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VOCALIZATIONS OF THE GUATEMALAN PYGMY-OWL
(GLAUCIDIUM COBANENSE)
KNUT EISERMANN
1
PROEVAL RAXMU Bird Monitoring Program, Coba´n, Alta Verapaz, Guatemala and
Apartado Postal 98 Perife´rico, 01011 Guatemala Ciudad, Guatemala
STEVE N.G. HOWELL
P.O. Box 423, Bolinas, CA 94924 U.S.A.
ABSTRACT.—The lowlands of the Isthmus of Tehuantepec separate the range of the Guatemalan Pygmy-Owl
(Glaucidium cobanense), recognized as a species in modern owl taxonomy and resident in the highlands of
southeastern Mexico, Guatemala, and Honduras, from the range of Mountain Pygmy-Owl (Glaucidium
gnoma) in the Mexican highlands northwest of the isthmus. Here we document hitherto undescribed
vocalizations of Guatemalan Pygmy-Owls in the Guatemala-Chiapas highlands. We recorded four different
vocalization types of adults: (1) territorial toot calls, (2) whiwhiwhi calls given by the female during nest-site
establishment, (3) soft toot calls of the male near the nest, and (4) copulation calls. The territorial toot calls
of Guatemalan Pygmy-Owls differed from those of Mountain Pygmy-Owls in Mexico. The mean individual
call rate of Guatemalan Pygmy-Owls was 3.4 60.5 notes/sec (n549 call series of six individuals), signif-
icantly higher than in Mountain Pygmy-Owls (1.9 60.3 notes/sec, n534 call series of eight individuals).
This new evidence of vocal differences supports modern taxonomic separation of both taxa.
KEY WORDS: Glaucidium gnoma; Glaucidium cobanense; Guatemalan Pygmy-Owl;Mountain Pygmy-Owl;
Northern Pygmy-Owl;vocalizations.
VOCALIZACIONES DE GLAUCIDIUM COBANENSE
RESUMEN.—Las tierras bajas del istmo de Tehuantepec aı´slan el a´ rea de distribucio´n de Glaucidium coba-
nense, reconocida como especie segu´n la taxonomı´a moderna de bu´hos y residente en las tierras altas de
Chiapas, Me´xico, Guatemala y Honduras, del a´rea de distribucio´n de Glaucidium gnoma en las tierras altas
de Me´xico al norte del istmo. Aquı´ documentamos vocalizaciones de Glaucidium cobanense de las tierras altas
de Guatemala y Chiapas que au´n no habı´an sido descritas. Cuatro diferentes vocalizaciones de adultos
fueron registradas: (1) llamado territorial, (2) serie de llamado vivivi de la hembra durante la fase de
establecimiento del sitio de anidacio´n, (3) llamado suave del macho cerca del nido, y (4) llamados de
copulacio´n. El llamado territorial de G. cobanense fue distinto del de G. gnoma del norte de Me´ xico. El
promedio individual del tiempo de llamadas fue significativamente ma´s ra´pido en G. cobanense (3.4 notas/
seg 60.5, n549 series de notas de seis individuos) que en G. gnoma (1.9 notas/seg 60.3, n534 series de
notas de ocho individuos). Esta nueva evidencia de diferencias vocales apoya la separacio´n taxono´ mica de
ambos taxones.
[Traduccio´n del equipo editorial]
The taxonomy of pygmy-owls of the Glaucidium
gnoma complex is vexed (Holt and Petersen 2000).
The American Ornithologists’ Union (1998 and
supplements) and Dickinson (2003) recognized on-
ly one species, Glaucidium gnoma, the Northern Pyg-
my-Owl, ranging from northwestern North America
through northern Central America. Modern treat-
ments, however, such as Marks et al. (1999) and
Ko¨nig and Weick (2008) recognized four species:
Northern (G. californicum), Mountain (G. gnoma),
Cape (G. hoskinsii) and Guatemalan (G. cobanense)
pygmy-owls. We follow the treatment of Marks et al.
