Three colonies of Great Cormorants Phalacrocorax carbo were surveyed in Tokyo Bay in order to estimate the number of fledglings per nest. Chicks over three weeks of age were considered to be fledglings, and the nest was classified as successful. The number of these chicks per nest was recorded at each colony. We compared the results with similar data collected during each breeding season between 1999 and 2004. Breeding success of each colony was found to fluctuate annually, and some significant differences in fledglings per nest were found between some colonies during some years.
2006 by Japan Bird Research Association