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Comparative Ecology of Cracids in Northern

Authors:
  • Fundación Simón I. Patiño
  • WWF Bolivia

Abstract and Figures

Este informe documenta a las comunidades de crácidos que ocurren en el Norte del Departamento de Santa Cruz, Bolivia. Se realizaron prospecciones de campo a través de transectos en línea en 11 sitios de la región. Seis especies de crácidos fueron registrados durante estos estudios: Ortalis guttata, Pipile cumanensis grayi, Penelope jacquacu, Penelope superciliaris, Crax fasciolata y Mitu tuberosa. Por lo menos cuatro especies de crácidos fueron registrados en la mayoría de los sitios de estudio, con cuatro de los 11 sitios albergando a las seis especies. Las seis especies de crácidos mostraron preferencias notables de habitat, con Crax, Mitu y Pipile que prefieren hábitats estacionalmente inundados, P. jacquacu bosques de Terra firme, P. superciliaris bosques secos, y Ortalis áreas abiertas de vegetación secundaria. Se encontraron normalmente en forma individual o en grupos sociales pequeños de 2-3 individuos. Una excepción notable a esta tendencia fue Pipile que frecuentemente se observó en congregaciones más grandes de hasta 19 individuos, sobre todo en árboles de higos fructificando. En un sitio de estudios a largo plazo Penelope y Mitu mostraron fuertes variaciones estacionaless en el tamaño del grupo. Las proporciones de encuentro de individuales y grupos variaron entre los sitios para todas las especies. En general, Penelope fue el género de crácido más abundante en un sitio dado, seguido por Mitu y Pipile, con Crax y Ortalis relativamente raras. También se estimaron densidades de la población para las especies de crácidos más comúnmente encontradas. En cuatro sitios con proporciones de encuentro relativamente alta de Penelope, las estimaciones de densidad fueron entre 15.9-22.4 ind/km 2 . En un sitio donde el esfuerzo de transectos fue relativamente alto, las estimaciones de densidad también fueron posibles para Mitu (12 ind/km 2) y Pipile (17 ind/km). Finalmente, se comparan los resultados de los estudios con otros sitios Neotropicales, y se identifican y discuten las amenazas mayores para los crácidos en la región de estudio. 68 Ecología Comparada de Cracídeos ao Norte de Santa Cruz, Bolívia -O presente trabalho relata comunidades de cracídeos que ocorrem ao norte de Santa Cruz, Bolívia. Foram conduzidos levantamentos por transectos lineares em 11 locáis ao longo desta região. Seis especies de cracídeos foram registradas: Ortalis guttata, Pipile cumanensis grayi, Penelope jacquacu, Penelope superciliaris, Crax fasciolata e Mitu tuberosa. Pelo
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Comparative Ecology of Cracids in Northern Dpto. Santa Cruz, Bolivia
R.B. Wallace+A, R.L.E. Painter+, D.I. Rumiz+*, L. Sainz*andA.B. Taber+
+ Wildlife Conservation Society, 185th Street and Southern Boulevard, Bronx, New York,
10460, U.S.A.
*Confauna - Museo de Historia Natural Noel Kempff Mercado, Santa Cruz, Bolivia.
ACorres.: R.B. Wallace, Wildlife Conservation Society - Madidi, Casilla 3-35181, San
Miguel, La Paz, Bolivia
Ecología Comparativa de Crácidos en el Norte del Departamento de Santa Cruz,
Bolivia - Este informe documenta a las comunidades de crácidos que ocurren en el Norte
del Departamento de Santa Cruz, Bolivia. Se realizaron prospecciones de campo a través
de transectos en línea en 11 sitios de la región. Seis especies de crácidos fueron
registrados durante estos estudios: Ortalis guttata, Pipile cumanensis grayi, Penelope
jacquacu, Penelope superciliaris, Crax fasciolata y Mitu tuberosa. Por lo menos cuatro
especies de crácidos fueron registrados en la mayoría de los sitios de estudio, con cuatro
de los 11 sitios albergando a las seis especies. Las seis especies de crácidos mostraron
preferencias notables de habitat, con Crax, Mitu y Pipile que prefieren hábitats
estacionalmente inundados, P. jacquacu bosques de Terra firme, P. superciliaris bosques
secos, y Ortalis áreas abiertas de vegetación secundaria. Se encontraron normalmente en
forma individual o en grupos sociales pequeños de 2-3 individuos. Una excepción
notable a esta tendencia fue Pipile que frecuentemente se observó en congregacioness
grandes de hasta 19 individuos, sobre todo en árboles de higos fructificando. En un sitio
de estudios a largo plazo Penelope y Mitu mostraron fuertes variaciones estacionaless en
el tamaño del grupo. Las proporciones de encuentro de individuales y grupos variaron
entre los sitios para todas las especies. En general, Penelope fue el género de crácido
s abundante en un sitio dado, seguido por Mitu y Pipile, con Crax y Ortalis
relativamente raras. También se estimaron densidades de la población para las especies
de crácidoss comúnmente encontradas. En cuatro sitios con proporciones de
encuentro relativamente alta de Penelope, las estimaciones de densidad fueron entre 15.9-
22.4 ind/km2. En un sitio donde el esfuerzo de transectos fue relativamente alto, las
estimaciones de densidad también fueron posibles para Mitu (12 ind/km2) y Pipile (17
ind/km ). Finalmente, se comparan los resultados de los estudios con otros sitios
Neotropicales, y se identifican y discuten las amenazas mayores para los crácidos en la
región de estudio.
