A tentative report on the comparative analysis of forest bird communities

Abstract

1. Census data of forest birds obtained by the author and his coworkers during 1966 and 1972 in JIBP-CTS and other projects or private surveys, are here analysed tentatively by using 'bird community curves' and other graphs.
2. All the raw data were obtained by line transect census in which passing time through every different forest habitat was recorded so as to calculate number of individuals per hour (N/h), the 'time-density' of birds which can be used as abundance index.
3. The data of time-density (N/h) were presented in a 'bird community curve', drawn with N/h on Y-axis and species on X-axis, arranged left to right from high to low value of N/h. Thus, the curve combines the relative number of individual (N/h) and number of species, therefore quantitatively representing the bird community.
4. The position of each species or related species can be checked or indicated by special marks on a bird community curve for the purpose of comparative analysis.
5. The area between X, Y axis and bird community curve represent the carrying capacity of the habitat for that bird community, and may be used as the bird communty index of the habitat or as the index of habitat value for the bird community. These indices are of numerical nature based on N/h and relative biomass index can be calculated from it by multiplying species' individual body weight.
6. Ecological grouping of forest birds was made by rough divisions of upper, middle and lower forest layer inhabitants for the purpose of analysis of bird distribution in the forest of each type. Group A comprises tits and other small species of upper to middle layers, including insect and tree-fruit eaters. Group B consists of warblers, flycatchers, etc., the small insect eaters, chiefly of middle or lower layer. Group C, chiefly small or middle sized thrush group and wren, etc, of ground foraging habits. Group D, the ground foraging Emberiza spp., which are granivorous and insect eaters, including however tree bud eaters such as bulfinch or grosbeaks, etc., and also shrikes. Group E is represented by middle sized woodpeckers and cuckoos with specialized food habit. Group F is formed by midde to large birds which inhabit upper layer (crow family, etc.) or ground layer (pheasants) (Being very few in record the birds of prey are not included).
7. As the result, small birds are far dominant in number over others occupying all the upper, middle and lower forest layers and the middle layer of the forest is considered to be the layer where small birds have evolved their diversity without pressure of larger birds which chiefly inhabit upper or lower layers.
8. The bird community curves can be classified into principal 3 types: 1. Mixed forest type 2. Broad leaved forest type and 3. Needle-leaved forest type, with other combined types. These were shown characteristically by graphs based on data from 13 habitats in Mt. Fuji area. Curves obtained from data of many other mountains from Hokkaido to the Ryukyus supported these types or showed variations due to avifaunal differences in bird community (With decreasing palearctic species toward the south to the Ryukyus, therefore showing abreviated shorter bird community curves). The seasonal difference of bird community curves of a same forest type was also shown for habitats of Mt. Fuji area.
9. For relative comparison of habitat selection by related species of birds represented by time-density (N/h) in 13 different habitats in Mt. Fuji area, circle and rod graphs were also used.