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Articles DISCOVERY OF TWO NEW LOCALITIES FOR TODD’S PARAKEET PYRRHURA PICTA CAERULEICEPS USING DISTRIBUTION MODELS: ENHANCING KNOWLEDGE OF A LITTLE KNOWN NEOTROPICAL BIRD HALLAZGO DE DOS NUEVAS LOCALIDADES PARA EL PERIQUITO DE TODD PYRRHURA PICTA CAERULEICEPS EMPLEANDO MODELOS DE DISTRIBUCIÓN GEOGRÁFICA: INCREMENTANDO EL CONOCIMIENTO DE UN AVE TROPICAL POCO CONOCIDA Esteban BOTERO-DELGADILLO1 *, Carlos Andrés PÁEZ 1 and Jeyson SANABRIA-MEJÍA1
SUMMARY.—Todd’s parakeet Pyrrhura picta caeruleiceps is a geographically isolated race of painted parakeet P. picta, a widespread species. Several authors highlight the need to recognize Todd’s parakeet at the species level, and despite past efforts to find new populations, no new locations have been found. We applied a Species Distribution Model (SDM) to guide a 30-day survey during 2011 to increase information on its geographic distribution. Surveys resulted in the discovery of two new populations in Los Motilones Mountains, on the north-eastern boundary of Colombia with Venezuela. Our field surveys support previous arguments of a continuous geographic range from the northern part of the Eastern Cordillera to the Perijá Mountains. However, we did not find birds at the base of the Colombian slope of the Perijá Mountains, and confirming its absence there requires further study. Habitat loss at the three localities visited was high, with most remaining habitat represented by continuous gallery forests located on steep and humid slopes at higher altitudes. If conditions for population maintenance are only present in those patches, it will be necessary to identify forest fragments that help maintain connectivity between populations on the northernmost part of the Eastern Cordillera and the Perijá Mountains. More surveys in the Perijá Mountains and in Venezuela are also recommended. This study provides further evidence of the usefulness of species distribution models to increase available information on rare or little known taxa. Key words: Colombia, field surveys, habitat loss, Los Motilones Mountains, probability of presence, painted parakeet, Perijá Mountains.
1
Selva: Investigación para la conservación en el Neotrópico, C/ 43 27A-55 Of. 201, Bogotá, Colombia.
*
Corresponding author: esteban.botero@selva.org.co
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RESUMEN.—El periquito de Todd Pyrrhura picta caeruleiceps es una raza geográficamente aislada del periquito pintado P. picta, una especie de amplia distribución. Varios autores han resaltado la necesidad de reconocer al periquito de Todd como especie, y pese a los esfuerzos para encontrar nuevas poblaciones, no se ha encontrado una nueva localidad recientemente. En este estudio se usó un modelo de distribución geográfica para guiar un muestreo de 30 días en 2011 que incrementase la información sobre su distribución. Fruto de ello fue el descubrimiento de dos poblaciones en la serranía de Los Motilones, en el límite nororiental de Colombia con Venezuela. Los muestreos apoyan previos argumentos sobre la continuidad de su rango geográfico desde el norte de la Cordillera Oriental hasta la Serranía del Perijá. No obstante, no encontramos esta ave en la vertiente colombiana del Perijá, por lo que confirmar su ausencia allá será clave. Observamos una alta pérdida de su hábitat en las tres localidades visitadas, encontrando que la mayoría del hábitat remanente estuvo representado por bosques de galería continuos en pendientes elevadas y húmedas a mayores elevaciones. En el caso de que las condiciones propicias para el mantenimiento de sus poblaciones se encuentren en estos bosques, será necesario identificar fragmentos que mantengan la conectividad de las poblaciones desde la Cordillera Oriental hasta el Perijá. Se requiere más estudio en la Serranía del Perijá y Venezuela. Este trabajo provee evidencia adicional de la utilidad de los modelos de distribución geográfica para aumentar la información sobre taxones poco conocidos. Palabras clave: Colombia, estudios de campo, pérdida de hábitat, periquito pintado, probabilidad de presencia, Serranía de Los Motilones, Serranía del Perijá.
