The E i g h t N o r t h American Caribou W o r k s h o p ,
Whitehorse, Y u k o n , Canada,
2 0 - 2 4 A p r i l , 1998.
Predation rate by wolves on the Porcupine caribou herd
Robert D . Hayes & D o n a l d E . Russell
1
1
2
2
Y u k o n Department of Renewable Resources, B o x 5429, Haines J u n c t i o n , Y u k o n Y O B 1L0, Canada
([email protected]).
Canadian W i l d l i f e Service, 91782 A l a s k a H i g h w a y , Whitehorse, Y u k o n Y 1 A 5 B 7 , Canada ([email protected].).
Abstract: Large migratory catibou {Rangifer tarandus) herds i n the A r c t i c tend to be cyclic, and population trends ate
mainly driven by changes i n forage or weather events, not by predation. W e estimated daily k i l l rate by wolves on adult
caribou i n winter, then constructed a time and space dependent model to estimate annual w o l f (Canis lupus) predation
rate
(P annual)
on adult Porcupine catibou. O u r model adjusts predation seasonally depending o n caribou d i s t r i b u t i o n :
Pannual = IKdaUy*
W
*Ap(2)*Dp.
In our model we assumed that wolves k i l l e d adult caribou at a constant rate
(Kda,iy,
our studies and elsewhere; that w o l f density (W) doubled to 6 wolves 1000 k m
2 1
0.08 caribou w o l f day ) based on
1
on a l l seasonal ranges; and that the
average area occupied by the Porcupine caribou herd ( P C H ) i n eight seasonal life cycle periods (Dp ) was t w o times
gteater than the area described by the outer boundaries of telemetry data (Ap /1000 k m ) . Results from our model pro2
jected that wolves k i l l about 7600 adult caribou each year, regardless of herd size. T h e model estimated that wolves
removed 5.8 to 7.4% of adult caribou as the herd declined i n the 1990s.
O u r predation rate model supports the hypothesis of Bergerud that spacing away by caribou is an effective antipredatory strategy that greatly reduces w o l f predation on adult caribou i n the spring and summer.
Key words: Canis lupus, k i l l rate, Rangifer tarandus, Y u k o n .
Rangifer, S p e c i a l
Introduction
d e v e l o p q u a n t i t a t i v e m o d e l s for e s t i m a t i n g
Migratory barren-ground
dus)
Issue N o . 1 2 , 5 1 - 5 8
caribou
herds s h o w w i d e p o p u l a t i o n
{Rangifer taranfluctuations
have been e x p l a i n e d b y changes i n forage,
preda-
t i o n rates o n m i g r a t o r y c a r i b o u herds.
that
I n t h i s paper, w e present data o n w i n t e r k i l l rate
climate,
by wolves o n adult caribou w h e n P o r c u p i n e n u m -
p r e d a t i o n a n d harvest (as r e v i e w e d i n K l e i n , 1 9 9 1 ) .
bers were h i g h . W e c o n s t r u c t
V a r i o u s researchers have p o i n t e d o u t t h e d i f f i c u l t y
rate m o d e l that i n c l u d e s constants f o r w o l f d e n s i t y
of separating
a n d k i l l rate that are a p p l i e d to c h a n g i n g
interactions
of forage-climate-preda-
a simple predation
seasonal
t i o n w h e n t r y i n g t o d e t e r m i n e t h e cause o f c h a n g e
range use a n d densities o f c a r i b o u . W e discuss w h y
in caribou abundance (Gauthier & Theberge, 1 9 8 6 ;
p r e d a t i o n b y w o l v e s is n o t t h e m a i n force l i m i t i n g
Thomas, 1995; A d a m s
N a t i o n a l Research
wolf
etal.,
Council,
{Canis lupus)
1995; Bergerud, 1996;
the size o f the P o r c u p i n e h e r d i n t h e 1 9 9 0 s .
1 9 9 7 ) . T h e effects o f
predation on migratory
barren-
Study area
g r o u n d c a r i b o u were p o o r l y u n d e r s t o o d i n t h e past,
W e c o n d u c t e d o u r p r e d a t i o n rate research i n 1 9 8 9
m a i n l y because arctic w o l v e s were m i g r a t o r y a n d
in
difficult
&
R i c h a r d s o n M o u n t a i n s . P r e d a t i o n studies t h a t w i n -
J a m e s , 1 9 8 2 ) . R e c e n t studies i n arctic A l a s k a ( D a l e
tet were p a r t o f a larger s t u d y o f w o l f e c o l o g y c o n -
et al,
to follow
(Kuyt,
1 9 9 4 ; B a l l a r d et al,
1 9 7 2 ; Stephenson
1 9 9 7 ) a n d C a n a d a (P.
C l a r k s o n , G o v e r n m e n t o f the N o r t h w e s t T e r r i t o r i e s ,
u n p u b l . ; R . Hayes, unpubl.) provide new data about
a
14 4 5 0
km
ducted between
2
study
area
i n the N o r t h e r n
1987 a n d 1993 i n the northern
Y u k o n (R. Hayes, unpubl.).
Our
s t u d y area s t r a d d l e d the n o r t h e r n b o u n d a r y
a r c t i c w o l f m o v e m e n t s , range use a n d t h e i r k i l l i n g
of the Y u k o n a n d N o r t h w e s t Territories
rates o n c a r i b o u . T h e s e data were r e q u i r e d t h e i r t o
The
Rangifer,
S p e c i a l Issue N o . 1 2 , 2 0 0 0
main
study
area
included
the
(NWT).
Northern
51
R i c h a r d s o n M o u n t a i n s a n d the eastern p a r t o f the
p e r i o d s a l o n g the Y u k o n C o a s t a l P l a i n . T h e
Y u k o n C o a s t a l P l a i n . T h e s t u d y area was b o u n d e d
t h e n m i g r a t e s t o v a r i o u s t r a d i t i o n a l w i n t e r i n g areas
b y the
in
B l o w and B e l l Rivers
to
the
West,
the
the
Richardson
Mountains,
Eagle
herd
Plains,
M a c K e n z i e D e l t a to the E a s t , the R a t R i v e r to the
O g i l i v i e M o u n t a i n s and southern Brooks Range i n
S o u t h , a n d the A r c t i c C o a s t to the N o r t h . T h e s t u d y
A l a s k a . D u r i n g the w i n t e r 1 9 8 8 - 8 9 , a large o f n u m -
area
ber o f P o r c u p i n e c a r i b o u w i n t e r e d i n o u r s t u d y area.
included
Aklavik
two
communities
(population
801)
and
in
Fort
the
NWT,
MacPherson
(878, Statistics Canada 1996).
