Spatially Explicit Population Modeling for California Condor

Overview:  California Condors (Gymnogyps californianus) remain critically endangered despite significant efforts to recover the species through captive breeding and reintroductions over the last three decades.  While there are several factors that affect condor mortality (Rideout et al. 2012, Bakker et al. 2016), lead toxicosis remains the primary threat to the condors long-term survival and recovery (Finkelstein et al. 2012). The species’ recovery plan was last updated in 1996, and since then interest has developed in modifying the spatial extent and other elements of the recovery effort. Consequently, a significant need now exists for a forecasting model capable of evaluating how the condor population is likely to respond to proposed changes in its management, particularly as we plan to expand the recovery effort into unoccupied portions of the range and potentially modify the number of condors released per year.

While a population viability analysis (PVA) model is currently in development for the California condor, it is not spatially-explicit.  A spatial forecasting model will allow USFWS to evaluate how the distribution of resources, threats, and management efforts affect condor population viability at local and regional scales, making it possible to more rigorously prioritize mitigation activities.  A spatial PVA will also allow us to more fully utilize map-based datasets, and make it possible to generate mapped model outputs that aid in effectively communicate our findings to stakeholders.

Management Need:  USFWS efforts to improve California condor population distribution and viability would be enhanced if the Agency were to have access to a simulation modeling toolkit that could be used to quantify and prioritize management activities in silico, prior to updating policies or committing funds. We seek here to develop such a tool. Our model would be constructed in HexSim (www.hexsim.net), a tool that USFWS has used, or is using, to develop PVA’s for the northern spotted owl, barred owl control, and Fender’s blue butterfly. HexSim is a well-established and thoroughly vetted scientific application (see publications listed on the model website).

Key questions that we will attempt to answer, using model simulations, include:

1. How will the addition of carefully chosen new release sites affect the population growth and spatial distribution of the California condor?

2. Can potential release sites be prioritized geographically based on their expected contribution to local and regional population growth rates?

3. What are reasonable population and geographic recovery targets (including timeframe) given available habitat and food resources, expected population growth, and the results from our simulations?

4. What is the most efficient (least cost and time) reintroduction strategy for achieving population and geographic targets?