Raven Scavenging Favours Group Foraging in Wolves
Vucetich, Peterson & Waite, Animal Behaviour, 67/6 (June 2004), 1117-1126
Wolves, Canis lupus, routinely live in large packs that include unrelated individuals and mature offspring. Studies show that individual wolves that live in large packs suffer reduced foraging returns. Therefore, group hunting and group living (sociality) in wolves is generally thought to be favoured by indirect fitness gains accrued through kin-directed altruism. However, we show that kin-directed altruism cannot account for groups that include mature offspring or unrelated individuals. We also present an analysis that incorporates a previously ignored feature of wolf foraging ecology, namely the loss of food to scavenging ravens, Corvus corax. By accounting for this process, we show that individuals in large packs do indeed accrue foraging advantages. In the hypothetical absence of this scavenging pressure, an individual would maximize its rate of prey acquisition, and minimize its risk of energetic shortfall, by foraging with just one other individual. However, incorporating the effect of scavenging by ravens leads to a dramatic increase in the predicted group size. Our analysis indicates that per capita gains are highest in the largest observed packs. The greater food-sharing costs in a larger pack are more than offset by smaller losses to scavengers and increased rates of prey acquisition. Thus, in contrast with previous interpretations, the selfish benefits of social foraging appear to contribute to the maintenance of sociality in wolves after all. We explore whether such benefits favour group living in various social carnivores that hunt large prey and are thus vulnerable to scavenging.
The Recovery, Distribution, and Population Dynamics of Wolves on the Scandinavian Peninsula, 1978-1998
Webakken, Sand, Liberg & Bjrvall, Canadian Journal of Zoology, 79 (April, 2001): 710-725 (16 pp)
In 1966 the gray wolf (Canis lupus) was regarded as functionally extinct in Norway and Sweden (the Scandinavian peninsula). In 1978 the first confirmed reproduction on the peninsula in 14 years was recorded. During 20 successive winters, from 1978–1979 to 1997–1998, the status, distribution, and dynamics of the wolf population were monitored by snow-tracking as a cooperative Swedish–Norwegian project. After the 1978 reproduction in northern Sweden, all new pairs and packs were located in south-central parts of the Scandinavian peninsula. Between 1983 and 1990 wolves reproduced each year except 1986, but in only one territory. There was no population growth during this period and the population never exceeded 10 animals. In 1991 reproduction was recorded in two territories. After that there were multiple reproductions each year and the population started growing. In 1998 there were 50–72 wolves and six reproducing packs on the peninsula. Between 1991 and 1998 the annual growth rate was 1.29 ± 0.035 (mean ± SD). A minimum of 25 litters were born during the study period. The early-winter size of packs reproducing for the first time was 6.2 ± 1.4 wolves (n = 9), and this decreased with time during the study. The size of packs that had reproduced more than once was 6.4 ± 1.8 wolves (n = 12), and this increased with time over the study period. All but 1 of 30 reported wolf deaths were human-caused. The annual mortality rate was 0.13 ± 0.11, and this decreased with time during the study period. The minimum dispersal distance was 323 ± 212 km for males and 123 ± 67 km for females. Of 10 new wolf territories where breeding occurred, only 1 bordered other, existing territories. The distance from newly established wolf pairs to the nearest existing packs was 119 ± 73 km. Simulation of population growth based on known reproductions and mortalities showed a close similarity to the results from population censuses up to the mid-1990s. To what extent this population is genetically isolated is at present unclear.
Recovery of Traditional Techniques of Livestock Protection from Wolf Predation in Portugal
Ribeiro, Almada & Petrucci-Fonseca, World Wolf Congress 2003
Different techniques were traditionally developed by shepherds to reduce wolves' predation on livestock. The most widespread was the use of Livestock Guarding Dogs (LGD). Nevertheless, in the last decades the use of LGDs decreased and the knowledge of their education is being lost. In Portugal, Grupo Lobo initiated a project to recover the use of LGDs and contribute to the conservation of the endangered Iberian wolf by reducing man-wolf conflicts deriving from wolf damages on livestock. Since 1998 forty dogs from two Portuguese breeds of LGDs were placed in flocks in the North and Centre of the country, where the wolf still exists. Their behavioural development was monitored until adulthood and their efficiency evaluated. Since the criteria of the amount of damages is influenced by several factors difficult to assess, for a correct evaluation of LGDs performance a behavioural analysis should be considered. Most of the adult dogs (83%) are trustworthy and attentive to the flock and proved to be efficient in preventing wolf predation. Inquiries to shepherds have revealed the use of other protection methods until 1950, namely different types of light-mobile barriers, similar to fladry, a technique traditionally used in Eastern Europe for hunting wolves. These recent findings increase the trust on the use of fladry as a prevention method for wolf predation. The implementation of traditional methods of livestock protection emerge as a valid contribution to wolf conservation strategies worldwide.
