AERIAL SURVEYS FOR BEAVER IN MACKENZIE DISTRICT
NORTHWEST TERRITORIES"'
CANADIAN ~iiLDUFE SERVICE, FORT SMI'IH, N. W. To
The purpose of this paper is to describe the methods used
in making extensive aerial surveys for beaver .in wilderness areas and to
indicate briefly what ty:pe of results are obtained and hovr they may be
used.
The beaver, Castor canadensis, still occupies an important
place in the economy of the aborigines (Indians and Eskimos} of the
Mackenzie District, North;~est Territories, and accordinglY,, new or improved
methods of beaver management are constantly being sought. Knowledge of
the distribution and abundance of the beaver is considered to be of prime
importance in establishing seasons and regulating harvests. The area of
the Mackenzie District is 527,000 square miles~ of which about 300,000
square miles are south of timberline. Ground transportation in the area is slow, and the aeroplane was the only possible way in which adequate coverage could be obtainedo o:>i The first experiments with aerial surveys were carried out in Nc.o ~I 1947 and 1948. The object or these early surveys was merely to locate areas
~ in which the beaver population was depleted. In 1949, Kelsall (unpublished 0• l!) LO report in the files of the Canadian Wildlife Service} attempted to locate r-- M M ARLIS -' ALASKA RESOURCES LIBRARY & INFORMATION SERVICES 3150CSTREET, SUITE 100 ANCHORAGE, ALASKA 9950.3 - 2 - and ~let t~e active colonies in two areas in the southern part or the
Mack~zie Jistrict. Kelsall's basic methods have been extended and refined during subsequent surveys in 1951 and 1952. The writer is indebted to
D.R. ~look and E.H. McEwen of the Canadian Wildlife Service who have taken part in aerial surveys and contributed to the development of the· techniques
employed.
03JECT!VES
The two major objectives of the surveys were --
1. TO examine all parts of the Mackenzie District and evaluate
the ;uality of beaver habitat.
2. To dev:elop an index: of abundance which can be used either
to compare the beaver populations of different areas, or to follow the trends
in the beaver population of a given area over a period of time •
.METHODS
Before descrihing methods in detail, it is necessary to point
out certain difficulties which were encountered. First~ because of the large
ness o~ the area, the coverage had to be extensive rather than intensive.
Second, as many of our flights exceeded the normal range of the light aircraft
used, it was necessary to carry gasoline and oil in the cabin of the aero
plane. Certain areas'- e.g. the north shore of Great Bear Lake, could not be
reac~ed even then because gasoline caches are few and widely· scattered in
that area. Third, the standard map sheet is on a scale of eight mil .. to one
inch~ l~t~ough the general quality of these maps is good, it is impossible .•. ..
.. 3 -
to portray the smaller features accurately on this scale. Finally, there
is a scarcity of physiographic data for this entire area. Few elevations
and ~o contours are shown on the standard maps, and the personal knoNledge
of the inY.estigators is therefore importanto
The method of surveying consists in flying along a pre-
arranged route ~~th an observer on each side of the aircraft recording in a
notebook all evidence of the presence of beavero Parallel colwnns ure ruled
on a page in tlle notebook and headed: Time, Feed Beds, Lodges, Dams, Runways,
. Remarks. For each observation, the time is recorded to the nearest minute
and then a stroke is entered in the appropriate column. Where two or more
beaver "signs" are obviously associated - for example: a feed bed {1} in
front of a lodge, the observations are entered in the same lineo However,
if the "signs" are not related· - for example: a lodge in each of two adjacent
lakes, each is entered on·a separate line in the notes. Whenever large,
easily identified landmarks are passed, the time is recorded and the nature
of the reference point is entered in the Remarks column. Brief note& on topography, vegetation, recent fires, or other observations of possible
significance are also made from time to timeo Table 1, which contains part of a specimen page from the field notes, will help to clarify the methodo
(1} This is the term applied almost universally by trappers in the North west Territories .to the mass of sticks ~vhich the beavers store up in advance for winter useo The term is used throughout this paper. - 4
T'o.Jle 1 - ~ract from field not·es for 19 September, 1952, to illustrate the method of recording observations.
