Contains account of observations and counts made at the Barrow base camp, an 80-acre area, and on the adjacent tundra on the mass movements of the brown lemming. Age composition; male-female ratio; condition of digestive tract, adrenals, reproductive organs, etc., were studied. Causes of this emigration (changes in food supply and cover) as well as similar movements earlier in this region and in Scandinavia are discussed

Thompson, Daniel Q.

English

University of Calgary Journal Hosting

T H E  1 9 5 3  L E M M I N G   E M I G R A T I O N  A T  P O I N T  B A R R O W ,  A L A S K A  I Daniel Q. Thompson* D URING the summers of 1950 to 1954 the writer studied the ecology of the  brown lemming, Lemmus trimcronatus (Richardson), at  the  Arctic Research  Laboratory,  Point  Barrow, A1aska.l Field work was begun one year after the mass die-off of 1949, described by Rausch (1950). The  first indi- cation of recovery  in  the  lemming  population  from  the 1949  die-off was evident in August 1951, when a phase of proliferation began which continued into 1952 and 1953. Early in June 1953 the onset of a phase of declining lemming numbers was marked by a mass movement that  attracted brief but  widespread notice. The present paper describes certain biological characteristics of this interesting population phenomenon. When I arrived at  Barrow  in mid-May 1953, the  tundra was covered with snow about 11 inches deep. Air temperatures varied from 15' to 19°F and essentially winter conditions prevailed until the end of May. Several hundred snap-traps were set under the snow in May to obtain lemmings. Signs of lemmings, clippings and droppings, were found on almost every square foot of the tundra. iMost  of the snow mantle had been undercut by a network of ground-surface  tunnels  made by lemmings  looking for  food (Fig. 1). Later measurements determined that lemmings had clipped over 99 per cent of the  standing  vegetation. On May 3 1 air temperatures rose to 35°F and the  snow  mantle  began to melt rapidly. Prior to this thaw, individual lemmings had made very brief appearances only on the surface of the snow. During the first days of June, however, lemmings began to make prolonged  excursions  over  the  snow  surface. On  June 3 wandering lemmings appeared  in the broad  gravel  streets of Barrow base camp, which stretches for one-half mile along the shore of the Arctic Ocean. Their appearance  aroused  much  interest  among  the oil exploration workers, who had never seen lemmings behaving like this before. Lemming activity on the surface of the snow increased the next day, June 4, and it was apparent that there was mass unrest in the population. Lemmings could be seen scurrying  about  on  the  snow  surface  in all habitats; they continued to appear in the camp streets, and many wandered beyond the camp on to  the arctic ice pack that was grounded along the shoreline. In order to follow  changes  in the density of wandering lemmings, a  daily search of the Barrow camp, an 80-acre area, was begun on June 6.  Each day *Department of Zoology, University of Missouri, Columbia, Missouri. 1This study was supported  by  the US. Office of Naval Research and  the  Arctic Institute of North America. 37 c 38 THE I 9 5 3  LEMMING EMIGRATION AT  POINT BARROW,  ALASKA DEPTH OF SNOW L L  29 3 0  MA i JU Fig. 2. Schematic representation of the phenology of the 1953 mass dispersal of brown lemmings at Point Barrow. THE 1953 LEMMING EMIGRATION .4T POINT BARROW,  ALASKA 39 Fig. 3. Area of abundance of brown lemmings in 1953 shown by stipple. all lemmings sighted throughout the camp were promptly pursued and, with few exceptions,  captured. Each evening  acareful  search was made for lemmings which had sought cover under fuel drums, heavy equipment, and construction  materials  in  storage  on  the  dry,  gravel-surfaced  camp  area.  Since an  unknown  number of lemmings  doubtless  moved through  the  camp  without being  detected, the results  only  indicate the approximate  magnitude  of  emigra- tion from the adjacent tundra, but observations on the rate of movement of individual  lemmings  in the camp area suggest that  at least two-thirds of those entering the area were captured (Fig. 2). The taking of 50 lemmings  on June 6 does not indicate a great influx on that particular day; rather, this striking  number  represents  an  accumulation of lemmings throughout  the  camp area from  June 3 to  June 6 ,  when  the  first  special  effort  was made to capture them. The greater part of the movement  occurred  over  a  period of five days, June 4 to  June 8, during  which 7 3  lemmings were taken on  the 80-acre area, an average of nearly one lemming per acre. The average daily catch was one per 5 acres. Wandering lemmings were seen daily in the camp streets until June 13,  but by then the period of maximum movement had passed. A few emigrants entered camp in the last two weeks of June, and the last lem- ming was captured  in  camp  on  July 1. I t  should be emphasized that the mass movement did not resemble the spectacular migrations reported from Scandinavia (Elton, 1942, p. 21  3 ) .  