68
Ecología Comparada de Cracídeos ao Norte de Santa Cruz, Bolívia - O presente
trabalho relata comunidades de cracídeos que ocorrem ao norte de Santa Cruz, Bolívia.
Foram conduzidos levantamentos por transectos lineares em 11 locáis ao longo desta
região. Seis especies de cracídeos foram registradas: Ortalis guttata, Pipile cumanensis
grayi, Penelope jacquacu, Penelope superciliaris, Crax fasciolata e Mitu tuberosa. Pelo
menos quatro delas estavam presentes em cada um dos locais examinados, com quatro
dos onze locais apresentando todas as seis especies. Todas as seis especies mostraram
notável preferencia de habitat, com Crax, Mitu e Pipile ocupando preferivelmente
habitats que sofrem inundacoes periodicamente, Penelope jacquacu ocupando florestas
de terra-firme, P. superciliaris florestas mais secas, e Ortalis áreas abertas de
crescimento secundario. Os cracídeos foram encontrados individualmente ou em
pequeños grupos de 2 ou 3 aves. Urna excecáo notável foi Pipile, frequentemente vista
em congregacoes de até 19 aves, especialmente em figueiras. Em um local de estudo a
longo-prazo, tanto Penelope quanto Mitu mostraram forte variacão sazonal no tamanho
dos grupos. Taxas de encontros grupais e individuáis variaram entre todos os locais para
todas as espécies. De maneira geral, Penelope foi a espécie de cracídeo mais abundante,
seguido de Mitu e Pipile, com Crea e Ortalis sendo observados raramente. Densidades
populacionais também foram estimadas para as especies mais comumente encontradas.
Em quatro locais onde Penelope é fácilmente observada, as estimativas de densidades
variaram entre 15,9 e 22,4 indivíduos/km2. Em um local onde os transectos foram
realizados mais intensivamente, estimativas de densidades também foram feitas para Mitu
(12 aves/km2) e Pipile (17 aves/km2). Finalmente, os resultados dos estudoso
comparados com outros locáis neotropicais, e as principáis ameacas aos cracídeos em
cada regiãoo identificadas e discutidas.
69
Abstract - This report documents the cracid communities occurring in northern Dpto.
Santa Cruz, Bolivia. Surveys employing line transects were conducted at 11 sites across
the region. Six cracid species were registered during these surveys: Ortalis guttata,
Pipile cumanensis grayi, Penelope jacquacu, Penelope superciliaris, Crax fasciolata and
Mitu tuberosa. At least four cracid species were registered at most survey sites, with four
of the 11 sites boasting all six species. All six cracid species showed notable habitat
preferences, with Crax, Mitu and Pipile preferring seasonally flooded habitats, Penelope
jacquacu terra-firme forests, P. superciliaris drier vine forests, and Ortalis open second
growth areas. Cracids were usually encountered as individuals or in small social groups
of 2 - 3 birds. A notable exception to this trend was Pipile, which was frequently
observed in larger congregations of up to 19 birds, especially in fruiting fig trees. At one
long-term study site both Penelope and Mitu showed strong seasonal variations in group
size. Group and individual encounter rates varied between sites for all species. In
general, Penelope was by far the most abundant cracid genus at a given site, followed by
Mitu and Pipile, with Crax and Ortalis usually relatively rare. Population densities were
also estimated for the more commonly encountered cracid species. At four sites with
relatively high Penelope encounter rates, density estimates ranged between 15.9 - 22.4
individuals/km2. At one site where transect effort was relatively high, density estimates
were also possible for Mitu (12 inds/km2) and Pipile (17 inds/km2). Finally, the results of
the surveys are compared with other Neotropical sites, and the major threats to cracids in
the study region are identified and discussed.
