The effects of forest fragmentation on bird species in Madagascar : a case study from Ambohitantely Forest Reserve on the central high plateau.
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Date
1995
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Abstract
Considering the high rate of endemism in Madagascan
organisms, which are mostly restricted to forest ecosystems,
and the accelerating rate of deforestation affecting the
island, it is critical to understand the effects of forest
fragmentation on Malagasy biota to allow for better management
of species within ecosystems. Ecological and human-induced
changes have led to the disappearance of forest from vast areas
of the island, including on the central High Plateau.
The Ambohitantely Special Reserve, located on the central
High Plateau at 1500 m asl, was selected as the study site for
research on the effects of forest fragmentation on forestependent
bird species in Madagascar. The Ambohitantely
special Reserve covers 5600 ha of which 50% are natural forest,
35% are anthropogenic grassland savannah and 15% are exotic
plantations. The forest, described as East Malagasy moist
montane forest, is 2737 ha in area, of which 1487 ha are
comprised of 513 forest fragments scattered around the largest
block totalling 1250 ha. To investigate the effects of forest
fragmentation on forest-dependent bird species, seven forest
fragments were selected, ranging from 0.64 ha to 136 ha, in
addition to the largest block, referred to as the control site.
The bird species composition and relative abundance in
different-sized fragments were assessed in reference to the
control site, by using a combination of two standardized
sampling methods: mistnetting and point-counts. A total of
1804 mistnet-days were accrued, 1026 in the control site and
778 in the seven forest fragments, leading to the capture of
491 birds of 26 species. A total of 160 point-counts was made
at 39 different sample plots totalling 53 h 29 min of
censusing, and a record of 30 species.
A total of 72 bird species including 54 breeding forest affinities of the avifauna of Ambohitantely were defined with
reference to 32 forest sites scattered across Madagascar.
The species composition in all fragments are fully nested
subsets of the control site and the species distribution in the
fragments does not represent random subsets of the control
site. The analysis of the bird communities in different size
fragments indicates that the occurrence of bird species
reflects a regular pattern of species extinction in relation to
decreasing size of forest fragment. Species composition is
discussed in reference to Ambohitantely's long history of
isolation that may have led to extirpation of bird species from
this site. The higher bird taxa decrease in number or totally
disappear as a result of their ecological specialization.
Equally, they are the most affected by edge effects (e. g.
Atelornis pittoides). The main ecological trends in
disappearance or extinction of species is a decrease in the
number of small-bodied insectivorous understorey species and
mid- and upper-stratum small-bodied insectivorous and
nectarivorous species. Insectivorous species are particularly
affected by forest fragmentation and three forest-dependent
species found in Ambohitantely Forest are particularly
sensitive to forest fragmentation: Newtonia amphichroa,
Calicalicus madagascariensis, and Cyanolanius madagascarinus.
The biological (flora species composition and forest structure)
and the physical (temperature, moisture, and light) changes
generated by the fragmentation of the forest have a greater
impact on highly specialized foraging guilds and this explains
the pattern of current bird species composition in
Ambohitantely Forest.
The influence of forest fragmentation on the altitudinal
migration process is debated and conservation measures such as
the establishment of forest corridors are proposed to improve
the protection of biota found in the Ambohitantely Special
Reserve.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.
Keywords
Forest birds--Madagascar., Forest birds--Ecology., Forest birds--Habitat., Theses--Zoology.