The Ecology of Hydric Hammocks - USGS National Wetlands ...

from censuses of a 13.5-ha hydric hammockin Hillsborough River State Park,Hi 1 l sborough Co., Florida (Wool fenden1967; 1968). Inis site supported 366individuals of 16 species per 40.5 haduring breeding versus 411 individualsof 33 species during winter. Speciesof overwintering migrants identifiedon this site (in addition to thosejust 1 i sted) include eastern phoebe,hermit thrush, ye1 low-be1 1 ied sapsucker,solitary vireo, ovenbird, orange-crownedwarbl er, palm warbler,common ye1 1 owthroat, and Americangoldfinch. Much attention has beengiven recently (e.g., Pasquier 1982)to the role of Neotropical forests insupporting populations of migrantpasserines that breed in eastern NorthAmerica, but the same role of forestsof the southeastern United States, andhydric hammock in particular, is lesswidely recognized. This role needs tobe much better documented and pub1 i -ci zed.Long-term trends in populations ofbreeding birds in Florida, based onbreeding bird survey counts from 1969to 1983 in all habitats, revealed significantchanges in the number of severalspecies occurring in hydric hammock(Cox 1987). These included increasesin number of the mourning doveand osprey and decreases in number ofthe northern fl icker, brown-headednuthatch, northern mockingbird, easternbl uebi rd, 1 oggerhead shrike, ye1 -1 ow- throated warbler, prairie warbler,common ye1 lowthroat, red-winged blackbird,and eastern meadowlark. Threeof the declining species are cavitynesters.4.3.2 Selected SoeciesThe wood duck (Aix sponsa) usuallyforages elsewhere but nests in cavitiesof live trees, including those inhydric hammock. This habitat may beimportant to wood ducks because of itsabundance of den trees and its proximityto water. Acorns and other mastare important fall and winter foods ofwood ducks (Landers et al. 1976).Wood ducks prefer to forage for mastfallen into shallow water or on theforest floor adjacent to water, and wehave observed this behavior in floodedhydri c hammocks.Wild turkey (Meleagris gallopavo)were subject to market hunting inFlorida until that commerce was bannedin 1901. The population in Gulf Hammockin 1948-49 was considered"reasonably good" (estimated at 500 to600 birds, or one per 71 ha of suitablehabitat) but far below carryingcapacity (Swindell 1949). Major pressureson the population were consideredto be hunting, which increasedafter World War 11, and reduction ofhabitat qua1 i ty by succession andcanopy closure foll owing 1 umbering.The lowest densities of turkeys in thearea are in extensive hammock unbrokenby clearings, which would providepoults with a suitable abundance ofinsects. Turkeys shift to the hammocksin autumn when acorns are avail -able and to hammock edges, flatwoods,and clearings in late winter and earlyspring when new herb growth becomesavai 1 abl e.The ivory- bi 11 ed woodpecker(Campephi 7us principal is) once inhabitedhydric hammock, as well as itsmodal habitat of river swamp and cypressswamp. Records of originaldistribution of this bird in "marlhammocks" (Tanner 1942) were up theSt. Marks River (Wakulla County);Pumpkin and Cal i fornia Swamps (DixieCounty) ; Suwannee Hammock, Rosewood,Otter Creek, Gulf Hammock, and Sim'sRidge (Levy County) ; Crystal River(Citrus County) ; Tampa (Hi11 sboroughCounty); Manatee County; Enterpriseand Turnbull Hammock (Volusia County) ;Jim Creek (Orange County); TaylorCreek and Wolf Creek (Osceol a County) ;Highl ands Hammock (Highl ands County) ;and Caloosahatchee region (LeeCounty) . The avai 1 able density esti -mates are that one pair of ivory-billsneeded 15.5 to 44 square kilometers ofgood habitat; the same stands supportedroughly 72 pileated woodpeckersand 252 red-be1 1 ied woodpeckers. Virginhydric hammock is characterized byvery old and standing dead trees,which supported the woodpeckers' maindiet of larvae of borers fbuprestid