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N()I~IH~'VILSTI~]I~N NATUI,tAI.,IST
82:1-6
SPRING
2001
S U R V I V A L , C A U S E S O F M O R T A L I T Y , A N D R E P R O D U C T I O N IN T H E
A M E R I C A N M A R T E N IN N O R T H E A S T E R N O R E G O N
EVELYN L. BULL AND T H A D W. HEATER
Pacific Nortlmxest Research Station, 1401 Gekeler Lane, La Grande, OR 97850 USA
ABSTRACT--Survival rates, causes of mortality, and reproduction in the American marten
(Martes americana) were determined in northeastern Oregon from 1994 until 1997 with radiocollared martens. The probability of survival of m~irtens >-9 mo old was 0.55 for 1 yr, 0.37 for
2 yr, 0.22 for 3 yr, and 0.15 for 4 yr. The mean annual probability of survival was 0.63 for 4 yr.
Twenty-two of 35 radiocollared martens died. Of the 18 martens killed by predators, 8 were
killed by bobcats (Lynx rufus), 4 by raptors, 4 by martens, and 2 by coyotes (Canis latrans), based
on necropsies and circumstantial evidence at kills. Three martens died of exposure and 1 of
collar entrapment. Of 13 reproductive efforts, 4 females weaned >-1 kit, 8 efforts failed, and the
outcome of 1 was unknown. Predation of adult females prior to weaning was the source of reproductive failure for some efforts•
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Key words:
reproduction
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American marten, Martes americana, survival, mortality, northeastern Oregon,
U n d e r s t a n d i n g t h e d e m o g r a p h y of p o p u l a t i o n s of t h e A m e r i c a n m a r t e n (Martes americana) p r o v i d e s t h e o p p o r t u n i t y to e v a l u a t e t h e
effects of h a b i t a t a l t e r a t i o n o n t h e species. H a b itat a l t e r a t i o n , p r i m a r i l y b y l o g g i n g of l a t e - s u c c e s s i o n a l c o n i f e r forests, h a s b e e n l i s t e d as t h e
p r i m a r y c a u s e of t h e p o p u l a t i o n d e c l i n e in are a s w h e r e m a r t e n s h a v e b e c o m e e x t i n c t or a r e
c u r r e n t l y t h r e a t e n e d (Yeager 1950; A r c h i b a l d
and Jessup1984; Thompson and Harestad
1994). In t h e w e s t e r n U n i t e d States, r e d u c e d
d i s t r i b u t i o n or a b u n d a n c e of the m a r t e n h a s
b e e n r e p o r t e d in n o r t h e r n coastal C a l i f o r n i a
( G i b i l i s c o 1994) a n d in t h e C o a s t R a n g e i n
O r e g o n ( M a r s h a l l 1996) d u e to l o g g i n g . Logg i n g of l a t e - s u c c e s s i o n a l c o n i f e r f o r e s t s removes coarse woody debris and large-diameter
s t r u c t u r e s u s e d as r e s t a n d d e n sites, c o v e r
from predators, and foraging areas considered
e s s e n t i a l t h r o u g h o u t m a n y p a r t s of t h e i r r a n g e
(Bull a n d o t h e r s 1997).
A b u n d a n c e a n d p o p u l a t i o n p a r a m e t e r s of
t h e A m e r i c a n m a r t e n a r e u n k n o w n in t h e Blue
M o u n t a i n s in n o r t h e a s t e r n O r e g o n . T h e Nat i o n a l F o r e s t M a n a g e m e n t Act of 1976 m a n d a t e s t h a t v i a b l e p o p u l a t i o n s of all v e r t e b r a t e
species be maintained on federal land (USDA
1978). K n o w l e d g e of s u r v i v a l rates, m o r t a l i t y ,
a n d r e p r o d u c t i o n is n e c e s s a r y to e f f e c t i v e l y
manage marten populations. Our objective was
to d e t e r m i n e s u r v i v a l , c a u s e s of m o r t a l i t y , a n d
reproduction in American martens in our
study area.
~++
.
