Less birds is a good thing?
According to the Dominion Post Environment Minister Nick Smith said the clean-up effort and the reduced number of dying birds was encouraging, with regards to New Zealand’s worst environmental disaster with the grounding of Rena on the Astrolabe Reef.
Although at first glance a reduced number of dying birds may appear to be a good thing, the underlying process driving this trend is not clear. It could be that most birds at risk to the oil spill have already died, and the reduced number of dying birds is in fact because there are no more birds alive left to die.
Statistically, what are confounded here are the population size and the probabilities of detection and impact (from the oil spill). When the total number of birds being found dead has declined, we don’t know if the population size has remained relatively stable, but the number being detected and impacted has declined, or if the population size has declined, but the number being detected and impacted has remained constant. In both cases the calculation of the absolute number of birds being recovered comes out the same, but under the first scenario, the impact of the oil spill has declined, whereas in the second, the oil spill is having the same impact.
I hope for the sake of the birds it is the first scenario, as Nick Smith hopes, because as Minister of Conservation Kate Wilkinson says, “it’s not their fault.”