Conclusions

This review of the literature comprising almost 400 articles strongly suggests that there is no one broadly accepted method for assessing waterbird habitat quality. Directly measuring breeding success and survival rate are the most reliable measures, but it is unfeasible to obtain these data in many cases. A variety of proxy measures are available, but their interpretation requires substantive contextualisation and a good understanding of their appropriateness to a specific project aim.
In general, if it is not possible to measure direct demographic parameters, projects should consider the suite of available proxy measures (Table 1) and consider which are most suitable to their site, budget and timeframe. Often, developing a protocol based on multiple proxies will increase confidence in results over the use of a single proxy. For example, studies investigating the comparative habitat quality of multiple sites could use a combination of waterbird abundance, behaviour and body condition coupled with a measure of prey availability to gain insight into which site(s) are providing better food resources. Studies assessing if a single site is profitable for waterbirds from an energy perspective (i.e. habitat quality is sufficiently high to support population growth) could use a combination of waterbird behaviour and available energy density to assess whether daily energy requirements are being met at the site. All studies using proxy measures should be mindful of the potential for interactions between features of the habitat (e.g., prey abundance and prey accessibility) to influence the direction of the relationship between habitat conditions and resultant demographic rates.