M o o s e d e n s i t y is l o w a n d m o s t m o o s e w i n t e r i n
the l i m i t e d r i p a r i a n forests a l o n g the
W e s t u d i e d w i n t e r k i l l rate across 3
ecoregions
(Smits,
Bell River
1 9 9 1 ) . F e w m o o s e w i n t e r e d i n the
north
( O s w a l d & S e n y k , 1 9 7 7 ) : the N o r t h e r n M o u n t a i n s ,
slope d r a i n a g e s , w h e r e we c o n d u c t e d m o s t o f p r e d a -
the C o a s t a l P l a i n , a n d B e r r y C r e e k . W e have p a r a -
tion
phrased descriptions of physiography and
( 1 9 8 7 ) c o u n t e d a b o u t 9 0 0 sheep i n 1 9 8 6 .
vegeta-
studies.
In
the
same area,
B a r i c h e l l o et
t i o n f r o m O s w a l d a n d S e n y k ( 1 9 7 7 ) . M o s t o f the
( Y u k o n Fish and W i l d l . Br., unpubl.) counted
n o r t h e r n Y u k o n was a g l a c i a l r e f u g i a t h a t n o w lies
m u s k o x e n o n the Y u k o n C o a s t a l P l a i n i n
within
m a i n l y to the west o f o u r s t u d y area.
the
Northern
zone
of c o n t i n u o u s
Mountains
permafrost.
The
includes
the
Ecoregion
al.
C . Smits
157
1993,
O t h e r large predators i n the s t u d y area i n c l u d e
C o a s t a l P l a i n E c o r e g i o n lies b e l o w 1 5 0 m asl. T h e
(Ursus arctos) ( N a g y , 1 9 9 0 ) , b l a c k bear
(Ursus americanus) i n the t a i g a , l y n x (Lynx canadensis)
a n d w o l v e r i n e (Gulo gulo). A r c t i c fox (Alopex lagopus
eastern p a r t o f the Y u k o n C o a s t a l P l a i n i n c l u d e f o u r
innuitus) are r e s r r i c t e d to coastal areas ( Y o u n g m a n ,
R i c h a r d s o n M o u n t a i n s w h e r e elevations
exceed 1 5 0 0
commonly
m above sea l e v e l (asl). M o s t o f the
b r o w n bear
(Corvus corax)
watersheds: the P e e l , B i g F i s h , a n d B l o w R i v e r s a n d
1975). Ravens
Rapid
t h a t c o m p e t e w i t h w o l v e s at k i l l s .
Creek.
The
Richardson
Mountains
are
are the m a i n scavengers
d r a i n e d b y the W i l l o w , R a t , F i s h a n d B e l l R i v e r s .
T h e B e r r y C r e e k E c o r e g i o n f o r m s the
southwest-
ern f l a n k o f the s t u d y area, a n d ranges f r o m flat to
Materials and m e t h o d s
gently r o l l i n g terrain w i t h uplands below 600
W e u s e d r a d i o t e l e m e t r y t e c h n i q u e s ( M e c h , 1974)
m
asl, a n d v a l l e y s b e l o w 3 0 0 m asl. T h e area is d r a i n e d
b y the B e l l , P o r c u p i n e , E a g l e a n d D r i f t w o o d R i v e r s .
M o s t o f the s t u d y area is o p e n tree-less t u n d r a ,
s t u d y p r e d a t i o n b e h a v i o u r o f w o l v e s . A f t e r we
located a w o l f pack by
fixed-wing
to
first
a i r c r a f t , we d i s -
patched a helicopter (Bell 2 0 6 B ) and i m m o b i l i z e d
except a l o n g p r o t e c t e d valleys w h e r e there are i s o -
wolf
(Picea mariana), w h i t e
spruce (Picea glauca) a n d b a l s a m p o p l a r (Populus balsamifera). T h e m a i n v e g e t a t i o n is sedge (Carex sp.)
a n d c o t t o n g r a s s (Eriophorum sp.) t u s s o c k t u n d r a .
D w a r f b i r c h (Betula sp.), w i l l o w (Salix sp.) a n d alder
(Alnus sp.) are f o u n d o n w a r m e r sites. C o o l e r sites
C h e m i c a l and E q u i p . C o . , Douglasville, Ga.) equip-
l a t e d stands o f b l a c k spruce
support
ericaecious
shrubs,
willows and
various
pack
members
with
Capchur
(Palmer
m e n t . M o s t w o l v e s received a dose o f Z o l e t i l ( A . H .
R o b i n s ) at 8 m g / k g , based o n a n e s t i m a t e d average
w o l f w e i g h t of 4 0
VHF
radio-collars
k g . W e attached
on
wolves
conventional
(Telonics,
Mesa,
Arizona).
W e s t u d i e d k i l l rates b y m o n i t o r i n g the d a i l y
forbs. R i p a r i a n spruce a n d b a l s a m p o p l a r forests are
activities
f o u n d o n the B e l l , D r i f t w o o d a n d P o r c u p i n e R i v e r s .
M a r c h to 16 A p r i l 1 9 8 9 f r o m a M a u l e L R 7 aircraft.
Shrub birch and w i l l o w dominate most
W e d e f i n e d p a c k size as the m e a n n u m b e r o f w o l v e s
a n d the forest understory.
Sedge a n d
openings
cottongrass
tussocks d o m i n a t e m o s t p o o r l y d r a i n e d o p e n areas.
Four
ungulate
species i n h a b i t
the
study
area:
o f seven
radio-collared
packs
from
seen i n the p e r i o d (Messier, 1 9 9 4 ; D a l e et al,
1995;
H a y e s et al,
23
1994;
2 0 0 0 ) . W e d e f i n e d k i l l rate as
the n u m b e r of c a r i b o u k i l l e d p e r w o l f p e r day. T h e
(Alces alces), D a l l sheep (Ovis dalli) t o t a l b i o m a s s (kg) o f c a r i b o u k i l l e d was
muskoxen
(Ovibus moschatus). T h e P C H m e a s u r e c o n s u m p t i o n rates o f w o l v e s . B a s e d
caribou, moose
used
and
o n data
increased f r o m 135 0 0 0 c a r i b o u i n 1 9 8 3 t o 1 7 8
in 1989;
(k).
an a n n u a l f i n i t e rate o f increase o f
Between
about
1989
160 000
and 1992
c a r i b o u (X=
000
1.048
f r o m S k o o g ( 1 9 6 8 ) w e e s t i m a t e d the l i v e w e i g h t s o f
adult
caribou:
male
107
k g , female
79
kg
and
the h e r d d e c l i n e d to
u n k n o w n c a r i b o u 8 6 k g . W e a s s u m e d the c o n s u m -
0.965, Fancy
able
et
al,
1 9 9 4 ) . T h e P C H t r a d i t i o n a l l y calves o n or near the
A r c t i c N a t i o n a l W i l d l i f e Refuge
in
northeastern
A l a s k a , t h e n spends the p o s t - c a l v i n g a n d
52
to
summer
biomass
live
weight
E a c h day, we l o c a t e d s i x w o l f packs (2-6
wolves)
( B a l l a r d et al,
was
1987;
75%
of
caribou
1997).
once i n the m o r n i n g ( 9 : 0 0 - 1 2 : 0 0 h ) . W e l o c a t e d the
Rangifer,
S p e c i a l Issue N o . 12, 2 0 0 0
Table 1. K i l l i n g rates by wolves on caribou i n our study, M a r c h and A p r i l
P a c k name
Blow River
Bell River
B l o w R.