INTRODUCTION Todd’s parakeet Pyrrhura picta caeruleiceps is one of the nine or so geographic races of the painted parakeet Pyrrhura picta (Collar, 1997; but see Remsen et al., 2012), a species whose taxonomic affinities have just started to be resolved (Joseph, 2000; Joseph, 2002; Joseph and Stockwell, 2002; Ribas et al., 2006). Recent works have supported the recognition of three of its subspecies at the species level (see Remsen et al., 2012), but there is still debate on the need to recognize the remaining races (Joseph and Stockwell, 2002; Arndt, 2008; see also Remsen et al., 2012), including the apparently allopatric Todd’s parakeet, sinú parakeet P. p. subandina and azuero parakeet P. p. einsenmanni (see Forshaw, 2010). The painted parakeet is considered as a species of least concern (LC) for conservation (BirdLife International, 2012), because despite its isolated and restricted distribution in northern Colombia and southern Panama, its range includes a vast area east of the Andes Ardeola 59(2), 2012, 237-252
(Ecuador, Peru, Bolivia, Brazil, Venezuela and the Guianas) (Collar, 1997). Due to this, little attention has been given to some of its restricted-range subspecies (BoteroDelgadillo and Páez, 2011a; 2011b). This is the case for Todd’s parakeet, which seems to be distributed only in the northernmost part of the eastern Andes of Colombia, and in Los Motilones and Perijá Mountains along the boundary between Colombia and Venezuela (Collar, 1997; Forshaw, 2010; Botero-Delgadillo and Páez, 2011b). This subspecies has lost ca. 70% of its original habitat within its Colombian distribution, and its area of occupancy within Colombia is predicted to be less than 3,700 km2 (Botero-Delgadillo et al., 2012). Given the extensive transformation of native forests throughout its range, and its presumed geographic isolation from other races of P. picta (Joseph and Stockwell, 2002; Botero-Delgadillo et al., 2012), this taxon should be considered a priority following IUCN criteria (see IUCN, 2011). Unfortunately, our knowledge of Todd’s parakeet is poor and there have been few
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efforts to gather ecological or distributional information since field surveys conducted by Todd (1947) and Phelps (1977) to describe P. subandina caeruleiceps and P. picta pantchkenkoi respectively. These latter two subspecies are no longer considered valid and both are treated as Todd’s parakeet P. p. caeruleiceps (Joseph and Stockwell, 2002; Arndt, 2008; Forshaw, 2010; Remsen et al., 2012). Recently, Fundación ProAves carried
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out a series of expeditions that confirmed the persistence of two populations in the type locality of Todd’s parakeet and nearby areas (Tovar-Martínez, 2010; Botero-Delgadillo and Páez, 2011b) but failed to find this taxon in new areas where it might be present. This was in spite of considerable effort being exerted through more than 20 field expeditions during more than six months (C. A. Páez, unpub. data).
FIG. 1.—Geographic range covered by historical records of Todd’s parakeet in Colombia and Venezuela. [Distribución geográfica de registros históricos del periquito de Todd en Colombia y Venezuela.] Ardeola 59(2), 2012, 237-252
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Considering that knowledge on geographic distribution is essential to accurately evaluate any taxon’s conservation priorities (Pimm and Jenkins, 2010), this study aimed to provide new ecological and distributional information on Todd’s parakeet, an isolated taxon requiring effective conservation actions (Botero-Delgadillo and Páez, 2011a; 2011b). To achieve this, we used a Species Distribution Model (SDM) to develop an efficient and less time consuming method for identifying new presence localities, and subsequently make a preliminary assessment of the current status of populations and habitat availability at new localities.
ments). We followed Chapman (2005) for data cleaning and selection using DIVA-GIS (Hijmans et al., 2006). Three localities were removed due to their spatial proximity (e.g. located within 1 km of each other). All remaining localities were used since there were no environmental outliers among them; all records fell inside the 95.0 percentile in five cumulative frequency curves of five climatic variables (annual mean temperature, isothermality, annual precipitation, temperature annual range and precipitation seasonality). Therefore, we used 15 records from the original dataset for subsequent modelling.
