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Bird community structure and convergence in Afromontane forest patches of the Karkloof/Balgowan range, KwaZulu-Natal.Wethered, Robyn. 13 December 2013 (has links)
Forest fragmentation is caused by the clearing of patches of indigenous vegetation for
agriculture, urban development, and other human land uses. Such action results in
patches of remnant natural vegetation being surrounded by altered vegetation. I
investigate the effects of forest fragmentation and matrix type on avian diversity and
assemblage structure in forest patches of the historically fragmented Karkloof / Balgowan
forest range, KwaZulu-Natal, South Africa. This study compares the bird assemblage
diversity and composition of indigenous forest patches surrounded by commercial
forestry (Gilboa complex) with that surrounded by natural grassland matrix (Balgowan complex). Insularisation of Afromontane Mistbelt forest in KwaZulu-Natal has led to loss of
species where forest fragments support fewer bird species than comparably sized patches
of mainland forest. Small fragments within natural grassland have fewer bird species per
unit area than larger fragments. Forest patch area-dependent density compensation is
evident and bird assemblages appear saturated. Bird assemblages are characterised by a
non-random species distribution pattern where area-dependent processes are dominant,
and the loss of species from fragments follows a deterministic sequence. In forests in the
plantation-dominated matrix no island-effect is detectable and it appears that forest
patches are converging on the same bird species richness, regardless of forest size. No
density compensation is evident and bird assemblages are not saturated. The sequence of
species loss from forest patches is not as predictable, where a random yet prominent
colonisation process exists. As commercial plantations provide suitable habitat cover for
movement of forest birds, colonisation of both distant and small indigenous forest
patches has been possible, reducing the effects of area-dependent extinction in the forest
patches but also resulting in lower species richness in larger patches.
Bird species of the Karkloof / Balgowan forest range appear to be fragmentation
adapted, and most species are resilient to further landscape change. Certain species are
however more prone to local extinction than others. The major predictors of extinction
risk are body size, abundance status, and feeding guild. Patch area is the dominant force
governing traits in the natural Balgowan complex where larger species with low natural
abundance and an insectivorous diet are most prone to local extinction. In the Gilboa
complex the nature of the plantation matrix appears to be masking the species natural
responses to fragmentation making it difficult to predict which species are most at risk.
In order to preserve maximum bird diversity, including high-risk species, the largest
intact forest units (≥302ha) must be conserved. Evidently, the nature of the matrix affects
avifaunal diversity and distribution in forest patches, and plantations have the capacity to
significantly alter bird assemblage structure and composition in indigenous forest
patches. Forest fragments must be considered as integrated parts of a complex landscape
mosaic, and this study emphasises the importance of understanding landscape-scale
processes. Knowledge of ecological and life history traits proves valuable for predicting community level response to landscape change. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.
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The effects of forest fragmentation on bird species in Madagascar : a case study from Ambohitantely Forest Reserve on the central high plateau.Langrand, Olivier. January 1995 (has links)
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. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.
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Avian population densities, habitat use, and foraging ecology in thinned and unthinned hardwood forests in Southwestern VirginiaGarrison, Barrett A. January 1986 (has links)
I examined impacts of thinning on bird population densities and habitat use in Appalachian mixed-hardwood forests during 1984 and 1985 at three thinned and three unthinned stands in the Jefferson National Forest, southwestern Virginia. Densities of shrubs, saplings, trees, and snags, canopy and ground cover, and foliage volume were the structural variables most influenced by thinning. Populations of shrub/understory birds were higher in thinned stands than unthinned stands. Canopy-dwelling species showed variable population responses to thinning.
Habitat use similarities were used to group 13 bird species into three categories: (1) shrub/conifer species included the tufted titmouse, blue-gray gnatcatcher, wood thrush, ovenbird, and hooded warbler, (2) generalist species included the eastern wood-pewee, red-eyed vireo, black-and-white warbler, and scarlet tanager, and (3) mature/deciduous species included the white-breasted nuthatch, solitary vireo, blackburnian warbler, and worm-eating warbler. Shrub, snag, and conifer density and ground cover were the four habitat variables most important in separating used from unused sites.
Foraging behavior and resource use of seven bird species were examined in two thinned and two unthinned stands. No differences in foraging methods or niche breadth were found between the stands for all species. Differences in foraging and tree heights were due to tree height differences between the stands.
For most species, foraging resource use was equal to availability. Short, small diameter trees were rarely used. Oaks were used most often, and red maple and conifers were rarely used for foraging. The opportunistic nature of avian foraging behavior and the vegetative differences between thinned and unthinned stands led to the foraging differences noted. / Master of Science
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Effects of prescribed burning on breeding birds in a ponderosa pine forest, southeastern ArizonaHorton, Scott Patterson, 1951- January 1987 (has links)
A moderately intense, broadcast, understory, prescribed burn in 3 previously unburned ponderosa pine stands in southeastern Arizona felled or consumed 50% of all ponderosa pine snags ≥ 15 cm dbh. Large moderately decayed snags were most susceptible to burning. Large snags in the early stages of decay were preferred as nest sites by cavity-nesting birds. Numbers of live woody plants were reduced by 40%, mortality was greatest among shrubs and small trees. Canopy volume was reduced by 19%, the greatest impact was below 5 m. No species of cavity-nesting birds, or birds that associated with understory vegetation disappeared in the first season after burning, but 3 species decreased, and 1 species increased in abundance. The minor impacts of a single treatment with broadcast understory burning on bird populations will be ephemeral, but a repeated burns could have greater, and more lasting effects on the avian community.
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