Crane species hold an important place in cultures around the globe -- figuring prominently, for example, in traditional Japanese art, which often highlights the graceful lines and mesmerizing dances of these large birds. Cranes, including Sandhill Cranes (Grus canadensis), also feature in North America art, where their penetrating calls and elaborate dances have found a place in the fabrics and painting and dance of Native Americans and our contemporary culture.
Wide interest in Sandhill Cranes has led to numerous crane festivals, usually when cranes congregate in large flocks during migration. Such interest has also led to the support of extensive research programs by State and Federal agencies, conservation organizations, and research universities. These programs have been directed in particular by Rod C. Drewien, Gary L. Ivey, Gary L. Krapu, Carroll D. Littlefield, Stephen A. Nesbitt, Thomas C. Tacha, Paul A. Vohs, and Lawrence H. Walkinshaw, leading to over 400 reports, book chapters, and peer-reviewed publications cited in the literature review for this account.
Sandhill Cranes are heavy bodied, long-necked, long-legged birds inhabiting open grasslands, meadows and shallow freshwater marshes. Migrating cranes often are readily observed foraging in cereal fields, particularly the stubble of harvested corn, and roosting along slow moving rivers and other fresh water bodies. Six subspecies of Grus canadensis (G. c. canadensis, G. c. nesiotes, G. c. pratensis, G. c. pulla, G. c rowani, G. c. tabida) organized into nine, sometimes overlapping, populations are currently recognized, including three non-migratory populations (Cuba, Florida, and Mississippi; see Distribution) and six migratory populations (Eastern Flyway, Mid-Continent, Rocky Mountain, Lower Colorado River, Central Valley, and Pacific Flyway) breeding from the northeastern United States through central Canada to Alaska and eastern Siberia ( Walkinshaw 1973 , Jones et al. 2005b ). The Mid-Continent Population is further divided for management purposes into two subpopulations (Gulf Coast and Western), although recent research suggests additional division into four subpopulations might have biological support ( Krapu et al. 2011 , see Distribution). The Central Valley Population is divided into northern and southern subpopulations.
Cranes can live for over 35 years in the wild. First breeding is deferred until 2 to 8 years of age, depending on the subspecies, population, and individual development, and roughly 0.3 young are raised per year to the age of independence ( Nesbitt 1992b ). Together, delayed age at first breeding and low annual productivity explain the slow population growth inherent in this species. This slow growth has been a key obstacle in the conservation and management of at-risk populations ( Tacha et al. 1989 , Drewien et al. 1995b , BDG).
Pairs and families constitute the primary social units, but at times cranes are highly gregarious with extended family members and unrelated birds roosting communally and feeding in large flocks, particularly during migration and on wintering grounds ( Drewien 1973 , Walkinshaw 1973 , Tacha 1988 ; RCD, Littlefield et al. 1994 , Tacha et al. 1994a , Ivey et al. 2005 , Krapu et al. 2011 ). Cranes are socially monogamous, often with long-term pair bonds and extended biparental care of young, although microsatellite DNA markers have recently revealed extra-pair fertilization in some cases ( Hayes et al. 2006 , Hayes 2007 , CDL, RCD). Clutch size is normally 2 eggs, occasionally 1, and rarely 3. Failed nesting often leads to renesting.
The scientific literature on Sandhill Cranes is organized largely by breeding populations where the term “population” is used in a broad, flexible sense to describe individuals breeding in generally defined areas (sensu Mills 2007b ). This approach was adopted during the early days of crane management in North America when habitat loss and overhunting had lead to distinct breeding populations separated by unoccupied areas. Using this approach, management actions applied to populations have been tailored to meet local and regional recovery goals.
Three unintended consequences of this approach can be confusing as readers initially develop an understanding of the continent-wide ecology of Sandhill Cranes (see Priorities for Future Research). First, as cranes become more numerous and better understood, some populations have begun to overlap, leading to inconsistencies in terminology. Second, some populations include more than one subspecies. Third, wintering areas often support cranes from more than one breeding population. Together, these sources of variation can make it difficult for readers to identify with certainty an author's intended scope of inference for a given study unless that scope is stated explicitly.
To minimize confusion, Appendix 1 provides a list of subspecies in each breeding population and summarizes breeding, migratory stopover, and wintering areas by population. We have also consistently organized each chapter, and each section within each chapter, by population from east to west. When information on a specific topic is available from only a subset of populations, we report that information, and leave implied that when other populations are not mentioned, no population-specific information is available.