METHODS
T h e s t u d y a r e a e n c o m p a s s e d a b o u t 400 k m 2
i n t h e Blue M o u n t a i n s in n o r t h e a s t e r n O r e g o n .
A p o r t i o n of t h e s t u d y a r e a c o n t a i n e d a b o u t 53
k m 2 of u n h a r v e s t e d c o n t i n u o u s forest, w h i l e
the surrounding portion was extensively harv e s t e d for t i m b e r ( a p p r o x i m a t e l y 80%) a n d w a s
f r a g m e n t e d b y p a r t i a l cuts, r e g e n e r a t i o n cuts,
a n d r o a d s . T h e l a n d s c a p e w a s a m o s a i c of
s t a n d s in 4 f o r e s t t y p e s ( J o h n s o n a n d H a l l
1990): l o d g e p o l e p i n e (Pinus contorta), g r a n d fir
(Abies grandis), s u b a l p i n e fir (A. lasiocarpa), a n d
D o u g l a s - f i r (Pseudotsuga menziesii). P e r m a n e n t
w a t e r i n t h e f o r m of s p r i n g s a n d s t r e a m s w a s
a b u n d a n t . T o p o g r a p h y of t h e s t u d y a r e a c o n sisted of moderately steep mountains dissected
b y d r a i n a g e s . T h e e l e v a t i o n r a n g e d f r o m 1320
to 1980 m.
D a y t i m e m a x i m a in s u m m e r n o r m a l l y exc e e d e d 24°C, a n d w i n t e r low t e m p e r a t u r e s
w e r e t y p i c a l l y b e l o w f r e e z i n g w i t h e x t r e m e s of
-15°C being common. Annual precipitation
a v e r a g e d 78 c m w i t h a b o u t 60% f a l l i n g as s n o w
d e p e n d i n g o n t h e elevation. A t t h e h i g h e s t elevations, snow was present from November
through April each year with maximum depths
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NORTHWESTERN NATUI~ALIST
of 1.5 m; at the l o w e s t e l e v a t i o n s , s n o w was present from December until March, with maxim u m d e p t h s of 0.5 m.
Based o n w i n t e r t r a c k s we o b s e r v e d , c a r n i v o r e s o t h e r t h a n m a r t e n s v a r i e d in a b u n d a n c e
in t h e s t u d y area. L o n g - t a i l e d w e a s e l s (Mustela
frenata), e r m i n e (M. erminea), c o y o t e s (Canis latrans), a n d b o b c a t s (Lynx rufus) w e r e c o m m o n
t h r o u g h o u t t h e s t u d y area. M o u n t a i n lions (Fells concolor) w e r e p r e s e n t b u t u n c o m m o n . We
f o u n d n o e v i d e n c e of fishers (Martes pennanti)
o r r e d foxes (Vulpes vulpes) b a s e d o n o u r s n o w tracking observations.
Although commercial trapping had been
permitted throughout the area before the
s t u d y , o n l y 28 m a r t e n s h a d b e e n t r a p p e d i n all
of U n i o n C o u n t y b e t w e e n 1983 a n d 1993. C o m mercial trapping was prohibited in the study
area during our investigation, so we considered
the population we investigated unharvested.
Martens were captured in cage-type live
t r a p s w i t h a t t a c h e d p l y w o o d b o x e s for s h e l t e r
f r o m D e c e m b e r to M a r c h a n d d u r i n g S e p t e m b e r 1993 to 1997. D u r i n g D e c e m b e r to M a r c h
a b o u t 40 to 50 t r a p s w e r e set for 5 d a y s e a c h
w e e k a n d c h e c k e d daily. I n S e p t e m b e r w e
trapped in suspected female home ranges.
