Nesting, Renesting, and Manipulating Nesting of Florida Sandhill Cranes

Abstract

Mean laying date of 53 Florida sandhill crane (Grus canadensis pratensis) nests during 1983-87 was 12 March. Mean clutch size for 99 nests was 1.72. Clutch size was not affected by laying date or clutch sequence. Seventy-eight percent of pairs that abandoned or had eggs removed from first or second nests renested; 38% of nests hatched successfully. Intervals between clutches were 18-20 days, irrespective of laying date or the number of days of incubation that preceded nest loss. Nest incubation during daylight hours was shared equally by males and females but was not uniformly distributed throughout the day. Removal of eggs was an effective method of prolonging nesting; however, it would be impractical to use egg removal to synchronize laying dates as part of a large-scale cross-fostering effort. J. WILDL. MANAGE. 52(4):758-763 A cross-fostering study conducted in the Rocky Mountain states revealed that sandhill cranes can foster-rear whooping cranes (Grus americana) and the adopted offspring will migrate along the route used by their foster parents (Drewien and Bizeau 1978). The success of this approach and the existence of a substantial population of nonmigratory sandhill cranes in Florida (Williams 1978) prompted an investigation into the possibility of and methodology for developing a nonmigratory population of whooping cranes in Florida similar to one that existed in Louisiana until the 1940's (Lowery 1974). No nonmigratory whooping cranes exist today; consequently, a study to predict the migratory propensity of a migratory species fosterreared by nonmigratory parents was undertaken in 1981 with greater sandhill cranes (G. c. tabida) as surrogates for whooping cranes (Nesbitt 1982). A problem with this approach that became apparent early in the study was the difference in laying dates between Florida sandhill cranes and greater sandhill cranes, and more importantly, whooping cranes in the wild or in captivity. There may be several ways to circumvent this problem: the photoperiod could be artificially manipulated to hasten egg production in captive cranes, or nesting of candidate, wild, foster parents could be prolonged. To establish nonmigratory whooping cranes using Florida sandhill cranes as foster parents in Florida, we needed an understanding of nesting biology of the resident subspecies. Prior knowledge of peak egg-laying dates, mean clutch size, renesting tendency, interval between clutches, nest attentiveness, and differences in nest attentiveness between sexes would aid in establishment and management of a nonmigratory flock anywhere in the southern United States. Published information on nesting of Florida cranes has come primarily from southcentral Florida. Walkinshaw (1949, 1973, 1976, 1982), Thompson (1970), and Bishop and Collopy (1987) described nests and nesting habitat. Walkinshaw (1985) also described nest attentiveness of male and female Florida sandhill cranes and greater sandhill cranes (Walkinshaw 1965a). Littlefield and Ryder (1968) presented additional information on nesting behavior of color marked male and female greater sandhill cranes in Oregon. The purpose of my study was to evaluate the possibility and best method of prolonging nesting in wild Florida cranes and gain greater understanding of their nesting biology. I appreciate the Florida Department of Natural Resources, Division of Parks and Recreation, for providing access to Paynes Prairie. F. M. and T. J. Cone, C. L. Brice, and H. M. and J. Z. Chitty allowed access to their property. Field assistance was provided by A. S. Wenner, S. T. Schwikert, and J. H. Hintermister V, R. D. Bjork, and K. S. Williams; their help was crucial to this study. Greater sandhill crane eggs used in Florida came from normal nesting pairs in Wisconsin or from captive pairs at the U.S. Fish and Wildlife Service's Patuxent Research Center in Laurel, Maryland. I am indebted to personnel with the Wisconsin Department of Natural Resources, International Crane Foundation, and Patuxent Wildlife Research Center. Financial support was provided, in part, by the U.S. Fish and Wildlife Service Endangered and Threatened Species Program.