2006 SOUTHEASTERN NATURALIST 5(4):621–636 Woodpecker Use of Forested Wetlands in Central Peninsular Florida David L. Leonard, Jr.1,2,* and I. Jack Stout1 Abstract - Habitat preferences for many woodpeckers are poorly known in many regions of North America. Seven woodpecker species use forested wetlands in peninsular Florida, yet no study has examined habitat use by woodpeckers in these forests. From September 1991 to August 1992, we used unlimited-distance point counts to sample birds at 32 stations in 2 forested wetland types (spring-fed and blackwater) in central Florida. We documented 1415 visual or aural woodpecker detections. Melanerpes carolinus (Red-bellied Woodpecker), Picoides pubescens (Downy Woodpecker), and Dyrocopus pileatus (Pileated Woodpecker) were common, accounting for 91% of all detections. Overall woodpecker abundance was greater in spring-fed forests than in blackwater forests. The relative abundance of 4 species was greatest during the fall and winter; this trend likely reflected shifts between habitats in response to fruit production as well as an influx of migrant Sphyrapicus varius (Yellow-bellied Sapsuckers). The relative abundance of Redbellied and Pileated woodpeckers was greatest at sites surrounded by extensive forest cover. Unlike other studies, we found no relationship between woodpecker abundance and tree or snag basal area. The presence of Quercus spp. (oaks) also did not appear important to woodpeckers. Compared to other studies, snag density in the forests we sampled was high. This may have reduced the importance of snags to woodpeckers or made detecting relationships difficult. A high density of Sabal palmetto (sabal palm) may have provided additional foraging and nesting/roosting sites that further contributed to the lack of correlations between woodpecker detections and the presence of snags and oaks. Introduction Woodpeckers are conspicuous, relatively sedentary residents of many forested habitats in North America (Short 1982). By excavating cavities that provide shelter and nesting sites for other species, woodpeckers play an important role in forest communities (Bednarz et al. 2004, Bull and Jackson 1995, Martin and Eadie 1999, Martin et al. 2004, Short 1982). Across a wide range of habitats, woodpecker abundance has been related to snag availability (Dickson et al. 1983, Shackelford and Conner 1997), forest age (Shackelford and Conner 1997), and the presence of oaks (Conner et al. 1994). However, few studies have described habitat features that influence the composition of woodpecker assemblages in the southeastern United States east of the Mississippi River. In Florida, no study has focused on the community structure of woodpeckers using forest areas adjacent to rivers. 1Department of Biology, University of Central Florida, Orlando, FL 32816. 2Current address - State of Hawaii Department of Land and Natural Resources, Division of Forestry and Wildlife, 1151 Punchbowl Street, Room 325, Honolulu, HI 96813. *Corresponding author - david.l.leonard@hawaii.gov. 622 Southeastern Naturalist Vol. 5, No. 4 Forested wetlands or riparian areas are important components of landscapes. Due to the juxtaposition of aquatic and terrestrial habitats, forested wetlands typically harbor greater species diversity of various taxa relative to the surrounding habitats (Gregory et al. 1991, LaRue et al. 1995). Forested wetlands have been found to be especially important to birds (Kwit et al. 2004, Murray and Stauffer 1995, Sallabanks et al. 2000), including cavity nesters (Sedgwick and Knopf 1986, 1990). Fruit or mast is an important component of the diet of some of the woodpeckers that occupy forested wetlands in Florida (Beal 1911, but see Boone 1963, Towles 1989). Compared to other local habitats, Florida hardwood forests support a higher diversity of fruiting and masting plant species (Ewel 1990, Ewel and Atmosoedirdjo 1987, Skeate 1987), and thus forested wetlands may provide critical habitat for certain woodpecker species. Unlike most non-migratory birds, some woodpecker species show a preference for large forested tracts (Robbins et al. 1989, but see Bender et al. 1998). In some regions of eastern North America, Melanerpes carolinus Linnaeus (Red-bellied Woodpeckers) prefer