine) were collected from each of five cranes immediately after defecation. Individual fecal samples were collected approximately at hourly intervals and assayed for corticosterone. We showed previously that serum corticosterone did not vary significantly following saline injection, but peaked significantly 60 min after ACTH injection. Maximal fecal corticosterone concentrations (ng/g) were greater (P < 0.10; median 1087 ng/g) following ACTH stimulation compared to maximal fecal corticosterone concentrations at the end of acclimation (day 7; median 176) and following saline treatment (median 541). In cranes under controlled conditions, fecal corticosterone concentration reflects serum corticosterone levels, fecal corticosterone, Grus canadensis pratensis, sandhill cranes, serum corticosterone levels.     

Coccidia of whooping cranes

Coccidial oocysts were observed in 6 of 19 fecal samples from free-ranging whooping cranes (Grus americana) and 4 of 16 samples from captive whooping cranes. Eimeria gruis occurred in four free-ranging whooping cranes and E. reichenowi in two free-ranging and two captive whooping cranes. Fecal samples from two captive cranes contained oocysts of Isospora lacazei which was considered a spurious parasite. Oocysts of both species of Eimeria were prevalent in fecal samples collected from three free-ranging Canadian sandhill cranes (G. canadensis rowani) from whooping crane wintering grounds in Texas. These coccidia were prevalent also in fecal samples from 14 sandhill cranes (of 4 subspecies) maintained in captivity at the Patuxent Wildlife Research Center in Maryland.     

Capture of sandhill cranes using alpha-chloralose

From 1990-2001, we made 188 successful captures of 166 different greater sandhill cranes (Grus canadensis tabida) through experimental use of alpha-chloralose (AC). Most captures took place during September (72.3%; n = 136), followed by August (14.9%; n = 28), and October (12.8%; n = 24). Territorial pairs were captured more successfully than family groups. Overall morbidity (6.4%) and mortality (4.3%) were lower than most other capture techniques for sandhill cranes. Exertional myopathy (EM) was the most common complication observed using AC (3.7%). Sedation level (chi5(2) = 25.9, P < 0.01) and month of capture (chi2(2) = 12.3, P < 0.01) were both associated with the presence of EM in cranes captured with AC. A logistic regression model suggests lighter sedation and the months of August and October are potential risk factors for EM in sandhill cranes captured with AC in Wisconsin (USA).     

The reproductive success of sandhill cranes in midwestern landscapes

A number of wildlife species have recovered from the brink of extinction to flourish and, in some cases, even become a commonly recognized urban species (e.g., Canada goose [Branta canadensis]). Broadly extirpated from much of their historical range in North America, the sandhill crane (Antigone canadensis) demonstrated this potential for population recovery. The trajectory of the eastern population of greater sandhill cranes is remarkable—perhaps as many as 90,000 cranes now occur throughout the same Great Lakes states that reported only dozens of birds less than a century ago. However, understanding future population growth of the species remains uncertain because breeding birds are increasingly exposed to the pressures of urban sprawl and a changing agricultural landscape. From 2009 to 2014 we investigated the survival of sandhill crane nests and young up to 11 weeks of age (the point at which they are capable of flight) in the core of the eastern population's range in central Wisconsin and at its peripheral extent in a rapidly developing urban region of northeastern Illinois, USA. We located crane nests via systematic surveys on foot and from helicopters, we then radio-tagged the young and monitored them until they died or were capable to sustained flight. Overall, young were more likely to hatch from nests in Illinois (60%) than in central Wisconsin (46%), regardless of differences in land cover surrounding the nest site. In contrast, the survivorship of young was positively correlated with urban land cover in both regions but higher in central Wisconsin (54%) than in northeast Illinois (27%). Overall, the probability of producing young was greater in landscapes with more urban development, regardless of region. We suggest that differences in predator composition, predator behavior, and crane density between rural and urban areas is the primary reason for the difference in crane productivity. Higher recruitment of sandhill cranes using urban landscapes may allow cranes to echo the population trajectory of urban Canada geese. We anticipate that sandhill cranes will continue to use urban landscapes, and likely expand their geographic range as breeding pairs benefit from the increased survivorship of young in those landscapes. © The Wildlife Society, 2019     

Avian pox in Florida sandhill cranes.

