'Songbird Survival' is a charity that has commissioned the 'Game and Wildlife Conservation Trust' to conduct an experiment to see what happens to the population of songbirds if you kill all the crows. The theory being tested is that crows have eaten all songbirds, and this experiment is a way to prove it.
The article suggests starting a butterfly conservation charity and conducting an experiment to see what happens if you kill all the songbirds (which have of course been eating all the butterflies' caterpillars...).