As large frugivores that make up a significant proportion of the avian biomass of most
Neotropical forests, cracids are considered an ecologically important taxonomic group
(Silva and Strahl 1991, Strahl et al. 1997). Their frugivorous diet and wide ranging
behaviour makes them effective seed dispersers (Silva and Strahl 1991, Sedaghatkish et
al. 1999). Cracids are also an important prey source for larger tropical forest predators
that are considered a 'keystone' trophic group within tropical forests (Terborgh 1992).
The cracids are an economically important taxonomic group (Silva and Strahl 1991,
Strahl et al. 1997). Several hunting studies across the Neotropics have demonstrated
their popularity as bush meat with indigenous peoples (Brooks 1999, Santos and Brooks
in prep.), mestizo colonists (Redford and Robinson 1987, Silva and Strahl 1991, Begazo
1997, Begazo and Bodmer 1998), and loggers (Townsend et al. in prep). They are
consistently the most hunted avian group in terms of biomass extracted (e.g. Redford and
Robinson 1987, Townsend 1996, Begazo and Bodmer 1998), and also rank high when
considering all game species harvested, especially when measured by number of
individuals harvested (Brooks 1999, Santos and Brooks in prep.).
Brooks and Strahl (2000) have outlined the threatened status of many cracid species and
produced an action plan for their conservation that recommended further surveys in
almost all countries. Previous research regarding the cracids of Bolivia has been largely
confined to Horned Currassow (Pauxi unicornis) ecological studies (Cox and Clarke
1988, Cox 1990, Cox and Clark 1997, Cox et al. 1997, Renjifo and Renjifo 1997) and
status surveys (Herzog and Kessler 1998, Mee 1999) in Amboro and Carrasco National
Parks. Other autecological studies focused on Wattled Currassow (Crax globulosa)
status (Hennessey 1998) and the Chaco Chacalaca (Ortalis canicollis) (Mamani this vol.).
Distributional information has come from national avifaunal species lists (ARMONIA
1995) or national cracid reports (Jordan 1997, Videz-Roca 1997) and a national cracid
survey which visited nine sites (Cox and Cox 1997). Additionally, regional surveys have
focused on the Andes (Fjeldsa and Mayer 1996) and eastern Panhandle of Dpto. Santa
Cruz (Brooks and Rojas unpubl. data).
Here we present cracid diversity and distributional information from surveys conducted
within two protected areas in northern Dpto. Santa Cruz: Noel Kempff Mercado National
Park and Rios Blanco Y Negro Wildlife Reserve. Information on habitat association,
relative abundance (expressed as group and individual encounter rates) and population
density estimates are also presented.
METHODS
Study Area
The 11 survey sites were distributed within and bordering two protected areas in
Northern Dpto. Santa Cruz: Noel Kempff Mercado National Park and the Rios Blanco Y
Negro Wildlife Reserve (Fig. 1). Noel Kempff Mercado National Park (PNNKM) is
situated on the Brazilian Shield geological formation in the northeastern corner of Dpto.
Santa Cruz, Bolivia, and is defined by the Guapore/Itenez river on its eastern and
northern edges, which also represents the border with neighbouring Brazil. The park
70
contains an array of markedly differing habitat types including open pampas, cerradâo
forest, and gallery forest on top of the Huanchaca plateau, a Precambrian escarpment
rising 200 - 400 m above the surrounding lowlands. Nevertheless, following a recent
expansion from 7060 km2 to 15,300 km2, the park now includes a vast expanse of lowland
forest. This lowland forest is broadly classified as humid forest of the Precambrian shield
(Killeen et al. 1993). The region is characterized by a marked dry season in the austral
winter, a mean daily temperature of 24°C, and an annual precipitation of approximately
1500 mm (Killeen 1996).
Figure 1 - A map of northern Department Santa Cruz showing the location of
PNNKM and RBYNWR and the sites sampled therein
Research was conducted at two sites within the park (Fig. 1). Between September 1991
November 1992 research was based at "Lago Caimán" (13°36'S, 60°55'W), a large
oxbow lake situated at the base of the northern tip of the Huanchaca escarpment and
approximately 21 km upstream from the tourist centre "Flor de Oro". Trails totalling 27
km were distributed across a ~30km2 área and passed through three distinct forest types:
low vine, tall, and sartenejal or seasonally flooded swamp forest (Wallace et al. 1998).
