Predicting leopard densities in Armenia

Igor Khorozyan is Asia's most dedicated leopard researcher and conservationist, who since the mid-1990s has been studying Caucasian leopards in Armenia - a critically endangered population of no more than 10-15 individuals that partially depends on immigrations from northern Iran.

As part of his strenuous efforts to find suitable leopard conservation areas he conducted a series of field studies in southern Armenia. His article "Presence – absence surveys of prey and their use in predicting leopard (Panthera pardus) densities: a case study from Armenia" was published in 2008, of which excerpts are presented here.

Prey scarcity affects felids by decreasing the proportion of productive females, delaying the age of first reproduction, reducing litter size, increasing offspring and adult mortalities, expanding home ranges, intensifying movements and increasing the numbers of transients and dispersing individuals – all of which worsen facets of viability. Prey abundance is the key factor determining the structure of female home ranges, whereas availability of females is most important for male home ranges. Thus, prey abundance determines felid requirements in space. However, space itself is also an important factor because solitary life and the generally exclusive home ranges of same sex individuals in most felids force their populations to occupy large tracts of good habitats above some threshold to maintain viability. For example, leopard populations require a minimum threshold value of 412 km2 to remain viable. This is why small and densely populated countries have problems in maintaining viable leopard populations, even though prey densities can be high in some areas.
It is important to predict how many individuals of P. pardus can survive in a given area on the basis of prey sufficiency and to compare predictive estimates with the actual number on the ground. If the predicted carrying capacity significantly exceeds the actual abundance, then factors other than prey availability might play a key role in determining felid densities, for example, human-caused mortalities or habitat loss. However, even in this case cats are likely to be more susceptible to dwindling prey resources than to direct human effects because they are able to withstand quite high human densities under favorable conservation and management policies. Interspecific competition is another possible cause of lower predator densities, but prey availability is again regarded as a priority determinant.
Prey scarcity might be one of the most likely reasons of leopard rarity in Armenia. To test this hypothesis, it would be reasonable to assess the biomass of the key prey species, predict leopard densities from the leopard density - prey biomass relationships and compare the predicted and actual leopard densities.

The goal of the present study was to compare the predicted and actual density and abundance of endangered leopards in the Nuvadi area, which is a priority leopard conservation area in southern Armenia. We achieved this by: (i) estimating the density, abundance and biomass of the key prey species, bezoar goat, wild boar and roe deer, through direct observations, presence–absence modeling and photo-capture rates; and (ii) predicting leopard abundance and density from total prey biomass and comparing it with the actual density/abundance obtained from camera-trapping and tracking.

Armenia - study area Field surveys were conducted in a 25 km2 plot to the north of the Nuvadi village on the Meghri Ridge, in the extreme south of Armenia, from May 2006 to March 2007. This area, spanning from 39° 01' N to 38° 56' N and from 46° 24' E to 46° 28' E, has been the wildest part of the entire 296.9 km2 block of the Nuvadi area, which is designated as a priority leopard conservation area, where all trails used by wildlife intersect. The terrain is very rough, rocky and mountainous, and is covered mostly with xerophilous juniper sparse forest and, in the deep canyons with dense shrubs and patches of mesophilous broadleaf forest. In the south, sparse forest changes to arid grassland. The boundary of the study plot was defined by lines connecting the outermost survey and camera-trap station points.

Multiple presence-absence surveys represented 30 daily routes (2 - 15 per site) walked during nine survey periods along the wildlife trails on mountaintops and in gorges. As the surveys were independent, surveys during which we detected animals did not affect the directions of subsequent surveys. Direct detections, that is, observations and vocalizations of the leopard's staple prey species (bezoar goat, wild boar and roe deer) were documented and the cluster size, sex/age composition, time and location were fixed by a GPS Magellan 310. All cases of possible double-counts of the same individuals were recorded. A cluster was considered to be a group of individuals of a species observed together. The study area consisted of four sites, each represented by two to five localities. The sites were large enough to assume population closure. We chose the sites on the basis of their topographic distinctness, assuming independence for the studied species, and that species known a priori to be common should be surveyed more intensively over fewer sites than vice versa.

Camera trapping took place in the same study area from August 2006 to April 2007 and comprised eight sampling occasions.

The locations of the camera stations were not stationary and the stations were moved down from an altitude of 1964.6 ± 120.8 m for the first sampling occasion (August–October 2006) to 1169.3 ± 66.7 m for the sixth–eighth occasions (January–April 2007), following animal migrations down to the foothills in response to deep snow at higher elevations.

The sampling effort for the camera-trapping was 4188 trap nights.

We obtained 416 independent pictures (76.6% of all) of the following mammals: wild boar (96 pictures, 23.1%), bezoar goat (76, 18.3%), red fox (72, 17.3%), European hare (48, 11.5%), gray wolf (39, 9.4%), Indian porcupine (35, 8.5%), brown bear (25, 6.0%), jungle cat (8, 1.9%), stone marten (6, 1.4%), roe deer (5, 1.2%), Eurasian lynx (3, 0.7%), wild cat (2, 0.5%) and leopard (1, 0.2%). The bezoar goat and wild boar were camera-trapped most commonly both in space and time and were captured on all sampling occasions.

We have estimated the total biomass of leopard prey as the sum of the biomasses of the bezoar goat, wild boar and roe deer, and the value obtained is 720.37 ± 142.72 kg/km2.

Bezoar goat

Photo by courtesy of I. Khorozyan, A. Malkhasyan and M. Boyajyan

The leopard density predicted from the total prey biomass in our study area is 7.18 ± 3.06 (range 4.12 - 10.23) individuals per 100 km2.
Male leopard of Nuvadi area

Photo by courtesy of I. Khorozyan, A. Malkhasyan and M. Boyajyan

Camera-trapping revealed the presence of one leopard in 25 km2 in 2006-2007 when prey surveys were conducted simultaneously. This value can be translated to four leopards per 100 km2, which is at the lower end of the predicted leopard densities given the available prey resources. Meanwhile, intensive tracking surveys conducted over the entire 296.9 km2 block of the Nuvadi area showed that this is a clear overestimate because there were no signs of other leopards in the area. Thus, adult leopards known to live here in previous years have disappeared.
The actual leopard density in the Nuvadi area is one individual per 296.9 km2 or 0.34 leopards per 100 km2. Why is it so low? Certainly, prey limitation is not a factor of concern because our prediction shows that the existing prey biomass is sufficient for the survival of 4-10 leopards per 100 km2. As food availability is most important for female leopards which, in turn, determine the status of males, the locally available prey base is favorable for the formation of a core population consisting of resident females and males. The most plausible explanation for the population plight is that poaching and disturbance caused by livestock breeding, gathering of edible plants and mushrooms, deforestation and human-induced wild fires are so high that they exceed the tolerance limits of leopards.