The lemmings appeared to be engaged in a haphazard dispersal or shuffle,  in  which 40 THE 1953 LEMMING EMIGRATION AT POINT BARROW, ALASKA Fig. 4. Wandering  lemming which had  taken up  temporary  residence  under  a  pile of construction material in the  camp  area. The erect  pelage and rounded body form are typical of lemmings  uffering fiom malnutrition and exposure. 5 June 1953. only  a small and  peripheral  part of the population pushed on to  the ocean ice. On several occasions, I  reconnoitred  the  ice  hoping to find  a  concentration of lemmings that would make mass collecting feasible, but densities of moving animals were too low to encourage efforts to obtain an adequate sample for population analysis. Reports from field observers indicated that the area of movement was confined to the northern tip of the coastal plain. Wandering lemmings were reported as far as 10 miles out  on  the ocean  ice  on  a front extending  approxi- mately 30 miles southwest and southeast along the coast from Point Barrow. I made a reconnaissance in July and  found  from a range  survey  that  the area in which lemmings had reached a peak abundance extended 30 miles inland from Point Barrow to  the vicinity of the Inaru River (Fig. 3). Behaviour of emigrant lemmings From  June 3 to 8, in  nine  periods of 15 to 20 minutes  each throughout  the day,  individual lemmings moving on  the surface of the  snow  were  watched to determine whether  their travel was oriented. In  every  instance  the  pattern of movement was erratic; some lemmings  moved  in  large  circles, some moved in all directions,  and  others  retreated to  the  point of origin. THE I 9 5 3  LEMMING EMIGRATION AT  POINT BARROW, ALASKA 41 Fifteen of the  wandering lemmings were  captured  and  caged at the  Arctic Research  Laboratory for observation. These captives  were  no  more aggressive than dozens of others studied in the previous three years; indeed, they were socially  tolerant to the  extent of huddling  together for warmth. The lemmings that wandered into  the  camp area showed  a  normal e tendency to occupy a home range. They took up temporary residence under a pile of lumber  (Fig. 4) or  other  protective cover  and  could be seen near  this cover for several days. One such transient established himself under a stock- pile of steel pipe, eluding my attempts to capture him for  four days. During this period his only apparent food was an old orange peel and the carcass of another wanderer. Cannibalism was common among wandering lemmings in the sense that live ones fed on the carcasses of those killed by camp vehicles. Comparison of emigrant and tundra1 lemmings T o  compare the density of lemmings in the camp area with that on the tundra, animals on a series of 60 census plots were counted during the period of  mass movement. In the most representative type of tundra  habitat,  an average of 42 lemmings per acre was captured. This contrasts sharply with the  total  catch of one lemming per acre in the camp area, iridicating that  the wanderers represented but a small fraction of the tundra population. The following table shows the comparison between some characteristics of the wandering and the tundra animals. Approximately 4 out of every 5 wandering lemmings captured in the camp or on the ocean ice were males Table 1. Comparison of wandering lemmings with those  captured a t  random  on the tundra. Body, adrenal, and testis weights are reduced to a body  length of 100  mm. Wandering  lemmings  Sample Tmdra lemmings Samplla Sex ratio 374dd/100 99 90 112 dd/lOO 99 458 Age ratio 10  juv./lOO ad. 90 18 juv./lOO ad. 458 Body  weight  (males only) 43 gm./100  mm. 36 49 gm./100  mm. 43 Adrenal  weight  (males only) 9.3 mg./100  mm. 15 8.6 mg./100  mm. 9 Greatest diam. of uterine horn 1.2 mm. 12 2.0 mm. 35 Testis weight 212  mg./100  mm. 24 253 mg./100  mm. 31 whereas the sex ratio was approximately one to one on the tundra. I t  seems that there were relatively fewer juveniles2 among the emigrant population; however,  this  difference is not significant  when  tested by  the chi-square method. The animals in which the body weight, adrenal weight, diameter of uterine  horn,  and testis weight  were measured were  taken at  random from the same size classes, and were captured on the same dates. Comparison of ‘The  “tundra” lemmings were captured one mile inland. Dispersal and  changes of habitat were probably occurring when  the sample was taken. 2Lemmings below 120 mm. in various stages of juvenile pelage are called juveniles; lemmings measuring 120 mm. or more are designated as adults. 