Potential distribution modelling METHODS Populations under study We have used all historical records for Todd’s parakeet for our analyses, including records listed as either P. subandina caeruleiceps or P. picta pantchkenkoi (see above). Eleven of the records used were distributed on the northern portion of the Eastern Cordillera within the Norte de Santander department in Colombia ). Seven records were located along the Los Motilones or the Perijá Mountains, three of them within the Cesar department in Colombia and the remaining four within the Zulia state in Venezuela (fig. 1).
Data collection and cleaning Geographical records were obtained from public databases including Project BioMap (http://www.biomap.net/), DATAves (2006) and eBird (http://ebird.org/content/colombia), and also from the literature (Phelps, 1977; Paynter and Traylor, 1981; Joseph and Stockwell, 2002; Rodríguez-Mahecha and Hernández-Camacho, 2002; Tovar-Martínez, 2010) and unpublished records (see acknowledgeArdeola 59(2), 2012, 237-252
Considering its good performance compared with other methods of climatic niche prediction (Elith et al., 2006; Ortega-Huerta and Peterson, 2008), especially with reduced sample sizes (Pearson et al., 2007), we used the MaxEnt algorithm for distribution modelling (Phillips, 2010). We employed the 15 geographical records and 15 variables from the 19 bioclimatic variables of the WorldClim database at 1 km 2 resolution (http://www.worldclim.org/) as input data. Bioclimatic variable selection was made following Graham et al. (2010), leaving out variables with redundant information such as isothermality, temperature seasonality, temperature annual range and precipitation seasonality. Detailed information on selected variables and their annual mean and range values for the region comprised by the 15 localities are summarized in table 1. Given the limited dataset, we selected a regularization constant equal to 1.0 in MaxEnt and linear and quadratic features for transformation of the environment variables to avoid model overfitting (Phillips et al., 2006; Phillips and Dudik, 2008; Elith et al., 2011). We used a 10,000 sample point background, and the model extent was restricted to eleva-
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tions above 100 m in Andean ranges from Peru to Colombia-Venezuela. We chose the logistic model output to represent distributions, given that it shows the taxon’s probability of occurrence within each 1 km2 grid with a value ranging from 0 to 1. Since resampling techniques have been recommended when modelling distributions with limited samples (Peterson et al., 2007), we selected the bootstrap option included in MaxEnt to evaluate the uncertainty around the model’s performance (Dormann, 2007; Elith et al., 2011). Thus, the mean value of the area
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under the Receiving Operative Characteristic curve (from now on AUC) for training data from bootstrap replicates was taken as a measure of our model’s performance and its uncertainty was assessed through the AUC’s standard deviation. To test model fit in relation to presence data, we used the mean values for the regularized training gain and the test gain (Phillips et al., 2006; Phillips and Dudik, 2008). Although there was no extreme climatic variability among records (i.e. there were no climatic outliers), our small dataset could have caused high varia-
TABLE 1 Bioclimatic variables selected for modelling the potential distribution of Todd’s parakeet and their annual mean and range values along the region comprised by the 15 historical records used. [Variables bioclimáticas seleccionadas para modelar la distribución potencial del periquito de Todd y sus valores medios anuales y rangos en la región con los 15 registros históricos utilizados.]
Bioclimatic variable
Annual mean value (annual range)
Annual mean temp.*
22.3 (16.1-26.7)
Mean monthly temp. Range*
10.5 (10.3-10.9)
Annual precipitation**
1682 (1446-2391)
Precip. of wettest month**
307 (236-379)
Precip. of driest month**
31 (18-45)
Precip. of driest quarter **
139 (92-187)
Precip. of wettest quarter **
808 (618-998)
Precip. of warmest quarter **
603 (432-660)
Precip. of coldest quarter **
267 (168-565)
Mean temp. of coldest quarter *
20.1 (15.1-26.2)
Mean temp. of warmest quarter *
23.5 (16.6-27.1)
Mean temp. of wettest quarter *
22.6 (16.2-26.9)
Mean temp. of driest quarter *
20.9 (15.4-26.4)
Max. temp. of warmest month*
27.4 (22.1-32.8)
* Temperature in °C. Min.: minimum; Max.: maximum.