large forested tracts over small ones (Kilgo et al. 1998, Robbins et al. 1989; but see Keller et al. 1993, Lynch and Whigham 1984, Noss 1991). Dyrocopus pileatus Linnaeus (Pileated Woodpeckers) also have been reported to prefer large tracts of undisturbed forest (Renken and Wiggers 1989, Robbins et al. 1989; but see Keller et al. 1993, Lynch and Whigham 1984). Here we present data on the abundance and diversity of woodpeckers relative to landscape and vegetative characteristics in 2 types of forested wetlands in central Florida: those bordering spring-fed and blackwater rivers. Study Area and Methods We selected 19 forested wetland sites bordering 10 tributaries of the St. Johns River in Orange and Seminole Counties in central Florida based on availability and access. Five of these tributaries were spring-fed and the remainder were part of blackwater river systems that drained the surrounding uplands (see Ewel 1990). Alluvial deposition and scouring during extensive late spring and summer flooding of blackwater rivers resulted in the surrounding forests usually having extremely sandy soils as well as an open understory. In contrast, the spring-fed sites had short hydroperiods, organic soils, and well-developed vertical vegetation structure (Ewel 1990). Several blackwater forests were embedded in an extensive matrix of native Pinus spp. (pine) forests. We used point counts to sample birds at each site (Blondel et al. 1981, Ralph et al. 1993). To minimize double counting of individual birds, we separated count stations by at least 160 m (O’Meara 1984). Within this constraint, we randomly located 32 point-count stations (stations hereafter) in the 19 sites; large sites (range of site widths: 60–5000 m) had up to 3 stations. No stations fell within ecotones. The primary author sampled each 2006 D.L. Leonard, Jr. and I.J. Strout 623 station twice per month from September 1991 to August 1992. All birds seen or heard during a 15-minute sampling period were recorded, but only woodpeckers are included herein. The direction and distance of each bird detected was noted to minimize double counting. All counts were made within 4 hours of sunrise on mornings without rain or fog, and with minimal wind. The sampling order of sites was randomized. We acknowledge the limitations of point-count methodology (e.g., variation in detection probabilities among species and effects of variation in bird density; Farnsworth et al. 2002, Howell et al. 2004, Norvell et al. 2003). For comparative purposes, we used the data in Dickinson (1978) and Shackelford and Conner (1997). We acknowledge that the methods used in these 2 studies were different from our survey methods; nonetheless, we believe the comparisons of the relative abundance of woodpeckers across the three studies is useful. Due to the linear and often continuous character of the sites, we used site width as a correlate of area (Keller et al. 1993, Kilgo et al. 1998, Smith and Shaefer 1992, Stauffer and Best 1980, Whitaker and Montevecchi 1999; but see Groom and Grubb 2001). We determined the width of each site, at each station, using aerial photographs (1:123 m), and determined the minimum distance from each station to the edge of the forest. Site width only included forested habitat (i.e., the width of rivers was not included). We also calculated the area of the largest continuous forested wetland and the area of the largest contiguous forest (all cover types) within 1 km of each station. At each station, we sampled the vegetation in 3 randomly selected 0.04- ha circular plots (James and Shugart 1970, James et al. 2001), and estimated the vegetative characteristics of each site using mean values from the circular plots. We measured the diameter at breast height (dbh) of trees and snags (i.e., standing dead trees) greater than 5 cm dbh and determined the number of trees and snags in 5 and 4 size-class categories, respectively. We estimated canopy coverage using a spherical crown densiometer and canopy height using a clinometer; estimates were based on 12 and 3 measures, respectively, per station. We estimated shrub density by counting all stems (< 5 cm dbh and 􀂕 1.5 m tall) in two 11.3-m transects transcribing each plot (James and Shugart 1970). We recorded the