Lead and condors: The isotopic evidence

In the following clip, Dr. Saba addresses the isotopic evidence presented before the commission. The isotopic data was alleged to show that the lead levels in condors not only increase in the wild, but that the isotopic ratios change from what they are in captivity to a ratio indicative of bullet lead.

(A quick primer on isotopic ratios: Lead occurs in several different isotopes. An isotope of an element is an atom of that element with one or more extra (or missing) neutrons. Some isotopes are unstable and break down via radiation. Lead has several stable isotopes. The ratios of these isotopes to one another can act as a fingerprint to distinguish one source of lead from another. Isotopic ratios are measured with a device called a mass spectrometer. This device separates the isotopes according to their mass.)

As Dr. Saba shows, the analysis of the isotopic ratios is seriously flawed. The researchers limited their sample to two bullet brands: Remington and Winchester. Dr. Saba found many different brands available in "condor country"; all with wildly different isotopic ratios. The result is that the condors' lead ratios should have dispersed, rather than coalesced around a single value, if bullets were really the source of lead in their diet.

This is damning evidence. In science we reject a hypothesis if we can devise an experiment that contradicts the predictions of the hypothesis. The condor/bullet hypothesis predicts that the lead found in condors will become more like that of bullets as time passes. The isotopic ratios of lead in bullets varies broadly. If the condors were getting lead from bullets, the lead in their blood would also vary broadly. It does not. It approaches a single value. Bullets cannot be the sole source, or even a major source, of lead in the condors' diet. Something else is poisoning these birds.