Diurnal bird raptors of Llanos de Moxos, Bolivia

Raptor abundance has been poorly documented in the Neotropics. Here we describe the abundance and composition of the diurnal bird raptor community of Llanos de Moxos, one of the largest and less studied Neotropical savannah. During four consecutive breeding seasons (i.e., August 2007 to February 2008, August 2008 to January 2009, August 2009 to January 2010, and August 2010 to January 2011), we monitored 11 transects and 30 points, searching for raptors’ activity. We detected 29 diurnal bird raptor species in the region, which represented almost half of diurnal bird raptor species of Bolivia. As expected, scavengers and generalists were most frequent and abundant diurnal bird raptors. The Llanos de Moxos shared 83% of raptor species with Venezuelan Llanos and 67% with Chaco wetlands. The Llanos de Moxos is an important migratory and conservation region for some species as Swainson’s hawk, Chaco eagle, osprey and peregrine falcon. The lack of effective protected areas in the region is concerning, and, thus, the establishment of such areas should be a conservation priority.


Introduction
Large savannahs usually sustain high density of bird raptors, especially scavengers and generalists (del Hoyo et al., 1994).While raptor abundance was widely described in the African region, it is poorly documented in the Neotropics (Sorley and Andersen, 1994;Seavy and Apodaca, 2002;Ferguson-Lees and Christie, 2005;Thiollay, 2007).Some savannahs of South America acknowledged some attention from raptor researchers.Raptor abundance was described in the Llanos of Venezuela, the Brazilian Cerrado and the Argentinean Wet Chaco (Di Giacomo, 2000;Jensen et al., 2005;Eduardo et al., 2007;Seipke, 2007).By the other hand, savannas as the Llanos de Moxos, received little or any attention from raptor's researchers.Even when all these savannahs are geographically distant one from another, they are ecologically similar, exposed to seasonal flooding, and with major vegetation types including grasslands, savannah woodlands, and gallery forests (Werneck et al., 2012).
Llanos de Moxos is one of largest savannas of South America with an approximately area of the size of the United Kingdom (i.e., 213.564 km 2 ).The lack of a network of roads first, and later the drug trafficking, constrain field research in this Bolivian region until the end of the twenty century (Brace et al., 1997).During the last two decades, some new vertebrate species were discovered or rediscovered in this region (Jordan and Munn, 1993;Balchin, 2007;Martínez and Wallace, 2007).Even concentrating the 41% of diurnal bird raptors of Bolivia, the Llanos de Moxos was poorly studied and the available information is limited (Hennessey et al., 2003;Herrera and Maillard, 2007;Berkunsky et al., 2012).Here we describe the abundance and composition of the diurnal bird raptor community of one of greatest Neotropical savannah, the Llanos de Moxos; and we compare this community with other diurnal bird raptor communities of Neotropical savannahs.

Study site
We conducted surveys in the Llanos de Moxos (from 12° to 16° S, and from 63° to 67° W), Beni Department, northern Bolivia (Figure 1).The Llanos de Moxos is a seasonally inundated savannah, interspersed with a complex mosaic of forest islands and riverine gallery forests, occupying the extremely flat Beni-Mamoré-Iténez basin in southwest Amazonia, situated between the Precambrian Shield to the east and the Andes to the west and south (Hanagarth and Beck, 1996).Numerous white-water rivers and hundreds of shallow, flat-bottomed lakes cover the landscape.The landscape is dominated by flat, low-lying areas, which are seasonally inundated and covered by completely open, treeless savannah (Mayle et al., 2007).Conversely, forest islands are scarce and restricted to raised areas (mounds), which are sufficiently elevated to escape annual flooding.Most of forest islands are eroded relics of natural levees or terraces of abandoned river canals, and therefore constitute fragments of former gallery forest (Langstroth, 1996).
Human presence in the study area occurs at low densities (1.4 people per square kilometer), with 43 settlements spanning the municipalities of Trinidad, San Javier, San Ramón, Santa Ana de Yácuma, San Andrés and Loreto.The primary occupation of the residents is cattle ranching (Hangarth and Sarmiento, 1990) as has been the case for several hundred years.The study was carried out on private lands (owner names are mentioned in acknowledgments).