42 THE I 9  j 3 LEMMING EMIGRATION .4T POINT BARROW,  ALASKA body-weight with body-length  indicates that  the wanderers  weighed  approxi- mately 20 per  cent less than  lemmings on  the  tundra.  Empty alimentary tracts  probably  accounted  for  much  of  this  difference, for the emigrants carried a normal amount of subcutaneous fat. Heavier adrenal gland weights are indicated for wandering lemmings, but the difference is not significant.l The  summer  reproductive season had begun at  the time of the mass dispersal. Pregnancies  were not  yet visible in  the females; therefore  the  diameter of the uterine  horn was used as an indicator of reproductive  activity.  These measure- ments  show that  the uterine  horn  diameters of emigrant females were  smaller than those of females of the same mean total length captured on the tundra over the same span of days. Likewise, the testis weights of emigrant males were  considerably less than  those of comparable tundra males. The differences between body weight, testis weight, and uterine horn size of the wandering and tundra lemmings were so great that they could be expected to  differ this much by chance alone less than two times out of a hundred;2 they can therefore be considered  real  differences. Causes of emigration Changes in available food and cover were the only factors that could be correlated with  the beginning and end of mass unrest  in the lemming  popula- tion. As the snow mantle melted and the winter tunnels collapsed, the lem- mings were  forced to venture on to the  scattered  bare  patches of tundra  (Fig. S), and were pitilessly exposed to weather and to avian predators; the newly uncovered tundra was still frozen, preventing the lemmings from using old burrows or forming new tunnels in the surface vegetation. By June 10 only ten per cent of the snow cover remained; the rest of the tundra had thawed sufficiently to allow the lemmings to use old burrows which were free of water,  and to make new  tunnels  in the moss carpet  which  underlies  the standing  vegetation  (Fig. 6). In addition  more  forage  was available as the moss carpet thawed, and the lemmings were able to dig out the crowns of grasses and sedges (chiefly Dupontia, Eriophorurn, and Carex spp.) which had previously been frozen in the sod. The growing season was also underway and each day added a millimetre of new growth to the grasses and sedges. By June 13 the surface thaw averaged three inches on hummocks and one inch in polygonal depressions, and the height of new green growth averaged five millimetres  in the depressions. The lemming  movement had subsided. As a means for relieving population pressure, the mass dispersal would seem to have had only a minor effect. Mortality from predators was a far more potent mechanism of population control. This was emphasized by the fact that an average of 11 dead lemmings per acre was found in 30 sample plots  on the  tundra. 1tz.0349; P= > .90. ZBody weight, tz3.101, P=<.Ol; testis weight, t=2.426, P=<.02; uterine horn size, t=3.125, P=<.O1. 44 THE I953 LEMMING EMIGRATION AT  POINT BARROW,  ALASKA Frequency of emigration Clarke (1940, p. 69) and Elton (1942, p. 469) reviewed the records of the emigrations of collared (Dicrostonyx) and brown lemmings in the Cana- dian Arctic. A4ore recently, Gavin (1945, pp. 229-30) reported an emigration of brown lemmings at the mouth of the Perry River in early May 1937. H e  noted that the movement continued for ten days and nights in an easterly direction,  and  estimated densities of one  lemming  per  square  yard. Gavin also refers to an earlier mass movement-southward-which he witnessed on King William Island in 1934; he considers this movement to  be of a much lesser magnitude than that at Perry River in 1937. Clarke (1940, p. 69) and Elton (1942, p. 469) point out that although emigrations are associated with peaks in population, the  number of emigrations are few  in comparison to  the records of peak abundance. The situation seems to be much the same in the Alaskan Arctic. Brower (1942, p. 123) recalls a mass movement of great proportions at Point Barrow in  late May 1888. H e  describes the  tundra as being black with lemmings coming from the southeast and moving seaward on a 10-mile front;  the main body took four days to pass the whaling station. Harmon Helmerick (J. W. Bee, personal  communication)  saw lemmings on  the  Arctic  Ocean ice 10 miles north of Pingok Island (nezr Beechey Point) in April and May 1946. This is an interesting observation, since it coincides with the peak lemming year of 1946 at Point Barrow. Stuck (1920, p. 227),  describing  lemming  movements in the Alaskan interior,  writes of a mass of floating,  dead, brown lemmings in  the Yukon River about 10  miles from the Canadian boundary in 1918.  