Puncture versus capture: which stresses animals the most?

The prerogative of animal welfare science includes wild species and ecological studies. Yet, guidance enshrined in legislation is narrowly derived from studies involving laboratory rodents; legitimacy for non-mammalian free-ranging species is thus debatable. The European directive 2010/63/EU illustrates this problem. It includes this key statement: "Practices not likely to cause pain, suffering, distress or lasting harm equivalent to, or higher than, that caused by the introduction of a needle…" which determines if the directive shall apply. Protocols involving surgery clearly fall within the scope of the directive: procedures are scrutinized, investigators and technicians must be qualified and various agreements are required (e.g. issued by an ethical committee). By contrast, non-invasive procedures, like mark-recapture population studies, merely need a permit from wildlife authorities (at least in most countries). Yet, blood sampling that implies the introduction of a needle-one of the most common practices in animals-could shift any study on the constraining-side of the directive, on the grounds that puncture impacts individuals more severely than capture. We examined the validity of the needle-threshold using the stress response of free-ranging snakes. Our results based on physiological markers show that blood sampling does not add any stress to that triggered by capture, and thus questions the usefulness of the needle-threshold to gauge welfare in wild animals. The specificities of studying wild species should be considered to redress captivity biased animal welfare policy.