N o . of
Total
N o . caribou
K g . caribou
K g . caribou
Pack
Period
N o . wolf
caribou
kg.
killed/wolf/
killed/wolf/
consumed/
size
(days)
days
killed
killed
day
day
wolf/day
12
25
300
9
776
0.03
2.59
1.94
2
7
14
3
274
0.21
19.57
14.68
3
6
18
2
195
0.11
10.83
8.13
Rat River
6
25
150
4
406
0.03
2.71
2.03
R a t R i v e r II
3
24
72
1
109
0.01
1.51
1.14
Trail River
3
14
42
2
195
0.05
4.64
3.48
Two
2
19
38
2
172
0.05
4.53
3.39
12
450
1989.
Ocean
member
B l o w R i v e r p a c k t w i c e a day, i n
the
W e a s s u m e d t h a t w o l v e s k i l l e d a d u l t c a r i b o u at a
t h a t w o l f d e n s i t y (W)
m o r n i n g a n d e v e n i n g ( 1 8 : 0 0 to 2 2 : 0 0 h). W e c o m -
c o n s t a n t rate (KMI );
p a r e d k i l l rate for m o r n i n g - o n l y s i g h t i n g s o f B l o w
to 6 w o l v e s p e r 1 0 0 0 k m o n a l l seasonal ranges; a n d
}
doubled
2
R i v e r w o l v e s , a n d for the c o m b i n e d m o r n i n g a n d
t h a t t h e average area o c c u p i e d b y the P C H each year
e v e n i n g t o test for t e m p o r a l bias i n o u r a b i l i t y to
i n e i g h t seasonal l i f e c y c l e p e r i o d s (Dp , see T a b l e
detect c a r i b o u k i l l s b y l o c a r i n g o t h e r p a c k s
was t w i c e as large as the average area d e s c r i b e d b y
once
2)
the o u t e r b o u n d a r i e s o f satellite t e l e m e t r y d a t a (Ap
daily.
M o s t p a c k s t r a v e l e d i n the n o r t h slope d r a i n a g e s
/1000 k m ; I n t . P o r c u p i n e C a r i b o u B o a r d 1 9 9 3 ) .
2
where snow conditions were heavily w i n d b l o w n i n
1989- W o l v e s a n d t h e i r p r e y carcasses w e r e d i f f i c u l t
to see because o f the c o n t r a s t i n g
mosaic
of open
Results
g r o u n d a n d s n o w fields. S n o w was u s u a l l y too w i n d -
Kill rate by wolves
packed
W e f o l l o w e d the d a i l y a c t i v i t i e s o f seven w o l f p a c k s
to
activities
backtrack
between
wolves
location
to
determine
points.
We
their
located
radio-collared wolves, then systematically
searched
for 17.1
± 3.1
( s t a n d a r d error o f t h e m e a n ) days
( T a b l e 1). T r a v e l i n g p a c k size was 4 . 4
± 1.4,
rang-
for a n y k i l l s i n a 2-3 k m area, u n t i l w e e i t h e r f o u n d
ing
k i l l s or w e were c o n f i d e n t w o l v e s h a d n o t m a d e a
w o l f - k i l l e d c a r i b o u a n d w e e x a m i n e d 13 carcasses i n
k i l l nearby.
s i t u . A l l were a d u l t s ( 8 M , 5F). T h e m e a n age
2
W e e s t i m a t e d a n n u a l predation rate as the p r o p o r -
f r o m 2 to 12 w o l v e s per p a c k . W e f o u n d
k i l l e d c a r i b o u was 6.1
± 0.7 y e a r s - o l d . T h e
23
of
lowest
tion of adult Porcupine caribou k i l l e d by wolves. To
k i l l rate was for w o l v e s i n the R a t R i v e r II
determine
( T a b l e 1) w h i c h scavenged f r o m m a n y h u n t e r k i l l s
the
rate
of
wolf
predation
on
P o r c u p i n e h e r d w e needed a m o d e l t h a t was
o n reasonable e c o l o g i c a l a s s u m p t i o n s a b o u t
and
c a r i b o u . F r o m w o l f surveys
Y u k o n ( R . H a y e s et al,
based
wolves
northern
u n p u b l . ) a n d i n o t h e r parts
o f the P C H range ( S t e p h e n s o n ,
we estimated
i n the
the
1994; C a r r o l , 1994),
a mean density of about
3 wolves/
pack
i n the area. A f t e r e x c l u d i n g this p a c k , w e e s t i m a t e d
the w o l f k i l l rate was 0.08
p e r w o l f ; or 7.5
± 0.03
c a r i b o u per day
± 2.7 k g o f c a r i b o u k i l l e d per w o l f
p e r day. W o l v e s c o n s u m e d
5.6
± 2.0
kg
caribou
each d a y i n w i n r e r .
W e d i d not
find
a difference
i n the n u m b e r
of
1 0 0 0 k m , g i v i n g a p o p u l a t i o n of 7 2 5 w o l v e s i n the
k i l l s seen for m o r n i n g - o n l y s i g h t i n g s o f B l o w R i v e r
e n t i r e range o f the h e r d . N o t a l l w o l v e s have c a r i b o u
wolves compared
a v a i l a b l e to t h e m each year, a n d the n u m b e r
musr
e v e n i n g s i g h t i n g s (n = 9 k i l l s , 0 . 3 6 c a r i b o u per p a c k
v a r y w i t h the area c a r i b o u o c c u p y d u r i n g d i f f e r e n t
per day). W e conclude that twice d a i l y locations d i d
2
phases o f t h e i r a n n u a l l i f e cycle
(e.g.,
spring migra-
t i o n , c a l v i n g , w i n t e r ) . T h i s means that w e
cannot
e s t i m a t e p r e d a t i o n rate b y s i m p l y a p p l y i n g a
kill
d a i l y rate to the e n t i r e
account
for c h a n g i n g d i s t r i b u t i o n s o f c a r i b o u a n d
m o d e l for e s t i m a t i n g a n n u a l p r e d a t i o n
Pannual = Z K d a i . y * W
Rangifer,
*Ap(2)*Dp.