Stuck's trail  companion, Walter  Howard, had seen a similar movement  in  earlier years. On  the Alaskan Arctic Slope the lemming is of no direct importance in the native economy  and  therefore receives little  attention  from  the local Eskimo. Nevertheless,  recollections of five reliable native  observers, whom I  interviewed,  were  in  substantial  agreement  that mass  movements, such as that of June 1953, have occurred  slightly  more  often  than  once  each decade. That is to say,  Eskimo  in  middle age recalled having seen two  or  three such  spring movements in the past two decades. One of these observers had lived inland for many years and remembered a movement of brown lemmings in autumn. In comparison with  the  brown lemmings in  arctic Alaska, the emigrations of the Norway lemming ( L e m u s  l e m u s )  in Scandinavia (Collett, 1895; Elton, 1942; Wildhagen, 1952) and  Finnish  Lapland (Pleske, 1884; Kalela, 1949) are  much longer in duration,  more  frequent  in  occurrence,  and involve greater densities of moving animals. The migrations of the Norway lem- mings are also more uniformly oriented as to direction of travel and involve greater distances. Several possible explanations can be found for these differences. First, there is great contrast in the topography of the two ranges. The lemming range in Norway is a high plateau which is intricately dissected by valleys and fiords. As Elton (1942, p. 216) and others suggest, any lemmings moving THE 19s 3 LEMMING EMIGRATION AT POINT BARROW, ALASKA 4s over  this  terrain  would  soon be trapped  in  one of these valleys and  funnelled into  the  fiords. The arctic coastal plain at Barrow, on the  other  hand, is a  flat shelf which scarcely rises above sea level, and would have no appreciable effect  in  orienting the movements of a wandering animal population.  Secondly, the habitats within the two lemming ranges are quite different. The  Alaskan arctic coastal plain is a monotonous expanse of grass, sedge, and lichen; in contrast the northern European range is a patchwork of altitudinally zoned vegetation  in  which the subalpine  zone is the  preferred  lemming  range. Thirdly, innate differences in the behaviour of the two lemmings exist. For example, the  Norway lemming is nocturnal  (Collett,  1895),  whereas the brown  lemming at  Point  Barrow is active a t  all hours from  June  until September. This may  be of no  particular  significance as regards the inclination to emigrate, but it does suggest rather sharp behaviour differences between the  two species. Kalela (1949)  regarded the “migrations” of the lemmings in  Finnish Lapland as a  peripheral  manifestation of a  much  greater  internal  shuffle  within the major lemming range. At Point Barrow during the 1953 mass movement of lemmings, a  relatively small fraction  only of the  tundra population  actually wandered out  on  to  the  arctic ice pack. I t  seems that these peripheral move- ments may also indicate an extensive internal shuffle within the coastal area. Population pressure was relieved much less by the mass dispersal than by mortality from predators, and the exodus of emigrants dropped off sharply as the surface of the tundra thawed, making food and cover available. In general, mass movements of the  brown  lemming seem to be less intense and less frequent than those reported for the Norway lemming in northern Europe. References Brower, C. D. 1942. ‘Fifty  years  below zero’. New York: viii -k 310 pp. Clarke, C. H. D. 1940. ‘A biological investigation of the Thelon Game Sanctuary’. Bull. Collen, R. 1895. ‘Myodes lemmus, its habits and migrations in Norway’. Cbristiania Vi&- Elton, C. 1942. ‘Voles, mice  and lemmings’. Oxford: 496 pp. Gavin, A. 1945. “Notes on mammals observed in the Perry River district, Queen Maud Sea”. J .  Mammal. Vol. 26, pp. 226-30. Kalela, 0. 1949. “Uber Fjeldlemming-Invasionen und andere i r reguke  Tierwanderungen mit einer Ubersicht der Kleinna ergradationen in Finnisch-Lappland 1900-1948”. Ann. 2001. SOC. Vanamo, Vol. 13, iv -f 90 pp. Pleske, T. 1884. “Ubersicht der Saugethiere  und  Vogel der Kola-Halbinsel. Theil 1. Saugethiere” in ‘Beitrage zur Kenntniss des Russischen Reiches  und der angrezenden Lander Asiens’. Ser. 2, Vol. 7, St. Petersburg: 212 p. Rausch, R. 1950. “Observations on a cyclic decline o P lemmings (Lemmus) on the arctic coast of Alaska during the spring of 1949”. Arctic, Vol. 3,  pp. 166-77. Stuck, H. 1920. ‘A winter circuit of our arctic coast; a narrative of a journey with dog- sleds around the entire arctic coast of Alaska’. New York: x + 360 pp. Wildhagen, A. 1952. ‘Om vekslingene i bestanden av smagnagere i norge 1871-1949’. Statens Viltznzders@kelser, Drammen: 192 pp. Nut. Mus. Can. No. 96, iv + 135 pp. Selsk. Forh. No. 3,  62 pp. 

The 1953 Lemming Emigration at Point Barrow, Alaska

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The 1953 Lemming Emigration at Point Barrow, Alaska

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