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Effect of Time and Barred Owl Playback on Winter Detection of Woodpeckers in East-Central Mississippi
H. Dawn Wilkins and Michael S. Husak

Southeastern Naturalist, Volume 5, Number 3 (2006): 555–560

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2006 SOUTHEASTERN NATURALIST 5(3):555–560 Effect of Time and Barred Owl Playback on Winter Detection of Woodpeckers in East-Central Mississippi H. Dawn Wilkins1,2,* and Michael S. Husak1,3 Abstract - Broadcast vocalizations have been used to augment winter point counts. We investigated the effects of time and Strix varia (Barred Owl) playback on woodpecker detection. Habitats were classified as upland pine, bottomland hardwood, and mixed pine-hardwood stands. Ten unlimited-radius, silent point counts of 3-min and 10-min duration were conducted in each habitat type on alternating weeks. During alternate weeks, silent counts followed by Barred Owl playback and postplayback counts were conducted. Detection was significantly greater during 10-min silent counts than during 3-min silent counts. We detected more woodpeckers after Barred Owl playback than during 3-min silent counts prior to playback. Species diversity was highest in mixed pine-hardwood stands, although abundance was lower than in hardwood stands. Mixed stands may not be able to support high woodpecker densities as well as bottomland hardwood forests. Introduction Playback of broadcast vocalizations has been used to augment counts of territorial birds during the non-breeding season (Graves 1996, Johnson et al. 1981, Lynch 1995, Mabey and Morton 1992, Sliwa and Sherry 1992). Playback has also been effective in increasing detectability of non-territorial wintering birds (Lynch 1995). Most playback studies use calls of conspecifics to elicit responses, but some studies have used predator calls to increase detection. For example, broadcasts of Glaucidium brasilianum Gmelin (Ferruginous Pygmy- Owl) calls significantly increased the detectability of hummingbirds in Mexico (Lynch 1995). Woodpeckers respond to the calls of Strix varia Barton (Barred Owls) and Otus asio Linnaeus (Eastern Screech-Owls) (Shackelford and Conner 1997, Wright 1991). Shackelford and Conner (1997) used playback of Barred Owl calls to increase the detectability of woodpeckers in Texas. Woodpeckers fill an important niche in forest ecosystems because they provide cavities for other vertebrates and invertebrates and help control harmful insect populations such as tree-killing bark beetles like Dendroctonus frontalis Zimmermann (southern pine beetle) (Dickson et al. 1979, Scott et al. 1977). Therefore, the abundance of secondary cavity-nesting species and harmful insect populations are dependent on the abundance and diversity of woodpeckers. In this study, we used unlimited-radius point counts to estimate woodpecker abundance in upland pine, bottomland hardwood, and mixed pine-hardwood stands in east-central Mississippi. We conducted both silent 1Department of Biological Sciences, Mississippi State University, Mississippi State, MS 39762. 2Current address - Department of Biological Sciences, University of Tennessee at Martin, Martin, TN 38238. 3Current address - Department of Biological Sciences, Cameron University, Lawton, OK 73505. *Corresponding author - 556 Southeastern Naturalist Vol. 5, No. 3 counts and counts using playback of Barred Owl calls to estimate woodpecker abundance. We compared 3-min and 10-min silent counts to determine if point duration increased detectability of woodpeckers. Also, we compared counts conducted prior to Barred Owl playback to post-playback counts to determine if detectability was increased. Finally, we examined differences in woodpecker diversity among different habitats. Methods This study was conducted at the Noxubee National Wildlife Refuge (NNWR) located in Oktibbeha, Noxubee, and Winston Counties in central Mississippi. The study site was divided into upland pine, bottomland hardwood, and mixed pine-hardwood stands. Pine stands were composed of Pinus taeda Linnaeus (loblolly pine) and P. echinata Miller (shortleaf pine), which were moderately stocked with pole timber (diameter at breast height (DBH) of 13–26 cm [5–10 in]). Bottomland hardwood stands were dominated by Quercus spp. (oaks) and Carya spp. (hickories) that were moderately to fully stocked with small to large sawtimber (DBH ≥ 28 cm [11 in]). Mixed stands were lightly to moderately stocked with pole timber and small sawtimber. Ten points were placed in each habitat type along trails and firebreaks with a minimum distance between points of 250 m (273.4 yd) (Ralph et al. 1993). We conducted unlimited-radius point counts once-a-week