number of palms in each circular plot by species (Sabal palmetto Walter, Serenoa repens Michaux, Rhapidophyllum hystrix Pursh) and age class (i.e., immature and mature); age class was based on size. The number of trees, snags, stems, and palms was averaged across the 3 plots and means were extrapolated to estimates per ha. We visually estimated the vertical vegetation density using a density board (MacArthur and MacArthur 1961) at two height categories (0–1.0 m, 1.1–2.0 m). Readings were taken from the 4 cardinal compass directions, converted to a percentage, and averaged for each station. We grouped all woodpecker detections into seasons: fall (September, October, November), winter (December, January, February), spring (March, April, May), and summer (June, July, August). We present total woodpecker detections as well as mean (± SD) detection rates. We assumed each 624 Southeastern Naturalist Vol. 5, No. 4 point-count station was independent. Thus, sample sizes were 13 and 19 for spring-fed and blackwater sites, respectively. We tested all variables for normality (Kolmogorov-Smirnov Test) prior to analysis. The relative abundance of the most frequently detected species (Red-bellied Woodpecker, Pileated Woodpecker, and Picoides pubescens Linnaeus [Downy Woodpecker]) was normally distributed. However, the variance of species detected at lower rates (e.g., Colaptes auratus Linnaeus [Northern Flicker]) was high, and results of statistical tests of these species should be viewed with caution. Despite this, results from parametric and non-parametric tests, comparing detection rates between sites and across seasons, were similar; thus, we used t-tests and ANOVAs for these comparisons. For multiple comparisons, we used Tukey’s HSD test. Several vegetation variables were not normally distributed, and we used non-parametric statistics to test for differences in the vegetation between forest types (Mann-Whitney U-tests). We adjusted significance values to P = 0.01 to minimize Type I errors due to multiple comparisons. We tested for correlations between woodpecker abundance and landscape variables using Spearman’s Rank Correlation. Finally, we used principal component anlaysis (PCA) to examine the underlying variation in vegetation variables and its potential relationship to woodpecker detection rates. All analyses were performed using SPSS (version 8.0 for Windows; 1998) and Minitab (Release 12; 1999). Results Differences in several of the vegetation variables confirmed that blackwater sites had a more open understory than those in spring-fed forests (Table 1). Sites within both forest types had similar basal area and densities of living trees and snags. However, Fraxinus caroliniana Mill. (pop ash) was a dominant component of spring-fed sites, but was uncommon in blackwater sites, and Quercus laurifolia Michaux (laurel oak) was the dominant tree species in most blackwater sites. Spring-fed sites supported several tree species (e.g., Tilia Carolina Mill., Ulmus Americana Linnaeus, Magnolia virginiana Linnaeus), albeit at low densities, that were for the most part absent from the blackwater sites. The first 4 principle components explained 61.3% of the variation in the vegetation data. The loadings from the components indicated that the underlying variation in the vegetation at each site could be attributed to: (1) basal area of trees and snags; (2) vertical density of vegetation (e.g., openness); (3) disturbances likely related to flooding events or tree falls; and (4) stem and saw palmetto density (Fig. 1). These results corroborate the above findings (Table 1) and further illustrate the differences in the relative openness of the 2 forest types. Spring-fed sites were wider than blackwater sites (1705 ± 2077 m versus 639 ± 1084 m, t = 1.9, 30 df, P = 0.067), and compared to those stations in blackwater sites, spring-fed sites had more continuous wetland forest cover (67 ± 25% versus 41 ± 26%, t = 2.9, 30 df, P = 0.009) and more continuous 2006 D.L. Leonard, Jr. and I.J. Strout 625 total forest cover within 1 km (88 ± 21% versus 54 ± 31%, t = 3.5, 30 df, P= 0.002). Many of the spring-fed sites were in protected areas. We documented seven woodpecker species (1415 detections), detecting 1.84 ± 1.49 woodpeckers