Wolves and moose on Isle Royale
Encyclopedia
Isle Royale
, the principal island of Isle Royale National Park
in the United States
, is home to a predator-prey relationship between wolves (Canis lupus) and moose
(Alces alces) that is unlike any other in the world. Because Isle Royale
is a small, isolated island, the two species are able to be studied with virtually no factor of human interaction, as the island is protected by its national park
status, and there is little migration of animals into and out of the island. The unique single predator-single prey relationship, where wolves are the only predator of moose
, and moose are almost exclusively the only prey for wolves, allows for precise research on predator-prey relationships, and of the fluctuation of the two populations.
The Isle Royale National Park
is made up of about 400 islands, and is in the northwest portion of Lake Superior
. It is about 50 miles (80 km) from Michigan
's shore, and 22 miles (35 km) from the Canadian
shore. The main island is about 45 miles (72 km) long, and nine miles (14 km) wide at the widest point, with an area of 205 square miles (530 km²). There are no roads, and no motorized vehicles are allowed on the island. Because there are no roads, nor any residential area, virtually all of the land on the island is wilderness
. The remoteness of Isle Royale leads to it having fewer visitors in one year than Great Smoky Mountains National Park
has in just one day. The park is closed from September to May during which the wolf-moose study personnel are the only humans resident on the island.
The relationship between wolves and moose on Isle Royale has been studied and researched for an unprecedented amount of time, which provides a rich background of research that aids in the better understanding of the two species and their interaction. The ongoing study, begun in 1958, is the longest study of either wolves or moose ever. Because of Isle Royale being an isolated island, neither wolves nor moose were there initially. Moose swam across Lake Superior
from Minnesota
in the early 1900s. For nearly fifty years the moose thrived, having no predator to dampen their population growth. In 1949 a pair of wolves wandered across an ice bridge made to the island during a harsh winter from Ontario
. But because only one pair of wolves migrated to the island, inbreeding
has posed problems to the wolves' existence. According to Rolf Pederson, a professor at Michigan Technological University
and the lead wolf-moose researcher, "Moose were isolated here 100 years ago. Most of the gene
s are still here, but they have enough population (to compensate). There are so few wolves that they have lost genetic variability. The scientific dogma suggests that they are not going to make it." In fact, all of the wolves' DNA
on Isle Royale can be traced back to one ancestor. The lack of genetic variability leads to inbreeding, and inbreeding in turn leads to mutations and fitness problems
. Wolves with mutations often are violently harassed, and sometimes killed because of their differences.
When initially studied, many researchers believed the two species would eventually reach a population equilibrium (which is believed to be about twenty-five wolves, and 1,500 moose). They have not yet shown any sign of settling into one, instead tending to fluctuate unpredictably. The highest number of moose on Isle Royale since being researched with the interactions of wolves was 2,442 in 1995. The highest number of wolves ever recorded on the island was fifty in 1980. The most dramatic decrease in the wolf population occurred when the canine parvovirus
was spread to the wolves on the island, introduced by a park visitor's dog (breaking the rules of the national park) in 1980 or 1981, causing a crash in the population; there were fifty wolves in 1980, but only fourteen by 1982. The population of the two species as of 2005 was 540 moose, which is the lowest recorded, and thirty wolves, which is considered rather high.
The density of the two species is very much dependent on the density of proper forage
. Because a moose's diet is 59% balsam fir
, any change in its density affects the density of moose. The consistent presence of moose on Isle Royale since 1900 has led to a dramatic decline in understory
growth of balsam fir. As of 2002, understory growth of balsam fir was at 5%, which is down 4% from 19th century rates, when it was recorded at 46%. The reliance of moose on balsam fir has led to a much higher concentration of the species on the east side of the island, where the plant is more plentiful. Birch
and aspen
trees, which are much healthier for moose, used to grow plentifully on the island, but have now mainly been replaced by the less nutritious balsam fir. Because balsam fir does not fulfill the amount of moisture moose need in their diet, they have recently been spotted eating snow, which is a very rare occurrence. They have also been sighted eating lichen
s, which is another very strange occurrence; researcher Rolf Pederson has compared it to eating dust. When the moose population grows too high, the balsam fir population crashes, which leads to a crash in the moose population. This leads to the continuing "see-sawing" of the moose population on the island. Crashes in balsam fir growth lead to malnutrition
, which is one of the most common killers, both directly and indirectly of moose. When there are too many moose for the amount of balsam fir, then many moose, especially young moose become plagued with malnutrition, which leads to arthritis
. Moose commonly die either directly from malnutrition, or, because they become emaciated, and slowed down by arthritis, they are picked out by a wolf pack
as easy prey, and are killed. The most common cause of malnutrition in moose is when calves are born during a winter with deep enough snow that browsing for proper forage is very difficult. The moose population should be able to rebound soon, because there are not as many moose as there have been in the past, which will allow for the balsam fir to grow back.