in each habitat type from 1 November 1997 to 1 February 1998. Unlimited-radius counts were selected over fixed-radius counts because woodpeckers can be heard and recorded accurately at a great distance (Ellison 1992). Counts began within a half-hour after sunrise and were completed within 4 hrs post-sunrise. All individual woodpeckers detected by sight or sound were recorded. Each observer made an effort to ensure that each individual was recorded only once to avoid multiple counts of the same individual at a particular point. Silent point counts (without the use of playback) of 10 min were conducted every other week within each stand. Silent point counts were divided into 0–3 min and 3–10 min intervals. During alternate weeks, 3-min silent counts were followed by playback of Barred Owl calls for 3 min followed by a 3-min postplayback silent count (modified from Shackelford and Conner 1997). The Barred Owl calls used for playback were from a dueting pair of owls giving typical Barred Owl calls and “hoo-waaahhh” responses. We used a portable tape player with a single speaker that was held with the speaker facing upwards to try and avoid directional bias. Target species at NNWR included: Melanerpes erythrocephalus Linnaeus (Red-headed Woodpeckers), M. carolinus Linnaeus (Red-bellied Woodpeckers), Picoides pubescens Linnaeus (Downy Woodpeckers), Colaptes auratus Linnaeus (Northern Flickers), and Dryocopus pileatus Linnaeus (Pileated Woodpeckers) which are all year-round residents of eastcentral Mississippi. The Nearctic migrant, Sphyrapicus varius Linnaeus (Yellow-bellied Sapsucker), also occurs at NNWR during the winter. Picoides borealis Vieillot (Red-cockaded Woodpeckers) and P. villosus 2006 H.D. Wilkins and M.S. Husak 557 Linnaeus (Hairy Woodpeckers) were also observed during the point counts, but in such low numbers that they were excluded from all data analysis. Chi-square goodness-of-fit tests were used to compare silent versus playback and 3-min versus 10-min counts. Using data from 10-min counts, analysis of variance on the ranked data (equivalent to the Kruskal-Wallis test) with Fisher’s protected LSD tests were used to compare the abundance of each species per habitat type. A diversity rarefaction using species richness was run on the total abundance of each woodpecker species from each habitat type to determine if the three stands were equally diverse using EcoSim (Gotelli and Entsminger 2000). Rarefaction was used to standardize all samples from the three different stands to a common sample size based on the same number of individuals (Gotelli and Graves 1996). This allows us to compare the samples directly using a 95% confidence interval because each sample is now based on the same number of individuals (Gotelli and Graves 1996). Results Playback of Barred Owl calls significantly increased the number of woodpeckers detected by 70% (Table 1). However, 10-min counts significantly increased the number of woodpeckers observed over 3-min counts by 102% (Table 2). For Red-headed Woodpeckers, Red-bellied Woodpeckers, Yellowbellied Sapsuckers, Downy Woodpeckers, and Norther Flickers, 10-min counts produced a greater increase in detection than the use of Barred Owl calls (Tables 1 and 2). Pileated Woodpeckers had a greater increase in detection with the use of Barred Owl calls over 10-min counts (Tables 1 and 2). Table 1. A comparison of woodpecker responses during 3-min silent counts and post-Barred Owl playback counts in east-central Mississippi. Pre- Post- Species playback playback % increase χ2 P-value Red-headed Woodpecker 78 117 50% 7.80 < 0.05 Red-bellied Woodpecker 112 181 61% 16.25 < 0.01 Yellow-bellied Sapsucker 79 106 34% 3.94 < 0.05 Downy Woodpecker 54 102 89% 14.30 < 0.01 Pileated Woodpecker 54 111 106% 19.69 < 0.01 Northern Flicker 111 213 92% 23.11 < 0.01 Total 488 830 70% 88.74 < 0.01 Table 2. A comparison of woodpecker responses during 3-min and 10-min silent counts in eastcentral Mississippi. Species 0–3 min 0–10 min % increase χ2 P-value Red-headed Woodpecker 63 147 133% 33.60 < 0.01 Red-bellied Woodpecker 106 201 90% 29.40 < 0.01 Yellow-bellied Sapsucker 28 57 104% 9.89 < 0.01 Downy Woodpecker 54 103 91% 20.29 < 0.01 Pileated Woodpecker 70 133 90% 17.55 < 0.01 Northern Flicker 79 166 110% 30.89 < 0.01 Total 400 807 102% 137.24 < 0.01 558 Southeastern Naturalist Vol. 5, No. 3 Red-headed Woodpeckers (F = 6.89, P = 0.0038), Red-bellied Woodpeckers (F = 26.70, P < 0.0001), Yellow-bellied Sapsuckers (F = 49.16, P < 0.0001), Downy Woodpeckers (F = 9.99, P = 0.0006), and Northern Flickers (F = 15.74, P < 0.0001) were strongly associated with bottomland hardwood stands (Fig. 1). Pileated Woodpeckers were observed equally in all three