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The calls of Sandhill Cranes are described as trumpeting, bugling, rattling, or croaking, but these adjectives do not fully convey the volume or quality of the sound produced by a mature Sandhill Crane. Several physiological adaptations enable cranes to vocalize as they do. These include tracheal elongation and coiling (see diagrams in Gaunt et al. 1987), tracheal reverberations with the sternum, and enlargement of the syrinx, the focal organ located at the base of the trachea (Gaunt et. al 1987, Klenova et al. 2007, Niemeier 1979).
Tracheal elongation and coiling into the sternum is an anatomical feature of all species of the genus Grus, and of some members of the closely related genus Anthropoides. The elongated trachea of cranes allows them to manipulate their formant frequency (frequencies at which the air vibrates or peaks of acoustic energy in a frequency spectrum) such that vocalizations are not typical of an animal of the cranes’ size, but of that of a larger bird (Fitch 1999). Tracheal elongation and subsequent manipulation of formant spacing may also provide acoustic indicators of individuals, and of a bird’s sex, sexual maturity, and age (Fitch and Kelly 2000). This information, if communicated, may help birds distinguish high quality mates. Since formant frequency dispersion is inversely related to body size or trachea length, it can also be used by researchers and managers to identify subspecies (Jones and Witt 2012).
Deliberate shortening of the trachea dramatically reduces the intensity (loudness) of a vocalization (Gaunt et al. 1987). Simultaneous tracheal coiling reduces the intensity even further, allowing cranes to moderate the intensity of their calls. Cranes can also adjust the pitch of their calls by moderating airflow through the syrinx (Goller and Suthers 1996). The syrinx allows cranes to generate low frequencies (Fitch, 1999) that travel further and with less distortion when produced among dense vegetation (such as occurs at a nesting site).
Beginning a day or so preceding pipping and continuing until about 9 to 10 mo of age, young cranes produce three distinct calls: Pipping Calls, Contact Calls, and Stress Calls (Voss 1976). The Pipping Call is made up of trills and peeps and is the first call to develop. The Contact Call can be described as a yelp, consisting of 3 or more high-pitched, broken notes and a sustained following note. The Stress Call consists of loud rapid slurred notes covering a wide frequency range, and lasting <5 s (Nesbitt and Bradley 1997). The change to the Unison and Guard Rattle calls of adults is preceded by a protracted process of tracheal elongation and intra-sternal coiling concurrent with the first uses of Purrs. The adult voice is acquired thereafter at about 10 mo (Tacha 1988).
Very young cranes produce Trills and Peeps. Adult calls are more varied, but fit in 3 categories: soft Purrs, loud Rattle Calls, and other calls, which together may exceed a dozen vocalizations.
Trills and Peeps. The first vocalizations to develop. The pre-hatching Trill is slow, with a lower fundamental frequency than those given later. Trills continue as contact calls after hatching, sounding like a steady trill lasting 0.2 to 0.4 s, and given 1-2/s. The Peep is a short, sharp stress call, first heard during pipping. Peeps are loud ascending calls lasting about 0.2 s, and given 1/s. Peeps are comparatively low frequency and given only during pipping. Chicks also produce a food-begging Peep given about 3/s and first heard ≤ 2 d hatching.
Purrs. Various Purrs are given in many situations (e.g., pre-flight, feeding, aggression). They are low amplitude, low intensity, and used for short distance communication within a flock or family group. In adults, Purrs are 4 to 12 muffled click-like sounds delivered at a rate of 12-20/s (Nesbitt and Bradley 1997). The Flight Intention Purr is a 2-part call with a rising inflection given during a preflight behavior (e.g., wing flapping, leaping; Tacha 1984) and immediately prior to an unforced flight (Voss 1976). It is not given when startled or following others to take off; thus its absence when a crane takes flight may be a cue to others to do the same. The Feeding Purr is the slowest of the Purrs and is almost constantly given when feeding. The Growl Purr is an aggressive signal given as part of the Low Bow display (see Behavior; Voss 1976, Nesbitt and Archibald 1981). This Purr is low frequency and low intensity, carrying only a few meters. Pre-copulation Calls are given in a series of calls, gradually rising in volume, and preceding copulation (Voss 1976). The Nesting Call is a Purr given at or near a nest during building, incubating, and brooding (Voss 1976). The loudest, highest-pitched, most rapidly delivered Purrs are Flight Purrs that occur only while in flight (Nesbitt and Bradley 1997). For sonograms of Purrs, see Nesbitt and Bradley (1997).