Time ~eed Lod.ges Dams Runways Remarks Beds
1438 Crossed Yuk:on-N.W.T. boundary
40 1 1
41 1 1 1
42 1
1 1
43 1 ) ) In same lake. 1 )
1 In a small lake
1 " " " It· Picked up small creek leaving lake. Good habitat. Bordered 44 1 by vlillows therefore visibility - \ goodo Broad. valley. 1 . I 45 1
1
1 1 5 -
Flight lines are plotted to sample the greatest amo~t and variety ot beaver habitat in the area to be covered. Where the beaver habitat consists mainly or streams, a number ot these are followed, and the course 1a planned in such a way that unproductive travel between watersheds is kept to a minimum. The pilot is instructed to tly along one side or the stream so that one observer devotes his tull attention to the stream while the other observer vi~vs some ot the tributaries, and usually, a number or small lakes which lie along the courseo Follovdng the main stream requires the intense concentration ot the observer which produces tatigueo When this occurs, the pilot shirts the aircratt to the other side or the s.tream which reverses the tasks ot the observerso
A course such as this can be tollowed accurately and reflown in a similar manner in subsequent surveyso
Vlhere the beaver habitat consists mainly ot lakes, the same method will otten succeed. Sometimes, however, the lakes are so numerous that they cannot all be portrayed on the map, and as individual lakes cannot be identified it is impossible to :f'ollovt a pre-arranged routa. To avoid this difficulty a technique is being developed whereby an attempt is made to fly along a straight line between recognizable points. At the same time the proportion ot lakes occupied by beaver is noted. The altitude at which the surveys are carried out varies with conditions. Stream courses are usually followed trom an elevation or 500 to
800 teet above the ground o When flying over lake country, however, it has --
heen found th::t beaver n:3ignrt is easily seen from an elevation of 2, 500 feet.
DISCU S.SI m:; JF E'lliODS
S·.qank and Glover (1948} and Crissey .(1949) apparently plotted
their obse:'Vations directly on large scale maps of the areas in Vlest Virginia
and Ne-.'; Yo::-k, respectively, which they surveyed. This_ was tried in the North west Terri :ori es and discarded in favour of the method described for two reasons.
First, the standard maps show insufficient detail, and second, detailed map
reading re:uires the observer to divide his attention betw·een the map and the
ground and may result in beaver "sign" being overlooked. Map reading is,
therefore 1 left to the pilot who follows the flight line marked on the map,
infor:J.s tte observers of their position on request, and points out prominent
landmarks as they are passedo
An examination of Table 1 will show that the field notes may be
readily cc~verted into the number of colonies seen. With few exceptions, each
line in tte notes represents a separate colony. The decision whether two or
more obse~vations represent one colony, or more than one, must be made at the
time and ~~tered in the notes accordinglyo Plotting colonies directly on the map does ~ot relieve the investigator of the responsibility of making similar
decisions,
The colony is the unit of beaver management in the Northwest
Territories. 3ach trapper is entitled to trap, each year, a number of beavers
not to e:xcaed the number of beaver colonies in his area. For this reason all
census fi,;~es are shown as the number of colonies seen, and no attempt. is made
to estima:e t~a total number of beavers they represent. 7
One problem, whic4 is always present when taking a census of beavers, is how to allow for "bank beavers" that live in burrows in theatream bank and do not build lodges. This difficulty has been partly overcome by delaying all survey flights until after Septanber l5o By this date most of the beavers are at work accumulating their winter food supply. These feed beds, or storage piles, are easily seen from the air and are taken as certain evidence of the presence of a.beaver colony.Crissey {epo cito] utilized this fact in making a beaver census in New York. Swank and Glover {op. cit.) carried out their census in April when feed beds were used up or carried away by spring · freshetso They considered that late autumn, after the leaves had fallen, would be a better season for taking a census because of increased visibility, but they apparently overlooked the more important factor of the presence of winter foodo
In certain cases, it is difficult to distinguish between an active and an inactive lodge when flying over themo If a feed bed is present, all doubt is removed. Occasionally, also, a single colony of beavers will maintain more than one lodge, but a single feed bed is the rule.