Special Issue N o . 12, 2 0 0 0
the
combined
morning
i m p r o v e o u r a b i l i t y to d e t e c t k i l l s
and
made
by
study packs.
fixed
w o l f population. To
w o l v e s , b o t h i n space a n d t i m e , w e c o n s t r u c t e d
not
to
the
(J?annual)'.
Predation rate by wolves
Based
on a daily k i l l
(Kjaiiy),
o u r m o d e l p r o j e c t e d that w o l v e s k i l l e d 7 6 0 0
rate o f 0 . 0 8
adulr
caribou
a d u l t c a r i b o u f r o m the P o r c u p i n e h e r d each
year.
A b o u t 8 4 % o f the a d u l t s were k i l l e d d u r i n g f a l l a n d
53
Table 2. Variables and values used in m o d e l i n g annual w o l f predation rare on Porcupine caribou herd. Values for D , a n d
;
A -were provided by Inr. Porcupine Caribou Board (1993).
p
W
Kdaity
A r e a of A v a i l a b l e
Wolf
D a i l y K i l l Rate by
Caribou
Density
AP
C a r i b o u l i f e cycle
Mean Area
N o . of Days
Period
1
_
1
Wolves on Caribou
2
120
25.9
51.8
6
0.08
62
27.4
54.8
6
0.08
3. C a l v i n g
11
8.8
17.6
6
0.08
4.
22
7.5
15
6
0.08
5. E a r l y S u m m e r
16
3.4
6.8
6
0.08
6. M i d S u m m e r
22
5.99
11.98
6
0.08
1. L a t e W i n t e r
2.
Spring
Post C a l v i n g
7. L a t e S u m m e r
and Fall M i g r a t i o n
62
12.8
25.6
6
0.08
R u t and Late F a l l
50
37.1
74.2
6
0.08
8.
1
i n 1000 k m units.
2
number of wolves per 1000 k m .
2
w i n t e r (Table 2, F i g . 1) w h e n c a r i b o u use the largest
areas, a l l o w i n g m o r e w o l v e s to c o n c e n t r a t e o n f a l l
a n d w i n t e r range. T h e
remaining
16%
of adults
were t a k e n i n s p r i n g a n d f a l l w h e n the herd's range
is s u b s t a n t i a l l y c o m p r e s s e d , a n d t h e i r a v a i l a b i l i t y to
wolves is l o w e s t (Table 2 , F i g . 1).
Because o u r p r e d a t i o n m o d e l does n o t d e p e n d o n
h e r d size, w e a p p l i e d i t to P o r c u p i n e census d a t a i n
1992,
1 9 9 4 a n d 1 9 9 8 . E a c h year the h e r d was c e n -
sused
with
photo
counts
in July
(D.
Russell,
u n p u b l . ) . T h e p e r c e n t calves was a n n u a l l y e s t i m a t e d
in M a r c h ( D . Cooley, Y u k o n F i s h and W i l d l .
unpubl.).
Our
model
estimated
that
wolves
r e m o v e d 5 . 8 % of a d u l t s i n 1 9 9 2 w h e n h e r d size was
160
000;
000;
6.3%
and 7.4%
i n 1994
w h e n h e r d size was
w h e n h e r d size f e l l to 1 2 9
000
1
Br.,
2
3
4
5
Seasonal Period
6
7
S
F i g . 1. Seasonal predation rate by wolves on P C H based
on model. Seasonal periods correspond w i t h n u m -
152
bers shown on Table 2.
in
1998.
required
for
Discussion
Peterson,
1993)
Kill rate by wolves
reproduction (Mech,
T h e d a i l y k i l l rate o f o u r s t u d y w o l v e s was s i m i l a r
rates were r e c o r d e d for arctic w o l v e s i n n o r t h w e s t -
to c a r i b o u - k i l l i n g w o l v e s i n A l a s k a ( 0 . 0 8
p e r w o l f p e r day, D a l e et al.,
Territories
(0.05
caribou,
1994)
caribou
and Northwest
survival (Mech,
1977;
Thurber
&
a n d above the 3.2 k g r e q u i r e d for
1977). S i m i l a r
consumption
e r n A l a s k a (5.3 k g o f moose a n d c a r i b o u , B a l l a r d et
al,
1997) a n d N W T (4.4 k g , P. C l a r k s o n , u n p u b l . ) .
P. C l a r k s o n , u n p u b l . ) ,
P r e v i o u s estimates o f w o l f c o n s u m p t i o n rate are
a l t h o u g h our p a c k k i l l rates were m o r e v a r i a b l e . W e
p r o b a b l y h i g h e r t h a n a c t u a l , because b i o l o g i s t s u s u -
s t u d i e d w o l f k i l l rate i n m a i n l y s m a l l packs o f 2-3
a l l y a s s u m e d t h a t w o l v e s eat a l l a v a i l a b l e b i o m a s s o f
w o l v e s (Table 1). H a y e s et al.
their kills (Carbyn, 1983;
(2000) found wolves
o f moose c o m p a r e d to larger p a c k s , w h i c h c o u l d also
1991; T h u r b e r & Peterson, 1993; Dale
explain our caribou predation data.
H a y e s et al.
T h e m e a n d a i l y c o n s u m p t i o n rate was 4 . 9 k g o f
c a r i b o u p e r w o l f , above the range o f 1.7 to 4 . 0
54
kg
raven
Fuller,
1985;
H a y e s et
B a l l a r d et
al,
1987;
Messier & Crete,
i n s m a l l packs h a d m u c h w i d e r v a r i a t i o n i n k i l l rate
1989;
etal,
al,
1995).
( 2 0 0 0 ) a d j u s t e d k i l l rates to a c c o u n t for
scavenging,
estimating
that
remove u p to half of consumable
Rangifer,
ravens
moose
can
biomass
S p e c i a l Issue N o . 12, 2 0 0 0
f r o m s m a l l w o l f p a c k s (2-3 w o l v e s ) . F i v e o f o u r
m a l e s . U s i n g o u r 1 9 9 2 w o l f p r e d a t i o n rate e s t i m a t e
study
of
packs
ravens
were
s m a l l a n d w e c o m m o n l y saw
ar c a r i b o u k i l l s . H o w e v e r , w e agree
with
B a l l a r d et al. ( 1 9 9 7 ) w h o e s t i m a t e d t h a t w o l v e s lost
c a r i b o u carcasses m o r e r a p i d l y t h a n
our model
projects
that
wolves
were
the early 1 9 9 0 s .