Rattle Calls. Rattle Calls are 7 to 20 very loud notes delivered at rate of about 15/s (Nesbitt and Bradley 1997). The mean fundamental frequencies for Rattle Calls are approximately 0.56 KHz for males and 0.93 KHz for females (Weekley 1985), and can be heard up to 4 km away. In flight these have rising or falling inflection, with a higher fundamental frequency than those given on the ground. Rattle Calls may be either Unison Calls or Guard Calls.
Unison Calls. A sexually stereotypic duet call generally given en route to and from feeding, loafing, and roosting locations (Nesbitt and Bradley 1997). The male part is lower pitched and more drawn out than the female’s staccato “tuck-a-tuck-a-tuck-a.”
Guard Calls. Often used in conjunction with Tall Alert Postures wherein the crane gives a slow even rattle when disturbed (Walkinshaw 1949, Archibald 1975), or used in unison by a pair or family group as an aggressive display when advertising or defending a nesting territory. The Rattle Call has a distinct antiphonal quality when delivered in flight as a pair flies over a defended territory. Older chicks (> 9 wk of age) participate in both Guard Calls and Unison Calls with their parents (SAN). In chicks, the Guard Call is a high-pitched, broken sound first ascending then descending in pitch, lasting about 0.45 s (Voss 1976). During migration (day or night) Rattle Calls are given by cranes on the ground in response to flying (often nonvisible) cranes also emitting Rattle Calls. This allows arriving individuals to locate cranes on the ground, especially at night. For sonograms of Rattle Calls, see Nesbitt and Bradley 1997.
Other Calls. Adults also give several other calls, reported here in order of increasing intensity. “Snores” have been reported from cranes on roosts (L. H. Walkinshaw, pers comm.) and are produced by orally tranquilized cranes (SAN). A shrill, diminuendo tremolo with a descending inflection is given by cranes in distress, as when captured. A short Purrt, 4 notes rising in pitch separated by unequal intervals, triggers an alert state in others in a flock and may be given as birds take flight or land. Yelps consisting of 3 or more high-pitched, broken notes and a sustained following note may serve as location calls (see Voss 1976) or to maintain or reestablish contact between flock or pair members separated by a greater distance than can be bridged by Purr Calls (Nesbitt and Bradley 1997). Moans and goose-like Honks are often interspersed among Rattle Calls and are intermediate between the full-voiced Rattle Call and a Purr. During aggressive behaviors, Sandhill Cranes produce a series of loud rapid slurred notes covering a wide frequency range, and lasting < 5 s (Nesbitt and Archibald 1981, Nesbitt and Bradley 1997, see Behavior). Also during aggressive behaviors, both among conspecifics or when mobbing a potential predator, the attacking bird delivers a loud Hiss inserted among other vocalizations.
See above. Unison Calls and Guard Calls are used in Duets to advertise territorial occupancy and boundaries and serve to avoid conflict among territorial adults. In other aggressive situations, Rattle Calls are used by dominant territorial pairs or individuals to intimidate intruding birds and drive them away. The Guard Call also is given also when birds (individuals, pairs, or flocks) mob a potential predator (Nesbitt and Bradley 1997; See Behavior).
Territorial advertisement calling via Rattle Calls increases with the onset of nesting season and declines through incubation. Other social calling increases during late summer and fall, as cranes become more gregarious. Calls are produced year-round from breeding seasons, through fall migration, winter, and spring migration, but are context specific. I.e., loud calls on breeding territories likely serve to maintain spacing, while loud calls during migration and wintering likely serve to bring cranes together.
Daily Pattern Of Vocalization
Sandhill Cranes are most vocal from about 30 min before sunrise through mid-morning. They are relatively quiet during mid-day, then become vocal again during late afternoon feeding, and when arriving at roosts or pre-roost gatherings. This pattern is observed throughout the year.
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