71
The second field site, "Las Gamas" (14°48'S, 60°23'W), was situated around an
abandoned airstrip situated on top of the escarpment in the southern region of the park
and was visited for five weeks during March/April 1993. Trails were located in three
patches of gallery forest and totalled 10.3km in length (Wallace et al. 1998).
The Rios Blanco Y Negro Wildlife Reserve (RBYNWR) is in northwestern Dpto. Santa
Cruz and constitutes part of the Bajo Paragua Forestry Reserve which is divided into a
number of forestry concessions of varying sizes (FAN/PL480/WCS 1994). The area
includes two distinct biophysical regions: the Beni alluvial plain extends west to the Rio
Blanco, and the Brazilian shield begins east of the Blanco (Fig. 1). The forests found
within the reserve are broadly classified as either humid forest of the Brazilian shield or
lowland humid forest (Killeen et al. 1993). Between 1992 - 1993 eight sites were
surveyed within the reserve for approximately three weeks each (Painter 1994). Five
sites were directly accessible through existing logging roads: Arroyo Chuchui, San
Martin, San Luis, Oquiriquia, and El Tutumo; and three others were accessible by river
and/or plane: Perseverancia, Pajaral, and Rio Negro de Caimanes. The locations of the
sites are detailed in Figure 1. Between 1995 -1996 a ninth site within the reserve, Tierra
Prometida (Fig. 1), was surveyed more intensively over 41 kms of trail (Sainz 1997).
This site included four distinct forest habitat types within a 670 hectare study plot:
seasonally flooded riverine, sartenejal, tall, and low vine. Three field trips of between 2 -
4 weeks were conducted over the course of a year; August/September 1995 (end of dry
season), October/November 1995 (start of wet season), May/June 1996 (start of dry
season).
Field Methods
Line transect methodologies were employed to survey the areas. Line transects have
been used extensively throughout the tropics as a means of surveying forested areas for
mammals and larger avifauna (Brockelman and Ali 1987, Emmons 1984, White 1994,
Cox and Cox 1997, Strahl and Silva 1997). With sufficient transect encounters, density
estimates can be calculated using this methodology and associated computer software
(Burnham et al. 1980, Buckland et al. 1993). However, since at least 40 encounters of
each species are recommended for reliable estimates many researchers have been
restricted to presenting relative abundances using encounter rates (Branch 1983, Mate
and Colell 1995). Ad libitum non-transect observations also provided information on
cracid diversity.
Diurnal transects were run by two observers in fair weather conditions between 06:00 -
11:30 brand 15:00 - 18:00 hr, along existing logging trails or roads and/or newly
established trails cut by the survey team. Transect speed ranged from 1-2 km/hr and
depended on trail conditions and associated noise levels. Periods of walking were
regularly interspersed with brief "listening stops" in order to increase the probability of
detecting more cryptic species. The following information was recorded for all cracids
encountered on transects: species, group size, date and time detected, observation
duration, transect position, habitat type, perpendicular distance from the transect trail to
the estimated geometric centroid of the group, and the vertical position of the group with
72
regards to obvious forest strata. Details regarding the transect census effort, study period,
and human activities at each site are presented in Table 1.
Due to the problem of distinguishing between fleeing individuals of the congeners Spix's
Guan (Penelope jacquacu) and Rusty-margined Guan (P. superciliaris) we treat these
species at the generic level in the analysis. Results are expressed as relative abundances,
calculated as the number of group encounters for each cracid taxa per 10 km censused.
Individual encounter rates are expressed as the number of observed individuals of each
cracid taxa encountered per 10 km censused. In order to standardize the area sampled per
unit distance walked at each site only transect observations within 20 m of the trail were
considered. Statistical procedures followed Siegel and Castellan (1988), and significance
was set at the 0.05 level.
