Birds surveyed in the harvested and unharvested areas of a reduced-impact logged forestry concession , located in the lowland subtropical humid forests of the Department of Santa Cruz , Bolivia

As part of a larger study of reduced-impact logging effects on bird community composition, we surveyed birds from December to February during the 2003-2004 wet-season within harvested and unharvested blocks of the La Chonta forestry concession, Department of Santa Cruz, Bolivia. The logged forest was harvested using reducedimpact logging techniques between one and four years previously. During point count surveys, we identified 5062 individual birds, belonging to 155 species, and 33 families. We provide a list of bird species found within the harvested and unharvested blocks of the concession for the benefit of other researchers assessing the responses of Neotropical avifauna to disturbance, and to facilitate increased understanding of the diverse bird assemblages found within the lowland subtropical humid forests of Bolivia. Introduction There are over 1400 species of birds known from Bolivia, with the majority of species found in the sub-tropical and tropical forests of lowland Bolivia (Pacheco 1998). Almost half of forests in lowland Bolivia are now granted to forestry concessions (Mostacedo and Fredericksen 1999). In 1996, a new forestry law was enacted to promote the sustainable harvesting of timber (Mostacedo and Fredericksen 1999). To achieve best-management practices, reduced-impact logging techniques have gained widespread application in Bolivia and, as of 2005, concessions covering over 2.2 million hectares had obtained certification by the Forest Stewardship Council (Forest Stewardship Council 2005). Here, we provide the results of a wet season bird survey of the harvested and unharvested areas on one of these certified concessions located in the lowland subtropical humid forests of the Department of Santa Cruz, Bolivia. Material and Methods Study site Our study area was located in the lowland subtropical humid forest of the Guarayos Forest Reserve, Department of Santa Cruz, Bolivia. Research was conducted in the 100000 ha forestry concession “La Chonta”. This is owned and managed by Agroindustria Forestal La Chonta (509000 to 545000 easting, 8275500 to 824900 northing; Figure 1). The forest has an average elevation of 320 m (range 230-390m). The soils consist of oxisols, ultisols, and inceptisols (Park et al. 2005). The mean annual temperature is 25° C with a mean annual precipitation of approximately 1560 mm. The region experiences a distinct dry season from May to October. The entire concession was subjected to legal and illegal selective logging of mahogany (Swietenia macrophylla), and Spanish cedar (Cedrela odorata) from ~1980 to 1995. The concession was certified by SmartWood in 1998. Harvesting procedure Approximately 2500 ha of forest is harvested annually over three contiguous 850 ha blocks (~4 x 2 km), yielding 50000 m of timber. Eighteen tree species were harvested during the time of this study (2003-2004) including Ficus boliviana, Hura crepitans, Terminalia oblonga, Cariana ianeirensis, C. estrellensis, and Pseudolmedia laevis. Average harvest intensity was approximately 4 trees per ha (Jackson et al. 2002). The forestry company Agroindustria Forestal La Chonta conducts inventories of harvestable trees one year prior to logging. The minimum size for harvest is 50 cm diameter at breast-height (dbh) for all species except F. boliviensis and H. crepitans, which are harvested above 70 cm dbh. One in five harvestable trees is required by law to be left as a Check List 2007: 3(1)


Introduction
There are over 1400 species of birds known from Bolivia, with the majority of species found in the sub-tropical and tropical forests of lowland Bolivia (Pacheco 1998).Almost half of forests in lowland Bolivia are now granted to forestry concessions (Mostacedo and Fredericksen 1999).In 1996, a new forestry law was enacted to promote the sustainable harvesting of timber (Mostacedo and Fredericksen 1999) 2005).Here, we provide the results of a wet season bird survey of the harvested and unharvested areas on one of these certified concessions located in the lowland subtropical humid forests of the Department of Santa Cruz, Bolivia.

Study site
Our study area was located in the lowland subtropical humid forest of the Guarayos Forest Reserve, Department of Santa Cruz, Bolivia.
Research was conducted in the 100000 ha forestry concession "La Chonta".This is owned and managed by Agroindustria Forestal La Chonta (509000 to 545000 easting, 8275500 to 824900 northing; Figure 1).The forest has an average elevation of 320 m (range 230-390m species not yet of harvestable size but above 30 cm dbh; 3. 'Vine thicket' points (N) of less than 12m in height and not possessing commercial trees above 10 cm dbh; 4. 'Gap' points (G) possessing a tree-fall gap caused by the felling of a tree (in the harvested blocks) or a natural tree fall (in the unlogged blocks) of greater than 50 cm dbh; and 5. 'Road' points (R) located on a primary north-south logging road in the logged forest, or along the main north-south access path in the unlogged forest.In total, 360 points was surveyed, equally distributed between the logged and unlogged forest, represented by 72 points of each of the five habitat categories.

