Using endogenous and exogenous markers in bird conservation

Abstract

Understanding how avian populations are structured spatially and temporally is fundamental to their effective conservation. Protecting migratory species in one jurisdiction or period of the annual cycle may be ineffective if they periodically move to areas where they are not protected or are exposed to factors that limit populations or cause their decline. Unfortunately, for most species, our understanding of connectivity between breeding, wintering or stopover sites during the annual cycle are poorly understood and there is an urgent need to define such connections in order to achieve more effective conservation. This paper provides an overview of the methods used to mark individuals in order to track their movements. Passive exogenous markers such as numbered rings or bands are typically ineffective for most avian species. Active exogenous markers such as satellite tags have provided significant breakthroughs but are still prohibitive financially and still cannot be applied to species under 200g. Endogenous markers such as DNA markers, trace elements and stable isotopes show significant promise as a means of moving forward the field of animal tracking. The advantage of these endogenous approaches is that they depend only on sampling a population once and so are not biased by limitations of mark-recapture methods. Nonetheless, all methods have disadvantages and the path ahead must consider multiple approaches to tracking avian populations.