The search for rare species – and the tools to help.

Found in: News

An accurate knowledge of rare species’ locations is important in development planning and impact assessments. Searching for rare species can be a daunting task when starting from scratch, but can be made more efficient by processes such as the incorporation of expert opinion and species distribution models. There are therefore several choices to consider before embarking on rare species searches.

In a recent edition of Journal of Applied Ecology, Olatz Aizpurua and colleagues (2015) set out to compare the effectiveness of habitat suitability models, expert judgement, and stratified random sampling to detect new locations of a threatened bird species. Briefly, the three approaches were as follows:

  • habitat suitability model - this was developed by combining known records of the bird species with 10 environmental variables using Maxent modelling software
  • expert opinion - seven experts were asked to give their opinion on likely occurrences of the bird, after being provided with locations of known occurrences
  • random sampling - the landscape was stratified into 10 environmental categories (strata) and samples were randomly placed a number in each strata proportional to its area.

The sites identified by the three approaches were then ground truthed by field visits and the predictions of the different approaches compared. Their results tell us something about the relative and combined value of habitat suitability models and expert opinion as compared to a random sampling approach.

Habitat suitability models found 95 new bird territories, expert opinion found 72, and the random stratified sampling found only 11 new territories. While the habitat model was slightly more effective than expert opinion, there was very little overlap between the territories identified by the two methods, suggesting that a combination of both approaches may be the most effective way of maximising new location discoveries. The study didn’t examine the relative costs of the different approaches. However, it is likely that elicitation of expert opinion is less time consuming than developing a habitat model. The development of the model is probably best thought of as an increased investment aimed at discovering more species locations.

Astron’s ecologists use a variety of species occurrence modelling approaches to identify regions of high species likelihood. These allow the surveys we conduct to be as effective and efficient as possible. Astron is also now working to combine expert opinion with species habitat models. For further information on the design and implementation biological surveys, please contact our Biodiversity Team via our online form or call us on (08) 9421 9600.



Aizpurua, O., Cantú‐Salazar, L., San Martin, G., Biver, G., Brotons, L. and Titeux, N., 2015. Reconciling expert judgement and habitat suitability models as tools for guiding sampling of threatened species. Journal of Applied Ecology, 52(6), pp.1608-1616

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