Biodiversity of the Rewa Head B Zoological Society of London ...

Results
In total 420 mist net hours were accumulated (140 hours per net) at the five netting
sites. 91 birds were caught, resulting in 41 different species being identified. Four birds
were unidentified; two of which were likely to have been female long-winged antbirds
(Myrmotherula longipennis). Twenty-three of the species caught in mist nets were not
observed during the drift transects.
The most frequently caught family was the Thamnophilidae with 15 of all species
and 27% of total number of individuals caught, followed by the Dendrocolaptidae (5
species) and Trochilidae (4 species). The most common species encountered in the
nets was the wedge-billed woodcreeper (Glyphorynchus spirurus).
Drift Spot Count Survey
Method
In conducting drift spot count surveys, we divided the river from the East-West Split at
N2° 37.740’ W58° 37.040’ down to Corona Falls at N3° 10.579’ W58° 40.433’, into 5 mile
stretches. Each stretch was surveyed once by drifting downstream with three spotters in a
boat, taking turns at inputting the data, resulting in a single surveyed transect of 60 miles.
We used a portable mp3 player containing the vocalisations of the birds of Venezuela to
identify calls and song. We kept to mid-river when it was narrow enough to cover both
banks, but when the river widened to over 40m we kept within 15m of one bank. To
standardise the surveys we attempted to maintain a steady speed of around 2 miles per
hour, by paddling through slower stretches though the speed invariably depended on the
volume of water flowing. Following heavy rains transect duration was shorter by at least
half an hour due to the increased flow. Occasionally it was necessary to break up a stretch,
such as when portaging. When this occurred we halted the count until the obstacle had
been passed. Spot counts were carried out in the morning, when animal activity was
greatest. However, due to the logistics of moving camp, several times we had to carry on
with conducting the surveys into the afternoon, when activity generally declined.
Figure 31. Crimson topaz (Topaza pella). In total nine
species of hummingbird were recorded in the Rewa.
22 Biodiversity of the Rewa Head
Results
We recorded over 4000 birds
during the transects, resulting in
the identification of 158 species
through both visual observation
and vocalisations. Through the
combination of sightings made
on drift transects, mist-netting,
opportunistic sightings and
vocalisations, we positively identified
187 species from 48 different
families. The most diverse family
observed was the Tyrannidae
(34 species) closely followed by
Thamnophilidae (31 species), then
Accipitridae (11 species), Psittacidae
(11 species), Ardeidae (10 species)
and Trochilidae and Thraupidae (9
species). The most abundant family
was the Hirudinidae comprising
20% of total observations,
followed by the Apodidae, with
16%, Psittacidae with 10% then
Icteridae with 5%.
Discussion
In August 2006 Ashley Holland led a Smithsonian Institution collecting expedition to the
Rewa, coordinated by Chris Milensky and Brian Schmidt. They set up two mist netting
sites, one above Corona Falls at Louis Creek (2 58’ 17” N, 58 35’ 37” W) and the other
below. Above the falls they erected 20 nets and netted for 10 days. Combining our data