Human-Altered Tree-Based Habitats and Their Value in Conserving Bird and Bat Diversity in Northeast Luzon, The Philippines - Smallholder Tree Growing for Rural Development and Environmental Services - page 357

A comparison of the results of the bat surveys with the bat species recorded in
the NSMNP (Mudar and Allen 1986; Danielsen et al. 1993; Balete et al. 1995;
NORDECO and DENR 1998; M. van Weerd unpublished data 2000-2007) shows
that the human-altered habitats are more important for the bats than for the birds of
northeast Luzon. The NSMNP has 36 recorded bat species (and two strictly mon-
tane species which are excluded from this comparison), 44 percent of the bat spe-
cies of the park also occur in our three study habitats (16 of 36). No new species
have been found outside the park. The bat species in our study habitats represent 58
percent of the fruitbats (7 of 12), 29 percent of the forest bats (5 of 17), 38 percent
of cave-roosting bats (9 of 24), 25 percent of globally threatened bats (1 of 4; only
1 record) and 42 percent of the endemic bats (5 of 12) known from the NSMNP.
Shrub-land has more bat species than Gmelina forest and homegardens but less
fruit bats (Table 16.2, Fig. 16.3A). Fruit bat species richness for Gmelina forest and
homegardens are similar (Fig. 16.3B) but homegardens have higher densities of
fruit bats (Fig. 16.3D). The higher bat species richness for shrub-land is the result
of the larger number of captured Microchiroptera species (all insectivorous). Most
of these have been captured only once or twice (Table 16.3). Microchiroptera,
which use echolocation to capture insects, are difficult to survey using mist nets
(Francis 1989), and the results on these species are therefore difficult to interpret.
Shrub-land may offer more insects than the two other habitats, or bats may hunt
lower to the ground thus increasing the chance to be captured in a mist net.
Estimated detection rates of all bat species range from 65 to 78 percent but for fruit
bats these rates are much higher (84 to 99 percent).
No correlations are found between bat species richness and abundance and habi-
tat structure variables. Although fruit bat densities are highest in homegardens, the
abundance of all bats and a sub-set of fruit-bats is negatively correlated to the
number of houses within 100 m of the centre of mist-net lines in Gmelina forest
suggesting human disturbance affects bats.
Forest bat species richness and abundance are negatively correlated to the dis-
tance to contiguous forest, yet, the correlations are statistically not significant. Our
results indicate that forest bats venture further into human-altered landscapes than
forest birds but are still restricted to habitats at a limited distance to contiguous for-
est. Of the two fruit bats which are classified as forest species, the globally threat-
ened endemic Haplonycteris fischeri has been captured only once: in Gmelina forest
near contiguous forest. The cave roosting endemic forest bat Eonycteris robusta has
been captured in homegardens and shrub-land near caves at a maximum of 3.7 km
from contiguous forest. The single individuals of three Microchiroptera forest bats
have been captured in shrub-land (two species) and in a homegarden (one species),
in both cases also near contiguous forest. No forest bats have been captured at loca-
tions far from forest (12.7 km and beyond). A caveat in our study is that we did not
survey localities at medium distances to closed-canopy forest. It is therefore not pos-
sible to determine a reliable maximum distance to contiguous forest at which most
forest bats forage. In contrast to forest bats, no relation has been found between the
abundance and species richness of cave roosting bats and the distance to caves. The