 WolvesWolf History, Conservation, Ecology and Behavior
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Wolfology Item # 363
Source:
v7, n4 (December 1993)
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Predation on Blackbuck by Wolves in Velavadar National Park, Gujarat, India
Yadvendradev V. Jhala
1993
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Abstract
The role of predation on the endangered blackbuck antelope (Antelope cervicapra) by the endangered Indian wolf (Canis lupus pallipes) in Velavadar National Park, Gujarat, India, was evaluated in terms of ratios of predator to prey. Food habits of wolves were determined from scat analysis and by direct observation. Consumption was estimated from unutilized portions of blackbuck kills. Wolves preyed primarily on blackbuck (88% biomass consumption), rodents and hares (Lepus nigricollis). Wolves consumed 4.62 kg/wolf/kill and made kills at an interval of 3.5 days. Daily consumption by wolves was estimated at 1.33 kg/wolf. The number of blackbuck killed annually per wolf was estimated between 35 and 39. Between 142 to 158 blackbuck per wolf were considered essential to maintain a stable blackbuck population. Managing the grassland habitat by annual removal of the exotic shrub Prosopis juliflora, minimizing human disturbance to wolves at kills, and reducing predation on blackbuck by feral dogs were some ways to ensure continued viability of this wolf-blackbuck system.
 When an endangered predator species preys on an endangered prey species in an ecosystem that is maintained by management, it becomes essential to evaluate the role of predation to aid in making conservation and management decisions. Such a situation exists in the 34-km2 Velavader National Park, Gujarat, India, where the wolf (Canis lupus pallipes) preys on the blackbuck (Antelope cervicapra). Mesquite (Prosopis juliflora), an exotic shrub, threatens to become the dominant plant in the semi-arid grassland ecosystem, converting it into a thorn forest -- a habitat unsuitable for blackbuck. However, Prosopis provides essential cover for the wolf. The park is managed by annual eradication of Prosopis saplings from the grassland habitat and by providing some fodder for blackbuck in years of extreme drought. Shrub removal from areas where Prosopis is already established is likely to increase the carrying capacity (within limits) of the Park for blackbuck. Due to a severe drought from 1985 to 1987, the blackbuck population at Velavadar National Park declined from about 2000 in 1986-1987 to 895 by summer of 1988; the population later increased to 1344 by summer of 1990. Since the establishment of this preserve in 1969, the blackbuck population has fluctuated around 1850. The primary cause of population declines since 1969 has been natural calamities such as cyclones and droughts. Wolves were considered to be migrant visitors to the park, and wold predation on blackbuck was a rare event. Within the past few years wolves have become residents of the park, and wolf predation on blackbuck is quite common. During the course of this study, a single wolf pack was observed to use Velavadar National Park and surrounding areas.
This study estimates the consumption rates and food habits of wolves in Velavadar National Park. These estimates were used to compute predator-prey ratios to evaluate the impact of wolf predation on the Velavadar blackbuck population.
Methods
Food habits of wolves were determined from scat analysis. A total of 601 wolf scats was collected and examined....Bones, claw, hoofs, teeth, and hair of prey were used as criteria for prey indentification....
Blackbuck remains in wolf scats were distinguished into three groups: (1) black males, (2) fawns, and (3) others....Adult male blackbuck acquire a dark-tan to black coat color seasonally depending on their social status and breeding condition. There were more dark males during the breeding seasons (Fenruary/March/April and September/October) but some dark males were observed throughout the year....I could not differentiate between the remains of subadult blackbuck, adolescent blackbuck, nonblack adult males, and adult females in wolf scats. These age-sex classes were aggregated as a group (others) for analysis.
....The feeding activity of the pack and aggregations of crows (Corvus speldens), vultures...and jackals were clues for detecting fresh kills. If the pack was still feeding on the carcass, I waited until they finished and moved away before collecting data and samples. Whenever possible I reached the kill remains before most scavengers. Data were recorded on sex, age-class, weight of the kill remains, location, time and date, proportion and parts of the kill utilized, and the method of killing and injury. Data were obtained on 43 fresh blackbuck kills. Data from only those kills where the following criteria were satisfied were used for analysis of consumption:
(1) The number of wolves to have fed from the carcass was known with reasonable certainty....
(2) The amount eaten was estimated by the difference between kill remains and the estimated weight of the killed blackbuck (based on age and sex).
