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Communal Roosting and Foraging Behavior of Staging Sandhill Cranes

Introduction


Sandhill Cranes of the midcontinent population acquire nutrient reserves for migration and reproduction while on staging areas along the Platte and North Platte rivers in Nebraska (Krapu et al. 1985). Cranes roost communally at night in shallow waters of wide river channels or other wetlands and spend the days foraging in flocks on surrounding uplands (Krapu et al. 1984, Folk and Tacha 1990). Little is known concerning the specific functions of communal roosting and flocking to staging cranes beyond a probable advantage of reducing the risk of predation through increased predator detection (sensu Pulliam 1973, Caraco 1979) or evasive behaviors unique to groups. In some species of birds, communal roosts may serve as information centers, increasing foraging efficiency (Ward and Zahavi 1973; Waltz 1982, 1987; but see Bayer 1982; Stutchbury 1988 for contrary opinions). Foraging efficiency can also be increased through local enhancement (Hinde 1961) or use of alternative diurnal roosts (Caccamise and Morrison 1986, 1988).

In the Platte River Valley, loss of communal roosting habitat has resulted in high densities of staging cranes (Krapu et al. 1984) prompting a need to evaluate spatiotemporal use of existing habitat and choice of foraging sites. In this paper, we examine (1) characteristics and use of activity ranges relative to energy expenditure and food availability, (2) the role of communal roosts in foraging behavior, (3) habitat preferences, and (4) influence of group size and predation on foraging and other behaviors. We also discuss social factors as they pertain to staging behavior in Sandhill Cranes.


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