The distributional change of Skylarks Alauda arvensis in Tokyo, central Japan, was studied in the 1970s and 1990s. There was a precipitous decline in the number of sightings of Skylarks in Tokyo from 101 survey squares in the 1970s to 28 in the 1990s. Discriminant analysis revealed that the key factors affecting the occurrence of Skylarks were the area of fields, grasslands, and shores. In Tokyo the total area of fields significantly decreased from the 1970s to the 1990s, and the fields themselves became fragmented, but there were no significant changes in the area of grasslands and shores. The area of fields was the most important factor in the 1970s, but became the third most important factor in the 1990s while shores became most important factor. The percentage of fields under wheat, as preferred by skylarks, decreased between the 1970s and the 1990s, while the percentage of vegetable fields increased. The decline of Skylarks breeding in Tokyo seems to have been caused primarily by the decline of the area of fields and by change in the type of crops.
2005 by Japan Bird Research Association