Agriculture Reference
In-Depth Information
Table 16.2
Survey effort and the number of observed bird and bat species and individuals for
three habitat types in the Cagayan Valley, northeast Luzon (Values in parentheses show the propor-
tion of total observed numbers of species or individuals)
Gmelina forest
Homegardens
Shrub-land
Total
Birds
No. of point counts
46
36
36
118
Resident bird species
38
27
47
58
Endemic species
7 (18%)
3 (11%)
6 (13%)
11 (19%)
Threatened species
0
0
1
1
Forest bird species
10 (26%)
5 (18%)
6 (13%)
15 (26%)
Total individuals
439
352
302
1,093
Forest bird individuals
63
12
16
91
Bats
No. of mist-net-lines
13
9
12
34
No. of mist-nets
53
25
49
127
No. of mist-net-nights
154
75
147
376
Bat species
9
9
12
16
Endemic species
3 (33%)
3 (33%)
4 (33%)
5 (31%)
Threatened species
1
0
0
1
Fruit bat species
6 (67%)
6 (67%)
5 (42%)
7 (44%)
Forest bat species
1 (11%)
2 (22%)
3 (25%)
5 (31%)
Cave roosting species
3 (33%)
4 (44%)
8 (67%)
9 (56%)
Total individuals
131
128
150
409
Fruit bat individuals
128 (98%)
124 (97%)
130 (87%)
382 (93%)
minute rest period after arrival, and were performed early morning and late after-
noon. Point counts were conducted by the first author and one experienced field
assistant following Kennedy et al. (2000) for taxonomy. Vocal and visual records
were noted with the number of individuals for each species per observation event.
Birds flying over the point count locality were not included unless they clearly
made use of the habitat, e.g., hunting swiftlets. Only resident species (Kennedy
et al. 2000) were included in analyses to avoid bias as a result of differences in
migration periods between migratory species. No fixed belt was used for the point
counts but distances from observer were estimated. Although the detectability of
bird species decreases with distance from observer, limiting a point count radius too
much possibly excludes species that are hesitant to move within close distance to
an observer and geometrically limits the survey area (Shankar Raman 2003).
Unlimited distance point counts need compensation of observer bias due to specific
differences in detectability. We followed other researchers in only using observations
within a radius of 50 m (91 percent of observation events) within which, in our
study, all species could still be vocally identified and assume our point count results
approximate total counts (Shankar Raman 2003). To assess the importance of the
three habitat types for birds belonging to different habitat preference guilds we cate-
gorized bird species into three groups: species primarily found in various types of
forest (forest species), species primarily found in open areas (open area species)
and species found in both open and forest like habitats (varied habitat species)
based on Kennedy et al. (2000). We further distinguished Philippine endemic spe-
cies (Kennedy et al. 2000) and globally threatened species (IUCN 2006).
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