STARVATION OF COMMON-TERN STERNA-HIRUNDO FLEDGLINGS DURING HEAT-WAVES

During 1989 and 1992 we observed an uncommon mortality of Common Tern fledglings at Wilhelmshaven, German North Sea coast, after lasting hea t periods, when sea water temperatures also rose to > 20 degrees C (Ta ble 1, Fig. 1). In 1989 19 % of the chicks died when at least 18d old, 1992 still 5 %, whereas during 1990 no deaths of this age class occur ed (Table 2, Fig. 2). In 1989 growth rates, maximum and fledging mass of the young were lower than in 1990 (Fig. 3). Investigations of food provisioning of the chicks, of food supply and parameters of reproduct ive biology indicated food shortage during both years characterized by hear mortality. Moreover the key food Herring Clupea harengus left th e Wadden Sea during the heat wave in 1989 (Fig. 4). The mortality seem ed not to have been caused directly by heat stress, but by food shorta ge enhanced by the heat period. Consequently in many cases food was no t sufficient to cover the demands of the fledged chicks for energy and for water.