(3) There was no (or negligible) loss due to scavenging.
(4) The wolves were not disturbed on the kill (they left the kill on their own accord and not due to human disturbance.)
(5) The interval between two or more consecutive kills was known; the wolf pack was located at least twice during a day (early morning and evening) for several consecutive days. On some occasions the wolf pack was followed at a distance on horseback from a kill site to their lying-up site for the day, their activities were observed again in the evening, and the pack was relocated the next morning. As wolves were observed to be less active during the hot hours of the day and as they normally spent several hours at a kill site, I feel reasonably confident that all blackbuck kills made by the wolves during these intensive monitoring periods were located by me.
Data from 13 such blackbuck kills, along with data on consumption of two goats of known weight that were killed and eaten by a known number of wolves were used to estimate the intake/wolf/kill. The average intake/wolf/day was estimated from the intake/wolf/kill and the average kill interval.
Information regarding food consumption and prey composition of the wolf's diet were used to estimate the average number of blackbuck killed/wolf/year....
Results
During this study, the wolves of Velavadar National Park subsisted almost exclusively on wild prey, a rare case for wolves in India. Though several prey species were recovered from wolf scats, three prey items -- blackbuck, rodents, and hares (Lepus nigricollis) -- constituted the majority of the diet.
....The detailed analysis of 127 scats with blackbuck remains estimated 40% to contain fawn remains....
Blackbuck, rodents and hare accounted for 94% of the biomass consumption by wolves....Nilgai (Boselophus tagocamelus), cattle, and sheep occurred rarely in the wolf's diet and in only one season. Remains of these species in wolf scats were likely the result of a single kill or scavenging incident....
During the course of this study the major cause of known mortality among blackbuck was wolf predation. Among 48 fresh blackbuck carcasses examined, 43 (90%) were wolf kills, two (4%) were killed by poachers, and two (4%) by dogs; for one the cause of death could not be ascertained. Wolves consumed an average of 4.62 kg per individual at each kill. The average kill interval during the intensive monitoring period was 3.5 days. Considering the contribution by other prey besides blackbuck to be negligible to the biomass consumption by wolves...during the interkill period, then food intake by wolves would be 1.33 kg/wolf/day. If the weight of an average Indian wolf was approximately 18 kg, wolves would then be consuming about 7.4% of their body weight in food per day. The average pack size for 1988-1990 (excluding pups 3 months old or younger) was 5.75. For a pack of six wolves with a mean consumption of 1.33 kg/wolf/day, the total annual consumption would be 2900 kg of prey....
During the few incidents when wolves were observed to hunt blackbuck, they seemed to rely on stalking as well as a chase. Most kills were made during the night. Wolves were observed to rely greatly on stalking at night to get close to blackbuck. Blackbuck rely primarily on sight to avoid predation by quick flight. Wolves were successful in killing adult blackbuck when hunting in packs or individually. The method of killing by the pack was primarily an attack on the rear of the antelope followed by evisceration. The blackbuck likely died from blood loss and shock. The technique of killing by a single wolf was a bite on the throat or at the base of the skull....
Wolves invariably opened the abdomen of prey. They preferred to feed first on the visceral organs and the rump....The forelimbs and the neck region were the next to be consumed. In the case of adult male blackbuck kills, the head could always be recovered from the kill site.
Adult blackbucks were rarely fully utilized by wolves. Wolves were not observed to continue feeding on a kill later than 2-3 hours after sunrise. This was a likely behavior to avoid the heat of the day or a result of disturbance from human activities during daylight hours. Wolves rarely returned to a kill. Usually scavengers -- feral dogs, jackel, foc (Vulpes bengalensis), crows, vultures, and eagles (Aquila rapax nipalensis) -- finished the remains within a few hours after the pack had left the kill for cover. A kill was considered fully utilized if all of the edible portion was consumed by wolves. Utilization of kills would depend on the time at which the kill was made, the weight of the prey, and the number of wolves to have fed from the kill. Kills made during the night were likely to be more efficiently utilized than kills made during the early morning hours. Only 16% of the kills were fully utilized. On average, blackbuck kills were 57% utilized. The number of adult blackbuck in Table 3 would need to be inflated by about 43% to account for under-utilization of kills. Thus, a pack of six wolves would kill between 59 and 84 blackbuck and about 150 blackbuck fawns (considering fawns to be 100% utilized) per year. The actual number of blackbuck killed per wolf would range between 35 and 39 per year.
