Body mass fluctuations and mortality in Common Tern Sterna hirundo chicks dependent on weather and tide in the wadden sea germany.

In three Common Tern colonies in the German Wadden Sea the relationships between mortality, body mass of chicks, weather and the tide-dependent change in the daily span of time favourable for feeding (TFO-DH) were studied. On the island Oldeoog weather fluctuations between years were more pronounced and wind-speed as well as minimum-temperatures were higher in than at the coastal colonies. Mortality of chicks was not significantly different between the colonies, but an Oldeoog chicks underweight were more frequent. In all colonies chick mortality was negatively correlated with minimum-temperature and positively with wind-speed; a positive relation to rain was found only on the coast. Multiple regressions indicate that mortality depended mainly on minimum-temperature, further on rain or wind-speed as well as on Oldeoog on the percentage of underweight chicks. This parameter correlated positively with wind-speed at Oldeoog and Augustgroden, and negatively with TFO-DH on Oldeoog only. The results confirm the direct dependence of chick mortality on weather and the indirect effect of wind-speed on chick body mass. Moreover on Oldeoog, chick body mass was linked with TFO-DH.

Becker P.H. & Specht R., ARDEA 79 (1): 45-56.