(1999) and Ko¨nig and Weick (2008), and our data
provide further support for the species status of G.
cobanense. The Guatemalan Pygmy-Owl occurs in the
highlands of northern Central America southeast of
the Isthmus of Tehuantepec, including in Chiapas
(Mexico), Guatemala, and Honduras, and is geo-
1
Email address: knut.eisermann@proeval-raxmu.org
J. Raptor Res. 45(4):304–314
E2011 The Raptor Research Foundation, Inc.
304
graphically isolated from Mountain Pygmy-Owl,
which occurs in the highlands northwest of the isth-
mus of Tehuantepec, in Mexico (Howell and Webb
1995, Ko¨nig and Weick 2008). Sharpe (1875a,
1875b) classified the Guatemalan Pygmy-Owl based
on the plumage coloration of rufous-morph individ-
uals. Because coloration is variable in pygmy-owls,
Sharpe’s classification has often not been accepted
(Salvin and Godman 1897–1904, American Orni-
thologists’ Union 1998). Marks et al. (1999) treated
the Guatemalan Pygmy-Owl as a species, but indicat-
ed that this status may not be warranted. Ko¨nig and
Weick (2008) recognized it as a species because of
vocal differences, but omitted a detailed description
of its vocalization.
More recently, classifications of Glaucidium species
based on differences in vocalizations (Ko¨nig 1994,
Howell and Robbins 1995, Robbins and Howell
1995, Robbins and Stiles 1999) have been supported
by DNA-sequence data (Heidrich et al. 1995, Wink et
al. 2008). Here we describe vocalizations of Guatema-
lan Pygmy-Owls from the highlands of Guatemala
and Chiapas, Mexico, and compare them to vocaliza-
tions of Mountain Pygmy-Owls from Mexico.
STUDY AREA AND METHODS
The Guatemalan Pygmy-Owl occurs above 1500 m
in the highlands of Chiapas, Guatemala, and Hon-
duras. Natural vegetation in these mountains are
pine (Pinus spp.), oak (Quercus spp.), and pine-
oak forests in less-humid sections, cloud forests in
most-humid areas, and coniferous forests of cypress
(Neocupressus lusitanica) and fir (Abies guatemalensis)
in the highest areas above 2500 m. Natural vegeta-
tion in the owl’s range is fragmented by agricultural
crops (corn, coffee, pasture land; Ochoa-Ganoa and
Gonza´ lez-Espinosa 2000, Cayuela et al. 2006, Eiser-
mann and Avendan˜o 2006, Eitniear and Eisermann
2009, Eisermann et al. 2011).
We describe vocalizations of Guatemalan Pygmy-
Owl based on recordings of 11 individuals during
occasional observations at seven sites in the Atlantic
and Pacific slope highlands of Guatemala and Chia-
pas, Mexico (Table 1). KE recorded vocalizations in
Guatemala with a Fostex FR-2LE (enhanced by
Oade Brothers Audio) digital recorder and Senn-
heiser M67 directional microphone with a sample
rate of 96 kHz. SNGH recorded vocalizations in
Mexico with an Olympus LS-10 digital recorder
and a Sennheiser M66 directional microphone with
a sampling rate of 44.1 kHz. Vocalizations were an-
alyzed and sonograms produced with software Ra-
ven Pro 1.3 (Cornell Laboratory of Ornithology
2008). Contributing researchers used different re-
cording equipment (Marantz PMD661, Marantz
PMD-222, Uher 4000 L, Sony TCM-5000EV, Sony
Table 1. Sample sites for recordings of Guatemalan Pygmy-Owls.
