- Female Pronghorn
History of Pronghorn in California
Pronghorn antelope are native to California and are an important species economically and culturally to citizens of the state. Their historic range included much of the Central Valley and southern and northeast areas of the state (yellow). Pronghorn prefer wide-open habitat including prairie and sagebrush plant communities, but over time this habitat has been depleted from agriculture, fire suppression, plant succession, invasive plants, and human development. Habitat loss has restricted the range of pronghorn to small, isolated populations in the Central Valley and northeastern corner of the state (brown).Although pronghorn are a high profile and hunted species in California, little is known about their populations in the state, including specific causes of mortality and survival and reproduction rates. Research from other states has indicated pronghorn are especially susceptible to drought conditions, predation, and poor food availability. Additionally, pronghorn often migrate seasonally and require suitable habitat and minimal obstructions to their movement during migration. To keep populations healthy, wildlife biologists need to understand more about the factors that influence the range and abundance of pronghorn.
Pronghorn abundance in California once exceeded 500,000 animals, but habitat loss largely reduced this number over time. In 1942, the California Department of Fish and Wildlife (CDFW) began conducting winter surveys to count the number of pronghorn annually. From 1956–1970 the estimated population was between 1800-3000 animals and then increased through the early 1990’s. During a severe winter in 1992/1993 the population in the northeastern corner of the state decreased by almost half, and their abundance remains near that number today.
Population recovery has not occurred as expected, suggesting factors are limiting pronghorn survival and/or reproduction in that area. Increased land development projects and invasive plants threaten remaining pronghorn habitat throughout northeast California, which need to be considered for future viability of this population. Evaluating the survival and reproductive rates of pronghorn in relation to their habitat use and movements can therefore provide essential information for their conservation.
The Institute for Wildlife Studies (IWS) and the California Department of Fish and Wildlife are working on a study which will collect information on survival and reproductive rates, as well as movements of pronghorn in northeastern California. Specific objectives for the study include identifying pronghorn:
1. Pregnancy rates
2. Survival rates of does and fawns
3. Physiological condition
4. Summer and winter ranges
5. Migratory behavior and location of migration routes and potential obstructions
6. Important seasonal habitat(s)
IWS staff will work closely with CDFW, private land owners, sportsmen, and other county, state and federal land agencies during this investigation in the hope of increasing our understanding of pronghorn biology and helping to ensure their populations remain healthy in northern California.
• Adult females are captured by netting from helicopter.
• Fawns are captured opportunistically and by locating birth areas using implant transmitter drop sites of their mothers.
Movements and survival
• Adult females are monitored using Iridium GPS collars, which collect a location on each animal several times a day.
• Fawns are monitored using expandable VHF collars, which we manually locate 1–7 times per week using a frequency specific to each fawn.
• If we hear a mortality signal from a collar, we investigate site where the collar is found and any pronghorn remains, looking for evidence (e.g., predator bite wounds) that suggests what killed the animal.
A portable ultrasound is used to determine if each adult female is pregnant or not by presence of caruncles or fetus.
Surveying habitat at coyote-eye-level
Satellite-collected images and ground-based surveys are used to collect habitat data which characterizes adult female locations and predation sites and fawn birth and predation sites.
Observation surveys are used to estimate the number of males, females, and fawns in each herd.
Blood samples are collected from adult females and fawns to determine several characteristics which indicate their nutritional condition.
• Coyote vocalization elicitation surveys are conducted to estimate the number of coyotes in the area.
• Fecal pellets are collected from adult females to understand their stress levels related to variation in predator risk across the study area.
Rollover ↓ for photo's (©2014)
In July and August we conduct coyote howl elicitation surveys to estimate coyote density throughout the study area. Coyote responses are triggered by broadcasting recordings of coyote howls with a game caller. These responses are recorded and analyzed to determine how many coyotes were present in each response group. Check out this video of a response group recorded near Tulelake back in August. What you see is called a spectrogram; a visual representation of the sound frequencies (y-axis) recorded over time (x-axis). See if you can visualize the sounds you hear in the recording using the spectrogram. Do you hear three different coyotes as they howl in unison? Do you hear the domestic dogs howl and then bark in the background?
Pronghorn antelope (Antilocapra americana) in northeastern California experienced a drastic population crash in the mid-1990’s and population abundance has not recovered to pre-crash numbers. Very little is known about this population and factors inhibiting the population from rebounding. The Institute for Wildlife Studies and the California Department of Fish and Wildlife began a collaborative project in March 2014 to study factors potentially limiting this pronghorn population.