A c c o r d i n g to F a n c y et al. ( 1 9 9 4 ) a n d W a l s h et al.
less o f t h e i r c a r i b o u k i l l s to ravens because w o l v e s
can consume
5.8%,
r e s p o n s i b l e for a b o u t 1/3 o f the a d u l t m o r t a l i t y i n
( 1 9 9 5 ) t h e g r o w t h o f t h e P C H is m o s t s e n s i t i v e t o
t h e y c a n c o n s u m e m o o s e - l e a v i n g less c a r i b o u b i o -
the s u r v i v a l rates o f females three years a n d o l d e r ,
mass for scavengers.
f o l l o w e d b y p r o d u c t i o n a n d s u r v i v a l rares o f calves.
B y b a c k - t r a c k i n g w o l f t r a i l s , D a l e et al.
(1994)
F a n c y et al. ( 1 9 9 4 ) s p e c u l a t e d that t h e d e c l i n e o f t h e
increased t h e i r e s t i m a t e o f k i l l rate because w o l v e s
P C H after 1 9 8 9 was related t o a c o m b i n a t i o n o f l o w
k i l l e d t h e n left t h e c a r i b o u carcasses before t h e n e x t
p a r t u r i t i o n rate o f > 3 - y e a r - o l d females i n 1 9 9 1 , a n d
underestimated
l o w e r e d c a l f s u r v i v a l i n M a r c h 1 9 9 2 . U s i n g stochas-
k i l l rate b y w o l v e s o n w o o d l a n d c a r i b o u b y l o c a t i n g
t i c m o d e l i n g , W a l s h et al. ( 1 9 9 5 ) s h o w e d t h a t a sur-
p a c k s once d a i l y , a n d r e c o m m e n d e d
back-tracking
v i v a l rate d e c l i n e o f a b o u t 3 % a m o n g a d u l t females
whenever possible. C l a r k s o n and Liepens ( u n p u b l .
or 4 % a m o n g calves c o u l d be e n o u g h to cause t h e
r a d i o l o c a t i o n . H a y e s et al.
(2000)
data) b e l i e v e d t h a t arctic w o l v e s r e m a i n e d close t o
P o r c u p i n e h e r d to d e c l i n e . O u r m o d e l p r o j e c t s t h a t
their
other
w o l v e s w o u l d have to nearly d o u b l e t h e i r p r e d a t i o n
b a c k - t r a c k i n g was n o t
rate to a c c o u n t for a n a d d i r i o n a l 3 % d e c l i n e i n a d u l t
kills
i n order
to protect
m i g r a t o r y p a c k s , therefore,
them
from
u s e f u l i n t u n d r a areas. W i t h o u t b a c k t r a c k i n g w e
female s u r v i v a l .
recorded a s i m i l a r k i l l rate as D a l e et al. ( 1 9 9 4 ) d i d
U s i n g d i f f e r e n t p r e d a t i o n rate m o d e l s , D a l e et al.
w i t h b a c k t r a c k i n g . W e had the advantage o f study-
( 1 9 9 4 ) a n d B a l l a r d et al.
ing
t h a t p r e d a t i o n b y w o l v e s was n o t t h e m a i n
s m a l l m i g r a t o r y packs that t r a v e l e d i n o p e n
( 1 9 9 7 ) also
determined
factor
t u n d r a areas, w h i c h p r o b a b l y r e m a i n e d near k i l l s f o r
l i m i t i n g c a r i b o u i n n o r t h w e s t e r n A l a s k a . B a l l a r d et
defense
al.
purposes
(P.
Clarkson,
unpubl.
data).
I n c r e a s i n g o u r o b s e r v a t i o n rate to each m o r n i n g a n d
(1997) estimated that wolves annually removed
about 6 - 7 % o f the Western A r c t i c caribou herd.
e v e n i n g d i d n o t increase o u r a b i l i t y to detect c a r i -
P r e d a t i o n b y w o l v e s is a n i m p o r t a n t factor l i m i t -
b o u k i l l s m a d e b y a p a c k o f 12 w o l v e s . D e s p i t e t h e
ing
w i n d b l o w n c o n d i t i o n s , w e reasonably e s t i m a t e d k i l l
(Gasaway
rate o f our s t u d y packs o n P o r c u p i n e c a r i b o u w i n t e r
Edmonds,
range.
s m a l l e r c a r i b o u herds
1995;
et al,
1 9 8 8 ; Seip,
M e c h et al,
i n Canada and A l a s k a
1983; Bergerud & Elliot,
1992; Hayes
&
1998). Current knowledge sug-
gests w o l f p r e d a t i o n acts i n a depensatory
Predation rate model
1986;
Gunson,
fashion
(i.e., i t increases as h e r d size d e c l i n e d ) w h e r e c a r i b o u
b y l o o k i n g at
are secondary p r e y to w o l v e s t h a t rely p r i m a r i l y o n
c a r i b o u a n d w o l f studies elsewhere. O u r study, D a l e
moose. W o l f p r e d a t i o n does n o t appear to be t h e
et al. ( 1 9 9 4 ) a n d P. C l a r k s o n ( u n p u b l . ) r e p o r t e d k i l l
m a i n cause o f p o p u l a t i o n c h a n g e for large m i g r a t o r y
rates o f 0 . 0 5 - 0 . 0 8 c a r i b o u w o l f
d a y . Thus, we
c a r i b o u herds i n the a r c t i c (Messier, 1 9 9 5 ; C r e t e &
changes to t h e v a l u e f o r
H u o t , 1 9 9 3 ; T h o m a s , 1995). Large migratory cari-
W e verified o u r m o d e l assumptions
believe that substantial
1
1
v a r i a b l e K^.i, are n o t j u s t i f i e d . O u t s t u d y ,
Parker
b o u herds t e n d to be c y c l i c , a n d p r e v i o u s p o p u l a t i o n
(1973), K u y t (1972), Thomas (1995) a n d Clarkson
trends have been
& L i e p i n s ( u n p u b l . ) a l l f o u n d a t w o - f o l d increase i n
w e a t h e r events (Crete & H u o t , 1 9 9 3 ; F a n c y et
l i n k e d to changes i n forage or
w o l f d e n s i t y o n w i n t e r range. W e h a d s u b s t a n t i a l
1994; Messier, 1995).
al,
t e l e m e t r y d a t a to evaluate seasonal P C H d i s t r i b u -
T h e l o w effect o f p r e d a t i o n b y w o l v e s is s u p p o r t -
t i o n f o r over t w e n t y years. T h u s , w e c o u l d n o t jus-
ed b y the h y p o t h e s i s o f B e r g e r u d ( 1 9 7 4 ) , w h o has
t i f y i n c r e a s i n g t h e areas o f a v a i l a b l e c a r i b o u m o r e
argued
than
e v o l v e d as a p r e d a t o r - a v o i d a n c e
t w o - f o l d . O u r m o d e l does n o t
incorporate
that
the m i g r a t o r y
behavior
caribou
Bergerud
caribou
calve o n
c h a n g i n g v u l n e r a b i l i t y to p r e d a r i o n , w h i c h M e c h et
( 1 9 9 2 ) believes
al. ( 1 9 9 8 ) f o u n d was a n i m p o r t a n t f u n c t i o n o f w o l f
s m a l l r e m o t e areas to 'space away' f r o m p r e d a t o r s .
p r e d a t i o n rate o n t h e D e n a l i c a r i b o u h e r d .
