Mangrove swamps provide two functions 

 for wading birds. First, they function as 

 feeding grounds. Two-thirds of these 

 species feed almost exclusively on fishes. 

 Although much of their diet is provided by 

 freshwater and non-mangrove marine areas, 

 all of them feed frequently in mangrove 

 swamps. White ibis feed predominantly on 

 crabs of the genus Uca when feeding in 

 mangroves (Kushlan and Kushlan 1975; 

 Kushlan 1979). Mollusks and invertebrates 

 of the sediments are principal foods of 

 the roseate spoonbill although some fish 

 are eaten (Allen 1942). Yellow-crowned 

 night herons and American bitterns eat 

 crabs, crayfish, frogs, and mice in addi- 

 tion to fishes. Snails of the genus 

 Pomacea are fed upon almost exclusively by 

 the limpkin. The sandhill crane is an 

 anomaly in this group since a majority of 

 its food is vegetable matter, especially 

 roots and rhizomes of Cyperus and 

 Sagittaria . Its use of mangroves is 

 probably minimal, occurring where inland 

 coastal marshes adjoin mangroves (Kushlan, 

 unpubl . data). The remaining 12 species 

 are essentially piscivorous although they 

 differ somewhat in the species and sizes 

 of fishes that they consume. 



Mangrove swamps also serve as 

 breeding habitat for wading birds. With 

 the exception of the limpkin, sandhill 

 crane, and the two bitterns, all wading 

 bird species in Appendix D build their 

 nests in all three species of mangrove 

 trees (Maxwell and Kale 1977; Girard and 

 Taylor 1979). The species often aggregate 

 in large breeding colonies with several 

 thousand nesting pairs (Kushlan and White 

 1977a). The Louisiana heron, snowy egret, 

 and cattle egret are the most numerous 

 breeders in south Florida mangroves (based 

 on data in Kushlan and White 1977a). 



In wet years over 90% of the south 

 Florida population of white ibis breed in 

 the interior, freshwater wetlands of the 

 Everglades; during these times the man- 

 groves are apparently unimportant, sup- 

 porting less than 10% of the population 

 (Kushlan 1976, 1977a, b). During drought 

 years, however, production is sustained 

 solely by breeding colonies located in 

 mangroves near the coast (Kushlan 1977a, 



b). Mangroves are critically important 

 for the survival of the white ibis popula- 

 tion even though they appear to be 

 utilized to a lesser extent than fresh- 

 water habitats. This pattern of larger 

 but less stable breeding colonies using 

 inland marshes and smaller but more stable 

 colonies using mangroves is also charac- 

 teristic of heron populations (Kushlan and 

 Frohring, in prep.). 



Table 5 gives the number of active 

 nests observed in mangrove regions during 

 the 1974-75 nesting season and the percen- 

 tage this represents of the entire south 

 Florida breeding population for the nine 

 most abundant species of waders and three 

 associated species. The dependence of 

 roseate spoonbills, great blue herons, 

 Louisiana herons, brown pelicans, and 

 double-crested cormorants on mangrove 

 regions is evident. Nesting by the red- 

 dish egret was not quantified during this 

 study although Kushlan and White (1977a) 

 indicated that the only nests of this 

 species which they saw were, in fact, in 

 mangroves. Further observations indicate 

 that this species nests in mangroves ex- 

 clusively (Kushlan, pers. comm.). Similar- 

 ly, the great white heron is highly depen- 

 dent upon mangroves for nesting; they use 

 the tiny mangrove islets which abound 

 along the Florida Keys and in Florida Bay 

 (Howell 1932). 



During many years the Everglades 

 population of wood storks is known to nest 

 almost solely in mangroves (Ogden et al. 

 1976); this population comprises approxi- 

 mately one-third of the total south 

 Florida population. Successful breeding 

 of all these mangrove nesters is un- 

 doubtedly correlated with the abundant 

 supply of fishes associated with man- 

 groves. Meeting the energetic demands of 

 growing young is somewhat easier in habi- 

 tats with abundant prey. This is 

 especially important for the wood stork 

 which requires that its prey be concen- 

 trated into small pools by falling water 

 levels during the dry season before it can 

 nest successfully (Kahl 1964; Kushlan et 

 al. 1975; Odgen et al. 1978). Breeding 

 activity by wading birds in mangroves 

 along the southwest and southern Florida 



63 



