I’m a Research Ecologist at the Smithsonian Conservation Biology Institute (SCBI) in Front Royal, VA.  My research interests focus on the factors that affect the abundance, distribution, and movement patterns of large terrestrial mammals.  I incorporate data collected in the field with remote sensing derived variables to relate to animal point locations, primarily collected via GPS-enabled devices.

I completed my PhD in Ecology with Dr. Randall Boone at Colorado State University in 2015 and was a member of the Graduate Degree Program in Ecology and the Natural Resource Ecology Laboratory.  My PhD focused on resident populations of wildebeest found across three study areas in southern Kenya.  These lesser known populations have experienced widespread decline over the past few decades.  I investigated the effects that anthropogenic disturbance is having on the movements, resource selection, and hormonal stress levels of these threatened populations.

An example 3D utilization distribution.

Since joining the Conservation Ecology Center at SCBI as a post-doctoral research scientist in 2015, I have worked on a large international effort to reintroduce scimitar-horned oryx to a portion of their native range in Chad, analyzed data to evaluate the occurrence distribution of critically endangered addax, and transitioned into a position as the Program Coordinator for Smithsonian’s Movement of Life Initiative.  This unique initiative, which brings together terrestrial, avian, and marine ecologists, endeavors to increase our collective understanding of how all living things, big or small, move across rapidly changing land and seascapes.

Some of the research projects I’ve worked on include:

Scimitar-horned oryx

Once widespread across desert regions in North Africa, scimitar-horned oryx (oryx, Oryx dammah) are now extinct in the wild due to overhunting and habitat loss.  Fortuitously, a wildlife trader captured a small population of oryx in the 1970s, providing the breeding stock for all captive oryx alive today.  In June 2016, a consortium of institutions led by the Environment Agency – Abu Dhabi, the Sahara Conservation Fund, the Smithsonian Conservation Biology Institute, the Zoological Society of London, and the Fossil Rim Wildlife Center, are working collaboratively with the government of Chad to return this majestic animal to a portion of its native range.

Juvenile scimitar-horned oryx enjoying the sunshine in Chad, the only free roaming population in the world. Photo credit: T.Wacher, Zoological Society of London.

Reintroduced animals are being released to the Ouadi Rimé-Ouadi Achim Game Reserve in Chad, a former stronghold of the species and one of the largest terrestrial protected areas in the world.  Because every individual reintroduced is important and because we are keenly interested in monitoring survival, nearly every individual is being fit with a satellite tracking collar.  The first group of 23 individuals were reintroduced in August 2016.

Addax/Dorcas gazelle

The Sahara desert is the largest desert region in the world, supporting a unique and charismatic flora and fauna.  Most impressive are the ungulate assemblages of the Sahelo-Saharan biome, historically including addax, dama gazelle, dorcas gazelle, and scimitar-horned oryx.  Over the past few decades, however, the Sahara has suffered a catastrophic decline in its megafauna as a result of overhunting, habitat loss, and desertification.  Of the 14 large vertebrates found across the region, four are now extinct in the wild, while most others persist across a small fraction of their former range.

Addax moving across shifting dunes in the Tin Toumma desert, Niger.  Photo credit: T. Rabeil, Sahara Conservation Fund

Since the early 2000s, the Sahara Conservation Fund has conducted repeated vehicle-based transect surveys to assess the occurrence of a variety of species.  We incorporated point count data collected during these surveys with remote sensing derived variables to assess the distribution of addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas) for which the ecology in the southern Sahara is virtually unknown. 

Predicted species occurrence for addax (A) and dorcas gazelle (B) across the Termit & Tin Toumma National Nature Reserve.

Our results show that addax declined significantly over the course of the study period.  Two variables, surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in models predicting species occurrence.  Dorcas gazelle inhabited areas further to the south of our study area, and were more positively associated with increased vegetation productivity than addax (i.e., addax are a hyper-arid species).  Both species were observed to have a strong negative response to human disturbance.  These predictive surfaces also provide the spatial information to help guide future field surveys across the region, with an eye towards locating small and geographically isolated populations.

Stabach, J.A., T. Rabeil, V. Turmine, T. Wacher, T. Mueller, and P. Leimgruber. 2017. On the brink of extinction – Habitat selection of addax and dorcas gazelle across the Tin Toumma desert, Niger. Diversity and Distributions 23:581-591.

White-bearded Wildebeest

Wildebeest are the dominant grazers across grassland savannahs in eastern and southern Africa.  Wildebeest are also recognized as keystone species, effecting nearly every aspect of the ecosystem from local biodiversity, grassland-tree dynamics, wildfire intensity, food web structure, and local economies.  Over the past 40 years, however, many resident populations of wildebeest have experienced widespread and precipitous declines.

An adult wildebeest moving across the Athi-Kaputiei Plains, Kenya. Photo credit: J.Worden, Gnu Landscapes.

To date, I have published two manuscripts from my PhD research on wildebeest.  This includes a study to investigate the hormonal stress response of wildebeest across a gradient of anthropogenic and climatic disturbance and a second manuscript investigating the effects of these same sources of disturbance on resource selection and habitat use.  As expected, the probability of finding a wildebeest across the landscape decreased as the number of humans increased.  Surprisingly, however, we did not observe a clear difference in hormonal stress levels between populations, except when conditions deteriorated.

Effects of the parameters biomass and human disturbance on quantified fecal glucocorticoid (fGC) metabolites.  Partial residuals (points) and loess smoother (dashed line) displayed.  See Stabach et al. 2015 for more information.

Support for this research was provided by the National Science Foundation and Sierra Trading Post.  I was also a recipient of the James E. Ellis Memorial Scholarship during my time as a graduate student, which funded much of my laboratory work to analyze fecal hormone metabolites at the International Livestock Research Institute in Nairobi, Kenya.

Stabach, J.A., G. Wittemyer, R.B. Boone, R.S. Reid, and J.S. Worden. 2016. Variation in habitat selection by white-bearded wildebeest across different gradients of human disturbance. Ecosphere 7(8): 1-17.

Stabach, J.A., R.B. Boone, J.S. Worden, and G. Florant. 2015. Habitat disturbance effects on the physiological stress response in resident Kenyan white-bearded wildebeest (Connochaetes taurinus). Biological Conservation 182: 177-186.