Cutaneous elevations were present on the feet, legs and heads of four Florida sandhill cranes, Grus canadensis pratensis, (one free-living, three penreared birds). As a result of examination of the elevations by light- and electron microscopy, it was determined that the lesions were caused by poxvirus. This is the first record of pox in cranes in North America.     

Potential natural exposure of Mississippi sandhill cranes to aflatoxin B1.

A survey was conducted to determine if carcinogenic mycotoxins were present in foods consumed by Mississippi sandhill cranes (Grus canadensis pulla). Samples of field corn (Zea mays) (n = 111) and chufa (Cyperus esculentus) (n = 20), obtained in 1987, 1988 and 1989 on the Mississippi Sandhill Crane National Wildlife Refuge (MSCNWR) and nearby private lands were analyzed for aflatoxin B1(AB1), ochratoxin A and sterigmatocystin using thin layer chromatography. Chufa samples were negative for all three mycotoxins. Aflatoxin B1 was found in corn at concentrations from 5 to 5,000 ppb; the other mycotoxins were not found in corn. Contaminated corn was found in 72% of all corn fields, but the proportion of contaminated fields was 57 to 100% for the 3-yr period. Contamination with AB1 was greatest in corn obtained from the ground post-harvest. Overall, 32% of corn samples from the ground had levels greater than or equal to 200 ppb with a mean of 427 ppb (range = 5 to 5,000 ppb) in contaminated fields. In 1989, mean AB1 concentration in corn on the ground was 5 to 1138 ppb for individual fields. The concentration of AB1 was less than or equal to 200 ppb in all corn samples from upright stalks. The study demonstrated that AB1 is available to sandhill cranes and at levels that may pose a serious health threat.     

Haemoproteus balearicae and other blood parasites of free-ranging Florida sandhill crane chicks

We obtained blood smears from 114 Florida sandhill crane (Grus canadensis pratensis) chicks in Osceola and Lake Counties, Florida, USA, during 1998-2000. Leucocytozoon grusi was observed in 11 (10%) chicks; Haemoproteus antigonis was observed in eight (7%) chicks; and three (3%) chicks were infected with Haemoproteus balearicae. One chick infected with H. balearicae suffered from severe anemia (packed cell volume = 13%) and was later found moribund. At necropsy this bird also had severe anemia and damage to the heart possibly due to hypoxia. This is the first report of H. balearicae in free-ranging North American cranes.     

Population and Harvest Dynamics of Midcontinent Sandhill Cranes

Sandhill cranes (Antigone canadensis) inhabiting the midcontinent of North America have been hunted since the 1960s under management goals of maintaining abundance, retaining geographic distribution, and maximizing sustainable harvest. Some biologists have raised concerns regarding harvest sustainability because sandhill cranes have lower reproductive rates than other game birds. We summarized demographic information in an age-structured matrix model to better understand population dynamics and harvest. Population indices and recovered harvest since the early 1980s suggest midcontinent sandhill cranes have experienced an average long-term annual growth of 0.9%; meanwhile, harvest has increased 1.8% annually. Adult survival and recruitment rates estimated from field data required modest adjustments (1–3%) so that model-derived growth rates matched growth estimated from a long-term survey (0.887 adult survival and 0.199 females/breeding female). Considering 0.9% long-term annual growth, sandhill cranes could be harvested at a rate of 6.6% if harvest was additive to natural mortality (assumed to be 0.05) or 11.3% if harvest mortality compensated for natural mortality. Life-history characteristics for long-lived organisms and demographic evidence suggested that hunter harvest was primarily additive. Differential harvest rates of segments of sandhill cranes in the midcontinent population derived from differential exposure to hunting suggested potentially unsustainable harvest for greater sandhill cranes (A. c. tabida) from 2 breeding segments. Overall, demographic evidence suggests that the harvest of sandhill cranes in the midcontinent population has been managed sustainably. Monitoring activities that reduce nuisance variation and estimate vital and harvest rates by subspecies would support continued management of sandhill cranes that are of interest to hunters and bird watchers. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.     

