Productivity of Sandhill Cranes in South Central Florida

Abstract

Selected reproductive parameters of sandhill cranes (Grus canadensis pratensis) were monitored in south central Florida from 1973 to 1979. Means and ranges () of percentage of pairs with young, brood size, and number of juveniles/100 adults were 38.9 (28.6-78.3), 1.42 (1.24-1.50), and 27.7 (18.6-56.5), respectively. Dates of 8 nests with eggs ranged from 23 February to 26 May; mean number of eggs in 7 clutches was 1.86. Percentage of pairs with young, assumed to be an index of the number of breeding adults, was strongly correlated (r = 0.99) with juveniles/100 adults, whereas brood size was not (r = 0.12). Most (97%) variation in percentage of pairs with young was explained by rainfall in January and March, with high winter rainfall apparently stimulating reproduction and high March rainfall reducing productivity. Drainage of southern Florida wetlands during the past 50+ years has probably altered the quantitative relationship between amount of rainfall and crane reproduction and may be a factor in local variation in productivity in areas with similar rainfall regimes. J. WILDL. MANAGE. 47(1):178-185 The Florida sandhill crane is a nonmigratory subspecies of the sandhill crane occurring from the Okefenokee Swamp in extreme southeastern Georgia to southern Florida. Although no actual censuses of this subspecies have been conducted, recent estimates of the total population range from about 4,000 to 6,000 (Braun et al. 1975, Williams 1978, Nesbitt 1982). Williams (1978) concluded that the population is probably undergoing a slow decline. The subspecies is currently classified as threatened by the Florida Game and Fresh Water Fish Commission. Less is known about the reproductive biology of Florida sandhill cranes than for the northern, migratory subspecies (G. c. tabida and G. c. rowani). Most of the available reproductive data for the Florida population is from the Loxahatchee National Wildlife Refuge (N.W.R.), Palm Beach County (Thompson 1970) and the Kissimmee Prairie region (Walkinshaw 1949, 1973, 1976, 1979). Additional information on reproductive parameters of Florida sandhills in other parts of the range and under varying environmental conditions is needed to better assess the present status and possible future trends of the population and to provide a sound basis for its management. This paper reports on productivity of cranes in south central Florida from 1973 to 1979. Principal support for the study was provided by Archbold Expeditions, Inc. An aerial survey in 1973 was made possible through the cooperation of the U.S. Fish and Wildlife Service and funding from the New York Zoological Society. I thank R. L. Buckbee, D. E. Carter, R. Carter, D. Durrance, J. W. Fitzpatrick, J. Freeling, B. Kittleson, J. F. Lincer, C. E. Lohrer, E. C. Lohrer, F. E. Lohrer, W. McDiffett, D. Moskovits, A. Smith, J. A. Stallcup, A. M. Waggener, Jr., C. E. Winegarner, G. E. Woolfenden, D. J. Worley, and F. M. Yusko for aid in surveys or records of pairs and family groups. I also thank J. H. Hendrie, D. B. Childs, J. B. DeVane, G. Darroh, W. Prescott, W. J. Scarborough and Sons, Lykes Brothers, Inc., and Bright Hour Ranch for allowing access to their lands.