Birds of Tokachi district, Hokkaido

3. Relationship between vegetation cover and avifauna in Obihiro

Abstract

A study of the urban and suburban avifauna in the breeding season was conducted in relation to vegetation cover in Obihiro, Hokkaido, from 1976 to 1978. From the central part of the city to agricultural lands, 157 study plots (500×500m²) were established. Vegetation cover included parks, yards, shrines, cultivated fields, grasslands, shelter belts, woodlots in agricultural land, vacant lots, river beds and so on and was classified generously into two groups: wooded area and grassland. The percentage of vegetation cover on each plot was calculated on the basis of air photographs and a map of wooded area of Obihiro. Each plot was censused once at least by a strip census method from late May to early July, the total distance of transect censused being 278.7km. In addition to these, only bird species observed were recorded twice at least on each plot.
Common species in plots in which vegetation cover was less then 10% were Passer montanus, Motacilla alba, Carduelis sinica, Corvus corone and Columba livia var. domestica. In addition to these species, the regularly occuring species increased as the percentage of vegetation cover increased: they included Emberiza spodocephala, Sturnus cineraceus, Cuculus canorus, Saxicola torquata and Acrocephalus bistrigiceps in the plots with 11 to 20% of vegetation cover, Gallinago hardwickii, Alauda arvensis and Lanius bucephalus in the plots with 21 to 60% of vegetation cover, and Dendrocopos major, Anthus hodgsoni, Erithacus calliope, Parus major and Uragus sibiricus in the plots where vegetation cover was more than 60%. The species which prefer wooded area occurred mainly in the higher percentage of vegetation cover. Thus the number of bird species observed increased as the percentage of vegetation cover increased, although the increase in the number of bird species was inconsiderable in the higher percentage of vegetation cover. The relationship between the number of bird species (y) and percentage of vegetation cover (x) is y=4.1744+0.3542x-0.0020x².
Paralleling the trend in changing number of species, bird species diversity (H') increased from A (wooded area is less than 10%) through B (wooded area is 11-20%) to C (wooded area is more than 20%). The increase in diversity was found with increase in the percentage of grassland within A group. The similar trend was found in B and C groups, respectively. Bird species diversity was the highest in habitats having both woodlots and grassland.