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

4.3 BIRDS4.3.1 Community StructureMore is known about the community ofbirds of hydric hammocks than aboutother groups of animals 1 iving there,but very little is known about specificbird populations in this habitat.The most common year-round resi -dents are the red-shouldered hawk,barred owl , red- be1 1 ied woodpecker,pifeated uoc~~ecker, northern f! ic4er,American crow, fish crow, blue jay,Carol ina wren, tufted ti tmouse, Carolinachickadee, and northern cardinal.The most common summer residentsare the great crested flycatcher,northern parul a warbler, and summertanager. The most common winter residentsare the eastern phoebe, Americanrobin, house wren, ruby-crownedking1 et, ye1 1 ow-rumped warbler, Ameri -can galdf inch, and whi te-throatedsparrow.Three variants of this habitat wereincluded in the study of flora andfauna of the route of the proposedCross-Florida Barge Canal (FloridaGame and Fresh Water Fish Commission1976). Raw data from that study havebeen analyzed by Humphrey and Nesbitt[1989] and are summarized in Table 11.rnastal hydric hammock wat characterizedby the highest absolute numberof kingfishers, fish crows, hermitthrushes, ye1 low-rumped warblers,northern cardinals in winter, andwhite-throated sparrows. This was theonly habitat in which gray kingbirdswere recorded. In1 and hydric hammockwas characterized by the highest absolutenumber of red-shouldered hawks,mourning doves, pileated woodpeckers,Carol ina wrens, bl ue-gray gnatcatchers,and black-and-white warblers.The loblolly pine variant of hydrichammock was characterized by the highestabsolute number of black vultures,downy woodpeckers, hairy woodpeckers,American crows in winter, wood pewees,brown-headed nuthatches, yellowthroatedvireos, and summer tanagers.Large, rare species for which hydrichammock was important included nestingospreys and American swallow-tailedkites (Elanoides forficatus) and post-breeding wood storks (Rycteriaamericana). an endanqered species.Hydric hammock supported large numbersof overwintering passeri nes. Notrecorded in these samples but veryabundant, especi a1 ly foraging over theedge of hydric hammock with marsh andwith fl atwoods, were flocks of overwinteringtree swal 1 ows (Iridoprocnebicolor).Bird communities in the three typesof hydric hammock (Table 11) were consistentlyamong the most diverse ofthose of 14 habitats in the region.In the breeding season, the diversityindex H1(Shannon and Weaver 1949) washighest in loblolly pine hydric hammock,second in rank in coastal hydrichammock, and fifth in inland hydrichammock. As measured by number ofspecies, diversity in the breedingseason ranked fourth, fifth, and sixthin the three types of hydric hammock.In winter, diversity as measured bynumber of species was higher in thethree types of hydric hammock than inany other habitat, and diversity asmeasured by H' was highest in inlandhydric hammock, fourth in rank in hydricloblolly pine hammock, and eighthin coastal hydric hammock. Abundanceof birds, as measured by number of individuals,was intermediate in thethree types of hydric hammock.A1 though each of the three types ofhydric hammock can be differentiatedby a few species of birds occurringonly or in highest number there, thesimilarity of these bird communitiesis much more striking than their differences(Humphrey and Nesbi tt[1989]). This similarity is not limitedto hydric hammocks; it extends toall types of forests sampled in theregion, suggesting that bird communi -ties do not differentiate among typesof forests nearly as finely as doforesters and ecologists. Instead ofbeing habitat-specific entities, thesebird associations appear to form accordingto the adaptations of individualspecies in response to gradientsof various features of the environment.Humphrey and Nesbi tt suggestedtwo such gradients on the basis of theavai 1 able data--three-dimensional