Bird surveys
At each of the 360 survey points, we used an unlimited distance point-count method of surveying bird species abundance.All survey points were located at least 300 m from the nearest point, and at least 500 m from the edge of neighbouring treatment blocks.Surveys were conducted from December to February of the 2003-2004 wet season.Surveys began at first light (5:45-6:00 am), and continued until approximately 10:45 am.Counts were not undertaken if weather was poor (e.g.rain, high wind).This period overlapped with the daily peak in bird vocal activity.A day's survey consisted of visiting three points of each of the five habitat types (15 points in total).Each point was surveyed for 12 minutes.We included birds flushed from the survey point on approach by the observer, while birds flying over the survey area were not included in the analysis.
Due to the density of forest vegetation, most identifications were made acoustically, rather than visually.In addition to point counts, recordings of birds were made using a Sony TCM 5000 taperecorder that was attached to a Sennheiser ME66 microphone.These recordings were used as a supplement to in-the-field identification of vocalizing species.For unidentified species, symbolic representations of songs were noted.This was in addition to notes on the recording time, direction, and estimated distance to the call.This enabled the matching of subsequent identifications with abundance and distance information.Unknown recordings were identified using the CD-ROM Birds of Bolivia, 2.0 (Mayer, 2000), or by an expert (B.H).All research was approved by the relevant authorities and this study was conducted within the ethical guidelines of Australia and Bolivia.

Results and discussion
This survey was part of a larger study assessing the effects of reduced-impact logging on bird community composition and abundance.The list should be of benefit to other researchers assessing disturbance associated responses of Neotropical avifauna, and to facilitate increased understanding of the diverse bird assemblages found within the lowland subtropical forests of Bolivia.During point count surveys, we identified approximately 5 050 birds, belonging to 155 species, and 33 families (see Table 1).
Although avian species richness was nearly identical between the harvested and unharvested areas of the concession (logged 132 spp.; unlogged 133 spp.), this numerical equivalence obscures underlying differences in species composition.Our results suggest that the avian families Ramphastidae, Falconidae and Formicariidae were adversely affected by the logging activities in this forest.At the species level, concern may be warranted regarding the absence of the Barred-forest falcon and the lower abundances of Red-necked Woodpecker, Channel-billed Toucan, Red-billed Toucan, Black-faced Antthrush, Spot-backed Antbird, and Gray-fronted dove within the harvested areas of the concession.In contrast, the Black-throated Antbird, Yellow-tufted Woodpecker, Buffthroated Saltator, and Moustached Wren, appear to be currently benefiting from logging associated disturbance.
Due to temporal and seasonal variation in bird species vocalization and presence, results should be interpreted acknowledging the season of the survey and the time of day during which the surveys were carried out.It should also be acknowledged that the mere presence of a species in an area does not necessarily mean that the area possessed suitable habitat for that species' longterm persistence (O'Brien et al., 2003).At the time of the survey, the first logging rotation for the concession was not as yet completed, and disturbance processes associated with selective logging activity occurred from only one to four years previously.This temporal period of disturbance is well short of that by which most localized avian extinctions are predicted to occur following anthropogenic disturbance processes (Robinson 1999;Mason and Thiollay 2001).

Figure 1 .
Figure 1.Map of Bolivia with approximate location of the la Chonta forestry concession indicated within the department of Santa Cruz.
During pre-harvesting inventory, trees selected for felling are cleared of all vines from their bole.The forestry company uses a 'fishbone' harvesting strategy with a single primary northsouth road bisecting each 850 ha block.Skid trails are located 100-150 m apart and run in an eastwest direction on either side of the primary road.Chainsaw teams trained in directional felling techniques try to reduce damage to the residual stand during logging.Removal and loading of boles is conducted using rubber-tired skidders to reduce soil compaction.It is intended that blocks be re-cut in 25 to 30 years.
).The soils consist of oxisols, ultisols, and inceptisols(Park et  al. 2005).The mean annual temperature is The minimum size for harvest is 50 cm diameter at breast-height (dbh) for all species except F. boliviensis and H. crepitans, which are harvested above 70 cm dbh.One in five harvestable trees is required by law to be left as a seed tree.height, and disturbance type.Five habitat types were surveyed including: 1. 'Tall forest' points (T) with vegetation height over 20 m and possessing one of five commercial tree species (Ficus boliviensis, Hura crepitans, Cariniana estrellensis, C. ianeirensis, Terminalia oblonga) of harvestable size; 2. 'Medium forest' points (F) from 12-20 m in height and possessing a commercial tree of the afore mentioned five