Radiographic analysis of the development of the pelvic limb of captive-reared cranes (Grus spp.)

For captive-reared cranes, pelvic limb abnormalities in chicks have been identified as significant morbidity/mortality factors. An important component of the diagnosis of limb abnormalities is the understanding of the normal limb. This study was undertaken to describe the normal, radiographic development of the femur, tibiotarsus, tarsometatarsus, and fibula of the whooping crane (Grus americana), Florida sandhill crane (Grus canadensis pratensis), and Siberian crane (Grus leucogeranus). Crane chicks were anesthetized and their pelvic limb bone development evaluated radiographically on a weekly to bimonthly basis from one to fourteen weeks of age. Body weight, bone length, diaphyseal width, and physeal development and closure were evaluated. Based on the radiographic analysis, the gross development of the long bones of the pelvic limb of whooping, Florida sandhill, and Siberian cranes was found to be similar among the three species, and not dissimilar from other avian species which have been studied. Repeated handling, anesthesia, and radiographic exposure did not produce any behavioral, developmental, or physical abnormalities in the studied cranes when compared to cranes of the same species raised using the same methods. This is the first work to describe pelvic limb bone development in these species. © 1996 Wiley-Liss, Inc.     

Geographic distribution of the mid-continent population of sandhill cranes and related management applications

The Mid-continent Population (MCP) of sandhill cranes (Grus canadensis) is widely hunted in North America and is separated into the Gulf Coast Subpopulation and Western Subpopulation for management purposes. Effective harvest management of the MCP requires detailed knowledge of breeding distribution of subspecies and subpopulations, chronology of their use of fall staging areas and wintering grounds, and exposure to and harvest from hunting. To address these information needs, we tagged 153 sandhill cranes with Platform Transmitting Terminals (PTTs) during 22 February–12 April 1998–2003 in the Central and North Platte River valleys of south-central Nebraska. We monitored PTT-tagged sandhill cranes, hereafter tagged cranes, from their arrival to departure from breeding grounds, during their fall migration, and throughout winter using the Argos satellite tracking system. The tracking effort yielded 74,041 useable locations over 49,350 tag days; median duration of tracking of individual cranes was 352 days and 73 cranes were tracked >12 months. Genetic sequencing of mitochondrial DNA (mtDNA) from blood samples taken from each of our random sample of tagged cranes indicated 64% were G. c. canadensis and 34% were Grus canadensis tabida. Tagged cranes during the breeding season settled in northern temperate, subarctic, and arctic North America (U.S. [23%, n = 35], Canada [57%, n = 87]) and arctic regions of northeast Asia (Russia [20%, n = 31]). Distribution of tagged cranes by breeding affiliation was as follows: Western Alaska–Siberia (WA–S, 42 ± 4% [SE]), northern Canada–Nunavut (NC–N, 21 ± 4%), west-central Canada–Alaska (WC–A, 23 ± 4%) and East-central Canada–Minnesota (EC–M, 14 ± 3%). All tagged cranes returned to the same breeding affiliation used during the previous year with a median distance of 1.60 km (range: 0.08–7.7 km, n = 53) separating sites used in year 1 and year 2. Fall staging occurred primarily in central and western Saskatchewan (69%), North Dakota (16%), southwestern Manitoba (10%), and northwestern Minnesota (3%). Space-use sharing indices showed that except for NC–N and WC–A birds, probability of finding a crane from one breeding affiliation within the home range of another breeding affiliation was low during fall staging. Tagged cranes from WC–A and EC–M breeding affiliations, on average, spent 25 and 20 days, respectively, longer on fall staging areas in the northern plains than did WA–S and NC–N birds. Cranes in the NC–N, WA–S, and WC–A affiliations spent 99%, 74%, and 64%, respectively, of winter in western Texas in Hunting Zone A; EC–M cranes spent 83% of winter along the Texas Gulf Coast in Hunting Zone C. Tagged cranes that settled within the breeding range of the Gulf Coast Subpopulation spent 28% and 42% of fall staging and winter within the range of the Western Subpopulation, indicating sufficient exchange of birds to potentially limit effectiveness of MCP harvest management. Harvests of EC–M and WC–A cranes during 1998–2003 were disproportionately high to their estimated numbers in the MCP, suggesting more conservative harvest strategies may be required for these subpopulations in the future, and for sandhill cranes to occupy major parts of their historical breeding range in the Prairie Pothole Region. Exceptionally high philopatry of MCP cranes of all 4 subpopulations to breeding sites coupled with strong linkages between crane breeding distribution, and fall staging areas and wintering grounds, provide managers guidance for targeting MCP crane harvest to meet management goals. Sufficient temporal or spatial separation exists among the 4 subpopulations on fall staging areas and wintering grounds to allow harvest to be targeted at the subpopulation level in all states and provinces (and most hunting zones within states and provinces) when conditions warrant. Knowledge gained from our study provides decision-makers in the United States, Canada, Mexico, and Russia with improved guidance for developing sound harvest regulations, focusing conservation efforts, and generating collaborative efforts among these nations on sandhill crane research and management to meet mutually important goals. © 2011 The Wildlife Society.     