SITE,DATE,AND RESEARCHER
GEOGRAPHIC
COORDINATES
COUNTRY,STATE/
PROVINCE
ELEVATION
(m) HABITAT
Reserva Chelemha´, Yalijux mountain
(January–April 2010, KE)
15u239N, 90u049W Guatemala, Alta Verapaz 2100 cloud forest edge
Reserva K’antı´ Shul, Yalijux mountain
(10 April 2010, KE)
15u249N, 90u049W Guatemala, Alta Verapaz 2300 cloud forest
Sanimtaca´, Sacranix mountain
(13 February 2010, KE)
15u299N, 90u289W Guatemala, Alta Verapaz 1500 pine-oak forest
Finca El Recuerdo, Cerro El Amay
(16 October 2010, KE)
15u279N, 90u469W Guatemala, Quiche´ 1700 pine-oak forest
Finca San Sebastian, Acatenango
volcano (4 January 2011, KE)
14u319N, 90u509W Guatemala,
Sacatepe´quez
1900 coffee plantation
with old growth oak
(Quercus sp.) shade
Finca Chilax, Xucaneb mountain
(24 November 2010, J.P. Cahill)
15u239N, 90u219W Guatemala, Alta Verapaz 1600 cloud forest edge
San Cristobal de las Casas, Chiapas
(3 March 2007, SNGH)
16u419N, 92u329W Mexico, Chiapas 2400 pine-oak forest
34 km SE of San Cristobal de las Casas,
Chiapas (13 March 2010, SNGH)
16u369N, 92u229W Mexico, Chiapas 2400 pine-oak forest
14 km SE of San Cristobal de las Casas,
Chiapas (15 March 2009, N. Athanas,
XC31724)
16u399N, 92u329W Mexico, Chiapas 2400 pine forest
DECEMBER 2011 GUATEMALAN PYGMY-OWL VOCALIZATIONS 305
TC-D5 Pro II). Voucher recordings were archived at
the Macaulay Library (Cornell Lab of Ornithology,
Ithaca, New York, U.S.A.; http://macaulaylibrary.
org). Voucher photographs were archived at VIREO
(Academy of Natural Sciences, Philadelphia, Penn-
sylvania, U.S.A.; http://vireo.acnatsci.org).
To compare call rate (notes/sec), length (sec),
and frequency (kHz) of notes between Guatemalan
Pygmy-Owls and Mountain Pygmy-Owls, recordings
of eight individuals from Mexico were analyzed.
SNGH recorded a bird at Cerro San Felipe, Oaxaca
(17u119N, 96u389W) on 19 March 2010. The other
recordings of Mountain Pygmy-Owl used for our
analysis were previously archived at the Macaulay
Library (ML) or at xeno-canto (xeno-canto.org,
XC): ML17195 (Sinaloa, 13 March 1976, T.A. Parker
III), ML53150 (Sinaloa, 30 March 1991, L.R. Macau-
lay), ML57735 (Jalisco, 13 March 1985, D. Delaney),
ML57736 (Jalisco, 13 March 1985, D. Delaney),
ML57737 (Jalisco, 13 March 1985, D. Delaney),
ML136513 (Sinaloa, 29 December 2001, M.J. Ander-
sen), XC9671-74 (La Cumbre, Oaxaca , 27 February
1995, A. Chartier). Locations where recordings were
obtained were plotted (Fig. 1).
For analyses, we marked onset and offset of sig-
nals in the sonograms using the curser in Raven Pro
1.3. Depending on the recording distance, one or
several harmonic frequencies were recorded, but
the fundamental frequency was always the dominant
one, and was used for all analyses. To lower bias of
signal onset and offset caused by manual signal se-
lection, we used the following robust signal mea-
surements determined with Raven Pro 1.3 for statis-
tical tests of significant differences (Charif et al.
2008): center frequency, center time, and Inter
Quartile Range (IQR) duration of notes. In addi-
tion, we measured peak frequency per note, which
is the frequency with the maximum power [dB]).
Figure 1. Localities of voice recordings of Guatemalan (Glaucidium cobanense) and Mountain Pygmy-Owls (G. gnoma)
and geographic ranges of both species. Recording sites: 1—Finca El Recuerdo, Quiche´, 2—Sanimtaca´ , Alta Verapaz, 3—
Finca Chilax, Alta Verapaz, 4—Chelemha´ Reserve, Alta Verapaz, 5—Finca San Sebastian, Sacatepe´ quez, 6–8—San Cris-
tobal de las Casas, Chiapas, Mexico, 9–10—La Cumbre, Oaxaca, Mexico, 11–13—Volca´n de Fuego, Jalisco, Mexico, 14—
Barranca Rancho Liebre, Sinaloa, Mexico, 15—El Palmito, Sinaloa, Mexico, 16—Durango highway, Sinaloa, Mexico.
CH—Chiapas, Mexico, GT—Guatemala, HN—Honduras, JA—Jalisco, Mexico, OA—Oaxaca, Mexico, SI—Sinaloa, Mex-
ico, SV—El Salvador.