C a p t u r e d m a r t e n s w e r e i m m o b i l i z e d (Bull a n d
o t h e r s 1996), a g e d , a n d f i t t e d w i t h r a d i o c o l l a r s
( H o l o h i l Inc., C a r p , ON, C a n a d a ) . R a d i o c o l l a r s
for f e m a l e s w e i g h e d 28 g (4% of a v e r a g e b o d y
w e i g h t ) , w h i l e r a d i o c o l l a r s for m a l e s w e i g h e d
35 g (3% of a v e r a g e b o d y w e i g h t ) . R a d i o c o l l a r s
t r a n s m i t t e d for at l e a s t 18 too. A l l s u r v i v i n g
m a r t e n s , e x c e p t 2 (1 t r a n s m i t t e r failed, a n d 1
marten was never relocated), were recollared
e a c h y e a r for t h e d u r a t i o n of t h e s t u d y . A g e w a s
d e t e r m i n e d b y a n a l y s i s of c e m e n t u m a n n u l i o n
the teeth of martens recovered after death
(Poole a n d o t h e r s 1994). For i n d i v i d u a l s w i t h o u t a k n o w n a g e (as e s t i m a t e d b y c e m e n t u m
annuli analysis), juveniles and adults were dist i n g u i s h e d b a s e d o n d e g r e e of t o o t h w e a r at
c a p t u r e ( S t r i c k l a n d a n d o t h e r s 1982).
To m o n i t o r s u r v i v a l , r a d i o e o l l a r e d m a r t e n s
were located and visually observed an average
of o n c e p e r w e e k i n w i n t e r a n d t w i c e p e r w e e k
i n s u m m e r . If a m a r t e n r e m a i n e d i n t h e s a m e
r e s t site for > 4 to 6 c o n s e c u t i v e v i s i t s ( e x c e p t
f e m a l e s w i t h kits), w e a t t e m p t e d to d e t e r m i n e
if t h e r e h a d b e e n a m o r t a l i t y b y a c c e s s i n g t h e
r e s t s i t e b y c l i m b i n g t r e e s or e x c a v a t i n g u n d e r
S2( I )
snow. T h e d a t e of d e a t h was d e t e r m i n e d to be
t h e last t i m e the m a r t e n m o v e d .
We c o m p a r e d the n u n ~ b e r of d a y s m a r t e n s
were alive with a functioning transmitter and
w h e n m o r t a l i t y o c c u r r e d a m o n g m a l e s , fem a l e s , a d u l t s , a n d juveniles. We d i d not i n c l u d e
m a r t e n s t h a t h a d lost or failed t r a n s m i t t e r s (as
d e t e r m i n e d f r o m r e p e a t e d o b s e r v a t i o n s of a radiocollared marten without detecting a signal),
h a d d i e d u n n a t u r a l d e a t h s , or h a d u n k n o w n
fates. We c l a s s i f i e d u n n a t u r a l d e a t h s as t h o s e
likely a s s o c i a t e d w i t h b e i n g c a p t u r e d ; we believe 1 m a r t e n s u c c u m b e d to h y p o t h e r m i a d u e
to e x p o s u r e d u r i n g e n t r a p m e n t . In o u r s u r v i v a l
analysis, juvenile survival was based on the
n u m b e r of d a y s a m a r t e n w a s m o n i t o r e d w h e n
<--16 too, w h e r e a s a d u l t s u r v i v a l w a s b a s e d o n
t h e n u m b e r of d a y s m o n i t o r e d w h e n a m a r t e n
w a s > 1 6 too. A l t h o u g h 12 m o h a s b e e n u s e d to
d i s t i n g u i s h j u v e n i l e s f r o m a d u l t s in s t u d i e s in
the northeastern United States (Hodgman and
o t h e r s 1997), w e s e l e c t e d 16 m o b e c a u s e all 6
dispersing juveniles that we monitored disp e r s e d u n t i l b e t w e e n J u n e a n d A u g u s t (14 to16
mo of age) and did not exhibit adult behavior
i n r e l a t i o n to h o m e r a n g e u s e un~:il 14 to 16 too.
S u r v i v a l e s t i m a t e s w e r e c a l c u l a t e d at 2-too
i n t e r v a l s for t h e r a d i o c o l l a r e d m a r t e n s , u s i n g
the Kaplan-Meier method, with modifications
for r e c r u i t m e n t (Pollock a n d o t h e r s 1989), for
t h e d u r a t i o n of t h e s t u d y a n d for e a c h y e a r of
t h e s t u d y . S a m p l e size l i m i t e d s u r v i v a l estim a t e s to all m a r t e n s , w i t h o u t s e p a r a t i n g t h e m
b y sex o r age.
