The platform transmitter terminal (PTT) is a locational telemetry device usually used for satellite tracking birds. The method of attaching a PTT using a harness system of Teflon-treated ribbons sometimes causes injury to the wing membranes of Great Cormorants Phalacrocorax carbo through abrasion of the skin by the ribbon. A Tesa-tape system is expected to decrease the probability of injury, although the durability of its adhesion has not been known. Therefore, we examined the durability of a Tesa-tape adhesion system by using dummy PTTs made from acrylic board. We captured six semi-domesticated cormorants and four wild cormorants and attached the dummy PTTs to the backs of the birds using Tesa-tape. Semi-domesticated cormorants were captured in March 2004 and in May-June 2006, and wild individuals were captured in October 2006. We attached the dummy PTTs to these cormorants, and observed them intermittently to determine the duration of adhesion. For seven of the ten cormorants, the date on which the PTT fell off was known within an error margin of 10 days, and those observations are presented here. The attachment durations of the dummy PTTs were divided into two categories: less than 30 days and more than 60 days. The longest attachment period was 81 days, but we have not deduced a reason that explains the varying attachment durations. When the dummy PTTs were attached to three semi-domesticated cormorants just before the molting season, however, two of them fell within 5 days. Therefore we recommend avoiding the molting season when attaching the PTTs with the Tesa-tape system, and we conclude that an attachment method using Tesa-tape is not durable enough to last for the three months to a year that is typically necessary for satellite tracking of cormorants.