during each 15-minute sampling period (n = 768). The Red-bellied Woodpecker was the most frequently detected species, and along with the Downy and Pileated Woodpeckers, accounted for 91% of all detections (Table 2). Sphyrapicus varius Linnaeus (Yellow-bellied Sapsuckers) were common only during the winter. Northern Flickers and M. erythrocephalus Linnaeus (Red-headed Woodpeckers) were restricted to spring-fed sites, while P. villosus Linnaeus (Hairy Woodpeckers) were restricted to blackwater sites. The latter 2 species were rarely detected and only were included in summary analyses and totals. Seasonal abundance of all species and species richness were higher during fall and winter (F = 16.9, 3 df, P < 0.001) than in spring or summer (F = 15.5, 3 df, P < 0.001; Table 2). Red-bellied Woodpeckers, Pileated Woodpeckers, Yellow-bellied Sapsuckers, and Northern Flickers were most abundant in the fall and/or winter (Table 2). Downy Woodpecker detections were seasonally variable. Overall woodpecker abundance was greater in spring-fed forests than in blackwater forests (Table 3). Despite this difference in overall abundance, the percent composition of the 3 most commonly detected woodpecker Table 1. Vegetation variables estimated (mean ± SD) from three 0.04-ha circular plots at each of 32 point count stations in forested wetland study areas in Orange and Seminole counties, Florida, 1991–1992. Forest type Variable Blackwater (n = 19) Spring-fed (n = 13) P-valueA Basal area snagsB 1.6 ± 2.1 2.4 ± 3.8 0.35 Basal area of treesB 31.2 ± 12.1 28.3 ± 6.8 0.99 Canopy cover (%) 83.7 ± 3.9 88.2 ± 3.1 < 0.01 Canopy height (m) 23.5 ± 3.3 28.0 ± 3.7 < 0.01 Needle palmC 0.0 ± 0.0 125.2 ± 286.4 < 0.00 Sabal palm (immature)C 364.4 ± 610.4 1338.3 ± 715.7 0.01 Sabal palm (mature)C 294.4 ± 225.2 237.7 ± 146.8 0.60 Saw palmettoC 716.5 ± 693.2 24.3 ± 62.8 < 0.00 Trees 5–8 cm dbhC 126.5 ± 66.6 120.2 ± 89.1 0.08 Trees 9–15 cm dbhC 177.8 ± 80.8 179.6 ± 82.1 0.95 Trees 16–23 cm dbhC 118.9 ± 47.2 109.8 ± 47.0 0.91 Trees 24–38 cm dbhC 113.1 ± 60.4 129.3 ± 63.0 0.17 Trees >39 cm dbhC 78.8 ± 41.4 77.7 ± 32.1 0.92 Number of snagsC 62.1 ± 41.4 39.5 ± 40.0 0.05 Snags 5–16 cm dbhC 27.6 ± 30.5 40.8 ± 25.9 0.06 Snags 17–28 cm dbhC 2.6 ± 4.0 10.1 ± 11.7 0.05 Snags 29–40 cm dbhC 5.1 ± 9.9 6.1 ± 11.4 0.52 Snags > 41 cm dbhC 3.9 ± 6.5 2.6 ± 5.6 0.54 StemsB 638.1 ± 620.5 466.2 ± 358.4 0.74 Vegetation density (0–1 m; %) 26.1 ± 19.9 54.0 ± 15.4 < 0.00 Vegetation density (1–2 m; %) 21.3 ± 14.6 52.1 ± 19.5 < 0.00 AMann-Whitney U-Test Bm2 per ha CNumber per ha 626 Southeastern Naturalist Vol. 5, No. 4 species was similar. The exception was the Downy Woodpecker. Although the detection rate of this species was similar between the 2 forest types, it Figure 1. First four principle components (% variation explained) summarizing the vegetation characteristics of 32 point-count stations in Orange and Seminole counties, FL, and scores from each station. Open circles represent forested wetlands along spring-fed rivers, and closed circles represent forested wetlands along blackwater rivers. 2006 D.L. Leonard, Jr. and I.J. Strout 627 comprised a larger percentage of the detections in blackwater forests compared to spring-fed forests. Within forest types, seasonal differences in woodpecker detections were similar to overall seasonal (Table 2) and site (Table 3) differences, with the Table 2. Total detections for both forest types combined, mean (± SD) seasonal detections, and mean seasonal totals and species richness of woodpeckers from 768 point counts at 32 stations in Orange and Seminole Counties, FL, 1991–1992. Means sharing a superscripted letter within rows are significantly different (P < 0.05; ANOVA, Tukey’s HSD test). Fall2 Winter Spring Summer Mean Mean Mean Mean Species1 Total ± SD Total ± SD Total ± SD Total ± SD Total RHWO 4 - 1 - 1 - 1 - 1 RBWO 681 0.98AB 189 0.98CD 189 0.83 AC 159 0.75 BD 144 ± 0.76 ± 0.82 ± 0.86 ± 0.78 NOFL 32 0.06A 12 0.09 BC 17 0.02 B 3 0.01 AC 1 ± 0.24 ± 0.29 ± 0.12 ± 0.07 YBSS 92 0.12 A 22 0.32AB 61 0.05 B 9 - 0 ± 0.37 ± 0.51 ± 0.21 DOWP 195 0.34A 66 0.26 50 0.16 A 31 0.43 48 ± 0.55 ± 0.54 ± 0.40 ± 0.62 HAWO 4 - 1 - 1 - 1 - 1 PIWO 407 0.67 AB 129 0.58 111 0.44 A 84 0.43 B 83 ± 0.63 ± 0.69 ± 0.59 ± 0.62 Total 1415 2.19 A - 2.24 BC - 1.50 B - 1.45AC - ± 1.50 ± 1.70 ± 1.26 ± 1.29 Richness 7 3.44 AB - 4.00 CD - 2.72 AC - 2.75 BD - ± 1.05 ± 0.92 ± 0.89 ± 0.62 1RHWO = Red-headed Woodpecker, RBWO = Red-bellied Woodpecker, NOFL = Northern Flicker, YBSS = Yellow-bellied Sapsucker, DOWO = Downy Woodpecker, HAWO = Hairy Woodpecker, PIWO = Pileated Woodpecker; see text for scientific names. 