306 EISERMANN AND HOWELL VOL. 45, NO.4
We determined mean individual center frequency
(Hz) and IQR duration (sec) of notes for each bird
using each note as a replicate unit. Mean individual
call rate (notes/sec) was determined by using each
call series as a replicate unit. Call series were de-
fined by pauses longer than intervals between calls.
For the calculation of call rate, only call series with
.3 calls were assessed. The time lapse of a call series
was limited by the center time of the first and the
last note.
Figure 2. Sonograms of territorial toot call of Guatemalan Pygmy-Owl (Glaucidium cobanense): (a) Toot call of a brown
morph male singing in the nest territory at 60 m from the nest (recording ML #161746, 12 March 2010, K. Eisermann);
(b) Single toot note of the same recording. Axes represent time and frequency according to the voice recording archived
at the Macaulay Library.
Table 2. Different parameters of territorial toot calls of Guatemalan Pygmy-Owl (Glaucidium cobanense) and Mountain
Pygmy-Owl (G. gnoma).
SPECIES
MEAN CALL RATE IN
NOTES/SEC (6SD)
MEAN LENGTH
(SEC)OF EACH
NOTE (6SD)
MEAN INTER QUARTILE
RANGE DURATION
(SEC)OF EACH
NOTE (6SD)
MEAN PEAK
FREQUENCY (HZ)OF
EACH NOTE (6SD)
MEAN CENTER
FREQUENCY (HZ)OF
EACH NOTE (6SD)
G. cobanense
a
3.4 60.5 0.11 60.02 0.032 60.009 1098.1 629.0 1094.6 628.6
n549 call series n52570 notes n52570 notes n52570 notes n52570 notes
G. cobanense
b,c
4.2 60.6 0.10 60.01 0.025 60.008 1126.2 637.6 1118.9 636.6
n5114 call series n51149 notes n51149 notes n51149 notes n51149 notes
G. gnoma
d
1.9 60.3 0.12 60.02 0.030 60.009 1096.8 656.6 1093.7 657.9
n534 call series n51399 notes n51399 notes n51399 notes n51399 notes
a
n56 individuals.
b
n55 individuals.
c
Vocalization elicited by playback, or unknown whether elicited by playback or spontaneous.
d
n58 individuals.
DECEMBER 2011 GUATEMALAN PYGMY-OWL VOCALIZATIONS 307
Figure 3. Sonograms of (a) rapid whiwhiwhi call of female Guatemalan Pygmy-Owl and (b) female duetting with male
(fundamental marked with brackets) emitting soft toot call. Axes represent time and frequency according to voice-
recording archived at the Macaulay Library (ML #161747, 12 March 2010, K. Eisermann).
308 EISERMANN AND HOWELL VOL. 45, NO.4
To assess relationships between Guatemalan and
Mountain Pygmy-Owls we used an unweighted pair-
group average (UPGMA) cluster analysis of vocali-
zations based on the Euclidean distance of call rate
(mean numbers of notes/sec) using PAST 2.08 soft-
ware (Hammer et al. 2001). Because call rate can
differ between spontaneously calling owls and those
responding to playback, we used only recordings of
spontaneous territorial toot calls of Mountain Pygmy-
Owls and Guatemalan Pygmy-Owls for comparative
analyses.
To compare vocal parameters between both spe-
cies, we first calculated individual means of the
length of each note, IQR duration, and center fre-
quency of each note. Means are reported 61 stan-
dard deviation (SD). A permutation test for equality
of means with a50.05 using PAST 2.08 software
(Hammer et al. 2001) was used to compare individ-
ual means between both species. This is a nonpara-
metric test, where observations are randomly moved
among the groups, and compared with the tstatistic
(the number of permutations is given with the test
results). We used this test because data were not
normally distributed, and the assumption of n.3
in each sample (Hammer 2011) was met.
RESULTS
We recorded four vocalization types of adult Gua-
temalan Pygmy-Owls. In addition to territorial toot
calls, three different vocalizations of a breeding pair
near the nest were documented.