Table 1 - Census details of 11 survey sites sampled
Survey Site
Lago Caimán
Las Gamas
Perseverancia
Pajaral
Arroyo Chuchui
San Martin
R. Negro Caimanes
San Luis
Oquiriquia
El Tutumo
Tierra Prometida
Reserve
PNNKM
PNNKM
RBYN
RBYN
RBYN
RBYN
RBYN
RBYN
RBYN
RBYN
RBYN
Trnsct. km
328.43
50.4
165
98
54.8
69
101.6
108.9
93.2
99.7
453.6
Study Period
Year Round
Mar-Apr
Jun-Jul
Aug
Oct
Nov
Jun
Aug
Sep
Sep-Oct
Aug-Nov/May-Jun
Human Activities
None
None
Ecotourism
Commercial Hunting
Logging/Hunting
Logging/Hunting
Commercial Hunting
Logging/Hunting
Logging/Hunting
Logging/Hunting
Logging/Hunting
RESULTS
Diversity and Distribution
Six cracid species were registered within both protected areas: Speckled Chacalaca
(Ortalis guttatá), Blue-throated Piping Guan (Pipile cumanensis grayi), Spix's Guan
(Penelope jacquacu), Rusty-margined Guan (Penelope superciliaris), Bare-faced
Curassow (Crax fasciolata) and Razor-billed Currassow (Mitu tuberosa). All six species
were registered at four of the sites: Arroyo Chuchui, Lago Caimán, Perseverancia and
Tierra Prometida, with the latter three of these sites being the most heavily sampled (see
Tables 1 and 2). Las Gamas had the least number of cracid species with only the two
Penelope congeners registered. At Pajaral, Rio Negro de Caimanes and El Tutumo all
73
species except Penelope superciliaris were registered, with the remaining sites all having
four species registered. Thus, P. superciliaris appears absent from the Beni alluvial plain
and the border between this biophysical region and the Brazilian shield probably
represents a distributional limit for this cracid species. The most widespread species was
Penelope jacquacu that was registered at all sites visited, with Mitu tuberosa apparently
absent only at Las Gamas. The other four species were not recorded at 3 or 4 of the 11
sites sampled (Table 2).
Table 2 - Diversity, distribution and group (and individual) encounter rates (per
10km) for cracids at 11 survey sites
Survey Site Ortalis Pipile Penelope spp. Mitu Crax
Lago Caiman
Las Gamas
Perseverancia
Pajaral
Arroyo Chuchui
San Martin
R. Negro Caimanes
San Luis
Oquiriquia
El Tutumo
Tierra Prometida
*
0.06(0.12)
0.10(0.31)
0.18(0.36)
0.14(0.43)
*
*
0.07(0.13)
0.15(0.37)
0.18(0.24)
-*
0.18(0.18)
0.39(1.08)
0.28 (0.55)
1.29(2.15)
0.20 (0.30)
0.62 (3.20)
2.04 (4.72)
2.78 (5.16)
0.85(1.39)
0.41 (0.92)+
1.28(3.10)
1.16(2.03)
1.38(2.17)+
2.66(5.14)
1.39(2.47)+
2.41 (5.22)+
1.48(4.61)
0.21 (0.30)
0.18 (0.24)
0.31 (0.41)
0.36 (0.55)
0.87(1.01)
0.98(1.77)
1,01 (1.47)
0.43 (0.64)
0.70 (0.90)
1.17(2.25)
*
0.06(0.12)
0.51(1.12)
*
0.59(1.08)
*
*
0.13(0.20)
* Denotes recorded in non-transect observation.
+ Only Penelope jacquacu positively identified as being present at field site.
Group Size
In terms of sociality, Mitu and Crax were usually encountered as either single birds or in
pairs, Ortalis and Penelope were most often encountered in slightly larger social groups
of 2 - 3 birds, and Pipile was usually either solitary or found in considerable
congregations at large fruiting sources. Figure 2 displays the mean groups sizes for the
five cracid taxa considered. Using all available data mean group size for Ortalis was
2.29 individuals (SD = ± 0.76, range = 1 - 3, n = 7). Mean group size for Pipile was 3.56
individuals (SD = ± 4.08, range = 1 - 19, n = 64), and the data from the Tierra Prometida
survey site indicate no significant seasonal variations in Pipile group size (Kruskal-
Wallis ANOVA, H = 3.77, d.f. = 2, P = 0.152). In contrast, Penelope showed significant
seasonal shifts in group size at this site (Kruskal-Wallis ANOVA, H = 6.43, d.f. = 2, P <
74
0.05). Overall mean group size for Penelope was 2.34 individuals (SD = ± 1.83, range =
1 - 15, n = 264). Similarly, results for Mitu showed a strong trend towards seasonal
variation in group size at Tierra Prometida (Kruskal-Wallis ANOVA, H = 5.96, d.f. = 2,
P = 0.051), and the overall mean group size was 1.69 individuals (SD = ± 0.86, range - 1
- 6, n = 117). Finally, the overall mean group size for Crax was 1.83 individuals (SD = ±
.71, range = 1 - 3, n = 18). Insufficient sightings prevented seasonal tests for Crax, as
well as Ortalis.
