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Breeding pairs establish territories 2-4 wk prior to building a nest and laying eggs (Drewien 1973). Earliest eggs are laid by individuals in non-migratory populations. In Florida, eggs are laid as early as December and as late as August (Bent 1926), though most eggs are laid Jan to May (Walkinshaw 1973, Nesbitt 1988). Average laying dates are 22 to 24 Feb in s.-central Florida and 12 Mar in n.-central Florida (Walkinshaw 1982). Estimated laying date by flightless individuals undergoing molt in late summer in Florida from 1972 – 2009 averaged 9 Jun; all were likely re-nestings (M. Folk. pers. comm.).
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 with a 16 Jun average hatch date for Banks I., Northwest Territories (Walkinshaw 1973). At Malheur National Wildlife Refuge, Oregon, nesting begins in early Apr, with peak nest initiation occurring about 21 Apr (Littlefield 1990; range = 25 Mar to 18 Jun). At other Great Basin nesting sites in e. Oregon, eggs are laid between mid-Apr and early May, and in late Apr to late May in mountainous regions (Littlefield 1999a). In ne. California, egg-laying begins in mid-Apr (earliest 11 Apr) with most in late Apr (latest 11 May), although one chick found on 9 Aug must have hatched between 15-21 Jun (Littlefield 1995a).
Renesting can occur up to 3 times/yr, as noted across the species’ range from Florida to the Sycan Marsh National Wildlife Refuge in Oregon (M. Stern pers. comm.), and Grays Lake, Idaho. The average interval between clutches is 19.5 d in Florida (Nesbitt 1988). Renesting in G. c. tabida is known only among pairs that lose their nests during the first half of the incubation period with an interval between clutches for one pair of 15 d (Drewien 1973). More recently, 2 pairs of the Rocky Mountain Population were observed renesting after losing hatched young < 1 wk old (RCD).
A nesting territory usually has several potential nesting sites that may be used. Which sex, if either, controls nest site selection is unknown. In se. Oregon, G. c. tabida males frequently initiate nest construction, but females rarely use a site the male selects. Once a nest site is selected, one bird, usually the female, stands on the nest mound and arranges nest material provided by both birds. Unfinished nest foundations or alternate nest starts often occur near active nests. These may represent an abandoned site or an intentional addition to the “nest area” that provides several elevated platforms for brooding and feeding the young. Most extra nest platforms are built by males (RCD). In Florida, Idaho, and Oregon, regardless of sex, when one member of a breeding pair dies, the surviving member retains the nesting territory with a new mate (Nesbitt and Tacha 1997, RCD).
In Michigan, G. c. tabida select nest sites in or near seasonally flooded emergent (non-woody) wetlands, while avoiding forested uplands (Baker et al. 1995). In Mississippi, water distribution and levels influence nest site selection within an area of otherwise apparently homogeneous habitat (Smith and Smith 1988). Sites chosen are usually marshes, bogs, or swales. These sites may abut open water or exist in small, isolated wetlands. Nests in expansive wetlands are usually within 300 m of the edge. The mean distance between nests in emergent vegetation and open meadows at Malheur National Wildlife Refuge, Oregon was 40 m (range = 0 to 345 m, n = 515; Littlefield 2001b).
Throughout most of the species’ range, the presence of standing water with emergent aquatic vegetation is an important characteristic of the nest site. Measured water depths under active nests have ranged up to 99.1 cm for nests built over open water (Thompson 1970). Mean water depth was 26.7 cm at 100 nests in central Florida (Dwyer 1990), 21.2 cm at 110 nests in s. Michigan (Walkinshaw 1973), 20.0 cm at 187 Idaho nests (Drewien 1973), 18.0 cm at 274 nests at the Sycan National Wildlife Refuge in Oregon (Stern et al. 1987), and 25.8 cm (range = 0 to 105 cm) for 881 nests at Malheur National Wildlife Refuge in Oregon (Littlefield 2001b).
