Cowlishaw and Dunbar 2000). In the same vein, Shankar Raman (1996)
interprets contrasting patterns of habitat use by northeast Indian forest pri-
mates in relation to feeding habits. For example, frugivorous hoolock gibbon
(Hylobates hoolock) was observed largely in primary forest habitats and has a
documented preference for fruits of certain primary forest tree species.
Phayre’s leaf-monkey (Presbytis phayrei), on the other hand, is a folivore pre-
ferring a group of early and midsuccessional trees and was not observed in pri-
mary forest.
Studies of neotropical birds typically identify several feeding guilds, some
of which we have already mentioned. Guilds are delimited in relation to the
preferred food type and the specific habitat component used during foraging
(from broad categories such as “canopy” and “understory” to more specific
ones such as “bark”) and whether activity is diurnal or nocturnal. The most
detailed classification of feeding guilds consulted by the present authors was
that of Robinson and Terborgh (1990), who identify 22 guilds. Species in
these guilds may additionally be considered generalists or specialists or
grouped in relation to the size of food articles taken (Fleming et al. 1987). The
studies of birds in shifting cultivation landscapes cited earlier mention several
hypotheses linking the community- and species-level patterns found to food
availability.
In some cases, the reduction or absence of preferred food sources in shift-
ing cultivation landscapes, in comparison with forest, might be linked to the
decline of forest bird populations. The small proportion of terrestrial forest
insectivores that follows army ant swarms is a clear example of how trophic
relationships may break down in human-influenced landscapes. Studies in
fragmented forests emphasize that these birds need to track several ant swarms
simultaneously, so they may disappear if forest fragments are of insufficient
size for the necessary numbers of swarms (Stouffer and Bierregaard 1995).
Although the decline of understory and terrestrial insectivores in disturbed
habitats has already been emphasized, whether or not such causal relationships
to ant swarms apply in shifting cultivation landscapes remains to be deter-
mined. For example, Johns (1991) believed that the frequency of army ant
swarms did not differ between the habitat types he sampled. It is also the case
that some terrestrial forest birds may experience physiological stress in the
microclimates of second-growth vegetation, so that this factor, rather than pat-
tern in food availability, could be responsible for responses of bird communi-
ties to habitat disturbance.
A variety of species or guilds of forest birds evidently use or prefer anthro-
pogenic habitat patches in shifting cultivation landscapes when foraging. The
insectivore-nectarivore guild, made up in the neotropics by hummingbirds
(Trochilidae), normally maintains or increases its representation in fallow veg-
etation because of the high abundance there of both floral and invertebrate
resources (Johns 1991; Andrade and Rubio-Torgler 1994). Johns (1991)
- The Biodiversity and Conservation Potential of Shifting Cultivation Landscapes 179