Statistical indicators and state-space population models predict extinction in a population of bobwhite quail

Background/Question/Methods

Early warning indicators of extinction thresholds have been developed for and tested in microcosm experiments, but verification in populations of wild animals has not occurred.  We developed a statistical indicator to detect a transcritical bifurcation extinction threshold that is robust to observational error present in data collected for monitoring purposes.  We then used our indicator to detect an extinction threshold using two independent data sets from a population of bobwhite quail (Colinus virginianus) located in southeastern Nebraska, USA.  Finally, we compared predictions derived from our statistical indicator to predictions from commonly used state-space population models.  Comparison of indicators to model based methods provides a standard to evaluate the predictive ability of indicators.     

Results/Conclusions

The extinction threshold was detectible using both data sets.  With our statistical indicator we estimated that the extinction threshold will be crossed in 2017 (2012−2028) using the whistle count (WC) data set and in 2012 (2009−2020) using the Breeding Bird Survey (BBS) data set.  Using state-space population models we estimated that our study population crossed the extinction threshold in 2010 (2002−2036) using the WC data set and in 2008 (1999−2064) using BBS data set.  Based on results from microcosm experiments, we expect extinction in our study population after crossing the extinction threshold, but the time to extinction and potential to reverse the extinction threshold are unknown.