North American Crane Working Group


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Chavez-Ramirez, F. Temporal dynamics and flock characteristics of sandhill cranes in the Platte River Valley, Nebraska. In: Folk, MJ and SA Nesbitt, eds. 2008. Proceedings of the Tenth North American Crane Workshop, Feb. 7-10, 2006, Zacatecas City, Zacatecas, Mexico: North American Crane Working Group. p. 162.


Reproduced by permission of the North American Crane Working Group.


I gathered information on crane flocks in the Platte River Valley during spring staging of 2002-2004. The objective of
this work was to evaluate hypotheses regarding flock size and formation using sandhill crane (Grus canadensis) flocks observed in
the Platte River Valley. Specifically, I wanted to: (a) evaluate the effect of period of migration, geographical location, and habitat
type on flock size, and (b) evaluate predictions regarding ecological theories of flock formation and behavior based on concentrated
resources, accessibility, social facilitation, and potential predation response. Flock size overall was influenced negatively by period
of migration (P < 0.001) and positively by geographical location (P < 0.01). Total crane abundance (55%) of flocks were located
in corn fields, but flock sizes were larger and significantly different (P < 0.001) in low grasslands (mean = 666.4). There were no
significant differences in flock size among other habitat categories (corn = 316, high grassland = 301.8, wet meadow = 214.4, and
alfalfa = 204.9). The proportion of cranes foraging in a flock in corn fields decreased over time while it increased in flocks foraging
in low grasslands. Proportion of cranes resting increased over time in corn fields while it decreased in low grasslands. There was
a negative relationship between flock size and proportion of cranes foraging in a flock in corn fields but not in grasslands. The
relationship between observed and predicted patterns (based on ecological flock formation theories) of crane flocks are evaluated
and discussed.