There are two theoretical advantages to using the proportion method of surveying the type of beaver habitat that consists mainly of lakeso
.First, 'it is highly improbable that a pilot could fly a course exactly as marked with an inadequate map as a guide, or that he could duplicate the transect exactly at another time. Thus, the actual lakes seen may not be identical from one survey to the next. Provided, however, that the sample strips are representative of the area as a whole, and are adequate in size, 8 it is thougtt that a change in the proportion of lakes occupied will be a vulid
indicator of u change in the beaver population 1 even though the transects are not duplicated exactly.
Second, the proportion method eliminates two interrelated variables which are other·•vise difficult to control - elevation above the ground and width of stripo .ill observer flying high can cover a 'iiider strip and survey more lakes than one flying low, but the ratio of occupied to unoccupied lakes seen by each should be the sameo
RESULTS
(lJ Evaluation of Habitat. .J.i. few generalizations may be made at this time regarding grades of beaver habitato The Slave-Liard-Mackenzie River system flows through a level plain known as the :Mackenzie Lov1lands~ which are considered to be a northern extension of the Great Central Plainso In general, the Mackenzie Lov;lands contain much favourable beaver habi tato To the east lies the Laurentian Plateau, composed of Precambrian rockso The topography of the plateau is typically rugged, and conditions have not favoured the formation or accumulation of soil or the development of forest growth, particularly of the deciduous species~ The beaver potential is therefore ~OWe A~ong the western boundary of the plateau, however, there is a zone of variable width ·•.rhere some soil has accumulated and where deciduous trees are reasonably numerouso There are some surprisingly large beaver populations in this narrow zoneo
~lest of the Mackenzie Lowlands lies the Cordilleran Plateau. No surveys have been carried out in this mountainous region as yet.
{2} The Index of abundance. Several uses of' the index of abundance are suggested by the results of surveys in the Fort Providence area in 1949 and 1951, and in the Fort Smith area in 1949 and 1952. Pertinent data are recorded in Table 2o ' I ~·• . .
•' Table 2 - A comparison of beaver "signs" observed on successive surveys in two areas in the southern part of Mackenzie District.. The initial survey in each area vzas carried out in 1949. The Fort Providence area was re~surveyed in 1951 and the Fort Smith area in 1952 ..
- . - --- ,_- Distance First Survey Second Survay Drainage Surveyed Feed Dams Feed Dams Apparent ---- (miles) Beds Beds Trend Fort Providence Area
1 .. Tributary of Kakisa River from the west 18 15 19 2il X2 2. South fork of upper Kakisa River 32 33 29 29 -- 2i .. Stream entering southwest corner of Tathlina Lake 16 1 8 X8
4., Streams entering Kakisa Lake from southeast 32 12 15 27 X2
5o Stream entering southeast corner of Tathlina Lake 13 6 11 li 12 X2
6 .. Redknife River 50 48 30 44 -~
7o I.aferte River 68 20 15 53 X2
8 .. Tributary of Kakisa River From Cameron Hills 29 6 9 12 X2
9o Swede Creek 41 2 9 14 X7
SUBTOTi'.L 299 6 148 145 222
Fort Smith Area
10 .. Tsu Lake to .Tack Lake 53 2i 1 12 9 X4
l1o .Tack Lake to Methleka Lake 14 8 4 16 8 X2
12 .. Thubun Lake· to Rocher RiYer 70 4 5 1.5 6 X2
SUBTOTAL 137 15 10 43 22i 10
The beaver population in the Fort Providence area 'NUS depleted in the early 1940's by a combination of destructive forest fires and heavy trapping pressure. Beavers were given year-round protection by law in 1945o
Trapping was permitted again in 1952. Both surveys were conducted during the period when there was no legal trapping of beavers.