Regurgitative Food Transfer Among Wild Wolves
Mech, Wolf & Packard, Canadian Journal of Zoology, 77 (August, 1999): 1192-1195 (4 pp)
Few studies of monogamous canids have addressed regurgitation in the context of extended parental care and alloparental care within family groups. We studied food transfer by regurgitation in a pack of wolves on Ellesmere Island, North West Territories, Canada, during 6 summers from 1988 through 1996. All adult wolves, including yearlings and a post-reproductive female, regurgitated food. Although individuals regurgitated up to five times per bout, the overall ratio of regurgitations per bout was 1.5. Pups were more likely to receive regurgitations (81%) than the breeding female (14%) or auxiliaries (6%). The breeding male regurgitated mostly to the breeding female and pups, and the breeding female regurgitated primarily to pups. The relative effort of the breeding female was correlated with litter size.
Relative Success of the Reintroduction of Mexican Wolves to Other Wolves in the United States
Kelly, Buchanan, Oakleaf, Phillips & Stark, World Wolf Congress 2003
During the past 16 years, 3 wolf recovery programs were initiated using the reintroduction of wolves as the mechanism to achieve recovery. The Mexican wolf recovery program is the most recent of these efforts and provides a significant point of comparison and contrast to the similar yet different efforts undertaken with red wolves in North Carolina and gray wolves in Yellowstone National Park and Idaho. The Mexican wolf program combines the unique challenges of each program into one. Like red wolf recovery, captive born and raised Mexican gray wolves were the release stock for reintroduction, and like gray wolf recovery in Idaho and Wyoming, but unlike the red wolf program, opportunities for wolf-livestock conflict are numerous in the current Mexican wolf reintroduction effort. Despite this unique combination of challenges, the current Mexican wolf reintroduction is succeeding. This success provides us an opportunity to evaluate the relative success of the Mexican wolf recovery program to date to the other wolf reintroduction efforts in the U.S. at this point in time. Many have characterized the Mexican gray wolf reintroduction as not successful but when compared to similar efforts the Mexican wolf program is found to be very successful biologically. At 5 years after the first wolves were reintroduced, second generation wild conceived and born offspring were documented within a normal generation time of 4 years, established packs are surviving and reproducing, and new packs are forming. Administratively, this success has been achieved by a collaborative management approach with State, Federal, Tribal and private participation in the reintroduction's day to day activities.
Reproductive Characteristics of an Exploited Wolf Population
McNay, Stephenson & Hoeff, World Wolf Congress 2003
In most wolf packs a single reproductively dominant female produces pups. However, examination of reproductive tracts collected from heavily hunted and trapped wolf populations in Alaska suggested higher pregnancy rates occurred in exploited populations. To assess the role of exploitation in stimulating high pregnancy rates and to estimate the contribution of secondary females to net productivity we captured, radio makred and closely monitored female wolves from an exploited wolf population in interior Alaska. We darted wolves from a helicopter, and performed 68 ultrasound scans for pregnancy over a 4-year period (1996-1999). Ninety four percent of primary (i.e. alpha) females were pregnant. Annual pregnancy among secondary females ranged from 40%-80% and was highest following intensive trapping. An estimated 61% of secondary female pregnancies contributed pups to summer wolf populations. Nine of 36 annual wolf packs contained more than one pregnant female; in each of 2 packs at least 4 females were pregnant. At least 5 of the 9 multiple pregnancy packs produced surviving, multiple litters. Overall, estimated pup survival among 18 in utero litters of primary females averaged 60% to autumn, but survival varied with pack socil structure. In utero through early autumn pup survival appeared to be lower in pairs with no previous offspring than in larger packs with offspring from previous years (0.48 vs. 0.65). Exploitation contributed to initial high pregnancy rates and multiple littering, but some packs produced multiple litters by reproductively co-dominant females in the absence of exploitation.
