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Sandhill Cranes are omnivorous, gleaning prey from the surface of the ground and capturing subsurface food by probing firm bottoms of lakes, and soft soils and mud with their bills (Walkinshaw 1949, 1973, Mullins and Bizeau 1978, Tacha 1987). They feed primarily on land or in shallow marshes with emergent vegetation, and often forage on waste grain in harvested fields, particularly during fall migration. Grit sites are important when cranes are feeding on waste grain.
Sandhill Cranes of the Mid-Continent Population spend 1.4% to 6.4% of their diurnal time searching for food, 0% to 17.1% gleaning surface foods, and 17.9% to 60.4% probing for subsurface foods (Tacha et al. 1987a). The frequency of these foraging activities does not vary among age, sex, or social classes, but juveniles spend 25% more time foraging than adults, and females 2% more time foraging than males. Adult pairs and family units spend 14% more time foraging than lone adults (Tacha 1987), presumably because solitary birds must constantly check for predators where birds in groups can partially rely on the vigilance of nearby birds (Krause and Ruxton 2002).
Opportunistic, omnivorous foragers that consume a variety of plant materials, small vertebrates, and invertebrates (Walkinshaw 1973, Mullins and Bizeau 1978, Ballard and Thompson 2000). Crane diet has likely changed substantially in the last century with the loss of natural prairie systems, substantial wetland drainage, and the development of large-scale agriculture. Crane’s exact diet varies considerably by season and location (Walkinshaw 1949, 1973), but cultivated grains are a major food item wherever available.
Details of Sandhill Crane’s diet are still poorly documented, except among hunted populations where funding is provided for research programs that will help inform management. Overall, animal prey comprises a low percentage of a crane’s overall diet (~5-10%), but is thought to be important in providing essential amino acids and calcium (Reineke and Krapu 1986). Animal prey includes insects, crayfish, earthworms, eggs and nestling birds, snakes, mice, and lemmings (Drewien 1973, Walkinshaw 1949, 1973, Bennett 1978, Mullins and Bizeau 1978, Reed 1988, Archibald and Lewis 1996).
Non-migratory subspecies eat insects and their larvae, snails, reptiles, amphibians, nestling birds, small mammals, acorns (Quercus spp.), berries, and tubers (Cyperus species, Hydrocotyle species, Nymphaea species, and Sagittaria species; SAN), and agricultural waste grains.
Among migratory populations, foods vary widely depending on what is available in various seasons and locations (Walkinshaw 1949, 1973). During breeding seasons, cranes consume primarily plant material, but have a diverse diet that is dependent on the breeding area of a given population and the nest-site location within that breeding area.
During breeding seasons in n. Michigan, cranes of the Eastern Flyway Population consume primarily berries and insects during summer. Diets of adults and young in se. Wisconsin include invertebrates and some small mammals and reptiles during early brood rearing. Non-breeding adults in se. Wisconsin eat mostly tubers of aquatic plants in spring and early summer, and cultivated grains in late summer (Walkinshaw 1973).
G. c. tabida of the Rocky Mountain Population consume 73% plants by total volume, and 27% insects and earthworms (Mullins and Bizeau 1978). Mullins and Bizeau (1978) found Sandhill Cranes eating primarily corn and insects during summer in Idaho. In Alaska, breeding cranes eat assorted berries and small mammals during the breeding season (Walkinshaw 1949). Cranes approaching breeding areas eat mostly tubers (Cyperacesae species) and gastropods (Iverson et al. 1982).
Sandhill Cranes of the Central Valley Population feed on mostly plant material along beaches with abundant cover of rockweed (Fucus species) and among salt marsh with sedges (Carex species), mudflats, and Pacific silverweed (Potentilla anerina pacifica; Roessingh and Penn, 2010).
Waste grains from agricultural crops, such as corn, barley, and wheat are the most important source of energy during migration and wintering (Stephen 1967, Lockman et al. 1987, Walker and Schemnitz 1987, Clark and Sugden 1990, Iverson et al. 1987, Tacha et al. 1985a; Appendix 2). Cranes of the Mid-Continent Population staging along the Platte River Valley in Nebraska and consuming agricultural grains increase body mass by 17% and 20% for adult females and males, respectively, during fall migration (Krapu and Johnson 1990) and by 30% and 34%, respectively, during spring migration (Krapu et al. 1985). However, there is likely significant variability in the rate cranes increase body mass due to arrival to the staging area, food availability, local weather, competition with migratory waterfowl, and the number of cranes in the area (Krapu and Johnson 1990).
