THE POPULATION DYNAMICS OF NEWFOUNDLAND CARIBOU by . ARTHUR T. BERGERUD B ...

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THE POPULATION DYNAMICS OF NEWFOUNDLAND CARIBOU
by .
ARTHUR T. BERGERUD
B.Sc. Oregon State University, 1953
M.Sc. University of Wisconsin, 1961
A THESIS SUBMITTED IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
in the Department
of
Zoology
We accept this thesis as conforming to the
required standard
THE UNIVERSITY OF BRITISH COLUMBIA
April, 1969
In presenting this thesis in partial fulfilment of the requirements for
an advanced degree at the University of British Columbia, I agree that
the Library shall make it freely available for reference and study.
I further agree tha permission for extensive copying of this thesis
for scholarly purposes may be granted by the Head of my Department or
by his representatives. It is understood that copying or publication
of this thesis for financial gain shall not be allowed without my
written permission.
Department of Zoology
The University of British Columbia
Vancouver 8, Canada
Date September 23, 1969
i
ABSTRACT
The population dynamics of caribou (Rangifer tarandus) on the Island
of Newfoundland were studied 1957 to 1967. Four herds were recognized and
censused: the Northern Peninsula — 450 animals in 1958 and 400 in 1966,
the Avalon Peninsula — 125 in 1957 and 720 In 1967., the'. Humber River —
130 in 1956 and 115 in 1964, and the Interior -- 4600 in 1957 and 6200
animals in 1966. The Island population 1900-1910 was estimated at 40,000
animals. After 1915 these herds rapidly declined and reached a low of
perhaps only 2000 animals by 1930.
The annual rate of increase Cr) of a ll the herds was low. The' Humber
and Northern Peninsula herds showed no increase while the Interior Herd
grew at only 0.044. The Avalon Peninsula Herd showed the greatest rate-
of-increase 1961 to 1967, r= 0.120. The potential r of Newfoundland
caribou is probably greater than 0.30. A herd of caribou introduced to
Brunette Island increased at r=0.352, from 17 to 100 animals in 5 years.
In the Interior Herd, birth rates were high and constant and averaged
0.85 calf per doe 2-years-of-age and older and 0.94 calf per doe 3 years
and older. Natural mortality rates were low beyond 6-months-of-age.
They were 4 per cent for does, yearlings, and calves and 9 per cent for
stags 2-years-of-age and older. The k i ll of stags by hunters was 11 per
cent and reduced the proportion of stags in the population.
The survival of calves to 6-months-of-age was strongly correlated
with growth of populations and appeared the main influence on numbers
(correlation coefficient r=0.922, P<0.01). The mortality of calves in
the first summer was high; an average of 69 per cent died in the Interior
Herd and in the Avalon Peninsula Herd 30 per cent of the calves died.
ii
The major cause of mortality of calves was apparently predation by
lynx (Lynx canadensis). As early as 2 weeks after calving, 27 per cent
of the calves were missing. They were apparently dragged into forest
cover by lynx. Of 114 dead or morbid calves located 74 per cent were
bitten by lynx, escaped and had developed cervical abscesses"; from- in
fections of Pasteurella multocida .
The two major factors limiting populations of caribou in Newfoundland
1900 to 1967 appeared to be lyn« predation of calves and shooting mortality
of adults. Poor recruitment and high loss to hunting probably caused the
decline of the herds 1915 to 1930. The primary factor limiting numbers
in the Interior and Avalon Herds, 1957 to 1967 was lynx predation of calves
in their first summer. Illegal hunting was probably important in the
Northern Peninsula and Humber River herds 1957 to 1967.