Although cranes typically nest over water in either attached or floating nests, they will also nest on dry ground (Layne 1982a), particularly G. c. nesiotes and arctic-nesting G. c. canadensis (Walkinshaw 1973, Drewien 1973, Valentine 1982, Nesbitt 1988). G. c. nesiotes nest on nearly level, dry grasslands (Walkinshaw 1953, Walkinshaw 1973, Aguilera et al. 2005), with nearby vegetation of scattered tropical pines (Pinus tropicalis), palmettos (Acoelorrhaphe wrightii), and bushes. The height and density of vegetation increases further away from G. c. nesiotes nests (Ferrer Sanchez et al. 2010). In Mississippi, nut-rush (Scleria baldwinii) is almost always found near nests, such that it could be used as an indicator of potential crane nesting (Valentine 1982). Cattails and sedges (Carex species and/or Scirpus species) are predominant around nests in s. Michigan; in the Upper Peninsula 12 of 13 nests were in sphagnum (Sphagnum species) bogs (Walkinshaw 1973).
Rocky Mountain Population G. c. tabida nesting in Idaho usually nest in grassy areas that include Juncus balticus and Carex species (Drewien 1973). Oregon nests are typically in stands of bur-reed (Sparganium eurycanpum) and hardstem bulrush (Scirpus acuta; Littlefield and Ryder 1968, Littlefield 2001b). Alberta nests are in open sedge marshes (Carlisle 1982). Alaska nests are in Sphagnum species or various grasses and sedges (Boise 1976). Nests on Banks I. and other areas of n. Canada and Alaska are in sand dunes 3 to 10 m high, completely dry with scattered dune grasses, or in marshes dominated by sedges and grasses (Walkinshaw 1973, Reed 1988).
Structure And Composition Matter
Generally construct nests in water where floating piles of aquatic vegetation, grass, mud, sticks, and moss separate vulnerable eggs and chicks from terrestrial predators (Lewis et al. 1977; see Behavior). In emergent aquatic sites, cranes collect nest material from the immediate surroundings and toss it over their shoulder, eventually forming a mound at the site with a characteristic vegetation-free “pluck-zone” surrounding the nest. 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 the dried residue of the preceding season’s growth to initiate nest construction. Later in the season, green material is added to the nest. When nesting occurs on dry ground, nests have minimal construction and no egg-cup. Regardless of the substrate, both sexes participate in construction that may last 1 d to 2 wk (Littlefield and Ryder 1968).
Nest size varies with substrate; nests built over standing water are considerably larger than nests built on dry sites. Floating nests are usually built up 10 to 16 cm above the water surface, with birds compensating for small increases in water levels by adding material to the nest. Length and width measurements vary from 98 x 113 cm in Michigan (Walkinshaw 1973), to 111 x 127 cm in Oregon (Littlefield 2001b), and 80 x 86 cm (SD = 31x36) in Idaho (Drewien 1973).
Throughout incubation, the sitting bird (particularly males) may add small amounts of material and continually rearrange the nest. The nest may adjust (float) to slight increases in water level, but pairs may select a new site for renesting if water levels change substantially. Successive nests in Oregon (within or between seasons) are usually near each other if water levels permit. The average distance between within-season renesting is 183 m (n = 6) (CDL), though use of the same nest for a within-season renesting also occurs (Dwyer 1990). Mean distance between first nests and renests in Idaho was 148 m (SD = 131, range 33-351 m, n = 4; Drewien 1973).
Sub-elliptical to long oval; average size 93.1 x 59.1 mm; average mass 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 is variable but generally pale brownish buff to light olive, irregularly marked with darker brown, reddish brown or pale gray. White, unpigmented eggs have also been reported (Radke and Radke 1988). The egg surface is semi-glossy to flat and smooth to irregularly grainy, with grain size sometimes quite large. Individual females consistently lay eggs similar in coloration, pattern, and size across years, which can enable researchers to identify when a new female has occupied a traditional territory (CDL).