** Precipitation values in mm.
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bility in predicted areas among model replicates and an overprediction of the taxon’s presence around areas with close presence localities (Botero-Delgadillo, unpub. data). To avoid this, we ran 1,000 bootstrap replicates to stabilize the standard deviations of the models’ entropy and prevalence (see Elith et al., 2011 for details on these concepts), meaning that variability in the predicted area and probability of occurrence within each 1 km2 grid among all runs was low. We therefore selected the mean value of all replicates as a consensus model to represent the Todd’s parakeet potential distribution.
Field surveys and population counts The logistic model output in ASCII format was imported into ArcGIS 9.3 (ESRI, 2008) to obtain a predicted area with occurrence probability grids at 1 km2 resolution. In order to select potential field survey areas, we initially discarded all cells with probability values < 0.6, and subsequently we pre-selected only zones with probability values ≥ 0.8 (see fig. 2). Since most records within Colombia come from the northern portion of the Eastern Cordillera in the Norte de Santander department (fig. 1), the focus of this study was to
FIG. 2.—Potential distribution model for Todd’s parakeet using the MaxEnt algorithm. A. Predicted area of occurrence with respective probability of occurrence values. B. Detail of the study area including historical records, municipalities, survey areas and model probability values. See the text for details on locations of study sites. [Modelo de distribución potencial del periquito de Todd utilizando el algoritmo MaxEnt. A. Área predicha de presencia con los respectivos valores de probabilidad de presencia. B. Detalle del área de estudio que incluye registros históricos, municipalidades, áreas de estudio y modelo con valores de probabilidad. Véase el texto para detalles de localización de los sitios de estudio.] Ardeola 59(2), 2012, 237-252
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FIG. 3.—Areas surveyed for Todd’s parakeet in Los Motilones and Perijá Mountains in Colombia. A. Spatial locations of study sites with respect to altitude and proximity to towns/municipalities and to some of the taxon’s historical records. Ordered from south to north study sites were: Chiriguaná, Becerril and Manaure. B. An adult perched on a snag at Chiriguaná. C. Two birds feeding in a guava tree Psidium guajava at Becerril. [Áreas de estudio del periquito de Todd en las serranías de Los Motilones y del Perijá, Colombia. A. Localización espacial de los sitios de estudio en relación a la altitud y proximidad a pueblos/ municipalidades y a alguno de los registros históricos del taxón. Ordenados de sur a norte los sitios de estudio fueron: Chiriguaná, Becerril y Manaure. B. Adulto posado en una vara en Chiriguaná. C. Dos adultos alimentándose en un guayabo Psidium guajava en Becerril.] Ardeola 59(2), 2012, 237-252
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confirm the subspecies occurrence along the Los Motilones and Perijá Mountains within the Cesar department (fig. 2). For logistical limitations, we took into account only sites with relative proximity to towns among all areas with high presence probabilities, favouring those located between 2 and 20 km away from any municipality (fig. 3). To ensure that any bird encountered corresponds to a new presence locality, a final requirement for survey site selection was a minimum distance of 20 km from known records of Todd’s parakeet (figure 3). Once all expedition sites were chosen and referenced geographically (see Results), we conducted surveys in July, August and October 2011 during 10 days/month from 06:30-12:30 h and 14:30-17:30 h. Because of topographical and logistical difficulties at each site, we were not able to define the extension and shape of any of the surveyed areas a priori. However, a minimum required area was fixed on 5 km2, and the maximum area covered varied depending on topography at each site, but in all cases searches were carried out at elevations between 400 to 2,200 m based on the taxon’s known altitudinal range (BoteroDelgadillo and Páez, 2011b). If birds were detected, we stayed 10 more days to make a first approximation of population status using vantage point counts (see Wunderle, 1994). One count per day for 10 days was made from 06:00 to 08:00 h. Because this method cannot be used to estimate detection probabilities (see Bibby et al., 2000), we could only estimate an interval for the population size at each locality. The intervals’ lower limit was set as the largest group observed on any one day while the higher limit was considered as the maximum number of individuals counted during any day. To avoid counting the same individuals more than once, two to three observers at different points gathered information simultaneously on the timing, flock size and flight direction of all detected groups (Wunderle, 1994). Ardeola 59(2), 2012, 237-252