Figure 2 - Mean group sizes for five cracid genera
Habitat Association
At Lago Caiman the Penelope genus showed habitat preferences which approached
significance (X2= 5.8, d.f. = 2, P = 0.055), whereas at Tierra Prometida this taxa showed
strong habitat preferences (X2 = 50.33, d.f. = 3, P < 0.001). At Lago Caiman individuals
of the Penelope genus were encountered most frequently in sartenejal (swamp) and tall
climax forests and considerably less frequently in lower vine forest. At Tierra Prometida
Penelope showed strong preferences for the seasonally flooded riverine forest compared
75
to three other local habitats including sartenejal forest. Both Mitu (X2 = 114.83, d.f. = 3,
P < 0.001) and Pipile (X2 = 44.28, d.f. = 3, P < 0.001) also showed highly significant
preferences for seasonally flooded riverine forest at Tierra Prometida.
Encounter Rates and Abundance
Group encounter rates for Ortalis were low for all sites where they were recorded on
transects (mean = 0.11 grps/10 km, SD = ± 0.05, range = 0.06 - 0.18), as were individual
encounter rates (mean = 0.27 inds/10 km, SD = ± 0.14, range = 0.12 - 0.43). Group and
individual encounter rates were particularly variable between sites for Pipile (mean =
0.41 grps/lOkm, SD = ± 0.39, range = 0.15- 1.29; mean = 1.01 inds/10 km, SD = ± 1.1,
range = 0.18 - 3.2). Individual encounter rates were significantly different between sites
where Pipile was recorded on transects (X2= 165.37, d.f. = 7, P < 0.001), being markedly
higher at two sites, Oquiriquia and Tierra Prometida.
Figure 3 - Overall mean group and individual encounter rates (ER's) for five cracid
genera in northern Department Santa Cruz, Bolivia. Note: Overall mean ER's are
calculated from those sites where each species was registered on transect surveys.
Mitu Penelope Pipile Crax Ortalis
Species
Group ER Individual ER
76
The combined Penelope species had the highest encounter rates for both groups (mean -
1.62 grps/10 km, SD = ± 0.76, range = 0.41 - 2.78) and individuals (mean = 3.36 inds/10
km, SD = ± 1.65, range = 0.92 - 5.22). Individual encounter rates were extremely
variable and significantly different between the 11 field sites (X2 - 93.84, d.f. = 10, P <
0.001).
Overall, Mitu was the second most frequently encountered cracid genus at the survey
sites (mean = 0.62 grps/10 km, SD = ± 0.37, range = 0.18-1.17; mean = 0.95 inds/10
km, SD = ± 0.68, range - 0.24 - 2.25), and were particularly common at San Luis, Rio
Negro de Caimanes, and Tierra Prometida. Individual encounter rates were significantly
different between the sites where Mitu was recorded on transects (X2 = 94.29, d.f. = 9, P <
0.001).
Crax was rarely encountered and observed on transects at four sites. Two of these sites,
Perseverancia and Tierra Prometida, had very low group encounter rates, whereas Pajaral
and Rio Negro de Caimanes had markedly higher values (see Table 2). Individual
encounter rates were significantly different between these sites (X2 = 32.17, d.f. = 3, P <
0.001). Nevertheless, overall group (mean - 0.32 grps/10 km, SD = ± 0.27, range = 0.06
- 0.59) and individual (mean = 0.63 inds/10 km, SD = ± .54, range = 0.12 - 1.12)
encounter rates were relatively low compared to other species (see Fig. 3).
For four of the sites visited we were able to calculate density estimates for the Penelope
genus; these estimates ranged from 15.9 - 22.4 inds/km2 (see Table 3) and the
corresponding encounter rates reveal that these sites are all relatively high Penelope
density areas. At Tierra Prometida sufficient encounters enabled density estimates for
Mitu tuberosa (12 inds/km2; cv = 17.2, Confidence Limits = 8.6 - 16.7, n = 53) and Pipile
cumanensis grayi (17 inds/km2; cv = 29.4, Confidence Limits = 9.7 - 29.9, n = 28).