2Fall = September, October, November; Winter = December, January, February; Spring = March, April, May; Summer = June, July, August. Table 3. Mean (± SD) and total species detections, and the percentage composition of all woodpeckers detected at 32 stations in two forest types in Orange and Seminole Counties, FL, 1991–1992. Spring-fed stations (n = 312) Blackwater stations (n = 456) SpeciesA Mean ± SD Total % Mean ± SD Total % P-valueB RHWO 0.01 ± 0.14 4 0.5 - 0 - na RBWO 1.16 ± 0.81 362 48.8 0.70 ± 0.76 319 47.4 < 0.001 NOFL 0.11 ± 0.31 32 4.3 - 0 - na YBSS 0.15 ± 0.40 46 6.2 0.10 ± 0.32 46 6.8 0.07 DOWO 0.26 ± 0.51 81 10.9 0.25 ± 0.48 114 16.9 0.79 HAWO - 0 - 0.01 ± 0.09 4 0.6 na PIWO 0.70 ± 0.68 217 29.3 0.42 ± 0.59 190 28.2 < 0.001 Total 2.38 ± 1.58 742 - 1.48 ± 1.30 - < 0.001 ARHWO = Red-headed Woodpecker, RBWO = Red-bellied Woodpecker, NOFL = Northern Flicker, YBSS = Yellow-bellied Sapsucker, DOWO = Downy Woodpecker, HAWO = Hairy Woodpecker, PIWO = Pileated Woodpecker. Bt-test 628 Southeastern Naturalist Vol. 5, No. 4 following exceptions. Red-bellied Woodpecker detections differed seasonally in blackwater sites (F = 3.13, 3 df, P = 0.026), but Tukey’s HSD test indicated no significant differences between any 2 seasons. In contrast, Redbellied Woodpecker detections in spring-fed sites did not differ by season (F = 1.77, 3 df, P = 0.154). Yellow-bellied Sapsuckers were more abundant in spring-fed sites (0.41 ± 0.57) during the winter than in blackwater forests (0.25 ± 0.46; t = 2.10, 190 df, P = 0.037). Finally, Downy Woodpeckers were more abundant in blackwater forests (0.34 ± 0.55) during the fall than in the spring (0.15 ± 0.40; F = 3.41, 3 df, P = 0.018). Differences related to landscape variables Red-bellied Woodpecker and Northern Flicker detections were more frequent in sites having an intact upland connection (28.4 ± 5.0 and 2.1 ± 1.9 detections, respectively) versus those with anthropogenic development (e.g., houses) in the uplands (17.0 ± 6.9 and 0.3 ± 0.8 detections, respectively; t– tests, P < 0.05). This pattern did not appear to result from differences in site width as the width of sites with an undeveloped upland (1082 ± 1860 m) was similar to those with development in the uplands (1057 ± 1272; t = 0.05, 30 df, P = 0.97). Landscape variables (e.g., site width, distance of station to edge, percent continuous forested wetland, and percent continuous total forest site width) were all correlated (rs = 0.37 to 0.65, P < 0.04). Red-bellied Woodpecker detections were correlated with percent of forest cover for spring-fed forests (rs = 0.74, P = 0.02), blackwater forests (rs = 0.75, P < 0.001), and for both forest types combined (rs = 0.83, P < 0.001). Pileated Woodpecker detections were only correlated with percent forest cover when both forest types were combined (rs = 0.53, P = 0.01). Downy Woodpecker and Yellow-bellied Sapsucker detections were unrelated to measured landscape features. Differences related to vegetation variables Significant correlations between the previous defined principle components and woodpecker detections were limited. The detection rate of Red-bellied Woodpeckers (rs = - 0.62, P < 0.001), Northern Flickers (rs = -0.70, P < 0.001), and Pileated Woodpeckers (rs = - 0.36, P = 0.045) were correlated with PC 2. Woodpecker detection rates were not correlated to PC 1. Detections of the 4 most common species were not related to tree or snag basal area or to the number of snags per size class (Spearman’s Rank Correlation, P > 0.05). Discussion Three broad patterns were evident from this study. First, in central Florida, forests bordering spring-fed rivers supported more woodpeckers than forests associated with blackwater rivers. The relative proportion of 3 of the 4 most commonly detected woodpeckers, however, was similar between the 2 forest types. Second, woodpeckers were detected most 2006 D.L. Leonard, Jr. and