Territorial Toot Calls. Among eleven individuals,
series of toot notes consisted of 1–300 notes, which
were spaced evenly or in pairs (Fig. 2). A bird in a
breeding pair could be identified as male; the sex of
the other birds remained unknown. The mean call
rate was higher in vocalizations elicited by broadcast
of conspecific calls (4.2 60.6 notes/sec, range 3.2–
6.8, n5114 call series of four individuals; Table 2),
than in vocalization not elicited by playback (3.4 6
0.5 notes/sec, range 2.8–5.4, n549 call series of 6
individuals) (permutation t-test, differences in
means 0.801, P,0.001, based on 1000 permuta-
tions). Mean individual length of each note among
six spontaneously vocalizing birds ranged between
0.08 and 0.13 sec and the mean length of each note
across all individuals was 0.11 60.02 sec; the mean
individual IQR duration ranged from 0.026 to
0.034 sec, and mean across all six individuals was
0.033 60.009 sec (Table 2). The mean individual
peak frequency of toot notes among six spontaneous-
ly vocalizing individuals ranged 1077.4–1112.9 Hz
(Table 2) and mean across all individuals was
1098.1 629.0 Hz.
Vocalizations Near the Nest. One breeding pair
of Guatemalan Pygmy-Owls was observed in the
Chelemha´ Reserve from 12 March to 17 April
2010. The owls occupied a human-made nest cavity
dug into a piece of a trunk of Brunellia mexicana
(Brunelliaceae), which was hung on a tree. The fe-
male was of the rufous morph and the male of the
brown morph (plate 14 in Marks et al. 1999), and
Table 3. Vocalizations other than territorial toot call of a breeding pair of Guatemalan Pygmy-Owls (voucher recording
ML #161747) (n51 individual for each vocalization type).
VOCALIZATION
TYPE
RANGE OF
NUMBER OF
NOTES/SERIES
MEAN CALL
RATE
(NOTES/SEC
6SD)
MEAN LENGTH
(SEC)OF EACH
NOTE (6SD)
MEAN INTER
QUARTILE RANGE
DURATION (SEC)OF
EACH NOTE (6SD)
MEAN PEAK
FREQUENCY
(HZ)OF EACH
NOTE (6SD)
MEAN CENTER
FREQUENCY
(HZ)OF EACH
NOTE (6SD)
Whiwhiwhi -call of
female
a
10–44 11.0 60.3 0.05 60.00 0.013 60.003 1551.9 647.3 1525.5 646.1
Krikrikri-call of
female during
copulation
b
2–3 36.5 62.4 0.03 60.01 0.008 60.003 1438.1 674.8 1443.7 668.3
Soft toot call of
male (fast part)
c
4–7 12.0 60.5 0.07 60.01 0.018 60.006 1020.4 624.6 1009.1 624.4
Soft toot call of
male (slow part)
d
4–7 4.9 60.4 0.09 60.01 0.023 60.005 1044.8 626.5 1041.1 627.0
a
n526 call series (in mean call rate column) and 419 notes.
b
n517 call series (in mean call rate column) and 50 notes.
c
n526 call series (in mean call rate column) and 186 notes.
d
n57 call series (in mean call rate column) and 38 notes.
DECEMBER 2011 GUATEMALAN PYGMY-OWL VOCALIZATIONS 309
the pair was observed copulating. Photographs of
both individuals are archived at VIREO (male: VIR-
EO #v06/60/004, 13 March 2010, C. Avendan˜o;
female: VIREO #v06/60/003, 12 March 2010, K.
Eisermann; pair: VIREO #v06/60/002, 12 March
2010, K. Eisermann). When the pair was establish-
ing occupation in the nest cavity, the male uttered
the toot call at a distance of 60 m from the nest. The
female near the nest often responded with a fast
series of short notes (11.0 60.3 notes/sec, n526
series), which can be described as a continued series
whiwhiwhi. Each series consisted of 10–44 notes with
a mean peak frequency of 1551.9 647.3 Hz (n5
419 notes). Up to seven harmonics were recorded
from 2600 Hz to 13 900 Hz (Fig. 3a, recording ML
#161747, 12 March 2010, K. Eisermann).