i ii
TABLE OF CONTENTS
Page
ABSTRACT i
TABLE OF CONTENTS . i ii
' ACKNOWLEDGEMENTS ' vi
LIST OF FIGURES , v ii
INTRODUCTION 1
METHODS • 4
The Exchange of Animals Between Herds and Populations.......... 4
Historical Research 5
Census 6
Measurement of Birth Rates 8
Measurement of Adult Mortality. 9
Mortality of Calves Overwinter. 9
Time and Amount of Early Mortality of Calves. 10
Determination of Cause of Mortality of Calves from Cervical
Abscesses 13
DISTRIBUTION OF HERDS AND POPULATIONS. 14
SIZE OF CARIBOU HERDS 18
Numbers 1900-1910 . 18
Numbers and Trends 1900-1956. 21
Numbers and Trends 1957-1967 23
BIRTH RATES. 26
Age of Breeding.. 26
Fecundity. 27
ADULT MORTALITY. . 32
Mortality Rates 32
iv
Natural Cause of Death... 34
Differences in Death Rates of Males and Females................ 38
Hunting Mortality of Adults............. 39
Role of Adult Mortality in Population Growth................... 40
DEATH OF CALVES IN WINTER. 43
EARLY MORTALITY OF CALVES. 48
Time and Amount ..................................... 48
Weather in Mortality of Calves. 54
Disease and Predation. . . . .. 55
Rejected Hypotheses of Pasteurella Etiology. 55
Experiments with Lynx to Isolate Pasteurella.............. 58
Predation by Lynx on Calves............................... 62
Experimental Removal of Lynx 64
Sex Vulnerability of Males Calves to Lynx Predation....... 67
Variation in Lynx Predation Between Areas................. 67
Variation in Lynx Predation Between Years................. 71
FACTORS LIMITING POPULATION GROWTH 1900 to 1967. ................ 76
Rate of Population Growth 76
Reproduction in Population Growth.............................. 78
Natural Mortality of Calves • 79
Predation by Lynx on Male Calves 82
The Decline of Caribou 1915-1930. 83
Lynx Predation and the Decline............................ 84
Hunting and the Decline 86
EVOLUTIONARY IMPORTANCE OF PREDATION. 88
Population Limitation by Predation by Wolf..................... 88
V
Lynx Predation in Natural Selection. .. — 91
SUMMARY. . .... 94
LITERATURE CITED. , 96
APPENDIX I TABLES 105
APPENDIX II ANALYSIS OF REPRODUCTIVE TRACTS. 133
BIOGRAPHICAL INFORMATION
\
ACKNOWLEDGMENTS
Through the years a group of dedicated wildlife management officers
walked at my side as we followed the caribou; I will always stand in
the debt of Stephen T. Hall, Michael J. Nolan, Bruce R. Porter, H. Lloyd
Russell, Samuel Kelly and Hainan . Whalen.
I wish to also thank wildlife officers David Lomond, Michael C.
Nurse, Raymond McGrath, Arthur Butt, Robert McNeily, and Michael Walsh
for their assistance. My experiences with pilots Austin Garrett and
Robert G. Winsor will long be remembered. The Canadian Wildlife Service
provided funds in three years and the services of four able summer
assistants, Ernest Stenton, Donald W. Simkin, Donald A. Blood, and
Keith Sandilands. Dr. John M. King journeyed to Newfoundland in 1958
and 1964- to conduct pathological investigations of young calves. Drs.
H.T. Gier and G.B. Marion examined the reproductive tracts of female
caribou. Administrative' assistance was provided by Douglas H. Pimlott,
who originated the study, Harry H. Walters, and Stuart S. Peters.
Assistance in preparing the manuscript was provided by Dr. James F.
Bendell, Dr. Peter A. Larkin, and Dr. I. McT. Cowan. Daniel T. Bergerud
drafted the plates for this report. I wish to acknowledge the assistance
of my wife, Wy. She travelled with me into many of the wilder sections
of the island and was a constant source of inspiration during the ten
years. This paper is dedicated to the memory of Stephen T. Hall. Steve
is gone but he will always be remembered by those of us that had the
privilege to trudge the barrens in his footsteps and share a pot of
coffee in his comradeship.
vii
LIST OF FIGURES
Figure Page
1. The location of caribou 1957-1967. . .. 3
T
2. Percentage of adult females with visible antlers 15
3. Observations of animals subsequent to two migrations
after tagging. 16
4. Number of caribou about 1900.. 19
5. Caribou numbers from aerial census 24
6. The snow profile at Gander 1957-58 and 1958-59. 28
7. Regression of counts of parous does on recruitment. 30
8. Survival curve of male caribou in the interior . 33
9. Caribou observation by hunters compared to recruitment 35
10. The regression of nose bots per doe in June on age and the
regression of nose bots per doe on warble parasites per
doe in June 37
.11. A weak calf observed in March 1959 44
12. The regression of recruitment of yearlings on recruitment
of calves 46
13. Calf survival to 11-months-of-age in the Interior Herd
in 1957 49
14. The survival of calves until October in relation to
mortality In June 51
15. Calf survival in the Interior and Avalon Peninsula herds
until 6-months-of-age 52
16. The percentage of calves in fall in the Interior, Avalon,
and Humber River herds, 1956 to 1967 53
17. The mean weight of calves at birth '56
18. Calves bitten by lynx that developed abscesses 57
v i ii
Figure Page
19. The Pot Hill calving ground..... 59
20. The canine teeth of a lynx skull inserted into four
lesions 60
21. Location of lynx trapped at Middle Ridge.......... 65
22. Male calves strayed farther than female calves from
their dams 68
23. The regression of the percentage of calves in the
Interior Herd in October on the sex ratio of calves
1-4 weeks of age 69
24. The regression of the per cent male yearlings on the
recruitment in June for the Interior Herd.................. 70
25. The survival of calves in eastern and central Newfoundland
on the total lynx harvested.. 73
26. Survival of calves in the Humber River Herd and
production of snowshoe hares 74
27. The regression of the rate-of-increase on survival
of calves until 6-months-of-age .80