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Single-brooded. Earliest eggs in nonmigratory populations. In Florida, first eggs as early as Dec but usually Jan (Walkinshaw 1973); can be as late as Aug (Bent 1926). Average laying dates for south central Florida 22 to 24 Feb (Walkinshaw 1982); mean laying date in north central Florida 3 Mar (SAN).
Renesting, up to 3 times/yr, noted in Florida; average interval between clutches 19.5 d (Nesbitt 1988). Renesting in G. c. tabida only among pairs that lose nests during the first half of the incubation period; interval between clutches for one pair was 15 d (Drewien 1973).
In migratory populations, mean nest initiation dates range from early Apr to late May (Walkinshaw 1973). Boise (1976) reported hatch dates in Alaska as 27 May to 1 Jun; 16 Jun the average hatch date for Banks Island, N.W.T. (Walkinshaw 1973).
Not known which sex (if any) controls nest site selection. In Florida, regardless of sex, the surviving member of a broken pair retains previous nesting area, even with new mate (SAN).
In Mississippi, water distribution and levels influence nest site selection within an area of apparently homogeneous habitat (Smith and Smith 1988). Sites chosen are usually marshes, bogs, or swales; may abut open water or constitute small, isolated wetlands. Nests in expansive wetlands are usually near (≤ 300m) the edge. Throughout most of the species’ range the presence of standing water with emergent aquatic vegetation is an important characteristic of the site. Water depth under active nests has ranged up to 99.1 cm for nests built over open water (Thompson 1970). Mean water depth at 100 central Florida nests: 26.7 cm (Dwyer 1990); at 110 nests in s. Michigan: 21.2 cm (Walkinshaw 1973); at 187 Idaho nest sites: 20.0 cm (Drewien 1973); at 274 Oregon nests: 18.0 cm (Stern et al. 1987).
Although cranes typically nest over water (attached or floating nests), they will nest on dry ground (Layne 1982a), particularly G. c. nesoitis and arctic-nesting canadensis (Walkinshaw 1973, Drewien 1973, Valentine 1982, Nesbitt 1988). Cuban cranes nest on nearly level, dry land sparingly grown to grasses (Walkinshaw 1973), with nearby vegetation of scattered tropical pines (Pinus tropicalis), palmettos (Acoelorraphe wrightii), and bushes. In Mississippi, nut-rush (Scleria baldwinii) is a key indicator species (Valentine 1982). Cattails and sedges (Carex spp. and/or Scirpus spp.) predominant in s. Michigan; in the upper peninsula 12 of 13 nests were in sphagnum (Sphagnum spp.) bogs (Walkinshaw 1973). Idaho nests usually in Juncus balticus and Carex spp. (Drewien 1973). Oregon nests typically in stands of burreed (Sparganium eurycanpum) and hardstem bulrush (Scirpus acuta, Littlefield and Ryder 1968). Alberta nests in open sedge marshes (Carlisle 1982). Alaska nests in Sphagnum sp. and/or various grasses and sedges (Boise 1976). Nests on Banks Island and other areas of n. Canada and Alaska in dunes 3 to 10 m high, completely dry with scattered dune grasses, or in marshes dominated by sedges and grasses (Walkinshaw 1973).
Structure And Composition Matter
Nests constructed of the dominant surrounding vegetation. Larger material forms the foundation, with a distinguishable egg cup formed and lined with smaller stems or twigs. Early in the nesting season, birds use dried residue of the preceding season’s growth; later in the season, green material used. Nests in dry sites have minimal construction, no egg cup. Both sexes participate; construction may last 1 d to 2 wk (Littlefield and Ryder 1968). Birds collect nest material from the immediate surroundings and toss it over their shoulder, eventually forming a mound. One bird, usually the female, stands on the mound and arranges the material.
Nest size varies with substrate; those built over standing water are considerably larger than dry-site nests. Nest measurements vary from 113 x 98 cm (Walkinshaw 1973) to 86 x 80 cm (Drewien 1973) usually built up 10 to 16 cm above the surface.
Throughout incubation, the sitting bird may add small amounts of material and continually rearrange the nest. The nest may adjust (float) to slight increases in water level. The birds may also compensate for small increases in water levels by adding material to the nest. A nesting territory usually has several potential nesting sites that may be used. Changing water levels cause a pair to select a new site for renests. Successive nests (within or between seasons) are usually near each other if water levels permit; the average distance between within-season renestings is 183 m (n = 6); use of the same nest for a subsequent renesting has occurred (Dwyer 1990).
