Baarspul, A.N.J. & J.-P. de Krijger, 1997. The role of demselflies and dragonflies and other insects in the chick-diet of Black tern (Chlidonias niger). Brachytron 1 (1): 6-10. Black terns (Chlidonias niger) have decreased in The Netherlands from over 15,000 pairs to less than 1,500 over the last 60-70 years. The species nests in fresh water habitats. Two hypotheses for the decline are loss of nesting places and decline of large insects, which are important food for the chicks. In 1995 observations were made on chicks in the Bargerveen (Drenthe) in a raised bog regeneration project, where large insects have become extremely numerous. The expectation was that the black terns in this area would perform very well. The Black terns fed their chicks exclusively on insects, mainly adult dragonflies, damselflies, waterbeetle larvae, and waterbugs. All chicks died at an age of 22-25 days. Post mortem analysis revealed severe rachitis. As shown in a rough calculation the chicks fed exclusively on insects, could not get enough calcium to develop feathers and bones. The raised peat bogs contained more calcium sources in the past (fish, snails). The pH has dropped from pH 5.9 to pH 4.0, due to acid precipitation. Thus, it is possible that the decline or disappearance of black tern populations in peat bog is caused by acidification. Two questions remain: 1. Why did the birds not answer to a calciumspecific hunger? Within 2km they could found fish, which is the main calcium source elsewhere. 2. What causes the decline of the tern populations in habitats where calcium sources are plentiful. It can not be excluded that the decline of large insects is one of the factors causing the decline of the black tern in these habitats.