I.J. Strout 629 frequently in the fall and winter. Third, we found few significant correlations among the measured landscape or vegetation variables and the detection rate of woodpeckers. Somewhat unexpected was a lack of correlation between the basal area or number of snags (in any size class) and woodpecker detections. Landscape variables differed between spring-fed and blackwater sites. Despite this, few landscape variables were correlated with the frequency of woodpecker detections. The detection rate of Yellow-bellied Sapsuckers and Downy Woodpeckers was not related to any measured variable. Landscape variables (e.g., percent forest cover) were related to detections of Redbellied and Pileated woodpeckers, and therefore these species do appear to be area-sensitive in central Florida. This relationship, however, may have been an artifact of habitat preferences unrelated to landscape variables, and spring-fed sites were wider and had a larger percentage forest cover within 1 km of point-count stations than did blackwater sites. In other regions, Redbellied and Pileated woodpeckers have been reported to be more abundant in large versus small forest tracts (Kilgo et al. 1998, Renken and Wiggers 1989, Robbins et al. 1989). However, these area-abundance relationships may be restricted to certain geographic regions as these species also have been reported to be area insensitive (Keller et al. 1993, Lynch and Whigham 1984, Noss 1991). Although the vegetative characteristics of spring-fed and blackwater sites differed, few significant relationships were detected between the measured vegetation variables and woodpecker detections. As indicated by the PCA analysis of the vegetation data, woodpecker detections were not related to the variables (i.e., basal area and number of snags) underlying much of the variation in the vegetative characteristic of the forests in this study. In contrast, many studies have noted correlations between vegetative variables (e.g., snag density) and woodpecker abundance (Dickson et al. 1983, Raphael and White 1984, Renken and Wiggers 1993, Shackelford and Conner 1997). Snags are important to woodpeckers for both foraging and nesting, and many studies have documented a relationship between snag density and woodpecker abundance and diversity (Dickson et al. 1983, Evans and Conner 1979, Raphael and White 1984, Shackelford and Conner 1997, Styring and bin Hussin 2004). Other studies, especially in the northeastern United States, have found snags to be a poor predictor of woodpecker abundance (Gunn and Hagan 2000, Welsh and Capen 1992). In the eastern Cascades, Haggard and Gaines (2001) reported that woodpecker density was highest in sites with a medium density of snags. They suggested that preferences for certain snag species may have resulted in this relationship. In central Florida, we found no relationship between snags (total number, number per size class, and basal area) and woodpecker abundance. In the forests we studied, snag density was high and may have contributed to this finding. Snag density reported by Shackelford and Conner (1997) was lower 630 Southeastern Naturalist Vol. 5, No. 4 than that documented in this study. In addition, woodpeckers forage on (D.L. Leonard, pers. observ.) and nest in cavities in sabal palms (Miller 1978, Stevenson and Anderson 1994). This abundant resource may have partially mitigated the importance of dicot snags; unfortunately, we did not quantify the number of dead sabal palms. Alternatively, in cottonwood floodplains, Sedgewick and Knopf (1986) found that the density of trees with large dead limbs was a better predictor of cavity density and breeding habitat for cavity nesters than snag density. We did not quantify density of trees with large dead limbs. Many studies, across a wide variety of geographic regions and habitats, have documented the importance of oaks as foraging sites for woodpeckers (Conner et al. 1994 and references therein). The abundance of woodpeckers documented in this study suggests that oaks where less important to woodpeckers than in other regions. In central Florida, oaks (Q. laurifolia, Q. virginiana Mill., Q. nigra Linnaeus) accounted for 43% of the overstory basal area in blackwater forests but only 14.5% in