C a u s e of m o r t a l i t y w a s d e t e r m i n e d b y ins p e c t i n g c i r c u m s t a n t i a l e v i d e n c e f o u n d at t h e
m o r t a l i t y site (tracks, fur, f e a t h e r s ) a n d
through necropsy. Martens killed by raptors
had the skin neatly peeled back and were partially c o n s u m e d w i t h t h e m e a t p i c k e d c l e a n l y
f r o m t h e b o n e s ; t h e s k e l e t o n w a s intact. M a m malian predators were identified primarily by
t h e i n t e r c a n i n e w i d t h of t e e t h m a r k s in t h e
m u s c l e a n d s e c o n d a r i l y b y e v i d e n c e at s i t e s of
predation. Intercanine widths were measured
o n s k u l l s f r o m n o r t h e a s t e r n O r e g o n of e a c h
s p e c i e s a n d d e t e r m i n e d to b e 22 to 27 m m for
b o b c a t s , 26 to 28 m m for c o y o t e s , a n d 10 to 12
m m for m a r t e n s (Bull a n d H e a t e r 1995). M a r tens killed by bobcats were often buried; Rue
(1981) a n d Rolley (1987) r e p o r t e d t h a t b o b c a t s
frequently cache or cover larger prey with
g r a s s , d i r t , sticks, or snow. M a r t e n s k i l l e d b y
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Number of Months
l . . . . .
36
i
48
FIGURE 1. K a p l a n - M e i e r s u r v i v a l estimates, calculated at 2-too i n t e r v a l s , for 35 r a d i o c o l l a r e d mar-
>--9 mo of age in northeastern Oregon, January
1994 to October 1997 (dashed line delimits 95% CI).
tens
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martens were usually not consumed, but often
h a d b r o k e n s h o u l d e r s , i n j u r i e s to t h e h e a d a n d
n e c k , a n d r e c e n t l y b r o k e n c a n i n e s (Bull a n d
H e a t e r 1995). All m a r t e n b o d i e s a t t r i b u t e d to
. mammalian predators had extensive hemorrhaging, indicating that predators had killed
the martens rather than scavenged them.
Reproduction was determined by the repeate d u s e of t h e s a m e r e s t site b y a f e m a l e for seve r a l w e e k s i n A p r i l or May, b y t h e o b s e r v a t i o n
of kits, or b y e v i d e n c e of l a c t a t i o n ( s u c k l i n g
r i n g s e v i d e n t ) o n f e m a l e s c a p t u r e d in S e p t e m ber. S u r v i v a l of kits to w e a n i n g w a s b a s e d o n
t h e i r p r e s e n c e w i t h f e m a l e s in A u g u s t ; h o w ever, b e c a u s e it is d i f f i c u l t to o b s e r v e kits, w e
m a y h a v e failed to o b s e r v e s o m e s u c c e s s f u l rep r o d u c t i v e efforts.
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RESULTS
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K a p l a n - M c i e r s u r v i v a l estimates on an
No
x.
Year
00
MARTI'N
annual basis, calculated at 2-too intervals, for 35 radiocollared martens >-9 mo of age in northeastern
Oregon, January 1994 to October 1997. Survival estimate for 1997 includes months from January
through October.
:,
06
04
ANI.)
D u r i n g t h e s t u d y w e c a p t u r e d 17 a d u l t s , 17
j u v e n i l e s (all c a p t u r e d w h e n >-9 m o old), a n d 1
kit ( c a p t u r e d w h e n d e p e n d e n t o n f e m a l e ) , of
w h i c h 22 w e r e k n o w n to h a v e d i e d f r o m p r e d a t i o n or e x p o s u r e , 10 w e r e a l i v e as of 1 O c t o b e r 1997, 1 s l i p p e d its collar, 1 t r a n s m i t t e r
failed, a n d t h e fate of 1 w a s u n k n o w n . O f 19
m a l e s ( a d u l t s a n d j u v e n i l e s ) m o n i t o r e d for a total of 9,341 d a y s , 13 d i e d of n a t u r a l c a u s e s (1
d e a t h / 7 1 9 days). O f 11 f e m a l e s ( a d u l t s a n d juv e n i l e s ) m o n i t o r e d for a t o t a l of 4,895 d a y s , 7
d i e d of n a t u r a l c a u s e s (1 d e a t h / 6 9 9 days). Seve n t e e n j u v e n i l e s w e r e m o n i t o r e d for a t o t a l of
2,788 d a y s w h i l e t h e y w e r e j u v e n i l e s , a n d 6 of
t h e m d i e d d u r i n g t h a t t i m e (1 d e a t h / 4 6 5 days).
