In this article, we analyse the case of the emigration and death of black necked swans in Southern Chile from a postnormal perspective. We show that in the presence of radical uncertainty, as it may happen when a socio-ecological conflict arises due to a sudden, catastrophic, shift in an ecosystem, one management approach is to consider multiple hypotheses that in turn should guide inclusive, multi-variable, adaptive management strategies. However, if influential members of society at the science-policy interface decide that only one hypothesis is true (a convenient hypothesis), then all alternative hypotheses become inconvenient; we have called this the '(in)convenient hypothesis syndrome' or (I)CHS. An extensive analysis of the case study, including social communications before, during and after the main ecological event, show that the conditions for the syndrome developed long before the shift in the ecosystem and that they were influenced by socio-political processes (some of which fall under Merton's self-fulfilling prophecy) occurring at many scales (from local to international). Our main proposal is that the syndrome is to be accepted as an element of the postmodern science-policy interfaces, originated because scientific results may support different hypotheses, some of which will have conflicting political repercussions. Copyright © 2013 Inderscience Enterprises Ltd.