Rescue of a Severely Bottlenecked Wolf (Canis lupus) Population by a Single Immigrant
Vila, Sundqvist, Flagstad, Seddon, Bjornerfeldt, Kojola, Casulli, Sand, Wabakken & Ellegren, Proceedings of the Royal Society of London, Series B-Biological Sciences, 270/1510, January 2003, 91-97
The fragmentation of populations is an increasingly important problem in the conservation of endangered species. Under these conditions, rare migration events may have important effects for the rescue of small and inbred populations. However, the relevance of such migration events to genetically depauperate natural populations is not supported by empirical data. We show here that the genetic diversity of the severely bottlenecked and geographically isolated Scandinavian population of grey wolves (Canis lupus), founded by only two individuals, was recovered by the arrival of a single immigrant. Before the arrival of this immigrant, for several generations the population comprised only a single breeding pack, necessarily involving matings between close relatives and resulting in a subsequent decline in individual heterozygosity. With the arrival of just a single immigrant, there is evidence of increased heterozygosity, significant outbreeding (inbreeding avoidance), a rapid spread of new alleles and exponential population growth. Our results imply that even rare interpopulation migration can lead to the rescue and recovery of isolated and endangered natural populations.
Restoration of the Gray Wolf in the Northwestern United States
Bangs, Fontaine, Jiminez, Meier, Neimeyer, Smith, Mack & Asher, World Wolf Congress 2003
Gray wolf (Canis lupus) populations were eliminated from the western United States by 1930. Naturally-dispersing wolves from Canada first denned in Montana in 1986. In 1995 and 1996 wolves from western Canada were reintroduced to central Idaho and Yellowstone National Park, Wyoming. By December 2002, nearly 700 wolves were being managed in those three states under the U.S. federal Endangered Species Act. Wolf restoration has proceeded more quickly, with more benefits (public viewing and restoration of ecological processes), and fewer problems (livestock and pets depredations) than predicted. However, between 1987 and December 2002, a minimum of 244 cattle, 594 sheep, 55 dogs, and 9 llamas were killed by wolves and nearly $250,000 was paid from a private damage compensation fund. The U.S. Fish and Wildlife Service relocated 117 wolves and killed 149. Management also included non-lethal tools such [as] harassment, barriers, guard animals, altering wolf activity patterns, livestock management, and practical research. Livestock losses by wolves remain rare compared to other causes of livestock death but are inordinately controversial. Because over 85% of adult wolf mortality is human-caused, the interagency recovery program focuses its efforts on addressing the concerns of people who live near wolves to increase their tolerance of non-depredating wolves. Wolves were reclassified from endangered to threatened status in spring 2002 to recognize their recovery and to increase options for problem wolf management. The wolf population has achieved its numerical, distribution and temporal recovery goal. The population will be proposed to be removed from the list of endangered species when the states of Montana, Idaho, and Wyoming finalize state wolf management plans that must regulate human-caused mortality so the population is not again jeopardized with extinction.
Review of Methods to Reduce Livestock Depradation: I. Guardian Animals
Smith, Linnell, Odden & Swenson, Acta Agriculturae Scandinavica, 50/4 (November 2000), 279 (12 pp)
The use of domestic animals to protect livestock was reviewed through visits to actual users, discussions with experts and a thorough literature search. Costs and benefits were analysed in terms of reduced livestock losses. The most common guardian animals are dogs, which have been shown to reduce predation (documented mostly for coyote) by 11–100%. Livestock guardian dogs have also been used effectively against bear, wolf and cheetah. Donkeys are also used as guardian animals, and their effectiveness lies in their natural herding behaviour and aggression, especially against canids. The effectiveness of donkeys varies considerably dependent upon the predator species and the temperament of the individual donkey. Llamas are also used as a guardian animal, with approximately the same characteristics as the donkeys, and will defend themselves against most predators. The use of guardian animals appears to be an effective tool for reducing livestock depredation and should be evaluated in areas with high predation losses against the cost of changing production systems.