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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.
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.
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).
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.
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
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).
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.
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.
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