Near the nest, the male uttered soft toot notes that
were faster and lower-pitched than the territorial
toot notes. Toots were grouped into 2–7 notes (12.0
60.5 notes/sec, n526 groups), slowing down at
Figure 4. Sonogram of vocalization of a pair of Guatemalan Pygmy-Owls during copulation. Fundamentals of the male
soft toot calls are marked with a bracket, fundamentals of female notes are marked with a bracket (F) and female chirping
krikrikri notes with bracket (Fc). Chip notes of a mobbing Magnificent Hummingbird (Eugenes fulgens) are marked with 1.
Axes represent time and frequency according to voice recording archived at the Macaulay Library recording (ML
#161747, 12 March 2010, K. Eisermann).
310 EISERMANN AND HOWELL VOL. 45, NO.4
the end into 2–7 notes with a rate of 4.9 60.4
notes/sec, n57 groups; Fig. 3b). The mean peak
frequency of the fast sections was 1020.4 624.6 Hz
(n5186 notes), and of the slow sections was 1044.8
626.5 Hz (n538 notes). A harmonic was recorded
at about 2050 Hz. During the first days of nest oc-
cupation the soft toot call was uttered in duet with
the female whiwhiwhi call series (Fig. 3b, recording
ML #161747, 12 March 2010, K. Eisermann). Duet-
ting also preceded copulation. During copulation
the male uttered the soft toot series, and the female
uttered a vocalization composed of a fast series of
36.5 62.4 notes/sec (n517 series), grouped into
2–3 notes with a mean peak frequency of 1438 6
75 Hz (n550 notes), and chirping notes ranging in
frequency from 2730 to 7705 Hz (peak frequency
5766 Hz), sounding like krikrikri (Table 3; Fig. 4,
recording ML #161747, 12 March 2010, K. Eiser-
mann).
Comparison of Guatemalan Pygmy-Owl and
Mountain Pygmy-Owl Toot Calls. A classification of
six spontaneously calling Guatemalan Pygmy-Owls
and eight Mountain Pygmy-Owls based on an un-
weighted pair-group average (UPGMA) cluster anal-
ysis using Euclidean distance of mean call rate re-
sulted in two main clusters supporting the
taxonomic differentiation (Fig. 5). The mean call
rate in spontaneous vocalizations in Guatemalan
Pygmy-Owls was 3.4 60.5 notes/sec (n549 call
series of 6 individuals), significantly higher than in
Mountain Pygmy-Owls (1.9 60.3 notes/sec, n534
call series of 8 individuals; permutation t-test: differ-
ences in means 1.431, P,0.001, based on 1000
permutation; Table 2, Fig. 6). The mean length of
each note was similar in Mountain Pygmy-Owl (0.12
60.02 sec) and Guatemalan Pygmy-Owls (0.11 6
0.02 sec; permutation t-test comparing individual
means of IQR duration: differences in means
0.0004, P50.9, based on 1000 permutations).
Mean individual center frequency of each note
was similar in Guatemalan Pygmy-Owls (1094.6 6
28.6 Hz) and in Mountain Pygmy-Owls (1093.7 6
57.9 Hz; permutation t-test comparing individual
means: differences in means 15.5, P50.7, based
on 1000 permutations).
DISCUSSION
Differences in vocalizations are useful to distin-
guish owl species (Ko¨ nig 1994, Howell and Robbins
1995), but variability among individuals can be con-
siderable (Galeotti et al. 1993, Otter 1996, Delport
et al. 2002, Grava et al. 2008) and thus only certain
vocal parameters are useful for specific separation.
The frequency of notes in Glaucidium can be highly
variable among different individuals (Galeotti et al.
1993), but call rate (tempo) was suggested as an
important means to distinguish among Glaucidium
species (Howell and Robbins 1995). We found that
Figure 5. Unweighted pair-group average (UPGMA) cluster analysis of call rates (notes/sec) of toot calls of Mountain
Pygmy-Owls and Guatemalan Pygmy-Owls from different Mexican states and Guatemalan provinces.
DECEMBER 2011 GUATEMALAN PYGMY-OWL VOCALIZATIONS 311
toot calls of Guatemalan Pygmy-Owls differed from
those of Mountain Pygmy-Owls. Call rate was signif-
icantly faster in Guatemalan Pygmy-Owls, and a clus-
ter analysis based on call rate grouped samples in
two distant geographic clusters that differentiated
Guatemalan from Mountain Pygmy-Owls. This new
evidence of vocal differences supports full-species
treatment of the taxon restricted to the highlands
of northern Central America: Guatemalan Pygmy-
Owl (Glaucidium cobanense Sharpe 1875), as previ-
ously proposed (Howell and Webb 1995, Marks et
al. 1999, and Ko¨nig and Weick 2008).