spring-fed sites. Conner et al. (1994) suggested that oak bark, because of its rugosity, may harbor abundant arthropods. Compared to many oak species, laurel oak has relatively smooth bark (D.L. Leonard, pers. observ.), and thus may support fewer or different arthropods compared to other oaks (see Jackson 1979); in all but one site, laurel oak was the most common oak species. In addition, sabal palms may have provided alternative foraging sites. For example, we often observed Red-bellied Woodpeckers gleaning prey from palms. Although acorns are an important component of the diet of Red-headed Woodpeckers (Smith et al. 2000), their importance to Red-bellied Woodpeckers is equivocal (Bent 1939, Boone 1963, Shackelford et al. 2000, Towles 1989), and they are unimportant in diets of the other species reported in this study (Bull and Jackson 1995, Moore 1995, Walters et al. 2002). The fact that woodpeckers were more abundant in spring-fed sites, which had much lower densities of oaks than blackwater sites, suggests that factors other than acorn availability influenced woodpecker abundance in the sites we studied. However, given the high annual variation in acorn production, a multi-year study may have resulted in a stronger correlation between oak density and woodpecker detections. Bird abundance has been linked to the abundance of fruit (Kwit et al. 2004, Skeate 1987), and hardwood forests often have higher fruit biomass than other habitats (Ewel and Atmosoedirdjo 1987, Kwit et al. 2004). Redbellied and Pileated woodpeckers, Northern Flickers, and Yellow-bellied Sapsuckers are seasonally frugivorous (Beal 1911, Bull and Jackson 1995, Moore 1995, Skeate 1987). In northern Florida hardwood forests, fruit availability peaks in fall and winter, and the number of frugivorous avian species is highest during these seasons (Skeate 1987). Thus, the phenology of fruiting species may have been responsible for the seasonal differences in detections of woodpeckers. Differences in the species composition and importance values of trees between the 2 forest types may have contributed 2006 D.L. Leonard, Jr. and I.J. Strout 631 to differences in woodpecker detections. The importance of sabal palm and saw palmetto fruit to woodpeckers is not well documented (see Bull and Jackson 1995, Moore 1995, Shackelford et al. 2000); however, based on the densities of palms in the two forest types, it is unlikely that their fruits were driving the differences in woodpecker abundance. Sabal palm density was similar between forest types, and saw palmetto was virtually absent from spring-fed forests. Spring-fed sites, however, had more fruiting dicot species (e.g., Nyssa sylvatica Marsh., Morus rubra Linnaeus), albeit at low densities, than blackwater forests. In addition, differences in the diversity and density of fruiting vine species (e.g., Smilax sp., Toxiodendron radicans Linnaeus, Vitis rotundifolia Michaux) may have contributed to the differences in woodpecker abundance between the forest types, but were not quantified during this study. The Downy Woodpecker, like most Picoides, is highly insectivorous (Beal 1911) and was the only species not showing a clear preference for forest type. Some aspects of the woodpecker community of central Florida were similar to that documented in forested wetlands in eastern Texas (Shackelford and Conner 1997) and in south-central Louisiana (Dickson 1978; Table 4). At all sites, woodpecker detections were highest in the fall and winter, and Hairy Woodpeckers were rarely detected. In eastern Texas and central Florida, the Red-bellied Woodpecker was the most common woodpecker. Differences in woodpecker abundance among the studies also were noted. In eastern Texas and south-central Louisiana, the relative abundance of Pileated Woodpeckers was low, while only the Red-bellied Woodpecker was detected more frequently than the Pileated Woodpecker in central Florida. Breeding-bird survey data, however, indicates that the Pileated Woodpecker is more abundant in the regions studied by Dickson (1978) and Shackelford and Conner (1997) than in peninsular Florida (Bull and Jackson 1995). The remaining geographic differences are likely the Table 4. Percent composition of the woodpecker community documented during year-round surveys in forested wetland communities from three different areas in the southeastern United States. SpeciesA Eastern TexasB South-central LouisianaC Central FloridaD RHWO 9.7 49.6 0.3 RBWO 35.4 16.2 48.1 NOFL 22.9 3.9 2.3 YBSS 6.8 25.9 6.5 DOWO 16.6 - 13.8 HAWO 9.7 1.0 0.3 PIWO 7.1 3.4 28.7 ARHWO = Red-headed Woodpecker, RBWO = Red-bellied Woodpecker, NOFL = Northern Flicker, YBSS = Yellow-bellied Sapsucker, DOWO = Downy Woodpecker, HAWO = Hairy Woodpecker, PIWO = Pileated Woodpecker. BShackelford and Conner 1997. CDickenson 1978. DThis study. 