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 354

shrub-land, a negative relationship (Spearman r = −0.674, n = 9, p < 0.05) was
found between the distance to contiguous forest and the average number of forest
bird species observed per point count. Whereas similar relationships seemed to
exist for the other two habitat types (Fig. 16.4B), these were not significant. A posi-
tive relationship (Spearman r = 0.733, n = 9, p < 0.05) was found between the dis-
tance to contiguous forest and the average number of resident bird individuals
observed per point count for shrub-land. This was also found for homegardens and
Gmelina forest (Fig. 16.4C) but the correlations were not significant.
The abundance of all bats and a sub-set of fruit-bats was negatively correlated to
the number of houses within 100 m of the centre of mist-net lines for Gmelina forest
(Spearman r = −0.900, n = 5, p < 0.05 for both correlations). For shrub-land, fruitbat
species richness was negatively correlated to the density of large trees (Spearman
r = −0.830, n = 8, p < 0.05) and to the distance to caves (Spearman r = −0.679,
n = 9, p < 0.05). Cave bat species richness and abundance were both positively
related to the distance to contiguous forest (Spearman r = 0.686, n = 9, p < 0.05 for
cave bat species richness and Spearman r = 0.714, n = 9, p < 0.05 for cave bat
abundance).

16.4 Conservation Importance of Human-Altered Habitats

in Cagayan Valley for Birds and Bats

A comparison of the bird species found in our study habitats with the species
known from the Northern Sierra Madre Natural Park (NSMNP) (Danielsen
et al. 1993; Poulsen 1995; NORDECO and DENR 1998; M. van Weerd unpub-
lished data 2000-2007) situated at the eastern fringe of the research area, shows
that the conservation value of the study habitats for forest, endemic and threatened
birds is very low. All bird species observed in our study habitats also occur in the
NSMNP. Although the bird species recorded in all three habitats (58 species) rep-
resent 32 percent of resident lowland birds identified in the NSMNP (179 species,
strictly coastal and montane species excluded), they only represent 13 percent (15
of 115 in total) of lowland forest birds, 15 percent (11 of 72) of endemic lowland
birds, and eight percent (1 of 12) of globally threatened lowland bird species in the
park. Of all bird species observed in the study habitats only 26 percent are forest
birds compared to 64 percent of lowland birds of the NSMNP. The resident bird
species found in the human-altered landscape of the Cagayan Valley are mainly
open area species and various-habitat generalists.
The representation of forest birds in the human-altered habitats is further very
low compared to findings in similar studies elsewhere. Hughes et al. (2002) report
that agricultural areas in Costa Rica serve as a habitat for 46 percent of the native
bird species found in the region. In Sumatra, 59 percent of bird species found in
lowland primary forest are also found in complex agroforestry systems (Thiollay
1995). Mixed-rural habitat in southern Peninsular Malaysia contains an estimated
28 to 32 percent of primary forest bird species of that region, including a number