~vo of the major streams in the area, the Redknife River and the south fork of the Kakisa River~ showed no apparent increase between 1949 and 1951, It is concluded therefore that their beaver populations were at saturation levels in 1949, and that the annual increment :probably left the parent streams to repopulate tributaries and other connected '.vaterweys. The indie:es of abundance were found to be 1.4 colonies per mile on the Kakisa and
1"0 colonies per mile on the Redknife. Until further evidence is obtained~ we are assuming as a hypothesis that any value in excess of 1.0 c'olonies per mile, as determined by the aerial method, represents a saturbted population.
The highest index so far obtained in lake country is lo4 colonies p·er mile which is well above saturation level. This was achieved on a transect on >vhich the proportion of occupied lakes was 46c 7 per cent. On the basis of this evidence, it is thought that about 50 per cent occupancy of lakes~ as determined by the aerial method, may represent a saturated population in lake countryo
The rate of increase in an unexploited beaver population is also
indicated in Table 2. On five drainages in the Fort Providence area 9 which apparently contained a fair residue of beaver in 1949, the amount of beaver
"sign" observed doubled in two years. On two streams» which were practically 11 .. devoid of beaver in 1949, explosive increases of seven- or eight-fold. were
j ••• notedo These streams were probably the recipients of surplus beavers from
"'" . . such saturated streams as the Kakisa and Redknife.
On three transects in the Fort Smith' area~ the am'ount of beaver
"sign" observed approximately tripled in three years, in spite of a limited amount o.f. tre..pping. in the 1ibird year (spring of .195Z).
rt is apparent from the foregoing that beaver can increase and spread at a rapid rate.
One further .interesting use of the survey data might be cited.
Fairly extensive surveys were carried out in the lower Mackenzie River basino
A part of the area surveyed was set aside in.l939 as a beaver preserve known as the .Mackenzie Delta Beaver Sanctuary and has been closed to t:tle hunting of . . . . beaver ever since. Flights totalling 170 miles were made.over various parts ' . . ' . of the Sanctuary, and 109 colonies were aeene These yield an index of Oe6 colonies per mile. Outside the Sanctuary, where trapping pressure has been continuous, 235 miles were surveyed and 72 colonies seen tor an index of 0.3 ., colonies per mile.The Sanctuary does not differ essentially in environmental conditions from the remainder of the area. rt is concluded therefore, that the areas open for the trapping of beaver are not at present populated to capacity, ......
. . . The beaver is one of the most important fur-bearing mammals in the Mackenzie District. Knowledge or its distribution and abundance is ' .
12 ..• considered basic to good management. Such knowledge can only be obtained in
this inunense wilderness area with the aid of the aeroplane.
A technique of aerial surveying is described. 1Ul beaver "signs"
are noted nnd used, but greatest reliance is place on locating the winter feed
beds which are taken as certain evidence of the presence of beavers.
The results obtained from aerial surveys in 1949, 1951, and
1952 have been used to maD three grades of beaver habitat. An index of abundance
(colonies per mile} has been used to identify saturated habitats, to study the
rate of ~opulation gain, and to demonstrate the beneficial effects of a
Sat;..:rtuary,
U T.SRATORE CITED
Sv1ank, Wendell G. and Fred A. Glover, 19413.
Beaver Censusing by Airplane. Jour. Wildlife
Mgnt. ,12:2:214, April, 1948.
Crissey, Walter F., 1949. The airplane in fish and
game work. Fish and Wildlife Bulletin No. 4,
New York State Conservation Department.
Presented to the 18th North American ;ilildlife Conference, Washington, D~C .• , March 9, l953o