Nest-Site Characteristics of Red-bellied and Red-headed Woodpeckers and Northern Flickers in East-Central Ohio

In order to understand more clearly what factors limit the reproductive success of primary cavity-nesting birds, it is important to examine and compare the nest-site characteristics of sympatric species in a variety of forest and woodland habitats. To add to the data already available on various woodpecker species in eastern and central North America, several nest-site and habitat characteristics were compared and quantified for 46 red-bellied woodpecker (Melanerpes carolinus), 26 red-headed woodpecker (M. erythrocephalus), and 44 northern flicker (Colaptes auratus) nest cavities. Flicker nest cavities had larger entrances and were located lower in trees than were red-bellied and red-headed woodpecker cavities. Red-bellied woodpeckers excavated fresh nest cavities surrounded by bark in living trees significantly more often than flickers and red-headed woodpeckers. Red-bellied woodpecker cavities were also located in limbs angling downward more often than those of flickers and red-headed woodpeckers, although the difference in frequency was not significant. The compass orientation of nest cavities was random in all species. Redbellied woodpeckers nested in forested areas with abundant ground vegetation more frequently than did flickers and red-headed woodpeckers. The continued existence of northern flickers and particularly redheaded woodpeckers in the Unglaciated Plateau region of Ohio is probably dependent on the continued existence of large dead trees in the region. OHIO J. SCI. 94 (1): 2-7, 1994 INTRODUCTION Woodpeckers and other cavity-nesting birds are largely dependent on dead or dying trees for nest sites (Conner et al. 1976, Evans and Conner 1979, Scott 1979, Mannan et al. 1980, van Balen et al. 1982, Raphael and White 1984) and indeed have become increasingly threatened by a reduction in the number of dead trees (snags) (Raphael and White 1984; Sedgwick and Knopf 1986,1990). Various lines of evidence suggest that nest sites for primary cavitynesting birds including woodpeckers are often limited: 1) suitable nest trees are frequently occupied by more than one cavity-nesting species (van Balen et al. 1982, Gutzwiller and Anderson 1987, Ingold 1990); 2) interspecific nest-site competition among woodpecker species as well as among woodpeckers and various secondary-cavity nesting species is common (Short 1979, Kilham 1983, Ingold 1989a); and 3) the numbers of some woodpecker species including red-headed woodpeckers {Melanerpes erythrocephalus) and northern flickers {Colaptes auratus) have declined in much of eastern and central North America during the past 25 years (Robbins et al. 1986, Peterjohn and Rice 199DThus the availability of suitable nest sites may be important when determining what factors limit the reproductive success of cavitynesting birds as well as when assessing population numbers and community composition among woodpeckers and other excavator species. Red-bellied woodpeckers {Melanerpes carolinus), redheaded woodpeckers, and northern flickers are primary cavity-nesting species broadly sympatric throughout much of eastern North America. In Ohio, red-bellied woodpeckers (RBW) are locally common permanent 'Manuscript received 22 September 1993 and in revised form 9 December 1993 (#93-22). residents while flickers are common breeding residents (Peterjohn and Rice 1991). Red-headed woodpeckers (RHW), however, are generally considered uncommon and only locally distributed in the Unglaciated Plateau region of east-central Ohio (Peterjohn and Rice 199DMany authors have presented data on the nest-site characteristics of one or more of these species (Dennis 1969, Reller 1972, Conner 1975, Jackson 1976, Kilham 1977, Stauffer and Best 1982, Gutzwiller and Anderson 1987, Harestad and Keisker 1989, Kerpez and Smith 1990, Sedgwick and Knopf 1990), but few have examined the characteristics of all three species concomitantly in a zone of sympatry. Moreover, few studies of this nature have been undertaken in Ohio. The objective of the present study was to quantify and describe various characteristics of the nest sites and nest trees of these species and to compare the results with those of similar studies conducted in other forest and woodland types in different regions. MATERIALS AND METHODS From late March through late August 1990-1992, active RBW, flicker, and RHW nest sites were located in and around New Concord, in Muskingum and Guernsey