Considering the potential finite rate of increase for blackbuck to be 1.25...158 blackbuck would be required per wolf to maintain a stable blackbuck population. The blackbuck population required to sustain predation by a pack of six wolves would range between 853 to 951 blackbuck....[A] stationary population of 1850 blackbuck (the average population for Velavadar National Park from 1973 to 1987) would support between 11 and 13 wolves.
Discussion
....Active dogs require about189 kcal/kg. If wolves were considered to have similar metabolic rates as dogs, then wolves would require 1,650 kcal/day for maintenance. This amount of energy would correspond to about 1kg of meat, an amount that is 5.5% of the wolves body weight. Timber wolves in the wild were observed to have much higher rates of intake in the wild than in captivity. An intake rate of 7.4% of body weight per day for the Veladavar wolf pack is within the range reported for wild wolves in North America.
Under-utilized kills were more likely to be located in the morning due to the feeding activity of the pack and the aggregation of scavengers. This conspicuousness may have been a possible source of bias towards underestimating kill utilization. For management purposes, underestimation of kill utilization would cause a more conservative estimate of the number of blackbuck required to sustain wolf predation. Human disturbance in the form of chasing wolves from kills and/or approaching wolf kills for collecting meat and hide should be minimized or totally eliminated. Wolves are likely to accustom themselves gradually to human presence and may continue to feed during daylight hours once persecution is stopped. This would possibly allow better utilization of kills, permitting the wolves to kill less often.
....During blackbuck population crashes caused by climatic catastrophes (like droughts and floods), and when the blackbuck/wolf ratio is below 142 blackbuck/wolf...it is likely that wolf predation would be noncompensatory and may become regulatory. There is strong evidence for social regulation among wolf populations of North America at densities dictated ultimately by prey availability. Pack size and territory size are regulated by mean prey size and prey density. It seems likely that due to the small size of the major prey (weight of an average blackbuck in the Velavadar population was 26 kg) and an absence of substantial alternate prey, the mean pack size in Velavadar National Park is not likely to increase much beyond that observed during the study period (5.57 wolves). Considering an extreme scenario where wolf numbers increased to 10 wolves -- a number likely to be achieved temporarily by recruitment of pups prior to dispersal or if two packs simultaneously used the park area -- then the number of blackbuck required would be 1710 individuals. This number of blackbuck is close to the the historical carrying capacity at Velavadar National Park. The blackbuck population continued to increase during the study period, even though the blackbuck:wolf ratio was close to the critical number....This suggests lack of regulation by wolf predation and that wolf predation was not completely additive to other mortality factors. At higher blackbuck population densities or when the blackbuck:wolf ratio is greater than 142 blackbuck per wolf (situations similar to that observed during this study, nutritional factors...are likely to be regulatory. During such conditions, a major fraction of wolf-caused mortality would likely be compensatory.
Wolf predation in Velavadar National Park does not currently seem to be a threat to the long-term survival of blackbuck in the region. Wolf predation is a major limiting factor, however, and would retard the rate of increase of the blackbuck population. Such an effect would be desirable in areas where blackbuck density reaches high levels, causing conflicts with local people due to substantial crop depredation.
....Predation on blackbuck fawns and adults by feral dogs is likely to be additive to wolf predaton when the blackbuck population is low. During such times, dogs would likely compete directly with wolves for vulnerable prey. During the course of this study, dogs were eliminated whenever sighted within the park. Thus, predation by dogs was minimal. This practice must be continued for the benefit of blackbuck as well as wolves.
Maintaining the current carrying capacity of the park by shrub removal from the grassland areas is likely to suffice for maintaining blackbuck:wolf ratios within critical levels. Removing established Prosopis shrubland to create more grassland habitat or developing saline habitats into grasslands would increase the carrying capacity (within limits) of the Park for blackbuck. Care should be taken to maintain Prosopis groves traditionally used by wolves as denning, rendezvous, and resting sites.
Velavadar National Park needs continuous management; habitat manipulation, minimizing human disturbance to wolves, and reducing predation by dogs on blackbuck are some ways to ensure continued viability of this endangered prey-predator system.
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