Adult and fawn capture
Fifteen of 17 (88%) adult females examined in 2015 were pregnant and fitted with vaginal implant transmitters. Analysis of blood serum drawn from adult females showed that some of the animals had low levels of copper and selenium, which are important trace metals for body growth.Survival rates and herd demography
Eight of the 30 adult females fitted with GPS collars have died during the study. Mortality causes include mountain lion predation (n = 5), predation by an unidentified predator (n = 2), and probable poaching (n = 1). Survival of adult females (n = 11) in 2014 over an annual period was 64% (standard error = 14.0), 91.2% (standard error = 8.3; n = 11) during March-June, 71.5% (standard error = 14.0; n = 10) during July-October, and 100% (n = 7) during November-February. Seasonal survival of adult females (n = 20 [2014 = 2, 2015 = 18]) during March-July 2015 was 84% (standard error = 8.4). Adult survival in 2014-2015 was lower than reported from other pronghorn populations with stable or growing numbers.
Half of the 24 fawns fitted with radiocollars died between February and October of their first year. Fawn mortalities were caused by combine harvester (n = 3), coyote predation (n = 2), weather exposure (n = 2), predation by an unknown predator (n = 2), and unknown causes (n = 3). Seasonal (May-July 2015) survival of fawns (n = 24) was 54.2% (standard error = 10.4), which was higher than seasonal fawn survival rates reported elsewhere.
The ratios of fawn to doe (0.6:1) and buck to doe (0.3:1) were consistent across years, but the yearling-buck to adult-buck ratio was less in 2014 (0.2:1) than in 2015 (0.5:1).
- Monitoring and habitat use
We recorded 138,177 GPS collar locations from 11 adult females captured in 2014 (n = 59,995) and 17 adult females captured in 2015 (n = 78,222). Of all habitatsavailable within the study area, adult females selected areas nearer to primary/secondary roads,riparian corridors, reservoirs, and areas composed of greater grassland and agriculture, but avoided forest, shrubs, higher elevations, and areas ofgreater vegetation productivity. Comparison of vegetation at used and nearby unused locations (n = 185) suggested that adult females selected habitats that provided greater visibility and food. Habitat selection surveys (n = 18) of neonatal fawn bed sites suggested that increased visibility and food availability were characteristic of areas at and around bed sites.
Assessing pronghorn distribution, movements, and habitat use in northeastern California
Annual Report Summary 2015
INSTITUTE FOR WILDLIFE STUDIES
Jared F. Duquette, Research Ecologist
Brian R. Hudgens, Senior Research Ecologist
David K. Garcelon, President
We tracked 11 and 19 adult females fitted with GPS collars, in 2014 and 2015 respectively, and 24 neonate fawns (10 females and 14 males) fitted with VHF radiocollars in 2015.
Pregnancy rate and nutritional condition
• Pronghorn are the only species in the scientific genus Antilocapra, making them a truly unique animal.
• Pronghorn are only found in North America and are not related to African antelope.
• Pronghorn were part of a diverse array of related species whose fossils have been found as far back as the Miocene epoch (20 million years ago).
• Lewis and Clark description of male pronghorn (1804):
“…in my walk I Killed a Buck Goat of this Countrey, about the hight of the Grown Deer, its body Shorter, the Horns which is not very hard and forks 2/3 up one prong Short the other round & Sharp arched, and is imediately above its Eyes the Colour is a light gray with black behind its ears down its neck, and its face white round its neck, its Sides and rump round its tail which is Short & white: Verry actively made, has only a pair of hoofs to each foot, his brains on the back of his head, his Norstrals large, his eyes like a Sheep he is more like the Antilope or Gazella of Africa than any other Species of Goat.“Illustration of male pronghorn from Lewis and Clark expedition
• Although pronghorn can outrun any of their current predators (e.g., coyotes), pronghorn developed their blazing speed because they evolved with predators, including cheetahs and hyenas, which once roamed North America about 10,000 years ago!
• Pronghorn often migrate seasonally, with some populations moving 150 miles one way!
• Horns are made of strings of keratin (like fingernails), which cover a bony inner sheath and are shed annually.
• Females have horns, but are much smaller than males.
• Males have black hair patch by jaw, females do not.
• Can live up to about 10 years in the wild.
• Pronghorn can see about 300 degrees around them without moving their head or eyes and can detect movement up to 4 miles away!
• Pronghorn prefer to duck under obstacles, such as brush or fences, rather than jumping them due to inadequate bone and muscle structure for doing so.
Background photo: Mark Gocke/USDA, cropped/enlarged, license