T w e n t y - f o u r m a r t e n s w e r e m o n i t o r e d for
11,448 d a y s d u r i n g t h e i r a d u l t life, a n d 14 d i e d
1994
1995
1996
1997
Mean
martens
monitoted
No.
martens
killed
14
15
18
14
5
4
7
4
Survival
estimate
95% CI
0.5455
0.6837
0.5803
0.7143
0.6310
0.2731-0.8179
0.4325-0.9349
0.3759-0.7847
0.4777-0.9509
0.3898-0.8721
d u r i n g t h a t t i m e (1 d e a t h / 8 1 8 days). T h e s i m i l a r i t y in s u r v i v a l b e t w e e n f e m a l e s a n d m a l e s
s u g g e s t s t h e r e w a s little d i f f e r e n t i a l m o r t a l i t y
b e t w e e n t h e s e x e s in t h i s p o p u l a t i o n for t h e d u r a t i o n of t h e s t u d y . P r o b a b i l i t y of s u r v i v a l of
m a r t e n s --> 9 m o old, for b o t h sexes, w a s 0.55
for 1 yr, 0.37 for 2 yr, 0.22 for 3 yr, a n d 0.15 for
4 y r (Fig. 1). M e a n a n n u a l s u r v i v a l rate w a s 0.63
(95% CI = 0.39-0.87; Table 1).
O f 22 m a r t e n s t h a t d i e d , 18 w e r e k i l l e d b y
predators, 3 died from exposure (hypothermia)
during the winter, and 1 marten died when the
c o l l a r c a u g h t o n a w o o d s p l i n t e r i n s i d e a hollow tree. E i g h t m a r t e n s w e r e k i l l e d b y b o b c a t s ,
4 b y r a p t o r s , 4 b y m a r t e n s , a n d 2 b y coyotes. N o
predation occurred between December and
F e b r u a r y , a n d t h e m a j o r i t y (67%) of p r e d a t i o n
occurred between May and August.
Bobcats killed 4 males and 4 females includi n g 1 j u v e n i l e of e a c h sex. R a d i o c o l l a r e d m a r tens were killed by bobcats between April and
N o v e m b e r . Four of t h e 8 m a r t e n s k i l l e d b y b o b cats w e r e b u r i e d , a n d t h e o t h e r 4 w e r e p a r t i a l l y
consumed. Coyotes killed 2 adult martens, 1 in
A p r i l a n d 1 i n A u g u s t . M o s t of 1 m a r t e n a n d
a b o u t 1 / 4 of t h e o t h e r w e r e c o n s u m e d b y coyotes.
R a p t o r s , e i t h e r n o r t h e r n g o s h a w k s (Accipiter
gentilis) or g r e a t h o r n e d o w l s (Bubo virginianus), k i l l e d 2 m a l e s a n d 2 f e m a l e s , 1 of w h i c h
w a s a j u v e n i l e female. R a p t o r s k i l l e d m a r t e n s
i n M a r c h , June, July, a n d A u g u s t .
M a r t e n s k i l l e d 4 m a l e s , of w h i c h 2 w e r e juveniles. Necropsies revealed extensive hemorr h a g i n g o n t h e b a c k of t h e h e a d , n e c k , a n d
s h o u l d e r s in all cases. T h r e e h a d r e c e n t l y b r o k e n c a n i n e s , a n d 3 h a d b r o k e n s h o u l d e r s . Mor-
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NORTHWESTI:]RN N A T U R A L I S T
tality from m a r t e n predation o c c u r r e d in May,
June, and July. In 3 of the cases, we k n e w resid e n t r a d i o c o l l a r e d males w e r e in the areas
w h e r e the males were killed.
