North American Crane Working Group


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Spalding, M.G., M.J. Folk, S.A. Nesbitt, and R. Kiltie. Reproductive health and performance of the Florida flock of introduced whooping cranes. In: Hartup, Barry K., ed., Proceedings of the Eleventh North American Crane Workshop, Sep 23-27, 2008, Wisconsin Dells, Wisconsin (Baraboo, WI: North American Crane Working Group, 2010), pp. 142-155.


Reproduced by permission of the North American Crane Working Group.


We retrospectively examined the reproductive parameters of 122 breeding-age whooping cranes (Grus americana) in a reintroduced flock in central Florida from 1992 to 2007. The flock performed poorly when compared with an existing wild flock for all reproductive parameters when controlled for age. Pairs first formed in 1995, nested in 1999, and the first chick fledged in 2002. By 2007, 19 of 63 clutches produced 25 chicks, 9 of which fledged. Drought conditions were ruled out as the sole cause of failure when the drought lessened and productivity increased, but not in all years. We examined adult health, mortality, gonad size and function, pair formation and duration, egg laying, hatching success, egg size, clutch size, fertility, and microorganisms cultured from eggs. Annual mortality was high (13%). The tendency for males to be killed when hitting power lines when females survived may be sufficient to explain the lack of males older than 10 years in this small population. As much as 65% of birds were delayed or non-reproductive due to morphologic abnormalities of the reproductive tract, pairing with sandhill cranes, or more commonly, due to unidentified causes. Pair duration was short (2 years). Extreme annual variability in fertility and hatchability (0-62%) suggest a disease or environmental influence. Captive parent pairs differed in the average reproductive value of their offspring and in the number of second generation wild offspring produced. The remaining small flock is at risk of extinction unless changes are made to improve contiguous wetland availability and reduce the hazards of power lines in these areas. Identification of innate reproductive qualities (behavioral, genetic, and morphologic) and improving survival behaviors may enhance the quality, and thus performance, of birds released.