Courtens, W.

Stienen, E.

Van de walle, M.

Open Marine Archive

- 60 -
WHY SANDWICH TERNS STERNA SANDVICENSIS WORK HARD IN THE 
NETHERLANDS AND LIVE LEISURELY IN BELGIUM 
Stienen Eric W.M.1, Wouter Courtens1 and Marc Van de Walle1  
Research Institute for Nature and Forest, Kliniekstraat 25,  
B-1070 Brussels, Belgium 
E-mail: eric.stienen@inbo.be  
Parent Sandwich Terns Sterna sandvicensis alternate brooding and foraging duties. While 
one parent is at sea foraging, the other parent attends the chick(s). During good foraging 
conditions this synchronised behaviour results in a constant presence of one of the adults 
at the colony site. If food consumption rate of the chick drops below critical levels, 
however, parents start to leave their chicks unattended at the nest. At Griend, an isle in the 
Wadden Sea hosting the largest Dutch colony, foraging effort of Sandwich Tern parents 
was strongly linked to diet composition of their chicks. In years with high proportions of 
sandeel in the chicks’ diet, parents left their chicks unattended more often. The reason for 
this is that sandeel are relatively long, conspicuous fish that are more easily lost to 
kleptoparasitising Black-headed Gulls Chroicocephalus ridibundus patrolling the colony 
site. High proportions of sandeel in the chicks’ diet resulted in a high incidence of robbing 
which in turn led to increased biparental foraging. By increasing the foraging effort 
parents were able to compensate for an imminent food shortage and counterbalance 
negative effects on chick growth and survival. Surpisingly, in Zeebrugge (Belgium) 
Sandwich Terns did not increase foraging effort when foraging conditions were poor. In 
some years chicks starved to death while parental attendance did not decrease. In such 
years, length frequency distribution of prey fish fed to the chicks showed anomalies 
suggesting that certain critical prey length were lacking from the chicks’ diet. In Sandwich 
Terns increasing energy demands of growing chicks are met by adjusting prey size rather 
than increasing input rate to the colony. Therefore a continuous prey length spectrum is 
needed for proper growth of the chicks. When a certain prey length is missing, parents 
may not be able to compensate by bringing more small fish (energetically not feasible) 
whereas longer fish cannot be swallowed by the chicks. In poor years, prey fish of 5-8cm 
were missing form the prey spectrum. The presence of this prey size was crucial for the 
survival of Sandwich Tern chicks in Zeebrugge. 


Why sandwich terns <i>Sterna sandvicensis</i> work hard in The Netherlands and live leisurely in Belgium

Abstract

Similar works

Full text

Available Versions

Open Marine Archive