coasts takes place throughout the year 

 (Table 6); at least one species of wader 

 breeds during every month. Colonies on 

 the mangrove islands in Florida Bay were 

 noted to be active nesting sites during 

 all months of the year except September 

 and October (Kushlan and White 1977a). 



The seasonal movements of wood storks 

 and white ibises between the various south 

 Florida ecosystems were described by 

 Ogden et al. (1978) and Kushlan (1979). 

 Mangrove ecosystems appear to be most 

 heavily used for feeding in summer (white 

 ibis) and early winter (white ibis and 

 wood stork). The remaining species of 

 wading birds appear to use mangrove areas 

 most heavily in the winter months, reflec- 

 ting the influx of migrants from farther 

 north. 



Wading birds play an important role 

 in nutrient cycling in the coastal man- 

 grove zone. Mclvor (pers. observ.) has 

 noted increased turbidity, greater algal 

 biomass, and decreased fish abundance 

 around red mangrove islets with nesting 

 frigate birds and cormorants. Onuf et al. 

 (1977) reported results from a small (100 

 bird) rookery on a mangrove islet on the 

 east coast of Florida. Additions of 

 ammonium-nitrogen from the bird's 

 droppings exceeded 1 g/m /day. Water 

 beneath the mangroves contained five times 

 more ammonium and phosphate than water 

 beneath mangroves without rookeries. 

 Although the wading birds were shown to be 

 a vector for concentrating nutrients, it 

 must be noted that this is a localized 

 phenomenon restricted to the areas around 

 rookeries in the mangrove zone. The 

 effect would be larger around larger 

 rookeries. Onuf et al. (1977) also 

 reported that mangroves in the area of the 

 rookery had increased levels of primary 

 production, higher stem and foliar nitro- 

 gen levels, and higher herbivore grazing 

 impact than mangroves without rookeries. 

 Lewis and Lewis (1978) stated that man- 

 groves in large rookeries may eventually 

 be killed due to stripping of leaves and 

 branches for nesting material and by 

 poisoning due to large volumes of urea and 

 ammonia that are deposited in bird guano. 

 This latter effect would be more 



pronounced in rookeries within mangrove 

 regions subject to infrequent tidal flush- 

 ing. 



9.3 PROBING SHOREBIRDS 



Birds in this group are commonly 

 found associated with intertidal and shal- 

 low water habitats. Wolff (1969) and 

 Schneider (1978) have shown that plovers 

 and sandpipers are opportunistic feeders, 

 taking the most abundant, proper-sized 

 invertebrates present in whatever habitat 

 the birds happen to occupy. 



Of the 25 species included in this 

 guild (Appendix D), two are year-round 

 residents (clapper rail and willet), two 

 breed in mangrove areas (clapper rail and 

 black-necked stilt), and the remainder are 

 transients or winter residents. Baker and 

 Baker (1973) indicated that winter was the 

 most crucial time for shorebirds, in terms 

 of survival. Coi ncidental ly, winter is 

 the time when most shorebirds use mangrove 

 areas. The invertebrate fauna (mollusks, 

 crustaceans, and aquatic insects) which 

 occur on the sediments under intertidal 

 mangroves forms the principal diet of 

 these species. Willets and greater 

 yellowlegs eat a large amount of fishes, 

 especially Fundulus , in addition to inver- 

 tebrates. Many of the species listed in 

 this guild obtain a significant portion of 

 their energy requirements from other habi- 

 tats, particularly sandy beaches, marshes, 

 and freshwater prairies. Of the species 

 in this guild, the clapper rail is prob- 

 ably most dependent on mangroves for 

 survival in south Florida (Robertson 

 1955), although in other geographical 

 locations they frequent salt and brackish 

 marshes. 



9.4 FLOATING AND DIVING WATER BIRDS 



Twenty-nine species of ducks, grebes, 

 loons, cormorants, and gallinules were 

 identified as populating mangrove areas in 

 south Florida (Appendix D). Eight species 

 are year-round residents while the 

 remainder are present only during migra- 

 tion or as winter visitors. 



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