Habitat assessment Our habitat characterizations are expected to represent a preliminary assessment of habitat suitability at survey localities and as a way to explain potential presences/absences, but they do not intend to be a definitive answer to any of the patterns observed. We used a GPS at all study sites to delimitate the area surveyed for further GIS analyses. Using ArcGIS 9.3, we combined study area polygons with 2008 Landsat derived geographic layers of land-use and ecosystems compiled in a public-access portal of the Land-use Planning Geographic Information System (SIG-OT in Spanish) of the “Agustín Codazzi” Geographic Institute of Colombia (http://sigotn.igac.gov.co/sigotn/). This was done mainly for estimating the percentage loss of original cover and the area of remaining vegetation within each surveyed area. Thereafter, we determined the area of remaining forests plus secondary forests, early successional areas and forestry plantations as a measure of the potential habitat for the taxon, considering the available information on habitat use for Todd’s parakeet and other Pyrrhura parakeets (Rodríguez-Mahecha and Hernández-Camacho, 2002; Botero-Delgadillo and Páez, 2011b). In order to compare habitat availability between areas where we found Todd’s parakeet and those where not, we estimated the extension of all habitats present within each site and compared ratios of available/unavailable areas. A ratio < 1 indicated that transformed areas were the dominant cover. These estimates were accompanied by in situ descriptions of human-derived landscape transformation as an indirect verification of our analyses. Finally, we calculated the distance to human settlements around all study areas and the proximity of settlements to forest remnants to infer potential pressures derived from human activities at all sites. This was also done using ArcGIS 9.3.
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RESULTS Modelling results Our model performed well according to the mean AUC values for training data (0.98 ± 0.007), and the standard deviation around the mean suggested that uncertainty surrounding the model’s performance was low. Standard deviations around the mean values of entropy (6.46 ± 0.3) and prevalence (0.03 ± 0.01) were also low, and tended to show the same values (i.e. stabilize) around the 600-700 replicates. The mean values of the regularized training gain (2.83 ± 0.35) and the test gain (3.63 ± 0.54) indicated that the consensus model fitted well around the presence data. However, the areas with the highest probability of occurrence were widespread along the Los Motilones and Perijá Mountains and thus were not concentrated on the localities used for modelling or their nearby areas (fig. 2). In general, the consensus model predicted the species to occur between 500 and 2,200 m.a.s.l. on both sides of the Perijá Moun-
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tains, Los Motilones Mountains and small portions of the northernmost part of the Eastern Cordillera (fig. 2). The species’ climatic niche (i.e. potential distribution) was predicted to cover ca. 8,000 km2.
Field surveys Three localities were chosen for field surveys based on the criteria described above (see Methods): site number 1 was located within the Chiriguaná municipality at the base of Los Motilones Mountains (we refer to this site as Chiriguaná hereafter). This was the southernmost site and was located 17.8 km southeast of the La Jagua de Ibirico; site number 2 was within the boundaries of the Becerril municipality (from hereon Becerril), located 18.8 km southeast from Agustín Codazzi; site number 3 was the northernmost location, situated at 3.4 km east of the Manaure municipality in the Perijá Mountains (hereon Manaure; figures 2 and 3). Details on study areas and search efforts are explained in table 2.
TABLE 2 Study sites and respective search effort for Todd’s parakeet during 2011 in Los Motilones and Perijá Mountains, north-eastern Colombia. [Sitios de estudio del periquito de Todd y área muestreada en cada uno de ellos durante 2011 en las serranías de Los Motilones y del Perijá, noreste de Colombia.]