Wolves use their intelligence to pick out easy moose prey, which they can outrun, and bring down. They do not go after healthy moose, unless they are completely desperate; a healthy moose in its prime years is very tough for any wolf pack
to bring down. Also, moose in their prime years commonly outrun wolves in a hunt; moose can cross snow two feet deep at 20 mph (32 km/h), faster than the best cross-country skiers
, and outrun wolves if the snow is soft. Even if wolves can catch up to a moose, they cannot always bring it down; researchers have found many bruises and scars on wolves that have not been successful when trying to kill healthy moose. Wolves pick out young moose calves, old moose, or moose plagued with disease or injury in order to increase their chances in successfully killing one. The typical moose that a wolf kills is about 12 years old, and suffers from arthritis, osteoporosis
, or periodontal disease, and in some cases all of them. Though moose are often infected by various diseases, approximately 80% to 90% of moose deaths on Isle Royale can be attributed to wolves. The number of calves and old moose has declined recently, placing the future of the wolves in doubt. Because moose make up nine-tenths of an Isle Royale wolf’s diet (the remainder being snowshoe hare
and beaver
), finding a young, old or sickly moose is imperative for survival. The average number of moose a wolf kills a month is between 0.44 and 1.69.
The wolf population
of Isle Royale
is, with the exception of a few loners and separate pairs, formed into three pack
s; the east pack, the middle pack, and the Chippewa Harbor pack. Wolves on the island have, historically, been separated into three or four packs, with each pack usually having between three and eight members, including two or three pup
s. The number of wolves in a pack depends mainly on the amount of snow
that fell in the previous winter. In winters with light snow, pups tend to leave the pack to find mates, so packs run at four or five members; in heavily snowy winters, the pups stay with the pack, which can reach ten to twelve members. If many members of a pack die, the pack dissolves and a new one forms within a year. One pack will dissolve about once every three years.
Hunting in packs increases wolves' chances of killing and feeding on moose: because it is nearly impossible for a wolf to bring down all but the weakest moose by itself, hunting in packs is the only effective way for wolves to kill moose. An Isle Royale wolf pack usually kills one moose every four to ten days during the winter. Wolf packs on the island have been known to fight to try to extend their territory and, thus, supply of moose. Recently, the east pack killed Chippewa Harbor pack's alpha male, as witnessed by John Vucetich, a professor at Michigan Technological University
and one of the lead researchers on the island, who believes that the Chippewa Harbor pack is now in grave danger of dying off without their leader.
raven
s. Ravens are tenacious scavengers that can easily dodge the strike of a wolf and are unbothered by them. Ravens can eat and store up to two pounds (1 kg) in a few days, which is minuscule compared to the storage capacity of wolves, which is up to eighteen pounds (8 kg) in just a few hours.
Other anti-social species have an effect, though rather small, on the relationship between wolves and moose on Isle Royale
. Before wolves hunted them to extinction
, coyote
s used to inhabit the island. Beaver
s and snowshoe hare
s also have an effect on both populations, because beavers and snowshoe hares are the only two animals that wolves prey on excluding moose, constituting a tenth of an Isle Royale wolf's diet. The beaver population has sharply declined since the arrival of wolves, but they still are present, and though they are not a prime food source for typical wolves, they are the second to moose as the most consumed animal by the wolves on the island. Beavers benefit both species, because they create aquatic macrophyte
s, which are very nutritional plants for moose, because they are a key source of sodium
, and also because they serve as easy prey for wolves. Unfortunately for the moose, beavers themselves also consume the macrophytes they create.