The Guatemalan Pygmy-Owl is resident in the
highlands of Chiapas, Guatemala, and Honduras.
The species also occurs in the volcanic highlands
of southern Guatemala, which suggests that it may
also occur in the similar volcanic highland of west-
ern El Salvador, where it has not yet been docu-
mented (Komar 1998). Both Mountain Pygmy-Owl
and Guatemalan Pygmy-Owl are highland species
that occur at elevations .1500 m (Howell and Webb
1995), and their geographic ranges are separated by
approximately 200 km in the lowlands of the isth-
mus of Tehuantepec. In other Glaucidium species,
classification based on vocal differences has been
confirmed by molecular analyses (Howell and Rob-
bins 1995, Robbins and Howell 1995, Robbins and
Stiles 1999, Wink et al. 2008), which have not been
done for populations from the northern Central
American highlands. Further analyses should also
Figure 6. Sonograms of typical toot calls of (a) Guatemalan Pygmy-Owl (ML #161746, 12 March 2010, K. Eisermann),
(b) Mountain Pygmy-Owl from Sinaloa (ML #17195, 13 March 1976, T.A. Parker III), and (c) Mountain Pygmy-Owl from
Oaxaca (XC #9672, 27 February 1995, A. Chartier) to the same time scale.
312 EISERMANN AND HOWELL VOL. 45, NO.4
include the Costa Rican Pygmy-Owl (Glaucidium cost-
aricanum), whose range is separated from Guatema-
lan Pygmy-Owl by approximately 500 km. The for-
mer species also gives fast-paced toot calls, which are
somewhat similar in pace to those of Guatemalan
Pygmy-Owl (Stiles and Robbins 1999, Howell and
Eisermann 2011).
ACKNOWLEDGMENTS
We appreciate the assistance of Jessie Barry, Matthew A.
Young, and Tammy Bishop of the Macaulay Library (Cor-
nell Laboratory of Ornithology) for archiving of sound
recordings and for providing recordings from Mexico.
Recordists contributing to the Macaulay Library facilitated
the comparison with birds from Mexico. We thank Nick
Athanas for his contribution of a recording from Chiapas,
Allen Chartier for contributing recordings from Oaxaca,
and John Paul Cahill for a recording from Alta Verapaz.
Claudia Avendan˜ o provided a photograph. We thank
Paula Enrı´quez for information on the distribution of
pygmy-owls in Chiapas, and Daniel Thomas for his assis-
tance in archiving photographs at VIREO (Academy of
Natural Sciences). KE appreciates hospitality and logisti-
cal support by Francisco Falla during observations at
Finca San Sebastian, Julio Garcı´a at Finca El Recuerdo,
and the hospitality and research permission in the Che-
lemha´ and K’antı´ Shul private nature reserves provided by
UPROBON and FUNDASELVA, and Claudia Avendan˜o
for field assistance. SNGH thanks Will Russell and WINGS
for supporting travels in Mexico, Chris Wood and Rich
Hoyer for company in the field, and Nathan Pieplow for
help with digitizing recordings. The manuscript was im-
proved through critical reviews by Loı
¨c Hardouin, Joseph
Buchanan, and two anonymous reviewers, and through a
review of English usage by Christina Riehl of the Associ-
ation of Field Ornithologists’ program of editorial assis-
tance. We appreciate statistical advice by Carlos Aven-
dan˜ o. This is a contribution of the PROEVAL RAXMU
Bird Monitoring Program, which is supported by U.S.
Fish and Wildlife Service, Stiftung Artenschutz (Ger-
many), Heifer International Guatemala, Verein Sa¨ch-
sischer Ornithologen (Germany), and Cayaya Birding
(Guatemala).
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Received 13 August 2010; accepted 14 July 2011
Associate Editor: Joseph B. Buchanan
314 EISERMANN AND HOWELL VOL. 45, NO.4