Sandhill Cranes lay 1-3 eggs per clutch, at 2-d intervals (Littlefield and Ryder 1968, Drewien 1973), with a mode of 2 eggs and a mean from several populations and subspecies of 1.90, range 1.76 (Boise 1976) to 1.98 (Walkinshaw 1973). Smaller clutch sizes are more common in northern breeding populations (Nesbitt 1989, Tacha et al. 1994). One 4-egg clutch produced by a G. c. tabida was observed in Oregon (Littlefield and Holloway 1987).
Incubation begins with laying of the first egg and continues until the second egg hatches or is abandoned (usually 1 or 2 d after hatching of first egg). Cranes will continue to incubate an addled or infertile clutch 10-15 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 29-32, n = 14, Drewien 1973).
Males and females share incubation duties equally during daylight hours, but only females incubate at night; thus females perform about 70% of the total incubation (Littlefield and Ryder 1968, Drewien 1973, Walkinshaw 1985, Nesbitt 1988). Nests are usually attended constantly. Throughout the species’ range in the contiguous U.S., incubating birds may occasionally leave the nest unattended for periods ≤1 h during cooler parts of the day (morning or evening), or depart briefly if the mate is late arriving for nest exchange. Nest exchanges occur several times during the day. If the male does not arrive within 2 h before sunrise the female often does not return to relieve him until evening (CDL).
Studies in Idaho of individually marked G. c tabida of the Rocky Mountain Population revealed nest attentiveness was related to the age of breeding individuals. Older, more experienced breeders were more attentive, rarely leaving nests unattended. In contrast, younger individuals more frequently left nests unattended for extended periods (RCD). During mid-day, the non-incubating bird may be found loafing near the nest, but usually roosts away from the nest at night.
Early in incubation eggs can survive only brief cooling (snow with low wind-chill factor; RCD, CDL). The tolerance of eggs to temperature fluctuations improves after 2 wk of incubation. By the last week of incubation, eggs can survive longer periods of neglect, provided they are not exposed to the heat of the day or direct solar radiation, and have not yet pipped (SAN, CDL, RCD).
Up to 72 h before hatching, parents give Purrs (see Sounds) in response to young vocalizing in the egg; this may help stimulate hatching (Archibald and Viess 1979, Hartman et al. 1987). Hatching begins with pipping where the young bird breaks the egg from inside. Hatchlings produce 3 distinct calls during pipping; the Contact Call, Pipping Call, and Stress Call (Voss 1976; see Sounds). The older embryo’s calls are believed to stimulate the younger embryo to begin pipping. Thus, the second egg frequently hatches after 29 d of incubation, not the usual 30 d.
Within 20 h of pipping, the chick begins rotating counter-clockwise and breaks the shell (Hartman et al. 1987). An average of 7.3 h elapse 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 one-day intervals (Walkinshaw 1973, Drewien 1973).
Parents may help break the shell of hatchlings when hatching is protracted. Upon emergence, parents may offer the chick small pieces of the shell and/or consume some of the shell themselves. Parents commonly carry the shell and membrane away from the nest (CDL, RCD, and C. B. Kepler and P. W. Sykes Jr., pers. comm.), though some fragments and occasionally large pieces of shell and the membrane may remain.
Condition At Hatching
Hatchlings are nidifugous (leave nest soon after hatching). Their down dries 2 to 3 h after hatching, by which time their eyes are open, they can sit up on their tibiotarsi, and sometimes even stand feebly. Shortly afterward they stand well. If necessary, young can leave the nest on foot or by swimming within 8 h after hatching (Walkinshaw 1973). More often, young leave the nest within 24 h of hatching. 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 acquire about half of their adult leg and wing length, though mass increases more slowly (Baldwin 1977). Thirty-five days after hatching, G. c. tabida and G. c. pratensis increase body weight by 14.0 to 14.5 times; G. c. rowani and G. c. canadensis by 17 times (Archibald and Viess 1979); 40 d after hatching, legs are almost full-grown and by 60 d, bill and wings are nearly adult size (Baldwin 1977). Growth is not complete until up to 10-12 mo of age when birds reach adult mass (Walkinshaw 1949). In yearling G. c. pratensis, adult mass can be attained at about 270 d, more than 6 mo after long bone growth is completed (Nesbitt et al. 2008b).