Though wolves are thought to contribute to the decline in beaver, researchers believe that the decline of aspen, the primary food source of beavers, which used to be plentiful, could have led to their decrease. Beavers have been exposed to predation by having to travel long distances to find only parts of the island where aspen remains. Snowshoe hares, the third most consumed animal by wolves on Isle Royale constitute a very small portion of the wolves' diet, because snowshoe hares are so difficult to catch. Researchers have found that wolves do not show much interest in preying on hares, and only feed on them incidentally. Snowshoe hares have a negative effect on moose as they eat some of the same vegetation that moose eat, which only contributes to the decline in appropriate forage for moose. The red fox is yet another animal that inhabits Isle Royale; red foxes mainly feed on snowshoe hares and occasionally scavenge on moose, or any other meat a wolf leaves behind. Wolves do not commonly kill foxes, though wolves have been observed killing foxes when they attempt to feed on an animal carcass.
plays a major role in the moose-wolf relationship as well. Since El Nino hit in 1998, the climate has warmed up, which has significantly affected the moose population across North America. The warmer climate in recent years has produced more tick
s, which consume the flesh of animals, making them more susceptible to anemia
, and bite off the hair of moose, exposing them to hypothermia
in cold weather. A moose can have tens of thousands of ticks feeding on its blood at one time, each sucking up to one mililiter of blood. The biting ticks cause a lot of discomfort for the moose, so they try to get the ticks off their bodies by biting off their hair, and rubbing up against trees. This preoccupies moose, and keeps them from browsing for food, which can lead to malnutrition. Compounded with blood loss, moose weakened by ticks are easier for wolves to kill. Ticks are more prominent in years where spring arrives earlier than usual, because when they fall on ground not covered in snow, then they can reproduce. Otherwise, they die out. Then, if the summer is hot, ticks are able to reproduce at a higher rate. Hot summers also lead to moose resting in the shade, or in the water to keep cool, making them easier prey for wolves. Also, hot summers lead to tougher foraging for moose which makes them less prepared and more vulnerable to the winter. Not only has the recent warming of Isle Royale hurt the moose, but completely opposite problems harm them also. Harsh winters pose significant problems to moose, because moose have problems finding food when there is too much snow on the ground. The less snow there is, the more freely moose can move around the island. When there is a significant amount of snow, moose stay in conifer swamp
s, making them easier prey for wolves, because they are more stagnant, and immobilized due to the snow. Deep or heavy snow decreases the speed and agility of moose that is necessary to evade wolf attacks, and calves born during a winter with particularly deep snow are more vulnerable to being weaker prey for wolves later on in their lives because of foraging problems that occur when the snow is deep.
The keen survival instincts of moose have been clearly evident from the studying of their actions on Isle Royale. Female moose (called "cows") have been spotted on nearby smaller islands, around the main island of Isle Royale, because they swim across to give birth. This allows for them to give birth and raise their young without the threat of wolves preying on their young when they are vulnerable. This also causes trouble for moose that are born in the winter, because they can no longer swim across the water to another island, and must raise the new calf in the snow. Once the calves are physically mature, they are able to swim back, and are then able to better protect themselves from wolves, as they are then in their prime years. This practice should theoretically help the moose population rebound in the future.
which led to the prominence of both the author and the topic. The book was published in 1966 by the Department of the Interior, having evolved from his doctoral thesis.
Isle Royale
Isle Royale is an island of the Great Lakes, located in the northwest of Lake Superior, and part of the state of Michigan. The island and the 450 surrounding smaller islands and waters make up Isle Royale National Park....
, the principal island of Isle Royale National Park
Isle Royale National Park
Isle Royale National Park is a U.S. National Park in the state of Michigan. Isle Royale, the largest island in Lake Superior, is over 45 miles in length and 9 miles wide at its widest point. The park is made of Isle Royale itself and approximately 400 smaller islands, along with any submerged...
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, is home to a predator-prey relationship between wolves (Canis lupus) and moose
Moose
The moose or Eurasian elk is the largest extant species in the deer family. Moose are distinguished by the palmate antlers of the males; other members of the family have antlers with a dendritic configuration...