Study site
Coordinates
Study area (km2)
Altitudinal range (m.a.s.l.) *
Survey period **
Chiriguaná
9° 24’ 7’’ N, 73° 19’ 22’’ W
4.7
513-1230
July 2011
Becerril
9° 53’ 19’’ N, 73° 8’42’’ W
8.1
400-1760
August 2011
Manaure
10° 23’ 56’’ N, 72° 59’ 36’’ W
9.1
698-2810
October 2011
* m.a.s.l.: meters above sea level. ** Surveys lasted between 10 to 20 days depending upon whether parakeets were encountered (see Methods).
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We found populations of Todd’s parakeet at Chiriguaná and Becerril (fig. 3). The new site at Chiriguaná was located ca. 32 km northeast from a recent record near the Curumaní municipality and ca. 41 km southwest of the only historical record in Los Motilones Mountains at Hiroca (fig. 3). The site at Becerril was located ca. 21 km south from Hiroca, Colombia, and 17 km east from Frontera in Venezuela, the type locality of P. p. pantchkenkoi (fig. 3). We failed to find the bird at Manaure, located at 39.6 km west from Las Lajas, where the most recent record of Todd’s parakeet in Venezuela occurred.
Population counts Forty-three records of Todd’s parakeet were obtained during 10-day counts at Chiriguaná, mostly consisting of flocks of between 3 and 10 birds (84% cumulative frequency), flying 0-10 m above the forest canopy (81% of observations). Thirty-six observations were made at Becerril, where in most cases flocks
contained 3-9 birds (88% cumulative frequency), and again, almost all birds were flying 0-10 m above the canopy (83%). According to the largest flocks observed and the maximum number of birds counted at both localities, populations would number between 90 and 121 individuals at Chiriguaná and between 31 and 65 individuals at Becerril.
Habitat assessment We found that the original vegetation cover (i.e. primary forest) had been completely transformed within both study areas where Todd’s parakeet was recorded, while it represented 27.6% (2.7 km2) of the total area at Manaure (fig. 4). However, when considering primary forest plus secondary forests and other types of secondary vegetation, we found that potential habitat for Todd’s parakeet covered similar areas at the three sites, but being slightly less at Manaure (table 3, fig. 4). This similarity among sites was also reflected in the estimation of the ratio of availa-
TABLE 3 Habitat assessment values for the three study sites where searches for Todd’s parakeet were carried out during 2011 in Los Motilones and Perijá Mountains, north-eastern Colombia. [Valoración del hábitat en tres sitios de estudio donde se efectuaron búsquedas del periquito de Todd durante 2011 en las serranías de Los Motilones y del Perijá, noreste de Colombia.]
Study site
Primary/ gallery forests (km2)
Remaining habitat* (km2)
Secondary vegetation (km2)
Potential habitat** (km2)
Cattle pastures (km2)
Annual crops (km2)
Availability ratio***
Chiriguaná Becerril Manaure +
0 0 2.1 (21.4%)
0 0 2.1 (21.4%)
3.1 (66.3%) 4.5 (55.2%) 2.5 (26.3%)
3.1 (66.3%) 4.5 (55.2%) 4.6 (47.7%)
1.5 (33.5%) 3.6 (44.7%) 5.1 (52.3%)
0.009 (0.2%) 0 0
1.9 1.2 0.9
* Remaining habitat was taken as primary or gallery forest remnants. ** Estimated as remaining habitat + secondary vegetation (including secondary forests). *** Estimated as potential habitat/cattle pastures + annual crops. +
Todd’s parakeet was not recorded at Manaure.