B y d o i n g so, they c a n f l o o d a large n u m b e r o f y o u n g
W e next e x a m i n e d h o w o u r p r e d a t i o n rate fit c u r rent k n o w l e d g e o f P o r c u p i n e c a r i b o u ecology. F a n c y
et al. ( 1 9 9 4 ) f o u n d m e a n a d u l t m o r r a l i t y rate for > 3 y e a r - o l d c a r i b o u was 1 5 % for females a n d 1 7 % for
Rangifer,
S p e c i a l Issue N o . 1 2 , 2 0 0 0
that m i g r a t o r y
of
strategy.
i n a s m a l l area w h e r e t h e p e r c a p i t a r i s k to b e i n g
k i l l e d b y a n y p r e d a t o r is l o w e s t .
Our
m o d e l does n o t e s t i m a t e p r e d a t i o n rate o n
calves, however, i t does s u p p o r t s t h a t ' s p a c i n g a w a y '
55
is also a n effective a n t i - p r e d a t o r y strategy o f a d u l t
t i o n s . T h e r e is a d e c l i n i n g g r a d i e n t o u t w a r d f r o m
caribou (Bergerud, 1 9 7 4 ; 1992; Thomas, 1995). In
these areas w h e r e l o w d e n s i t y c a r i b o u w i l l s t i l l be
late s p r i n g a n d s u m m e r , P o r c u p i n e c a r i b o u c o n c e n -
a v a i l a b l e to w o l v e s . W e e s t i m a t e d
trate o n the
plain of A l a s k a and Y u k o n ,
areas to be t w i c e the areas d e s c r i b e d
the
telemetry,
where
they
coastal
occupy
smallest
seasonal
range,
but
the
area
might
caribou-available
be
by
caribou
even
larger.
t h e r e b y r e d u c i n g t h e i r exposure to p r e d a t o r s (Table
H o w e v e r , w e needed to increase the c a r i b o u a v a i l -
2). A d u l t w o l v e s are l i m i t e d i n t h e i r a b i l i t y to t r a v -
able area i n o u r m o d e l b y
el there d u e to t h e i r r e q u i r e m e n t
took
to feed p u p s at
dens ( T h o m a s , 1 9 9 5 ; R . H a y e s , u n p u b l . data).
10%
wolves
or m o r e
show
strong
o f the
five-fold
adults.
preference
before w o l v e s
Third,
for c a r i b o u ,
arcric
and
time-
w o l v e s p r o b a b l y c o n t i n u e to search for c a r i b o u even
space d e p e n d e n t m o d e l for e s t i m a t i n g A f r i c a n l i o n
w h e n c a r i b o u appear to be absent (P. C l a r k s o n , pers.
p r e d a t i o n rate o n m i g r a t o r y w i l d e -
c o m m . ) . If P C H w o l v e s behave t h i s way, t h e n o u r
F r y x e l l et al.
(Panthera leo)
(1988) developed a similar
beeste (Connochaetes taurinus) t h a t s u p p o r t s the 'spac-estimates o f seasonal p r e d a t i o n rates c o u l d also be
ing-away'
advantage.
They
concluded
that
large
low.
m i g r a t o r y w i l d e b e e s t e herds c o u l d n o t be r e g u l a t e d
N e v e r t h e l e s s , o u r results are consistent w i t h o t h -
b y l i o n s , m a i n l y because l i o n s c o u l d not m a i n t a i n
er a r c t i c w o l f studies that f o u n d a u n i q u e l y m i g r a -
c o n t a c t w i t h herds y e a r - r o u n d , r e d u c i n g a n n u a l p r e -
t o r y b e h a v i o u r a m o n g wolves associated w i t h
d a t i o n rate.
r e n - g r o u n d caribou, naturally l o w w o l f densities, a
W e believe that the variables o f o u r m o d e l are
bar-
preference for c a r i b o u prey, a n d m o d e r a t e d a i l y k i l l
sizes
rates b y w o l v e s . T h e m o d e l w e present is based o n
because: 1) the area that c a r i b o u used seasonally was
d e t a i l e d k n o w l e d g e o f a d y n a m i c seasonal range use
s i m i l a r i n the 1 9 7 0 s w h e n the h e r d was a b o u t
pattern
useful
at
various
Porcupine
caribou
herd
100
by Porcupine caribou
t h a t was
available
0 0 0 c a r i b o u (Le R e s c h e , 1 9 7 5 ) ; a n d 2) as the h e r d
o n l y after decades o f r a d i o t e l e m e t r y studies. F u t u r e
declines
density-
p r e d a t i o n research s h o u l d be c o n d u c t e d to i n v e s t i -
d e p e n d e n t c h a n g e i n the w o l f f u n c t i o n a l response
gate w h e t h e r the a s s u m p t i o n s o f o u r m o d e l h o l d i n
(Dale
t h i s p e r i o d o f d e c l i n e d h e r d size.
remain
w e s h o u l d not e x p e c t a s t r o n g
et
199>4). T h u s ,
al,
constant. A l s o ,
wolf kill
taiga
rate s h o u l d
wolves
can
readily
s w i t c h to l o w d e n s i t y moose p r e y to s u r v i v e ( B a l l a r d
et al,
1997)
r e d u c i n g the n e g a t i v e effect o f d e c l i n -
i n g c a r i b o u a b u n d a n c e o n w o l f n u m e r i c a l response.
Acknowledgements
We
thank A . Baer for capturing and radio-tracking
wolves, and D . Denison of Coyote A i r Service for his
always
Data quality
A l t h o u g h o u r e s t i m a t e of m e a n d a i l y k i l l rate was
s i m i l a r to o t h e r studies, i t was b o u n d e d b y a w i d e
s t a n d a r d error. T h i s c o u l d be because the
sample
size o f packs was s m a l l , or the k i l l rate was u n d e t e s t i m a t e d for s o m e packs d u e to t e r r a i n or
keen
inrerest
in
flying
wolf
radiotelemetry.