(Alces alces) that is unlike any other in the world. Because Isle Royale
Isle Royale
Isle Royale is an island of the Great Lakes, located in the northwest of Lake Superior, and part of the state of Michigan. The island and the 450 surrounding smaller islands and waters make up Isle Royale National Park....
is a small, isolated island, the two species are able to be studied with virtually no factor of human interaction, as the island is protected by its national park
National park
A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individual nations designate their own national parks differently A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or...
status, and there is little migration of animals into and out of the island. The unique single predator-single prey relationship, where wolves are the only predator of moose
Moose
The moose or Eurasian elk is the largest extant species in the deer family. Moose are distinguished by the palmate antlers of the males; other members of the family have antlers with a dendritic configuration...
, and moose are almost exclusively the only prey for wolves, allows for precise research on predator-prey relationships, and of the fluctuation of the two populations.
The Isle Royale National Park
Isle Royale National Park
Isle Royale National Park is a U.S. National Park in the state of Michigan. Isle Royale, the largest island in Lake Superior, is over 45 miles in length and 9 miles wide at its widest point. The park is made of Isle Royale itself and approximately 400 smaller islands, along with any submerged...
is made up of about 400 islands, and is in the northwest portion of Lake Superior
Lake Superior
Lake Superior is the largest of the five traditionally-demarcated Great Lakes of North America. It is bounded to the north by the Canadian province of Ontario and the U.S. state of Minnesota, and to the south by the U.S. states of Wisconsin and Michigan. It is the largest freshwater lake in the...
. It is about 50 miles (80 km) from Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
's shore, and 22 miles (35 km) from the Canadian
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
shore. The main island is about 45 miles (72 km) long, and nine miles (14 km) wide at the widest point, with an area of 205 square miles (530 km²). There are no roads, and no motorized vehicles are allowed on the island. Because there are no roads, nor any residential area, virtually all of the land on the island is wilderness
Wilderness
Wilderness or wildland is a natural environment on Earth that has not been significantly modified by human activity. It may also be defined as: "The most intact, undisturbed wild natural areas left on our planet—those last truly wild places that humans do not control and have not developed with...
. The remoteness of Isle Royale leads to it having fewer visitors in one year than Great Smoky Mountains National Park
Great Smoky Mountains National Park
Great Smoky Mountains National Park is a United States National Park and UNESCO World Heritage Site that straddles the ridgeline of the Great Smoky Mountains, part of the Blue Ridge Mountains, which are a division of the larger Appalachian Mountain chain. The border between Tennessee and North...
has in just one day. The park is closed from September to May during which the wolf-moose study personnel are the only humans resident on the island.
Wolf-moose dynamics interactions
Lake Superior
Lake Superior is the largest of the five traditionally-demarcated Great Lakes of North America. It is bounded to the north by the Canadian province of Ontario and the U.S. state of Minnesota, and to the south by the U.S. states of Wisconsin and Michigan. It is the largest freshwater lake in the...
from Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
in the early 1900s. For nearly fifty years the moose thrived, having no predator to dampen their population growth. In 1949 a pair of wolves wandered across an ice bridge made to the island during a harsh winter from Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
. But because only one pair of wolves migrated to the island, inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
has posed problems to the wolves' existence. According to Rolf Pederson, a professor at Michigan Technological University
Michigan Technological University
Michigan Technological University is a public research university located in Houghton, Michigan, United States. Its main campus sits on on a bluff overlooking Portage Lake...
and the lead wolf-moose researcher, "Moose were isolated here 100 years ago. Most of the gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s are still here, but they have enough population (to compensate). There are so few wolves that they have lost genetic variability. The scientific dogma suggests that they are not going to make it." In fact, all of the wolves' DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
on Isle Royale can be traced back to one ancestor. The lack of genetic variability leads to inbreeding, and inbreeding in turn leads to mutations and fitness problems
Inbreeding depression
Inbreeding depression is the reduced fitness in a given population as a result of breeding of related individuals. It is often the result of a population bottleneck...
. Wolves with mutations often are violently harassed, and sometimes killed because of their differences.