counties, in east-central Ohio. The study area covers about 700 ha and consists of a variety of agricultural and forested habitats (Ingold and Densmore 1992). Within the larger study area, study sites were chosen randomly from a map. Woodpecker nests were located by listening for adults calling or excavating and by observing individuals flying to and from a particular area. Each active woodpecker cavity was observed for a minimum of 30 min once a week to determine occupancy and status. For each cavity tree a variety of nest-site parameters including cavity height (m), horizontal and vertical diameter of cavity entrance (cm), facing compass direction OHIO JOURNAL OF SCIENCE D. J. INGOLD of the entrance (degrees from north), angle of the cavity limb (vertical, facing up or down 1-45°, or facing up or down 46-90°), and diameter at breast height (DBH) of the cavity tree were determined. In addition, the presence or absence of bark around the cavity entrance, whether the cavity tree and limb were living or dead, and whether the cavity was of natural origin or excavated was noted. Finally, the number of small and large trees (2.5-10.0 cm DBH and >10 cm DBH, respectively) was quantified in a circular area of 0.04 ha around the cavity tree, and an estimated percentage of ground vegetation (<1.5 m) around the cavity tree using a profile board (values scored from 0 to 5: zero represented no ground vegetation and 5 represented maximum vegetation; see also Nudds 1977). Each variable that consisted of continuous data (cavity height, horizontal and vertical diameter of cavity entrance, tree DBH, and number of trees around cavity tree) was tested for equality of variances with the variance ratio test (Zar 1984). The horizontal and vertical diameters of cavity entrances and the number of small trees around the cavity tree had significantly unequal variances and were converted using logarithmic transformations (X = log[X+l]) (Zar 1984). Differences in nest-site parameters among species were determined with one-way analysis of variance. When differences were detected, Scheffe's Tests for multiple comparisons were used to detect differences between species. The data for state of tree and limb, bark, cavity angle, cavity origin, compass direction, and vegetation height were binomial or ordinal in nature, and with the exception of compass direction, were analyzed using contingency table Chi-square tests. The facing compass direction of nest cavities was tested for randomness in each species using the Rayleigh test which produces an r value (mean vector length) that is a measure of the concentration of nest orientations around the mean nest orientation (Batschelet 1981, Zar 1984; see also Kerpez and Smith 1990). RESULTS Forty-six active RBW, 44 flicker, and 26 RHW nest cavities were located, and dimensions of cavity entrances for 23 RBW, 32 flicker, and 18 RHW nests were determined. Five of six cavity-site variables that consisted of continuous data differed significantly among species (Table 1). Flickers had significantly larger horizontal and vertical cavity entrances than did RBWs and RHWs (P <0.05); moreover, RHWs had significantly larger horizontal entrances than RBWs (PO.05). The mean cavity height for flicker nests was significantly lower than the means for RBW and RHW nests (P<0.05), while the mean DBHs for cavity trees were statistically indistinguishable among species. RBWs chose nest sites in areas with significantly more larger and smaller trees around the cavity tree than did flickers and RHWs (JP <0.05), although flickers also nested in areas with significantly more smaller trees than RHWs (Table 1). Three of six cavity-site variables that consisted of binomial or ordinal data differed significantly among species (Table 2). RBWs nested in freshly excavated nest cavities in living trees with bark around the cavity entrance significantly more often than flickers and RHWs CPO.01). Conversely, status of the nest limb, angle of the nest limb, and the amount of ground vegetation around the cavity tree did not significantly differ among species (Table 2). The compass direction of nest cavities was not significantly different from a random orientation for RBWs (Fig. 1; r= 0.18, P>050, n = 46), flickers (Fig. 1; r= 0.09, P>0.60, n = 44), or RHWs (Fig. 1-r= 0.07, P>0.70, n = 26). DISCUSSION Nest Cavity Characteristics That northern flickers excavate cavities with larger entrances than RBWs and RHWs is not surprising given their larger size. Kerpez and Smith (1990) and McAuliffe