632 Southeastern Naturalist Vol. 5, No. 4 result of variation in the number of migrant woodpeckers or in the degree of habitat shifts by resident woodpeckers. In central Florida, a sizeable portion of seasonal variation appeared to be due to habitat shifts of Red-bellied and Pileated woodpeckers; the Yellow-bellied Sapsucker was the only migrant (Robertson and Woolfenden 1992, Stevenson and Anderson 1994). Wintering Northern Flickers and resident Red-bellied Woodpeckers moving into bottomland forests in eastern Texas (Shackelford and Conner 1997) and migrant Red-headed Woodpeckers and Yellow-bellied Sapsuckers in south-central Louisiana (Dickson 1978) were responsible for much of the documented seasonal variation in these studies. Depending on their breeding range, Northern Flickers winter from eastern Texas to central Georgia; individuals breeding in the Great Plains winter in eastern Texas and Okalahoma (Moore 1995). During the winter, Red-headed Woodpecker density is high in the Mississippi River Valley (Bock and Lepthien 1975, Root 1988). Although the number of wintering Northern Flickers in the panhandle and northern peninsula of Florida is high, few individuals winter in central peninsula Florida (Robertson and Woolfenden 1992, Stevenson and Anderson 1994). In Florida, Red-headed Woodpeckers are generally more common in the summer than in winter (Stevenson and Anderson 1994), suggesting that some individuals migrate north in the fall (Smith et al. 2000). Furthermore, in Florida (Belson 1995, Venables and Collopy 1989) and in many other areas throughout their range (Smith et al. 2000), Red-headed Woodpeckers are most common in open forests. This fact likely explains their near absence from the closed forests surveyed in this study. In peninsular Florida, Yellow-bellied Sapsucker abundance declines with decreasing latitude (Stevenson and Anderson 1995). This potentially explains the difference in the number of sapsuckers detected in Louisiana versus Florida. These observations explain some of the differences in the relative abundance of woodpeckers between central Florida and eastern Texas and south-central Louisiana. Relatively little is known about seasonal movements of Red-bellied and Pileated woodpeckers. Short (1982) reported that Red-bellied Woodpeckers are only “slightly migratory,” but may shift to favorable habitats in the winter (also see Shackelford et al. 2000). This corroborates the findings of Shackelford and Conner (1997) as well as our findings, although in southcentral Florida, banded Red-bellied Woodpeckers remained on nesting territories in Pinus palustris Mill. (longleaf pine) flatwoods throughout the year (D.L. Leonard, unpubl. data). Pileated Woodpeckers may wander seasonally, and there is some evidence of limited migration (Bull and Jackson 1995). Similar to the findings from other regions (Dickson 1978, Kilham 1976, Shackelford and Conner 1997), our results indicate that forested wetlands are important to the woodpeckers inhabiting central Florida, especially in the fall and winter. Spring-fed sites supported more species, and a greater abundance of woodpeckers than blackwater forested wetlands, suggesting a preference for these forests. Landscape features were responsible for little of 2006 D.L. Leonard, Jr. and I.J. Strout 633 these differences. We did identify correlations between some vegetative variables and woodpecker detections; however, these correlations often differed from other studies. Differences between central Florida forested wetlands and habitats in other regions (e.g., high snag density, presence of sabal palms) likely contributed to this disparity. 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