When initially studied, many researchers believed the two species would eventually reach a population equilibrium (which is believed to be about twenty-five wolves, and 1,500 moose). They have not yet shown any sign of settling into one, instead tending to fluctuate unpredictably. The highest number of moose on Isle Royale since being researched with the interactions of wolves was 2,442 in 1995. The highest number of wolves ever recorded on the island was fifty in 1980. The most dramatic decrease in the wolf population occurred when the canine parvovirus
Canine parvovirus
Canine parvovirus type 2 is a contagious virus mainly affecting dogs. The disease is highly contagious and is spread from dog to dog by direct or indirect contact with their feces. It can be especially severe in puppies that are not protected by maternal antibodies or vaccination. It has two...
was spread to the wolves on the island, introduced by a park visitor's dog (breaking the rules of the national park) in 1980 or 1981, causing a crash in the population; there were fifty wolves in 1980, but only fourteen by 1982. The population of the two species as of 2005 was 540 moose, which is the lowest recorded, and thirty wolves, which is considered rather high.
The density of the two species is very much dependent on the density of proper forage
Forage
Forage is plant material eaten by grazing livestock.Historically the term forage has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used more loosely to include similar plants cut for fodder and carried to the animals, especially...
. Because a moose's diet is 59% balsam fir
Balsam Fir
The balsam fir is a North American fir, native to most of eastern and central Canada and the northeastern United States .-Growth:It is a small to medium-size evergreen tree typically tall, rarely to tall, with a narrow conic crown...
, any change in its density affects the density of moose. The consistent presence of moose on Isle Royale since 1900 has led to a dramatic decline in understory
Understory
Understory is the term for the area of a forest which grows at the lowest height level below the forest canopy. Plants in the understory consist of a mixture of seedlings and saplings of canopy trees together with understory shrubs and herbs...
growth of balsam fir. As of 2002, understory growth of balsam fir was at 5%, which is down 4% from 19th century rates, when it was recorded at 46%. The reliance of moose on balsam fir has led to a much higher concentration of the species on the east side of the island, where the plant is more plentiful. Birch
Birch
Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...
and aspen
Aspen
Populus section Populus, of the Populus genus, includes the aspen trees and the white poplar Populus alba. The five typical aspens are all native to cold regions with cool summers, in the north of the Northern Hemisphere, extending south at high altitudes in the mountains. The White Poplar, by...
trees, which are much healthier for moose, used to grow plentifully on the island, but have now mainly been replaced by the less nutritious balsam fir. Because balsam fir does not fulfill the amount of moisture moose need in their diet, they have recently been spotted eating snow, which is a very rare occurrence. They have also been sighted eating lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
s, which is another very strange occurrence; researcher Rolf Pederson has compared it to eating dust. When the moose population grows too high, the balsam fir population crashes, which leads to a crash in the moose population. This leads to the continuing "see-sawing" of the moose population on the island. Crashes in balsam fir growth lead to malnutrition
Malnutrition
Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
, which is one of the most common killers, both directly and indirectly of moose. When there are too many moose for the amount of balsam fir, then many moose, especially young moose become plagued with malnutrition, which leads to arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
. Moose commonly die either directly from malnutrition, or, because they become emaciated, and slowed down by arthritis, they are picked out by a wolf pack
Pack (canine)
Pack is a social group of conspecific canids. Not all species of canids - notably the red fox - form packs. Pack size and social behaviour within packs varies across species.-Species which exhibit pack behavior:...
as easy prey, and are killed. The most common cause of malnutrition in moose is when calves are born during a winter with deep enough snow that browsing for proper forage is very difficult. The moose population should be able to rebound soon, because there are not as many moose as there have been in the past, which will allow for the balsam fir to grow back.
Wolves use their intelligence to pick out easy moose prey, which they can outrun, and bring down. They do not go after healthy moose, unless they are completely desperate; a healthy moose in its prime years is very tough for any wolf pack
Pack (canine)
Pack is a social group of conspecific canids. Not all species of canids - notably the red fox - form packs. Pack size and social behaviour within packs varies across species.-Species which exhibit pack behavior:...
to bring down. Also, moose in their prime years commonly outrun wolves in a hunt; moose can cross snow two feet deep at 20 mph (32 km/h), faster than the best cross-country skiers
Cross-country skiing
Cross-country skiing is a winter sport in which participants propel themselves across snow-covered terrain using skis and poles...
, and outrun wolves if the snow is soft. Even if wolves can catch up to a moose, they cannot always bring it down; researchers have found many bruises and scars on wolves that have not been successful when trying to kill healthy moose. Wolves pick out young moose calves, old moose, or moose plagued with disease or injury in order to increase their chances in successfully killing one. The typical moose that a wolf kills is about 12 years old, and suffers from arthritis, osteoporosis
Osteoporosis
Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...