F u n d i n g for this research was through the Inuvialuit
Final Agreement
and the Y u k o n Fish and W i l d l i f e
Branch. This paper was improved by comments from rwo
anonymous reviewers.
weather
constraints.
W e acknowledge
some s h o r t c o m i n g s
with
our
p r e d a t i o n rate m o d e l . A l t h o u g h the m o d e l fits c u r -
References
Adams, L. G . , Dale B. W . , & Mech L. D .
1995.
rent i n d i c e s o f the P C H , c o m p o n e n t s o f the m o d e l
Predation by wolves on caribou calves
need f u r t h e r v a l i d a t i o n . F i r s t , w e a s s u m e d t h a t Kda,iy
N a t i o n a l Park, Alaska. - ln: Carbyn, L . N . , Fritts, S.
i n the s u m m e r p e r i o d was the same as for w i n t e r .
W o l v e s are r e p o r t e d to s u r p l u s k i l l neonatal
a d u l t c a r i b o u ( M i l l e r et al,
and
1983; 1988; C . Gardner,
A l a s k a D e p . F i s h a n d G a m e , pers. c o m m . ) .
The
effecr
calf
of
wolf predation
recruitment
rate
on
changing
rates o f the P o r c u p i n e h e r d
u n k n o w n , a n d we d i d n o t i n c l u d e t h i s
remains
important
p o p u l a t i o n process i n o u r m o d e l .
Second,
the estimates o f the area t h a t
H . & Seip, D . R. (eds.). Wolves in a changing world: proceedings of the Second North American Wolf Symposium.
Canadian Circumpolar Institute,
U n i v . of Alberta,
Edmonton, Alberta, p p . 2 4 5 - 2 6 0 .
Ballard, W . B . ,
1987.
Whitman, J. S. & Gardiner, C . L.
Ecology of an exploited w o l f population i n
south-central Alaska. - Wildl. Monogr. 98: 54pp.
Ballard, W . B., Ayres, L. A . , Krausman, P. R., Reed,
D . J. & Fancy S. G . 1997. Ecology of wolves i n rela-
caribou
o c c u p y seasonally are based o n r a d i o t e l e m e t r y l o c a 56
i n Denali
tion to a migratory caribou herd i n northwest Alaska.
- Wildl. Monogr. 135: 47pp.
RangiCer, S p e c i a l
Issue N o . 12, 2 0 0 0
Barichello,
N . , Carey, J.
& Jingfors,
K . 1987.
Population ecology, range use, and movement patterns of dull
sheep (Ovis dalli dalli) in the northern Richardson mountains. Y u k o n Fish and W i l d l . B r . Rep. 125pp.
the aggregation, movement, and disturbance behavior
of caribou. - In: Geist, V . & Walther, F. (eds.). The
behavior of ungulates and its relations to management.
I . C . U . N . , Morges, Switzerland. (2): pp. 5 5 2 - 5 8 4 .
Bergerud, A . T . 1992. Rareness as an antipredator strategy to reduce predation risk for moose and caribou. 2001:
Elsevier A p p l i e d
Populations.
Wildlife
Science, N e w
York, pp. 1008-1021.
Bergerud, A . T . 1996. E v o l v i n g perspectives on caribou
population dynamics, have we got i t right yet? —
Rangifer, Special Issue N o . 9: 9 5 - 1 1 5 .
Bergerud, A . T . , & Elliot, P. P. 1986. Dynamics of
caribou and wolves i n northern B r i t i s h C o l u m b i a . Can. J. Zool. 64: 1 5 1 5 - 1 5 2 9 .
Carbyn, L . N . 1983. W o l f predation on elk i n R i d i n g
Mountain
N a t i o n a l Park,
M a n i t o b a . - J.
Wildl.
Manage. 47: 96.3-976.
Carrol, G . 1994. W o l f survey-inventory progress report.
-
In: H i c k s , M . (ed.). Wolf. Alaska D e p . Fish and
Game Fed. A i d i n W i l d l . Rest. Progr. Rep. Proj. W Crete, M . & Huot, J. 1993. Regulation of a large herd of
caribou,
summer
nutrition affects
calf
growth and body reserves of d a m s . - Can. J. Zool. 7 1 :
2291-2296.
Dale,
L. G . , & Boyer, R. T . 1994.
Functional response of wolves preying on barrenground caribou i n a m u l t i p l e prey ecosystem. - J.
Amm. Ecol. 63: 6 4 4 - 6 5 2 .
Harestad, A . S. 2000. K i l l rate by wolves on moose
i n the Y u k o n . - Can J. Zool. 78: 4 9 - 5 9 .
Hayes, R. D . , Baer, A . M . & Larsen, D . G . 1991.
Population dynamics and prey relationships of an exploited
and recovering wolf population in the southern Yukon.
Y u k o n Fish and W i l d l . B r . Rep. T R 91-1. 67pp.
Hayes, R. D . , & Gunson, J . R. 1995. Status and management of wolves i n Canada. - In: C a r b y n , L . N . ,
Fritts, S. H . & Seip, D . R . (eds.). Ecology and conservation of wolves in a changing world: proceedings of the Second
North
American
Wolf
Symposium.
Canadian
Circumpolar Insritute, U n i v . of A l b e r t a , E d m o n t o n ,
Alberta, pp. 21-23.
International
Porcupine
Caribou
Board.
1993.
Sensitive habitats of the Porcupine caribou herd. Porcupine
Caribou Management Board, Whitehorse, Y u k o n . 28
pp.
K l e i n , D . R. 1991. L i m i t i n g factors i n caribou population theory. - Rangifer Special Issue N o . 7: 3 0 - 3 5 .
barren-ground
W i n t e r w o l f predation in a m u l t i p l e ungulate prey
system, Gates of the A r c t i c N a t i o n a l Park, Alaska. In: C a r b y n , L . N . , Fritts, S. H . & Seip, D . R . Ecology
and conservation of wolves in a changing world: proceedings
of the Second North American Wolf Symposium. Canadian
Circumpolar Institute, U n i v . of Alberta, E d m o n t o n ,
Alberta, p p . 2 2 3 - 2 3 0 .
Edmonds, E. J. 1988. Population status, distriburion
and movements of woodland caribou in west centra!
Alberta. - Can. J. Zool. 66: 8 1 7 - 8 2 6 .
Fancy, S. G . , Whitten, K . R. & Russell, D . E. 1994.