Data collection
In this study, we considered diurnal bird raptors as those members of the Cathartidae, Pandionidae, Accipitridae and Falconidae families.Data were collected from early August up to late January during four consecutive breeding seasons (i.e., August 2007to February 2008, August 2008to January 2009, August 2009to January 2010, and August 2010to January 2011).Each season, a total of 11 transects (10 km each, unbounded) were travelled by two observers, and a total of 30 points (30 minutes each, unbounded) were completed by two simoultaneously observers with binoculars (10 x 42, and 10 x 52).In transects and points, we searched for raptors' activity and all detected individuals were counted (perched and flying).We detailed all detected individuals (perched or flying) from transect and/or point, and we documented the presence of juveniles and/or nests.
We easily recognized the observed species, and most of them were photographed.However, doubts were clarified with the aid of bird and raptor guides for identification (del Hoyo et al., 1994;Ferguson-Lees and Christie, 2005).We follow the South American Classification Committee for common and Latin names of birds (Remsen et al., 2017).Raptors were classified in residents or migrants according Bildstein (2004) and Ferguson-Lees and Christie (2005).Migrants were classified as complete migrants, partial migrants, irregular and local migrants (Bildstein, 2004).For each species, we estimated frequency as the number of sites (transect and points) where the species was detected by the total of surveyed sites; and relative abundance as the number of detected individuals per kilometer of transect.
We detected 10 migrant species.Three species are complete migrants (osprey, Swainson's hawk and peregrine falcon); three species are partial migrants (turkey vulture, snail kite, and plumbeous kite); and four species are irregular and local migrants (hook-billed kite, slenderbilled kite, aplomado falcon and american kestrel.Flocks of hundreds of Swainson's hawk were observed in late October and November in 2007, 2008, 2009and 2010.A flock of at least 15 hook-billed kites was observed near to a stream in October 2008.We observed breeding behavior in at least 47% of the species (Table 1).

Discussion
The richness of species was similar to other Neotropical savannahs.The 29 species of llanos de Moxos was close to the 30 species reported for the Venezuelan Llanos, and almost the double of the 15 species reported for Wet Chaco (Jensen et al., 2005;Seipke, 2007;Trejo, 2007).
As expected, scavengers and generalists were the most frequent and abundant diurnal bird raptors (Ferguson-Lees and Christie, 2005).The most common diurnal bird rap-  tors were black vulture, turkey vulture, southern caracara and savanna hawk; followed by other less abundant, but still frequent species generalists, such as turkey vulture, black-collared hawk, white-tailed hawk, yellow-headed caracara and American kestrel.The highest abundant, but less frequent (55%), species was the snail kite, which showed large congregates in flooded areas.This gregarious kite is common in flooded fields, streams and small lakes in the whole region (Brace et al., 1997).
Some habitat specialists have a low frequency, and this could be a consequence of a low availability of their specific habitats in the sampled area.This is the case of the os-prey and the slender-billed kite, two species detected only near to streams and/or rivers with high vegetation coverage.We failed to detect some forest associated species as forest eagles (e.g., harpy eagle, crested eagle, etc), hawks (genus Accipiter) and forest-falcons (genus Micrastur) reported for the Beni department (Hennessey et al., 2003).Our sampling was concentrated in Beni savannahs, a habitat where these species usually have a low detectability (pers.obs.).
The presence of flocks of migratory species suggests that the Llanos de Moxos would be an important steppingstone for these species.Large numbers of Swainson's hawk confirm the Llanos de Moxos as part of their con- tinental migratory route (Bildstein, 2004;Sarasola et al., 2007).Other large concentrations of raptors, as the case of hook-billed kite, also suggest migratory movements of these species in the region (Paulson, 1983).In the case of lonely migrants, the detection of a leg-banded osprey would be suggesting a wintering habitat in the Llanos de Moxos, and the detection of a single peregrine falcon may suggest the Llanos is also a wintering site and/or it is in it migratory route (Fuller et al., 1998).
Almost half (29 of 68 species, Hennessey et al., 2003) of diurnal bird raptor species of Bolivia were found in the Llanos de Moxos, including two globally threatened species, the chaco eagle and the orange-breasted falcon.The chaco eagle was found in almost one fifth of the surveyed sites, but always in low abundance.One breeding pair was located recently, confirming the reproduction of this endangered eagle in the region (Berkunsky et al., 2012).The orange-breasted falcon is globally considered as near threatened, being uncommon in the Llanos de Moxos, only detected once in a survey point.The Llanos de Moxos concentrated a good number and abundance of diurnal raptor birds and it is an important migratory and conservation area for these species.The lack of effective protected areas in the region is concerning, and the establishment of such areas should be a conservation priority (Herzog et al., 2005).

Figure 1 .
Figure 1.Geographic distribution of transects and points (black dots), where raptors surveys were conducted in the Llanos de Moxos, northern Bolivia.

Table 1 .
Jensen et al. (2005) andTrejo (2007)Diurnal bird raptors of Llanos de Moxos, Bolivia Diurnal bird raptors in Neotropical savannahs: conservation status and population trend (IUCN Red List 2017), relative frequency (sites with detection over the total surveyed sites) and mean relative abundance (± SD) of species observed between 2007 and 2009 in Llanos de Moxos, Bolivia (this work).Last two columns represent the species found byJensen et al. (2005) andTrejo (2007)in Venezuela llanos and Chaco wetlands, respectively.-: not detected.