Introduction


The wolf study in Yukon-Charley Rivers National Preserve (YUCH) was initiated in March 1993 to learn more about the wolves that inhabit the preserve. Prior to 1993, little was known about the population characteristics and ecology of these wolves. Several aerial winter wolf track surveys conducted during the previous decades provided information on the number and sizes of packs, from which the total population size was estimated. Harvest was estimated from sealing records and by interviewing local trappers and hunters. However, little information existed on pack movements and territory sizes, pup production, dispersal, mortality rates and causes, and predation characteristics. Our objectives for the study were to, 1) determine population size, productivity, survival patterns, and distribution of wolves in YUCH, 2) document temporal wolf movements and predation behavior related to moose and caribou distributions, and 3) evaluate wolf-prey relationships.


Study Area


Yukon-Charley Rivers National Preserve, which is comprised of over 2.5 million acres of remote wilderness, is located in eastern Alaska and is bordered on the east by Yukon Territory, Canada. The preserve straddles the Yukon River for 125 miles, and encompasses the entire 1.1 million acre watershed of the Charley River. Moose and caribou are the primary large prey for wolves in the preserve. Overall moose densities in YUCH are typical for interior Alaska, however, moose densities vary widely within the preserve. Caribou densities can fluctuate dramatically depending on the season and movements of the herd. Dall sheep, although not a primary prey of wolves in YUCH, occur in alpine areas and along the bluffs of the Charley River.

Recently, the objectives of the wolf project have changed. In late 1997, the Alaska Department of Fish and Game (ADFG) began conducting wolf control (sterilization and translocation) of wolf packs inhabiting areas adjacent to YUCH. Wolves inhabiting Yukon-Charley Rivers will be excluded from the wolf control activities. Currently, the primary objectives of this study are to identify wolf packs inhabiting YUCH, monitor their movements, and coordinate with ADFG in order to ensure YUCH wolves are not sterilized or translocated.

The primary objective of this Web Page, however, is to provide background information and preliminary results of the wolf study conducted in Yukon-Charley Rivers National Preserve during 1993-1996.


Methods

This study utilizes radio telemetry, which allows biologists to track and observe radio-collared wolves and their packmates. Wolves are first captured and radioed with collars that emit VHF signals, then tracked and observed by airplanes. The remoteness of the preserve, and lack of roads in the study area necessitates the use of aircraft to capture and track these wolves. This is currently the most efficient way to conduct a study of this kind. Satellite collars and collars equipped with Global Positioning satellite (GPS) technology are presently being developed and tested. These collars utilize satellites to record locations of instrumented animals, providing a means of remotely tracking wolf movements. Conventional VHF collars, however, are still the only means available to consistently and efficiently track and observe wolves in their natural habitat. This allows biologists to collect a variety of information including pack sizes, pup production, kill characteristics, wolf-prey interactions, and wolf mortality rates and causes.


Wolf Capture

In order to begin a radio telemetry study, wolves must first be captured and fitted with radio collars. The most common method for capturing wolves in Alaska utilizes aircraft to find and capture wolves. The capture operation is conducted during the winter when adequate snow cover allows for visually tracking wolves. When fresh tracks are encountered, the airplane follows the tracks to the wolves. The airplane keeps the wolves in visual contact until the capture helicopter arrives to immobilize the animal(s). Wolves are immobilized by a chemical injection which is delivered by a small dart fired by a biologist in the helicopter. Once immobilized, wolves are examined and fitted with a radio collar.


Wolf Examination

Immobilized wolves are examined to determine sex, age, weight, breeding status, and nutritional condition. Blood samples are usually collected for disease screening. Once the examination is complete, a radio collar is fitted around the animal's neck. The wolf is then left alone to sleep off the remaining effects of the immobilizing drug. Wolves are usually found back with their pack within a few hours after their capture.