Agricultural grains comprise most of the diet of cranes wintering in Texas, except for those in the South Texas Plains where cranes predominately eat nut-grass, chufa (Cyperus species), and tubers (Guthery 1975b, Ballard and Thompson 2000). Cranes wintering in the Gulf Coast of Texas at the Aransas National Wildlife Refuge consume high quantities of acorns and wolfberry, which are high in important ascorbic acids, iron, calcium, and essential amino acids not available in grain crops (Hunt and Slack 1989). How cranes in other wintering areas obtain these nutrients has not been identified.
Diets during migration and wintering are roughly similar among age, sex, and social classes (Reineke and Krapu, 1986, Ballard and Thompson 2000). One comparison found cranes feeding in cornfields consume >99% corn while cranes feeding on native grasslands and alfalfa fields consume 79 to 99% invertebrates (Reineke and Krapu 1986). In Texas, winter diet includes 5% animal matter. Wintering G. c. canadensis of the Mid-Continent Population in n. and central Mexico consume many grains, especially corn (Llanes 2012). These birds’ corn consumption is consistent despite changing availability, suggesting preference or specialization; instead of switching diets, cranes moved when corn availability became low (Llanes 2012). While not easily quantified, Sandhill Cranes wintering in New Mexico also consume below-ground foods, often in flooded areas; in one study chufa (Cyperus esculentus) was most consumed (Taylor and Smith 2005).
Nutrition And Energetics
Animal matter is important in crane diet, presumably because it provides essential amino acids and calcium rarely available in grain (Reineke and Krapu 1986). Protein content of adult cranes of the Mid-Continent Population varies little throughout the year (Iverson 1981, Krapu et al. 1985). Lipid reserves, an index to body condition, do vary however. These were measured in Mid-Continent Population cranes prior to fall migration from Last Mountain Lake, Saskatchewan, and again throughout their migration. Levels varied dramatically at key times of year, with the lowest levels occurring in mid-Aug, suggesting a period of relatively poor physical condition (Tacha et al. 1985a). By later in the fall, individuals gained an average 9 g lipid/d while eating high-energy grains. Lipid levels did not vary from when cranes departed Saskatchewan, through staging in Oklahoma and wintering in w. Texas, to spring arrival at stopover sites in Nebraska (Iverson 1981, Tacha et al. 1985a, 1987a). Individuals deposited an average 12.8 g lipid/d while in Nebraska and maintained these lipid levels through spring migration while crossing Saskatchewan and central Alaska to nesting areas in w. Alaska. They then lost 4 g/d during pre-nesting (Iverson 1981, Krapu et al. 1985, Tacha et al. 1987a).
The accumulation of lipids during fall in Saskatchewan and spring in Nebraska was possible because high-energy food resources (grain) were concentrated and accessible (Tacha et al. 1987a). Lipids levels were maintained during later stages of spring migration through regular stops at grain fields along the migratory route. Losses of lipids during pre-nesting were due to increased energy expenditures associated with low food availability, territorial defense, and egg production. Krapu et al. (1985) hypothesized that availability of cultivated grain allows cranes of the Mid-Continent Population to transport maximum lipid levels to nesting areas. Once there, lipids are used for early reproduction, allowing increased productivity compared to pre-agricultural development in the Great Plains and Alaska.
While protein is necessary for normal growth and maintenance, too much of it during development can cause skeletal abnormalities (Nairn and Watson 1972, Hedhammar et al. 1974, Serafin 1982). An experiment involving chick-rearing of G. c. tabida and G. c. pratensis found G. c. tabida grew faster on a high protein diet (32% by volume), but were afflicted by leg disorders (17%) and abnormal wing development (25%). G. c. pratensis grew more slowly than G. c. tabida, regardless of diet, but developed no abnormalities on a high protein diet.
Sandhill Cranes drink water with salinities up to 20 ppt (Haley 1987) by submerging the lower mandible to fill the beak, then raising the head to swallow (Tacha 1988). About 0.2% of daily time budgets are spent drinking. This does not vary among age, sex, or social classes.
Gerber, Brian D., James F. Dwyer, Stephen A. Nesbitt, Rod C. Drewien, Carol D. Littlefield, Thomas C. Tacha and Paul A. Vohs. 2014. Sandhill Crane (Grus canadensis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/031