Effects of the Felling of Roosting Forest on Roost Size and Site of Crows

Abstract

A forest on the campus of Joetsu University of Education has been used as a roost (max 18, 054 birds), mainly by the Carrion Crow (Corvus corone), throughout the year for at least 25 years. However, in spring 2002, the university cut down part of the forest to make a carpark. To examine the effects of the felling of roosting forest on roost size and site, we estimated roost size and located roost sites in spring 2002 and winter 2002-2003, and also analyzed roosting data from six past winters. Spring roost size decreased after the roosting forest was cut down. However, it was unclear whether this decrease in roost size resulted from disturbance. The effect of the felling of roosting forest on roost site in the spring was clear, because crows established a new roost near the cutover area. The effect of felling of the forest on roost size from September 2002 to March 2003 was also uncertain because the roost size showed no marked decline and its range was within that of past data. In contrast, the effect of the disturbance on roost site was clear, because crows made new roosts near the cutover area late in October and used them from November to December when the roost size was large.