Stephen T. Schwikert

Natal dispersal in florida sandhill cranes

Knowledge of natal dispersal is essential for understanding how nonmigratory crane populations expand and how this process can be augmented by relocation or reintroduction. We conducted a study from 1988 to 1999 and found that natal dispersal in Florida sandhill cranes (Grus canadensis pratensis) was female-biased. Females (n = 16) dispersed an average of 11.6 km from their natal territory. Male (n = 12) dispersal averaged 3.9 km. This difference was significant (P 0.05) or affected by gender (P > 0.05). Male philopatry and female-biased natal dispersal are consistent with theories of a resource-based mating system. Timing of the start of dispersal (family breakup) was found to be more closely tied to the females laying the subsequent clutch than to the age of the juvenile crane.

From the Field: Wing-molt patterns—a key to aging sandhill cranes

Abstract To refine and expand the accuracy of a potential technique for aging sandhill cranes (Grus canadensis), we investigated wing molt in 1,076 migratory and nonmigratory cranes captured in Florida between 1978 and 1997. The annual mode of primary and secondary flight feather replacement was incomplete, resulting in a pattern of varying age feathers that, along with other plumage characteristics, can be used to separate sandhill cranes into juvenile and 3 post-juvenile age groups. Juvenile cranes had even-age flight feathers and juvenile primary and secondary coverts. First-year subadults had even-aged primaries, and only the most distal primary coverts were still juvenile. Also, distal and most of the proximal secondaries were even-aged. Second-year subadults had even-aged distal primaries with a mixture of ages in the proximal primaries and had replaced more than half of all the secondaries. Adults had replaced some of both the distal and proximal primaries, giving the outer flight feathers a mixture of feather ages, and they had mixed-age distal and proximal secondaries. When used as an aging tool in the field, 92.6% of 109 recaptured post-juvenile aged cranes could be accurately assigned into one of the older age classes.