Demography of the Porcupine caribou herd. 1983¬
Fryxell, J. M . , Grever, J. & Sinclair, A . R. E. 1988.
W h y are migratory ungulates so abundant? - Ameri131:781-798.
north-central Minnesota. - Wildl. Monogr. 105: 4 l p p .
P.
E.
i n the
Northwest
Dep. Fish and Game, Fed Aid in Wildl. Rest.
Project W-17-5. Juneau. 21 pp.
Mech, L . D . 1974. Current techniques i n the study of
elusive wilderness carnivores. - Int. Congr. Game Biol.
Mech, L . D . 1977. Population trend and winter deer
consumption in a Minnesota w o l f pack. Pages 55-83 In: P h i l l i p s , R . L . & J o n k e l , C. (eds.). 1975 Predator
Symposium. Montana Forest and Conservation Experiment Station, U n i v . of Montana, Missoula, Montana.
Mech, L. D . , Adams, L. G . , Meier, T . J.,Burch, J . W . ,
& Dale, B. W . 1998. Wolves of Denali. University of
Minnesota Press, Minneapolis. 227 pp.
Messier, F. 1994. Ungulare popularion models w i t h predation: a case study w i t h N o r t h A m e r i c a n moose.
-
Ecology 15: 4 7 8 ^ 8 8 .
Messier, F. 1995. T r o p h i c interactions i n two northern
systems.
-
Wildlife
Research 22:
131-146.
Messier, F., & Crete, M . 1985. Moose-wolf dynamics
and the natural regulation of moose populations.
Fuller, T . K . 1989. Population dynamics of wolves i n
Gasaway, W . C . , Stephenson,
range
Le Resche, R. E . 1975. Porcupine caribou herd studies,
wolf-ungulate
1992. - Can. J. Zool. 12: 8 4 0 - 8 4 6
can Naturalist.
caribou
Territories. - Can. Wildl. Serv. Rep. Ser. 2 1 : 36pp.
11: 3 1 5 - 3 2 2 .
Dale, B . W . , Adams, L. G . , & Bowyer, R. T . 1995.
Rangifer,
Hayes, R. D . , Baer, A . M . , Wotoschikowsky, U . &
Alaska
B., Adams
Shepherd,
Rangifer, Special Issue N o . 1: 1 3 7 - 1 4 4 .
Kuyt, E . 1972. Food habits and ecology of wolves on
24-2.
migratory
Alaska. - Wildl. Monogr. 84: 50pp.
Gauthier, D . A . , & Theberge, J . B . 1986. W o l f predation i n the Burwash caribou herd, southwest Y u k o n . -
Bergerud, A . T . 1974. T h e role of the environment i n
In: D . R . M c C u l l o u g h & R . H . Barrett (eds.).
Interrelationships of wolves, prey, and man i n interior
R . O . , Davis, J. L . ,
K . & Burris,
O . E. 1983.
S p e c i a l Issue N o . 1 2 , 2 0 0 0
-
Oecologia 6 5 : 5 0 3 - 5 1 2 .
Miller, F. L . , G u n n , A . Broughton, E . 1988. Surplus
k i l l i n g as exemplified by w o l f predation on newborn
caribou. - Can. J. Zool. 63: 295-300
57
A . 1983.
Stephenson, R. O . 1994. W o l f survey-inventory pro-
Mortality of migratory barren-ground caribou on the calv-
gress report. - In: H i c k s , M . (ed.). Wolf. Alaska D e p .
ing grounds of the Beverly herd, Northwest Territories,
F i s h and G a m e Fed. A i d i n W i l d l . Rest. Progr. Rep.
Miller,
F. L . , Broughton,
E. & G u n n ,
Proj. W - 2 4 - 2 , p p . 1 8 7 - 1 9 5 .
1981-83- Can. W i l d l . Ser. Occas. pap. 66. 23pp.
Nagy. J. A . 1990. Biology and management of grizzly bear
Stephenson, R. O . , & James, D . D . 1982. W o l f move-
on the Yukon north slope. Y u k o n Fish & W i l d l . B r . Rep.
ments and food habits i n northwest Alaska. - In:
H a r r i n g t o n , F . H . & Paquet, P . C . Wolves of the world:
67pp.
National Research Council. 1997. Wolves, bears, and
their prey in Alaska:
wildlife
biological and social challenges in
management.
National
Academy
Press,
W a s h i n g t o n . 207pp.
Oswald, E. T . , & Senyk, J. P. 1977. Ecoregions of Yukon
Territory. Fish, and E n v i r o n . Canada. 115pp.
Parker, G . R. 1973. D i s t r i b u t i o n and densities of wolves
perspectives of behavior, ecology, and conservation. Noyes,
Park R i d g e , N . J . , p p . 4 3 4 ^ 4 0 .
Thomas, D . C . 1995. A review of wolf-caribou relationships and conservation implications i n Canada. - In:
Carbyn, L. N . , Fritts, S. H . & Seip, D . R . (eds.).
Ecology and conservation of wolves in a changing world: proceedings of the Second North American Wolf Symposium.
w i t h i n barren ground caribou range i n northern m a i n -
Canadian Circumpolar Institute,
land C a n a d a . - J . Mammal. 54 (2): 3 4 1 - 3 4 8 .
E d m o n t o n , A l b e r t a , pp. 2 6 1 - 2 7 3 .
U n i v . of Alberta,
Seip, D . R. 1992. Factors l i m i t i n g woodland caribou
Thurber, J . M . & Peterson, R. O . 1993. Effects of pop-
populations and their interrelationships w i t h wolves
ulation density and pack size on the foraging ecology
and moose i n southeastern B r i t i s h C o l u m b i a . - Can. J.
Zool. 70: 1 4 9 4 - 1 5 0 3 .
Skoog, R. O . 1968. Ecology of caribou /Rangifer rarandus
granti) in Alaska.
P h . D . Thesis. University of C a l i -
fornia, Berkeley. 699 p p .
of gray wolves. -J.
Mammal. 74: 8 7 9 - 8 8 9 .
Walsh, N . E . , Griffith, B. & McCabe, T . R. 1995.
Evaluating g r o w t h of the Porcupine caribou
using a stochastic model. - J.
Wildl.
herd
Manage. 59:
262-272.
Smits, C. M . M . 1991- Status and seasonal distribution of
Youngman, P. M . 1975. Mammals of the Yukon Territory.
moose in the northern Richardson mountains. Y u k o n Fish
Publications of Z o o l . N o . 10. N a t i o n a l Museums of
& W i l d l . Br. Rep. T R - 9 1 - 2 . 63pp.
Canada, Ottawa. 192pp.
58
Rangifer,
Special Issue N o . 1 2 , 2 0 0 0