, or periodontal disease, and in some cases all of them. Though moose are often infected by various diseases, approximately 80% to 90% of moose deaths on Isle Royale can be attributed to wolves. The number of calves and old moose has declined recently, placing the future of the wolves in doubt. Because moose make up nine-tenths of an Isle Royale wolf’s diet (the remainder being snowshoe hare
Snowshoe Hare
The Snowshoe Hare , also called the Varying Hare, or Snowshoe Rabbit, is a species of hare found in North America. It has the name "snowshoe" because of the large size of its hind feet and the marks its tail leaves. The animal's feet prevent it from sinking into the snow when it hops and walks...
and beaver
Beaver
The beaver is a primarily nocturnal, large, semi-aquatic rodent. Castor includes two extant species, North American Beaver and Eurasian Beaver . Beavers are known for building dams, canals, and lodges . They are the second-largest rodent in the world...
), finding a young, old or sickly moose is imperative for survival. The average number of moose a wolf kills a month is between 0.44 and 1.69.
Wolf population dynamics
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
of Isle Royale
Isle Royale
Isle Royale is an island of the Great Lakes, located in the northwest of Lake Superior, and part of the state of Michigan. The island and the 450 surrounding smaller islands and waters make up Isle Royale National Park....
is, with the exception of a few loners and separate pairs, formed into three pack
Pack (canine)
Pack is a social group of conspecific canids. Not all species of canids - notably the red fox - form packs. Pack size and social behaviour within packs varies across species.-Species which exhibit pack behavior:...
s; the east pack, the middle pack, and the Chippewa Harbor pack. Wolves on the island have, historically, been separated into three or four packs, with each pack usually having between three and eight members, including two or three pup
Pup
Pup may refer to:In zoology:*Puppies, younger dogs*Pinniped young*Shark young*Rodent youngIn other uses:* Sopwith Pup, an aircraft used by the British in World War I* Beagle Pup, a 1960s British light aircraft...
s. The number of wolves in a pack depends mainly on the amount of snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
that fell in the previous winter. In winters with light snow, pups tend to leave the pack to find mates, so packs run at four or five members; in heavily snowy winters, the pups stay with the pack, which can reach ten to twelve members. If many members of a pack die, the pack dissolves and a new one forms within a year. One pack will dissolve about once every three years.
Hunting in packs increases wolves' chances of killing and feeding on moose: because it is nearly impossible for a wolf to bring down all but the weakest moose by itself, hunting in packs is the only effective way for wolves to kill moose. An Isle Royale wolf pack usually kills one moose every four to ten days during the winter. Wolf packs on the island have been known to fight to try to extend their territory and, thus, supply of moose. Recently, the east pack killed Chippewa Harbor pack's alpha male, as witnessed by John Vucetich, a professor at Michigan Technological University
Michigan Technological University
Michigan Technological University is a public research university located in Houghton, Michigan, United States. Its main campus sits on on a bluff overlooking Portage Lake...
and one of the lead researchers on the island, who believes that the Chippewa Harbor pack is now in grave danger of dying off without their leader.
Other species
Once a moose is brought down and killed, wolves have to compete with scavengingScavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
raven
Raven
Raven is the common name given to several larger-bodied members of the genus Corvus—but in Europe and North America the Common Raven is normally implied...
s. Ravens are tenacious scavengers that can easily dodge the strike of a wolf and are unbothered by them. Ravens can eat and store up to two pounds (1 kg) in a few days, which is minuscule compared to the storage capacity of wolves, which is up to eighteen pounds (8 kg) in just a few hours.
Other anti-social species have an effect, though rather small, on the relationship between wolves and moose on Isle Royale
Isle Royale
Isle Royale is an island of the Great Lakes, located in the northwest of Lake Superior, and part of the state of Michigan. The island and the 450 surrounding smaller islands and waters make up Isle Royale National Park....
