Eagles in the California Desert

Golden eagle home range, habitat use, demography and renewable energy development in the California desert

Golden eagle (Aquila chrysaetos) populations  in North America are declining. In California, golden eagles face a variety of threats and are listed as a species of concern by numerous state and federal agencies. In particular, development of renewable energy is a rapidly emerging and important concern that has the potential to impact eagles at all stages of their life history. There is a known history of golden eagle conflict with California wind energy plants, primarily through direct mortality from collisions. More recently, growth of the solar energy industry presents additional indirect risk to birds, primarily through habitat conversion and loss.

This project is funded by the US Bureau of Land Management and includes collaboration between Todd Katzner, Phil Turk, Adam Duerr and Trish Miller, all of West Virginia University, Michael Lanzone of Cellular Tracking Technologies, LLC, and David Brandes of Lafayette College. Daniel Driscoll of the American Eagle Research Institute leads our field trapping team.

Data Collection Methodology and Justification
Our research addresses five questions related to habitat use and home range and four related to population dynamics of these eagles. We will address questions of habitat use and home range with GPS-GSM telemetry and standard GIS analyses. We will address questions related to population dynamics with nest visits (productivity, occupancy), GPS-GSM telemetry (dispersal, mortality), and non-invasive genetic monitoring (occupancy trends).     
    Our data analysis is geared towards addressing a number of key questions of interest to the BLM, to our team and to golden eagle management in general. These are:
a) What is the home range of the golden eagle in the Mojave and Sonoran (Colorado) Deserts?
b) Do the size and/or area of home range use change seasonally, and are changes correlated with habitat quality, specific habitat features, human use, wind patterns, or other factors?
c) How do breeding and nesting affect home range size from year to year?
d) Does use within a home range change post-construction of a renewable energy facility?
e) What are the most critically important migration, wintering, and breeding areas in the desert?
f) What is the nest productivity of eagles in the Mojave and Sonoran (Colorado) Deserts?
g) What is the range and variance of natal dispersal distances, including movement patterns from sub-adult to adult?
h) What are the trends in territory and nest occupancy?
i) What is the primary cause of eagle mortality?

Initial data collection shows details of eagle movements in the Granite Mountains area. For a map showing the 15-minute and 30-second data we are collecting from three of our telemetered golden eagles, click here.

In addition, our team will focus on the following additional priorities:

1. Risk Modeling. We will model risk to eagles from renewable energy development to assist in evaluating management options for this species. Once we know where and when eagles spend their time, a critical  next step is to understand how eagles may respond to future renewable energy development within the California Desert District and surrounding lands.  Using the template our research team is implementing for  the central Appalachian region, we will develop new region-specific models that incorporate habitat and topographic features, eagle density and energy development, to assess potential risk from energy development to golden eagles. These models will incorporate direct (blade strike) and indirect (habitat loss from wind and solar) elements of risk. An important feature of our models is that we can not only identify where eagles are most at risk, but also identify other low risk areas where energy production will have minimal impact on eagles.

2. Frameworks for Improved Demographic Estimates. Effective population management requires a comprehensive understanding of demography. Our work is designed to provide the framework and the baseline data on which can be built an effective longer-term monitoring program. Our goal is to combine data from multiple data sources – telemetry, nest productivity and occupancy surveys, and genetic monitoring - to build a framework for tracking population trajectories and changes in demographic parameters (survivorship, dispersal, etc.) over time. In this framework, survival can be estimated through telemetry using known fate (mark-recapture) or multi-strata models (that simultaneously estimate survival and movement), as well as through non-invasive genetic monitoring.

3. Monitoring Framework for Adaptive Management. This research project presents a unique opportunity to initiate a rarely developed type of adaptive management program to understand the impact of future energy development on eagle populations. Our work will outline and initiate the first steps of a monitoring program for golden eagles that extends into the future in the context of energy development in the California Desert District. The monitoring will be designed to provide annual estimates of key demographic parameters – survival, dispersal, etc. – in and outside of areas with energy development. If then used in an appropriately-designed adaptive management program, where effects of energy development and continued evaluation of eagles can be incorporated, management can be adapted to best support a combined program of eagle conservation and sustainable development.