Table 3 - Density
Survey Site
Lago Caiman
San Luis
El Tutumo
Tierra Prometida
estimates for Penelope
N
71
29
26
71
Encounter Rate
Inds./10km
4.72
5.14
5.22
4.61
spp. at four sites
Dens. Est.
Ind./km2
15.9
22.4
18.2
20.7
CV.
16.3
23.6
26.9
18.2
95% Conf. Lim.
11.6-21.9
14.2-35.3
10.8-30.6
14.6-29.5
All density estimates are generated using uniform cosine models within the DISTANCE program.
DISCUSSION
78
Diversity and Distribution
The information on cracid diversity and distribution is in agreement with maps drawn up
following briefer surveys conducted at fewer field sites (Cox and Cox 1997). However,
Cox and Cox (1997) were able to identify and distinguish between two species of Pipile
in the Lago Caiman region: P.cumanensis grayi and P. cujubi. This and subsequent
observations in the area (Wallace pers. obs.) suggest that the Lago Caiman Pipile data
should be interpreted at the generic level. The broad agreement with less intensive
surveys suggests that many cracid species are relatively conspicuous compared to other
avifaunal groups. This ease of detection is associated with their large size, as well as
loud calling behaviour in most species. Thus, northeastern Dpto. Santa Cruz appears
absent of any rare cracid species, including the threatened Wattled Curassow (Crax
globulosa), which may be less easily detected during brief surveys (cf., Garcia and
Brooks 1997).
Group Size
The broad patterns of cracid sociality displayed during the study agree well with previous
research regarding these cracid genera (Strahl et al. 1997). Unfortunately, the nature of
the census data collected during these surveys prevents an analysis of the factors
determining the seasonal variations in Penelope and Mitu group sizes. Nevertheless,
these variations are presumably a response to fruiting patterns within the forest, as well as
reproductive seasonality. For example, Brooks (1997) indicates seasonal variation in
Ortalis flock size is accounted for by young-of-the-year added to flocks prior to dispersal
from the natal site. Many of the surveys took place during the dry season (May -
October) and cracid mating behaviour seems to coincide with the dry season in this
region (G. Cox pers. comm., Wallace pers. obs.).
Habitat Association
As has been outlined in previous surveys, Ortalis guttata seemed to prefer secondary
habitats, particularly river edges and forest borders (Cox and Cox 1997, Begazo and
Bodmer 1998, Brooks et al. this vol.). Similarly, Crax fasciolata showed clear
preferences for riverine habitats, indeed this species was only registered at sites where
transects met and/or followed major waterways (see Fig. 1). At Lago Caiman when
species identification of Penelope was possible, observations suggested that the
congeners showed differences in habitat preferences consistent with previous studies
(Cox and Cox 1997); P. jacquacu was found predominantly in taller terra-firme forest as
well as flooded forests, and P. superciliaris in drier, second growth forests. The cracid
habitat preferences evident at Tierra Prometida mirror results from a recent study of a
similar cracid community in Peru (Begazo and Bodmer 1998). The clear preferences
shown by Pipile cumanensis for seasonally flooded riverine forests at Tierra Prometida
are almost certainly a response to the fruiting patterns of the fig stands present in this
habitat. Fruiting patterns are known to influence the ranging patterns of other large,
gregarious frugivores in this region (Sainz 1997, Painter 1998, Wallace 1998), as well as
other parts of Amazonia (e.g., Cephalopterus in Peruvian Amazon; Brooks et al. 1999).
79
Encounter Rates and Abundance
The relative abundances of cracid genera at the survey sites appear to be typical of other
cracid communities, with Penelope the most abundant genus followed by either Mitu or
Pipile, and the two more habitat specific species {Ortalis guttata and Crax fasciolata)
almost always relatively rare at a given site harboring more than one species of cracid
(Silva and Strahl 1991, Torres 1997, Begazo and Bodmer 1998). Examining the relative
encounter rates in more detail (Table 2) suggests that the Tierra Prometida density
estimate for Pipile may be an anomaly for the region. Indeed, this represents one of the
highest Pipile density estimates recorded to date (Torres 1997, Begazo and Bodmer
1998), and only the neighbouring site of Oquiriquia (see Fig. 1) had comparable
individual encounter rates in this study. Both these sites were characterised by relatively
high densities of strangler figs (Ficus spp.), and fig abundance may well be a key
determinant of Pipile densities in this region, with piping guan aggregations often
associated with large fruiting fig trees (Fredericksen et al. 1999, Wallace per. obsv.).