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FIG. 4.—Habitat transformation at the three survey sites for Todd’s parakeet in north-eastern Colombia. A. Vegetation cover within and around Chiriguaná. B. Forest burning and clearance at Chiriguaná. C. Vegetation cover within and around Becerril. D. Forest remnants at higher elevations at Becerril. E. Vegetation cover within and around Manaure. F. Detailed legend. [Transformación del hábitat en tres sitios de estudio del periquito de Todd en el noreste de Colombia. A. Cobertura de la vegetación en y alrededor de Chiriguaná. B. Incendio y aclarado de bosque en Chiriguaná. C. Cobertura de la vegetación en y alrededor de Becerril. D. Remanentes del bosque a altitudes elevadas en Becerril. E. Cobertura de la vegetación en y alrededor de Manaure. F. Leyenda detallada.] Ardeola 59(2), 2012, 237-252
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ble/unavailable sites, although Chiriguaná exhibited a higher value compared with Becerril and Manaure (table 3). The dominant vegetation cover at Chiriguaná was composed of fragments of secondary forests and shrubby vegetation, separated mainly by cattle pastures (table 3, fig. 4). At Becerril, most areas were also covered by secondary vegetation, but bordered by extensive pastures to the north (table 3) and with primary forest fragments to the south (fig. 4). At Manaure, cattle pastures and savannas dominated the study site (table 3), which were also extensively distributed throughout Los Motilones Mountains despite the presence of primary forest remnants (fig. 4). Logging and forest clearance to create cattle pastures appeared to be the most important pressures on Todd’s parakeet habitat at Chiriguaná and Becerril (fig. 4B), and most forest fragments were separated by cattle pastures or transitional crops. At both localities, it was evident that pressures leading to deforestation decreased at higher elevations, where continuous remnants of primary forest persisted (figure 4D), only reaching lower altitudes on steep slopes along watersheds. Despite this configuration of habitats, Todd’s parakeet were most frequently observed near open areas in gallery forests or forest remnants associated with steep slopes far from human habitation. Although human settlements were located 8-10 km from the secondary forests surveyed both at Chiriguaná and Becerril (fig. 4), we found more than 10 farms distributed throughout both sites. In the case of Manaure, three main towns were located between 1.7-5 km from the study site, all associated with extensive (> 18 km2 each) zones for cattle nearby.
DISCUSSION The use of Species Distribution Models (SDM) to identify potential areas for studying Ardeola 59(2), 2012, 237-252
rare species and to prioritize the conservation needs of threatened taxa has increased recently (e.g. Elith and Leathwick, 2009; Freile et al., 2010). Here, we used SDM to design a 30-day survey during 2011 to increase information on the geographic range of Todd’s parakeet, a little known and presumably threatened subspecies of the painted parakeet (Botero-Delgadillo et al., 2012). Using this approach, we were able to discover two new localities for the taxon in the Los Motilones Mountains, a mountain massif where there was only one 50 year old record from Hiroca (see Paynter and Traylor, 1981). Our model appeared to represent the climatic and geographical distribution of this parakeet well, since all historical records were included within the predicted occupancy area, and both the variability of entropy and prevalence and the uncertainty of model fit were low. Field surveys confirmed that populations of this bird persist in Los Motilones Mountains, and supports previous arguments, based also on distribution models, suggesting a continuity in geographic range from the northern part of the Eastern Cordillera to the Perijá Mountains (Botero-Delgadillo and Páez, 2011b; Botero-Delgadillo et al., 2012). The absence of Todd’s parakeet at Manaure during our surveys may be explained by a variety of different reasons and we will briefly mention some of them. First, we cannot discard the possibility that birds were temporarily absent while making latitudinal or altitudinal migrations in search for food, since such local movements are common among Andean parrots and are presumed to occur in Pyrrhura parakeets (Collar, 1997; RodríguezMahecha and Hernández-Camacho, 2002; Botero-Delgadillo and Páez, 2011b). Second, it is possible that the population there could be smaller or harder to detect than in other localities, thus rendering a 10-day search effort insufficient to confirm its presence. Third, we may not have recorded the parakeet simply because its populations were extirpated from