The two most northerly nesting subspecies (G. c. rowani and G. c. canadensis) develop the fastest, while G. c. tabida and G. c. pratensis (more southerly nesters with the longest nesting seasons) develop more slowly (Baldwin 1977).
The acquisition of homeothermia (warm-bloodedness) is correlated with nesting range. G. c. pratensis (and presumably G. c. pulla and G. c. nesiotes), the three non-migratory populations, are poikilothermic at hatching (cannot regulate their body temperature). These subspecies require about 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 G. c. canadensis are homeothermic when hatched (Baldwin 1977). These data were collected from limited locations within the subspecies’ range. A broader sampling might indicate range related differences to be greater than subspecies differences. For example, more northerly nesting birds of all subspecies may be the most quickly homeothermic.
Young are brooded intensively after hatching, principally by the adult female (Walkinshaw 1973). Chicks may be brooded on the back or under the wings (especially in northern populations), and if the parent stands and begins walking chicks may remain in place to be briefly transported, but extensive parental carrying of young does not occur. The frequency and duration of brooding declines with age, such that brooding is infrequent 3 wk after hatching (longest 23 d; CDL).
Both parents feed young (Walkinshaw 1973) and generally keep them separated, perhaps to reduce sibling aggression, but perhaps also to minimize the likelihood that one predator could get both chicks. 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 become more self-feeding after half grown. Food items may be dropped at the feet of young by adults leading them to feeding opportunities. Food begging by young continues sporadically until independence, although occasionally parents will offer food to the chick, even without begging (Tacha 1988). These behaviors may be more socially (parent/chick bond) or physiological (hormonally stimulated) than nutritionally necessary.
Adults do not defecate at the nest (Walkinshaw 1973). Young leave the nest soon after hatch, so post-hatching nest sanitation does not occur.
Parental Care For Young
Perhaps because chicks are aggressive toward each other (see Behavior), when 2 chicks hatch, each is tended separately by one adult. Typically, but not universally, within 24 h of hatching the adult female leaves with the first hatchling, and the adult male leaves with the second (Drewien 1973). For the first 10-14 d after hatching, the area used by a pair with young is restricted to within ca. 200 m of the nest (Drewien 1973). Range increases daily, and by fledging may encompass the total nesting territory.
Not known to occur.
Thought to be generally uncommon, although inter- and intra-specific nest parasitism has occurred (Littlefield 1981c, Littlefield 1984).
Fledging usually occurs at 7 wk for G. c. canadensis. G. c. tabida of the Rocky Mountain Population fledge at 9.5-10 wk (Drewien 1973, Boise 1979). Juveniles generally remain with the parents for 9-10 mo, from nesting through fall migration, wintering and the first spring migration (Tacha et al. 1989, Drewien et al. 1999, see Behavior). In captive-reared young, mean age of first flight 53.4 d ± 2.4 SD (n = 32 (means ranged from 50.6 d for G. c. canadensis to 56.4 d for G. c. pratensis; Baldwin 1977). First flight in the wild is at 66 d for G. c. tabida (Oregon, CDL), and up to 75 d for G. c. pratensis (SAN) and G. c. tabida (Idaho, Drewien 1973).
Young become strong fliers soon after first flight. Though young can care for themselves, they still depend on parents for feeding opportunities and protection from aggressive (territorial) conspecifics and predators (Tacha 1988; see Behavior). Independence usually occurs during the first spring migration, or 30 to 60 d before the parents’ next clutch. In G. c. pratensis, mean age of independence is 295 d, (range 248–321 d, n = 16; Nesbitt 1992a). Young Sandhill Cranes begin associating with their peers in a non-breeding flock soon after leaving their parents (see Behavior), provided this opportunity exists. Young birds remain in these flocks until pairing begins. In G. c. tabida, yearlings will remain in pre-breeding flocks during their 2nd summer, but these groups rarely persist during migration or over winter. Yearlings 12-15 mo old do not pair in these summer flocks (RCD). Young non-breeders are the most mobile social class and are generally more nomadic and gregarious than adults (Nesbitt and Williams 1990).
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