habitat types (F = 1.47, P = 0.2486; Fig. 1). Red-cockaded Woodpeckers were observed only in mixed pine-hardwood stands (n = 8). Hairy Woodpeckers were observed in both mixed pine-hardwood (n = 5) and hardwood stands (n = 2). When species diversity curves are compared using 95% confidence intervals, the mixed stand was significantly more diverse than both upland pine and bottomland hardwood stands (Fig. 2). Pine and hardwood stands were not significantly different with respect to the diversity of woodpecker species observed (Fig. 2). Abundance was greatest in bottomland hardwood stands (Fig. 2). Discussion Similar to our findings, Shackelford and Conner (1997) observed a 71% increase in the number of woodpeckers observed when using playback of Barred Owl calls. Woodpeckers were observed to move towards the observer and became more vocal suggesting that playback increased detection. Although Barred Owl calls tend to increase the number of woodpeckers observed, the significant increase in the number of woodpeckers counted may be an artifact of remaining at the point longer. We found a greater increase in the number of woodpeckers observed for all species, except Figure 1. Woodpecker abundance in hardwood, mixed pine-hardwood, and pine stands in east-central Mississippi (RHWO = Red-headed Woodpecker, RBWO = Red-bellied Woodpecker, YBSS = Yellow-bellied Sapsucker, DOWO = Downy Woodpecker, PIWO = Pileated Woodpecker, NOFL = Northern Flicker). 2006 H.D. Wilkins and M.S. Husak 559 Pileated Woodpeckers, after 10-min silent counts than when using Barred Owl calls. Time is an important factor in increased detection for many species, but increased point-count duration reduces the number of points that can be completed per morning (Fuller and Langslow 1983, Hutto et al. 1986, Lynch 1995). The use of Barred Owl calls significantly increased detectability, therefore playback may shorten the length of time needed per point and increase the number of points that can be completed in a morning. Although many of the species were most strongly associated with hardwood stands, the mixed pine-hardwood stand had greater woodpecker diversity than pine and hardwood stands. All species were observed in the mixed habitat type. Although the endangered Red-cockaded Woodpeckers can be observed at Noxubee, the upland pine stands used in this study were too young to support them. Also, Red-cockaded Woodpeckers were not detected in hardwood stands, and Hairy woodpeckers were not observed in pine stands. Although mixed stands were more diverse, the abundance of woodpeckers observed was low indicating that mixed habitats may not be suitable for supporting most species at the same population size as bottomland hardwood or pine stands. Red-cockaded Woodpeckers were not observed in the young upland pine stands, and Hairy Woodpeckers are rare at Noxubee. In contrast, Pileated Woodpeckers were observed equally in all stands, possibly because their calls and drums can be heard for considerable distances. The estimated number of Pileated Woodpeckers found in each of these habitat types may be elevated because one calling individual could be counted at more than one point. Also, due to the patchiness of habitats at NNWR, Pileated Woodpeckers calling or drumming in the distance could be in a different habitat type than the one being sampled. Therefore, we would recommend using a Figure 2. Woodpecker species-diversity curves for hardwood, mixed pine-hardwood, and pine stands in east-central Mississippi. 560 Southeastern Naturalist Vol. 5, No. 3 distance greater than 250 m between points and using fixed-radius rather than unlimited-radius point counts to census Pileated Woodpecker abundance. Since these results were obtained during one winter, we recommend continued research into the effect of Barred Owl calls on woodpecker detection, not only during the winter, but throughout the year. Acknowledgments We thank David Richardson and the staff of the Noxubee National Wildlife Refuge for supporting this research. We also thank Doug Wood for helpful comments on the manuscript. Literature Cited Dickson, J.G., R.N. Conner, R.R. Fleet, J.A. Jackson, and J.C. Kroll. 1979. The role of insectivorous birds in forest ecosystems. Academic Press, New York, NY. 381 pp. Ellison, W.G. 1992. Identifying the rhythms of northeastern woodpeckers. Birding 24:351–354 Fuller, R.J., and D.R. Langslow. 1984. Estimating numbers of birds by point counts: How long should counts last? Bird Study 31:195–202. Gotelli, N., and G. Entsminger. 2000. EcoSim Version 5.52. Acquired Intelligence, Inc., Kesey-Bear, Jericho, VT. Gotelli, N., and G.R. Graves. 1996. Null Models in Ecology. 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