. Before wolves hunted them to extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
, coyote
Coyote
The coyote , also known as the American jackal or the prairie wolf, is a species of canine found throughout North and Central America, ranging from Panama in the south, north through Mexico, the United States and Canada...
s used to inhabit the island. Beaver
Beaver
The beaver is a primarily nocturnal, large, semi-aquatic rodent. Castor includes two extant species, North American Beaver and Eurasian Beaver . Beavers are known for building dams, canals, and lodges . They are the second-largest rodent in the world...
s and snowshoe hare
Snowshoe Hare
The Snowshoe Hare , also called the Varying Hare, or Snowshoe Rabbit, is a species of hare found in North America. It has the name "snowshoe" because of the large size of its hind feet and the marks its tail leaves. The animal's feet prevent it from sinking into the snow when it hops and walks...
s also have an effect on both populations, because beavers and snowshoe hares are the only two animals that wolves prey on excluding moose, constituting a tenth of an Isle Royale wolf's diet. The beaver population has sharply declined since the arrival of wolves, but they still are present, and though they are not a prime food source for typical wolves, they are the second to moose as the most consumed animal by the wolves on the island. Beavers benefit both species, because they create aquatic macrophyte
Macrophyte
A macrophyte is an aquatic plant that grows in or near water and is either emergent, submergent, or floating. In lakes macrophytes provide cover for fish and substrate for aquatic invertebrates, produce oxygen, and act as food for some fish and wildlife....
s, which are very nutritional plants for moose, because they are a key source of sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
, and also because they serve as easy prey for wolves. Unfortunately for the moose, beavers themselves also consume the macrophytes they create.
Climate effects
ClimateClimate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
plays a major role in the moose-wolf relationship as well. Since El Nino hit in 1998, the climate has warmed up, which has significantly affected the moose population across North America. The warmer climate in recent years has produced more tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
s, which consume the flesh of animals, making them more susceptible to anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
, and bite off the hair of moose, exposing them to hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
in cold weather. A moose can have tens of thousands of ticks feeding on its blood at one time, each sucking up to one mililiter of blood. The biting ticks cause a lot of discomfort for the moose, so they try to get the ticks off their bodies by biting off their hair, and rubbing up against trees. This preoccupies moose, and keeps them from browsing for food, which can lead to malnutrition. Compounded with blood loss, moose weakened by ticks are easier for wolves to kill. Ticks are more prominent in years where spring arrives earlier than usual, because when they fall on ground not covered in snow, then they can reproduce. Otherwise, they die out. Then, if the summer is hot, ticks are able to reproduce at a higher rate. Hot summers also lead to moose resting in the shade, or in the water to keep cool, making them easier prey for wolves. Also, hot summers lead to tougher foraging for moose which makes them less prepared and more vulnerable to the winter. Not only has the recent warming of Isle Royale hurt the moose, but completely opposite problems harm them also. Harsh winters pose significant problems to moose, because moose have problems finding food when there is too much snow on the ground. The less snow there is, the more freely moose can move around the island. When there is a significant amount of snow, moose stay in conifer swamp
Swamp
A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...
s, making them easier prey for wolves, because they are more stagnant, and immobilized due to the snow. Deep or heavy snow decreases the speed and agility of moose that is necessary to evade wolf attacks, and calves born during a winter with particularly deep snow are more vulnerable to being weaker prey for wolves later on in their lives because of foraging problems that occur when the snow is deep.
The keen survival instincts of moose have been clearly evident from the studying of their actions on Isle Royale. Female moose (called "cows") have been spotted on nearby smaller islands, around the main island of Isle Royale, because they swim across to give birth. This allows for them to give birth and raise their young without the threat of wolves preying on their young when they are vulnerable. This also causes trouble for moose that are born in the winter, because they can no longer swim across the water to another island, and must raise the new calf in the snow. Once the calves are physically mature, they are able to swim back, and are then able to better protect themselves from wolves, as they are then in their prime years. This practice should theoretically help the moose population rebound in the future.
Study
One of the first publications on the subject was the book "The Wolves of Isle Royale" by L. David MechL. David Mech
Lucyan David "Dave" Mech is an internationally recognized wolf expert, a senior research scientist for the U.S. Department of the Interior's U.S. Geological Survey , and an adjunct professor at the University of Minnesota in St. Paul...
which led to the prominence of both the author and the topic. The book was published in 1966 by the Department of the Interior, having evolved from his doctoral thesis.