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Manaure and neighboring areas. Although further survey effort and habitat assessment is required, current evidence suggests that habitat degradation in the entire region surrounding Manaure has been more severe compared than in nearby regions (Botero-Delgadillo and Páez, 2011b). In fact, this entire region is dominated by cattle pastures, semi-permanent crops and opencast mining operations (Botero-Delgadillo and Páez, 2011b); we therefore consider it unlikely that populations inhabiting extensive primary forests remnants around Las Lajas in Venezuela (fig. 3) could be also present on the Colombian side of the Perijá Mountains. Whatever the case, further study at wider spatial and temporal scales will be necessary to confirm its presence/absence in the Perijá range. Despite the fact that our criteria for survey site selection were intended to ensure that any record corresponded to a new presence locality, it is open to discussion as to whether birds at Chiriguaná and Becerril can be considered recently discovered populations of Todd’s parakeet or whether they relate to the same population. Parrots are extremely mobile birds with high dispersal capability, able to fly several kilometers in a day regardless of the landscape configuration (Collar, 1997; Rodríguez-Mahecha and Hernández-Camacho, 2002). However, Pyrrhura parakeets usually fly very close to the forest canopy (Collar, 1997; Gilardi and Munn, 1998) and seem to be sensitive to forest fragmentation (Botero-Delgadillo and Páez, 2011b). As has been suggested for other Andean species of Pyrrhura, our observations indicate that Todd’s parakeet can cross small open areas (Botero-Delgadillo and Verhelst, 2011; Botero-Delgadillo and Páez, 2011b), but apparently depend on a continuous canopy for movements at a landscape level (i.e. more than 20 km). Further study is needed to confirm if the dispersal capacity of Pyrrhura is reduced when forests have been severely transformed. Based on current evidence, we
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believe that birds at Chiriguaná and Becerril represent different populations. We also believe that the Chiriguaná population could be the same previously reported at Frontera in Venezuela, since only 12 km separates both areas and forests on both sides of Los Motilones remain connected (Botero-Delgadillo, unpub. data). Our surveys suggest that proximity to human settlements or even farms is perhaps the main threat at Chiriguaná and Becerril. Aside from deforestation, human presence exerts other pressures upon Todd’s parakeet populations, mainly capture for the pet trade. Some local people at both sites value this bird as a pet, as has been reported from other localities (see Tovar-Martínez, 2010), and fledglings are typically taken from cavity nests and subsequently raised before being sold (TovarMartínez, 2010; Botero-Delgadillo and Páez, 2011b). This situation could become critical since only 20% of the Todd’s parakeet known range is covered by protected areas in Colombia (Botero-Delgadillo et al., 2012). Increasing representation of the Todd’s parakeet range within protected areas on the Colombian side of Los Motilones and Perijá Mountains is critical, especially to ensure connectivity among primary forest remnants at higher elevations.
Concluding remarks Here we provide additional evidence on the potential usefulness of SDM to fill information gaps on rare or little known taxa. When interpreted cautiously, models based on climatic niche and occurrence probabilities can help design less time-consuming and more effective surveys, especially when logistic facilities or resources are limited. We encourage researchers to apply this valuable tool if appropriate geographical data are available. Considering that most of the Todd’s parakeet remaining habitat in Los Motilones Ardeola 59(2), 2012, 237-252
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Mountains is represented by continuous gallery forests located on steep and humid slopes at higher elevations, it is possible that conditions allowing for population growth (or at least maintenance) could be present in those patches. If so, it will be necessary to identify currently unprotected forest fragments that serve to maintain connectivity between populations distributed from the northernmost part of the Eastern Cordillera to the Perijá Mountains (if they remain there). Future studies should focus on confirming presence in other areas suggested by our model, such as the Colombian slope of the Perijá Mountains, and the junction of the Merida Andes and the Eastern Cordillera (Botero-Delgadillo and Páez, 2011b). Evaluating our entire model in Colombia and Venezuela is also a priority research need. ACKNOWLEDGEMENTS.—We thank Fonds für bedrohte Papageien and Strunden Papageien Stiftung for funding this work, and to René Wüst for his advice and ideas for the entire project. We especially want to thank Miguel Lentino and Juan Pablo López for sharing helpful information. Miguel Mejía, Pedro Pablo Contreras, Daniel Rodríguez and Ramiro Álvarez provided valuable help during field surveys. Nicholas Bayly, Sandra Escudero and Camila Gómez made thorough comments on an earlier version of this manuscript. Two anonymous reviewers made valuable comments that helped improve the manuscript.
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