Unfinished nest foundations or alternate nest starts often occur near active nests. The foundation may represent an abandoned site or an intentional addition to the “nest area” that provides several elevated platforms for brooding and feeding the young.
Sub-elliptical to long oval; average size 93.1 x 59.1 mm; average weight 161.2 g, with variation among subspecies and regions. Shell thickness ranges from 0.397 mm for G. c. pratensis to 0.550 mm for G. c. canadensis (Baldwin 1977). Color variable but generally pale brownish buff to light olive, irregularly marked with darker brown, reddish brown, or pale gray. White, unpigmented eggs reported (Radke and Radke 1988). Surface semi-glossy to flat and smooth to irregularly grainy, grain size sometimes quite large. Clutch size 1 to 3; mode is 2, mean from several populations and subspecies is 1.90, range 1.76 (Boise 1976) to 1.98 (Walkinshaw 1973). Eggs are normally laid at 2-d intervals (Littlefield and Ryder 1968, Drewien 1973).
Canada Goose (Branta canadensis), Trumpeter Swan (Cygnus buccinator), and Canvasback (Aythya valisineria) known to lay eggs in Sandhill Crane nests (Littlefield 1979, 1984; Drewien 1973); in some cases the cranes may have usurped the nest of the other species. Sandhill Cranes may parasitize each others nest (Littlefield 1981a) and those of Whooping Cranes (Kuyt 1989). Rare 3-egg clutches may be the result of dump nesting (Littlefield 1981a).
Begins with laying of first egg and continues either until the second egg hatches or it is abandoned (2 or 3 more d). Cranes will continue to incubate an addled or infertile clutch for 10 to 15 d beyond the normal incubation period (Nesbitt 1988). An incubation patch develops in both sexes on each side of the sternum. Mode incubation period is 30 d, mean 30.2, range 29 to 32, n = 14 (Drewien 1973). Males and females share incubation duties equally during daylight hours; females primarily at night, and thus about 70% of the total incubation (Littlefield and Ryder 1968, Drewien 1973, Walkinshaw 1985, Nesbitt 1988). Nests usually attended constantly. In Florida, incubating bird may occasionally leave nest unattended for periods ≤1 h during cooler parts (morning or evening) of the day. Nest exchanges occur several times during the day. During mid-day, the non-incubating bird may be found loafing near the nest, but may roost away from the nest at night.
During incubation, the non-incubating bird is more secretive than usual, even when not near of the nest. If disturbed, they often crouch rather than walk or fly away.
Viability of eggs improves after 2 wk of natural incubation. By the last week of incubation eggs can survive periods of neglect, provided they are not exposed to heat of the day or direct sun (SAN).
Ten to 39 h before pipping, the inner membrane (air cell) is broken and the chick begins to vocalize (Archibald and Viess 1979, Hartman et al. 1987). Hatchlings produce 3 distinct calls during pipping; the Contact call, Pipping call, and Stress call (Voss 1976). Parent gives purrs during the later stages of incubation, perhaps in response to or as stimulus to hatching. Within 20 h after pipping, the chick begins rotating counter-clockwise and breaks the shell (Hartman et al. 1987). An average of 7.3 h elapses between the beginning of rotation and emergence. Mean period between the first break in the shell (pipping) and emergence is 26.5 h (range 11 to 48 h; Archibald and Viess 1979, Hartman et al. 1987). In a 2-egg clutch, the eggs hatch at 1-d intervals (Walkinshaw 1973, Drewien 1973).
Slow-to-emerge young may receive some prodding and assistance with shell breaking from the parents. Upon emergence, parents may offer the chick small pieces of the shell and/or consume some of the shell themselves. They may also carry the shell and membrane away from the nest (C. B. Kepler and P. W. Sykes Jr., pers comm.). Some fragments and occasionally large pieces of shell and the membrane may be left at the nest.
Condition At Hatching
Nidifugous (leave nest soon after hatching); down dries 2 to 3 h after hatching, eyes are open, young sit up on tibiotarsi, may stand feebly. Shortly afterward they stand well and within 24 h after hatching are able to leave the nest. Mean weight for 15 G. c. tabida chicks at hatching was 114.2 g, bill length 22.7 mm, tarsus 44.2 mm, wing cord 33.7 mm (Walkinshaw 1973).