Baseline and stress-induced plasma corticosterone during long-distance migration in the bar-tailed godwit, Limosa lapponica

The specific roles of corticosterone in promotion of avian migration remain unclear even though this glucocorticosteroid is elevated in many migrating bird species. In general, glucocorticosteroids promote metabolic homeostasis and may elicit effects on feeding and locomotion. Because the migratory stages of refueling and flight are characterized by distinct behaviors and physiology, the determination of corticosterone levels during each stage should help identify potential processes in which corticosterone is involved. We measured baseline levels of corticosterone in bar-tailed godwits (Limosa lapponica) during two distinct stages of migration: (1) immediately after arrival at a false stopover site just short of the Wadden Sea and (2) throughout the subsequent 4-wk refueling period on the Wadden Sea. Plasma corticosterone was higher in arriving than in refueling birds. In addition, corticosterone increased with size-corrected body mass during the refueling phase, suggesting that corticosterone rises as birds prepare to reinitiate flight. Therefore, elevated corticosterone appears associated with migratory flight and may participate in processes characterizing this stage. We also performed a capture stress protocol in all birds and found that corticosterone increased in both arriving and refueling godwits. Therefore, the normal course of migration may be typified by corticosterone concentrations that are lower than those associated with stressful and life-threatening episodes.     

Use of surrogate parental models and age periods in a successful release of hand-reared sandhill cranes

Ten sandhill crane chicks were reared in isolation from humans to prepare them for an experimental wild release. They were imprinted on realistic models using crane brooding calls and were fed by crane-like puppets. Six of the chicks were simultaneously imprinted on a human in a crane costume. The other four chicks were introduced to this surrogate parent at 5–7 days of age. The chicks were fed natural foods by the parent at two wild sites, one of which, the release site, was a staging area for migratory cranes. Observations were made on their behavioral development, including the time spent close to the model or costumed parent and the percentage of time spent foraging. The chicks spent the initial month close to the surrogate parent but moved away more to forage during the second month. The chicks regressed to again spend a great deal of time near the parent during the third and fourth months. They were released during this regressive period by removing the surrogate parent. All five of the released chicks showed increased interest in wild cranes within days of the release and formed a continuous association with wild cranes within 30 days. Four of the five were relocated by telemetry the following spring back in Wisconsin. These young juvenile cranes were excellent candidates for release due to their adaptable nature and their level of social development. The artificial stimuli of the surrogate parent helped the chicks to generalize their attachment to wild cranes. Once with wild cranes they quickly learned additional survival skills.     