Radio Telemetry

Small transmitters on the collars emit signals, which are heard (through electronic receivers in the aircraft) as beeps, on distinct frequencies. Each radio collar emits a signal on a distinct frequency, which allows biologists to determine which animal they are tracking. Special receivers are used which scan a range of frequencies during radio tracking flights. When a signal is heard, the scanner is stopped on that frequency and the airplane begins tracking towards the animal. As the airplane gets closer to the radio-collared animal, the signal becomes louder. Once the wolf is observed, we record information such as the number and colors of wolves present, the location, the behavior, vegetation, terrain, and any other interesting details. The wolves are not always observed. Factors such as vegetation, mottled snowcover, and wind turbulence may prevent the pilot/observer team from observing the animal(s).


Wolf Physical Characteristics

During March 1993 to March 1996, 29 wolves were captured and radio collared.


Age (years) estimated by tooth wear (P=pup; less than 1 year old at time of capture);


Weight measurements are in pounds;


Body and tail length measurements are in centimeters;


Canine (usually an upper) measurements are in millimeters;


Fat measurements were subjectively estimated by feeling rib, hips, rump and back areas for fat reserves.


Pack Summaries


Through early 1997, we have monitored 15 associations (lone wolves, pairs or packs) arising from the radio-collared wolves captured throughout the study area. Pack histories for all packs studied within Yukon-Charlery Rivers National Preserve are available.


Territories and Movements

The territory characteristics of wolf packs within Yukon-Charley vary widely. Some pairs and packs appear to maintain 'typical' territorial home ranges, and rarely, if ever, are observed outside of their usual territory. Other packs, however, cover great distances and are regularly located within known home ranges of neighboring packs. Two packs that we have documented traveling extensively within, and outside, the preserve are the Cottonwood and Three Finger packs. During 1993 to 1997, the Cottonwood Pack's home range area averaged 1250 square miles, which is among the highest ever reported for wolves in North America. The Three Finger Pack has not ranged over as large an area as the Cottonwood Pack, but the pack frequently takes extended forays during past winters, spending several months in localized areas as far as 75 miles outside their main territory. The movements of the Three Finger Pack appear to be closely associated with wintering concentrations of the Fortymile Caribou Herd, which currently numbers around 25,000 animals.


The reasons for such variability in movements of wolf packs that live geographically close to each other are not clearly understood. The prey base available to packs is probably the major factor in determining wolf movements. We do know that the moose densities in the Cottonwood and Three Finger packs' home ranges are lower than elsewhere in Yukon-Charley Rivers. Additionally, caribou use of the preserve during the study has been mainly in the southern, mountainous portions of the preserve, which encompasses the Three Finger and Cottonwood packs' home ranges.

The extensive movements of the Three Finger and Cottonwood packs are most likely a result of low moose densities in their territories, which means there are less vulnerable moose available for these wolves to hunt during the winter. Wolves must then either search a larger area for vulnerable moose, and/or prey upon caribou. If caribou are present in large numbers within their territories, the pack can 'stay at home'. If caribou are not abundant nearby, the packs then may have to travel through neighboring pack territories to larger concentrations of caribou. We are currently analyzing our data collected during this study to test these relationships.


Wolf Population

The wolf population in Yukon-Charley Rivers is estimated to have ranged between 42 and 86 wolves during March 1993 and March 1996.


Winter Wolf Behavior

We followed radio-collared wolf packs on a daily basis during two 30-day periods in March 1994 and March 1995, and one 15-day period in November 1994, in an effort to determine activity, prey selection, kill rates, and carcass utilization. Wolves were located every day, and back-tracked to the previous day's location to find kills or pack members that would otherwise be missed. Upon visually locating the wolves, we recorded the pelage color, number and activities (behavior) of individual wolves.


Mortalities and Causes

As of February 1997, there have been twelve known mortalities of wolves radio-collared during this study. Eight of the radio-collared wolf mortalities occured within the preserve. Four of those were harvested legally by trappers or hunters, while the deaths of the remaining four were due to natural, non-human causes (two were killed by other wolves, one died of internal injuries as a result of ingesting porcupine quills, and one died of other, unknow, natural causes). The four radio-collared wolves that died outside the preserve were all considered dispersers, and all were trapped legally.