Growth And Development
Chicks begin feeding within 24 h of emergence. G. c. tabida chicks (n =13) 1.0 to 1.5 d after hatching increase body mass by an average of 1.9 g, bill length by 1.2 mm, tarsus length by 3.7 mm, and wing cord length by 1.7 mm (Walkinshaw 1973). By 12 to 13 d of age, 3 G. c. tabida chicks from Idaho averaged 315 g (Drewien 1973). By 20 to 30 d of age, young have acquired about half of their adult leg and wing length; mass increases more slowly (Baldwin 1977). Thirty-five days after hatching, G. c. tabida and pratensis have increased body weight 14.0 to 14.5 times; rowani and canadensis 17 times (Archibald and Viess 1979); 40 d after hatching, legs are almost full grown; by 60 d, bill and wings are almost adult size (Baldwin 1977). Growth not complete until 10 mo of age (Tacha et al. 1985b). The 2 smallest, most northerly nesting subspecies (G. c. rowani and canadensis) develop the fastest, while eastern tabida and pratensis (more southerly nesters with the longest nesting seasons), develop the slowest (Baldwin 1977).
The acquisition of homeothermia (warm-bloodedness) is correlated with nesting range. G. c. pratensis (and presumably pulla and nesiotis) are poikilothermic at hatching (cannot regulate their body temperature), requiring ± 24 h to become fully homeothermic, G. c. tabida are heterothermic (partially able to regulate body temperature) at hatching and fully homeothermic after ± 9 h; G. c. rowani and canadensis are homeothermic when hatched (Baldwin 1977).
By 8 h after hatching, young can leave the nest and swim, if necessary (Walkinshaw 1973). Male sometimes leads first-hatched young away from nest within 24 h; more often, it leaves with the second-hatched (Drewien 1973). Area used by a pair with young is restricted to within a few hundred feet of the nest for the first 10 d or 2 wk after hatching (Drewien 1973). Range increases daily, and may encompass the total defended territory by fledging.
Siblings aggressive and conflicts frequent, ending only when a dominant individual emerges (Drewien 1973, Layne 1982b). Sibling aggression may be one reason why even though cranes typically lay 2 eggs, only 1 is usually raised (Miller 1973). Aggressiveness mediated by food (Quale 1976); more pairs raise 2 young in years of abundant food. Intense sibling aggression begins within 2 d of hatch, wanes after 3 mo (Miller 1973, quoting R. C. Erickson pers comm.).
Young brooded intensively after hatching, principally by female (Walkinshaw 1973). Frequency and duration of brooding decline as young age; brooding infrequent 2 to 3 wk after hatch.
Both parents feed young (Walkinshaw 1973). During the first 10 d or so after hatching chicks are mainly fed bill-to-bill by parents. Food items too large for a chick to take whole (particularly animal items) may be broken by a parent and fed in pieces, young are primarily self-feeding when about half grown. Food items may be dropped at their feet by adults leading them to feeding opportunities. Food begging by young continues sporadically until independence; occasionally parents will offer food to the chick, even without begging (Tacha 1988). These behaviors may reinforce the parent/offspring bond rather than provide nutrition.
Adults do not defecate at the nest (Walkinshaw 1973). Young leave the nest soon after hatch, so post-hatching nest sanitation not needed.
Parental Carrying Of Young
Though chicks may be brooded on the back, parental carrying of young has not been reliably documented.
Not known to occur.
Not known to occur.
Young remain with their parents (usually within a few meters) until 9 to 10 mo of age (Tacha 1988); independence usually occurs 30 to 60 d before parents’ next clutch. In G. c. pratensis, mean age of independence is 295 d, (range 248–321 d, n = 16; Nesbitt 1992). Juveniles begin associating within a subadult/nonbreeder flock soon after leaving their parents. They remain in these flocks until pairing begins.
After first flight, young are soon strong fliers and may begin migration with parents only days later. Though young can care for themselves, they still depend on parents for feeding opportunities and protection from aggressive (territorial) conspecifics and predators (Tacha 1988). Sub-adults are the most mobile social class and are generally more nomadic and gregarious than adults (Nesbitt and Williams 1990).