Corticosterone levels as indicators of habitat quality: effects of habitat segregation in a migratory bird during the non-breeding season

During the non-breeding season, many species of territorial migratory birds exhibit a non-random pattern of habitat distribution, with males and females occupying different habitats. In this study, we examined possible physiological consequences arising from such habitat segregation in one migrant passerine species, the American redstart (Setophaga ruticilla), on its non-breeding grounds in Jamaica, West Indies. For 2 years, we measured concentrations of corticosterone, at the time of capture (baseline) and 30 min after capture (profile of acute corticosterone secretion), in redstarts in two distinct habitats, one occupied predominately by males and one mostly by females. All redstarts in both habitat types exhibited similar concentrations of baseline corticosterone levels in fall (October), whereas in spring (March–April), redstarts in female-biased habitat exhibited significantly higher baseline levels regardless of age or sex. In fall, all individuals in both habitats exhibited significant increases in corticosterone concentration with capture and handling, but in spring only redstarts (both sexes) in male-biased habitat continued to exhibit acute corticosterone secretion. Redstarts in female-biased habitat had elevated baseline corticosterone levels and reduced acute corticosterone secretion. In spring, baseline corticosterone concentration was negatively correlated with body mass, suggesting muscle catabolism associated with high corticosterone concentrations or possibly that birds are leaner as a result of increased foraging effort. These results indicate that redstarts (primarily females) in female-biased habitats suffered a decline in physiological condition, which could in turn influence their departure schedules, migration patterns and even their condition and arrival schedules on the breeding grounds. Thus, segregation of populations into habitats of different quality during the non-breeding period may have ramifications throughout the annual cycle of such migratory species. Furthermore, these results show the usefulness of plasma corticosterone levels as indicators of physiological condition and thus habitat quality for birds during the non-breeding period. Received: 14 November 1997 / Accepted: 9 March 1998     

Pulmonary lesions in disseminated visceral coccidiosis of sandhill and whooping cranes

Fifty cranes, consisting of 46 sandhill (Grus canadensis) and four whooping cranes (Grus americana), were studied. Eighteen sandhill cranes and the four whooping cranes were naturally infected with disseminated visceral coccidiosis (DVC). The remaining sandhill cranes were chicks experimentally infected with oocysts of Eimeria reichenowi and/or E. gruis; five chicks served as controls. There were no clinical signs attributed to respiratory infection. Necropsy of naturally infected adult birds revealed nodules in many organs, including the lung, air sacs, trachea and nares. Artificially infected sandhill cranes and the whooping crane chicks that died from DVC had congestion and consolidated areas in the lung with frothy fluid in the airways. Grossly visible nodules were observed from 10 days postinoculation. Granulomatous pneumonia and tracheitis were observed with light microscopy. Lesions were associated with merogonic and gametogonic stages of eimerian coccidia. Granulomas and granulomatous foci contained parasitized large mononuclear cells. Merogonic stages were seen in lymphoid cells by ultrastructural examination. Oocysts were observed in the trachea and bronchial mucosa and admixed with exudate in the airways, indicating that crane eimerians can complete their life cycle at these sites. Of the few eimeriid coccidia that have extraintestinal stages of development in birds and mammals, only the species in cranes complete their life cycle in both the digestive and respiratory tracts.     

Comparison of fecal glucocorticoid metabolite concentrations in hand- versus parent-reared whooping cranes (Grus americana)

Endangered whooping cranes (Grus americana) have been produced in captivity for reintroduction programs since the 1980s, using techniques such as artificial insemination, multiple clutching, and captive-rearing to speed recovery efforts. Chicks are often hand-reared (HR) by caretakers in crane costumes, socialized into groups and released together, unlike parent-reared (PR) cranes that are raised individually by a male/female crane pair and released singly. HR cranes historically exhibit greater morbidity rates during development than PR cranes, involving musculoskeletal and respiratory system disease, among others. We hypothesized that HR crane chicks exhibit a higher baseline fecal glucocorticoid metabolite (FGM) concentrations during the development compared with PR chicks. Fecal samples were collected between 15 and 70 days of age from HR (n = 15) and PR (n = 8) chicks to test for differences in FGM concentrations using a radioimmunoassay technique following ethanol extraction for steroids. Linear mixed model analysis suggests increasing age of the chick was associated with an increase in FGM (p < .001). Analysis also supported the interaction between rearing strategy and sex of the crane chick (p < .01). Female PR chicks had greater FGM concentrations than all other groups (PR male, p < .01; HR female, p < .001; and HR male, p < .001). This result suggests that there may be an effect of rearing strategy on stress physiology of whooping crane chicks, especially among females. Further research is needed to investigate whether the FGM concentrations are reflective of true differences in stress physiology of young cranes and whether this may impact health and conservation success.     