Mitu relative abundance is also impressive at Tierra Prometida, with the corresponding
density estimate relatively high compared to most studies to date (Silva and Strahl 1991,
Torres 1997, Begazo and Bodmer 1998), suggesting that fig aggregations may also
influence Mitu densities.
The Penelope density estimates are much higher than those obtained at sites surveyed by
Begazo and Bodmer (1998) in Peru (0.22 - 5.46 birds/km2), but do seem comparable with
results from a survey at Manu in Peru (19.8 birds/km2; Torres 1997), and for congeners at
a number of survey sites in Venezuela (5 - 40 birds/km2; Silva and Strahl 1991). The
consistently high densities and relative encounter rates of Penelope within this region are
surprising given that other large frugivore specialists such as spider monkeys (Ateles
chamek) are typically rare unless considerable local habitat diversity is apparent (Wallace
et al. in press). The greater mobility afforded by flight may allow guans to exploit local
periodic booms in fruit availability over a larger area than spider monkeys.
Intriguingly, a second more recent primate survey at the non-hunted Lago Caiman site
(Rocha 1997) detailed markedly reduced Penelope densities (2.6 inds/km2; cv = 22.2,
Confidence Limits 1.7 - 4.0, n = 23). However, this survey was concentrated within a
500 ha study plot and was therefore not as wide ranging as the survey reported herein,
and moreover took place over a briefer period (four months). Thus, it may reflect spatial
or temporal variations in Penelope abundance. Certainly fruit abundance in the lowland
habitats was below average for the year during the months of the second survey (Wallace
1998).
Previous authors have discussed the problem of generating sufficient transect encounters
with which to make a reliable density estimate for all but the most abundant wildlife
species (Cox and Cox 1997, Strahl and Silva 1997, Peres 1999, Painter et al. in prep.).
Burnham et al. (1980) recommend a minimum of 40 encounters, preferably 60 - 80, for
use with the computer programme DISTANCE. This study demonstrates the difficulty of
calculating density estimates for the genera Ortalis, Pipile, Crax and Mitu; only at Tierra
Prometida, where encounter rates for Mitu and Pipile were markedly higher and transect
80
effort more intense, were density estimates possible. For Crax and Ortalis a sufficient
sample size was not possible even by combining all sites sampled (a total of 1622.6
transect km) as suggested by Peres (1999). Nevertheless, line transects permit rapid
surveys for cracid diversity, and provide useful encounter rates which can be used for
inter-site and habitat comparisons, and/or long term monitoring at selected locations.
Long-term monitoring of logged sites should be encouraged and will provide more
substantial evidence on the effect of habitat disturbance on cracid populations, but only if
confounding hunting factors are eliminated. Logging associated hunting is the most
obvious and immediate threat to cracid populations in forestry concessions. Hunting
carried out by Bolivian logging crews and employees is probably unsustainable, and is
more intensive than subsistence by hunting local communities (Townsend et al. in prep.).
In terms of wildlife conservation, the importance of imposing strict anti-hunting
regulations in forestry concessions cannot be overstated. At present extraction
intensities, logging associated hunting probably has the most negative effect on larger
wildlife species in lowland Bolivia (Rumiz et al. in press).
ACKNOWLEDGEMENTS
We would like to thank the Bolivian National Secretariat for Protected Areas for
permission to work in Noel Kempff Mercado National Park and the Rios Blanco Y Negro
Wildlife Reserve. The research at Lago Caiman was funded as part of a grant to A. Taber
from the Wildlife Conservation Society (WCS). Considerable logistical support was
gratefully received from F.A.N. (Fundacion Amigos de la Naturaleza) at the
administrative level in Santa Cruz, and whilst in the field from all residents at Flor de
Oro, particularly the park guards. The RBYNWR surveys were funded as part of a grant
to F.A.N, and WCS from Secretaria Ejecutiva PL-480 Titulo III-USAID/B. We thank
Rudy Guzman and the late Pavlik Nikitin who coordinated the RBYNWR project
activities and field visits. The studies at Tierra Prometida were funded through a student
undergraduate thesis grant to L. Sainz from the Bolivian Sustainable Forestry Project
(BOLFOR), which is financed by USAID and the Bolivian Government. The local
BOLFOR office in Santa Cruz also provided logistical support during this field work.
Finally, Dan Brooks made invaluable comments on earlier drafts of this manuscript.
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