Breeding expansion of sandhill cranes in Quebec

Sandhill cranes (Antigone canadensis) were broadly extirpated from much of their historical range in North America at the beginning of the twentieth century. Various conservation-related legislation, such as the United States Migratory Bird Treaty Act, have assisted with population recovery. The eastern population of sandhill cranes has been growing rapidly since the 1980s and is thought to have expanded its geographic range to Quebec, Canada. Understanding the colonization and habitat use by the species in previously unoccupied breeding areas is necessary to develop and apply management measures. Using a dynamic occupancy modeling approach, we investigated the recent colonization and extirpation patterns of sandhill cranes in Quebec from 2004–2019. We combined data from 3 data sets (helicopter surveys, breeding bird atlas surveys, and eBird) to increase the spatial coverage and the number of species occurrence records while accounting for imperfect detection probability. Detection probability was highest for the helicopter survey (0.70), whereas the 2 other data sets had relatively low detection levels (0.10–0.26). Based on a simulation study, we found that excluding the eBird data from the analysis produced more biased estimates than excluding the atlas and helicopter survey data sets. Throughout the study, sandhill cranes seemed to have completed their colonization of western Quebec and only recently started to nest in eastern areas. Initial occupancy increased with wetland cover and colonization probability increased weakly with the cover of agricultural areas, suggesting that in our study area sandhill cranes rely essentially on natural wetlands during the breeding season.     

Plasma corticosterone concentrations in European robins during spring and autumn migration

To estimate differences in hormonal mechanisms of regulation of spring and autumn migration in European robins Erithacus rubecula, the plasma corticosterone (CORT) concentrations were compared in birds caught during both migratory seasons. A total of 414 blood samples were analyzed. It was found that the baseline and stress-induced CORT concentrations in free-living robins during spring migration were practically twice as high as during autumn passage. Our results demonstrate that autumn and spring migrations are independent stages of the avian annual cycle. Probably, the increase in the CORT concentrations in spring can be considered to be physiological preparation for the breeding season.     

Sperm head length as a predictor of fecundity in the sandhill crane, Grus canadensis.

Semen samples from 14 sandhill cranes were collected for 15 weeks. Mean sperm head length which did not vary significantly over weeks was found to be significantly correlated with fertility (P less than 0 . 04; r = 0 . 54, n = 14).     

Location and agricultural practices influence spring use of harvested cornfields by cranes and geese in Nebraska

Millions of ducks, geese, and sandhill cranes (Grus canadensis; hereafter cranes) stop in the Central Platte River Valley (CPRV) of Nebraska to store nutrients for migration and reproduction by consuming corn remaining in fields after harvest. We examined factors that influence use of cornfields by cranes and geese (all mid-continent species combined; e.g., Anser, Chen, and Branta spp.) because it is a key step to efficient conservation planning aimed at ensuring that adequate food resources are available to migratory birds stopping in the CPRV. Distance to night-time roost site, segment of the CPRV (west to east), and agricultural practices (post-harvest treatment of cornfields: idle, grazed, mulched, mulched and grazed, and tilled) were the most important and influential variables in our models for geese and cranes. Probability of cornfield use by geese and cranes decreased with increasing distance from the closest potential roosting site. The use of cornfields by geese increased with the density of corn present there during the early migration period, but field use by cranes appeared not to be influenced by early migration corn density. However, probability of cornfield use by cranes did increase with the amount of wet grassland habitat within 4.8 km of the field. Geese were most likely to use fields that were tilled and least likely to use fields that were mulched and grazed. Cranes were most likely to use fields that were mulched and least likely to use fields that were tilled, but grazing appeared not to influence the likelihood of field use by cranes. Geese were more likely to use cornfields in western segments of the CPRV, but cranes were more likely to use cornfields in eastern segments. Our data suggest that managers could favor crane use of fields and reduce direct competition with geese by reducing fall and spring tilling and increasing mulching. Moreover, crane conservation efforts would be most beneficial if they were focused in the eastern portions of the CPRV and in fields as close as possible to both known roosting and large amounts of wet grassland habitats. © 2011 The Wildlife Society.