We o b s e r v e d 2 males fighting in a tree in July;
1 of the males was r a d i o c o l l a r e d a n d was 2 to
3 yr old. The males w e r e facing each o t h e r on a
branch and had their jaws locked together. The
u n c o l l a r e d m a l e was t h r o w n off the branch or
fell, s o m e r s a u l t i n g t h r o u g h the b r a n c h e s to the
g r o u n d . The b r o k e n s h o u l d e r s we f o u n d in the
d e a d m a r t e n s could h a v e r e s u l t e d f r o m falling
or b e i n g t h r o w n out of trees. The broken can i n e s c o u l d result f r o m u s i n g their teeth to
fight.
We m o n i t o r e d 13 r e p r o d u c t i v e efforts: 4 succ e s s f u l l y w e a n e d -->1 kit, 8 efforts failed, a n d
the o u t c o m e of 1 was u n k n o w n . . Six females
h a d litters 1 yr, 2 females h a d litters f o r 2 cons e c u t i v e years, a n d 1 f e m a l e h a d litters for 3
c o n s e c u t i v e years. Six f e m a l e s d i d n o t h a v e litters, b u t they w e r e p r e s u m a b l y < 2 yr old. Four
r e p r o d u c t i v e efforts w e r e a s s u m e d to have
failed d u e to lack of o b s e r v a t i o n of females w i t h
kits d u r i n g A u g u s t , a n d 4 w e r e k n o w n to h a v e
failed b e c a u s e a d u l t s d i e d b e t w e e n A p r i l a n d
July, p r i o r to kit i n d e p e n d e n c e . R e p r o d u c t i v e
success v a r i e d a n n u a l l y : I of 2 r e p r o d u c t i v e efforts was s u c c e s s f u l in 1994; neither of 2 efforts
w a s s u c c e s s f u l in 1995; 2 of 4 efforts w e r e successful in 1996; a n d I of 5 efforts w a s successful
(1 u n k n o w n ) in 1997. O f the 4 s u c c e s s f u l efforts, 2 kits w e r e seen w i t h 1 f e m a l e a n d 1 kit
w i t h each of the o t h e r females. T w o of the fem a l e s w e r e 2 yr old w h e n they h a d kits; the
o t h e r females w e r e older.
DISCUSSION
Few s t u d i e s h a v e d e t e r m i n e d s u r v i v a l rates
for m a r t e n s in areas w i t h o u t t r a p p i n g ; no s t u d ies h a v e p u b l i s h e d s u r v i v a l rates f r o m the Pacific N o r t h w e s t . H o d g m a n a n d o t h e r s (1997)
f o u n d a n n u a l s u r v i v a l rates of 0.87 for a d u l t
m a l e s a n d 0.53 for a d u l t females in u n h a r v e s t e d p o p u l a t i o n s in Maine. Rates of n a t u r a l m o r tality h a v e b e e n e s t i m a t e d at 0.39 for j u v e n i l e s
, a n d 0.28 for a d u l t s p e r y e a r in Q u e b e c (Potvin
a n d Breton 1997). In N e w f o u n d l a n d , 13 of 40
r a d i o c o l l a r e d m a r t e n s d i e d d u r i n g a 19-mo
s t u d y w i t h m o r t a l i t y c o n c e n t r a t e d in the fall
a n d late w i n t e r ( F r e d r i c k s o n 1990). E n c e p h a l i tus c a u s e d the d e a t h s d u r i n g the fall, w h i l e
s t a r v a t i o n a n d p r e d a t i o n c a u s e d the m o r t a l i t y
82(1)
in late w i n t e r in Fredrickson's study. The iuveniles we m o n i t o r e d had higher rates of mot
tality than a d u l t s as r e p o r t e d by Potvin and
Breton (1997).
O u r s t u d y is 1 of few studies to doct, m e n t
p r e d a t i o n of m a r t e n s by raptors. A l t h o u g h
there has been s p e c u l a t i o n about such predation (Strickland and D o u g l a s 1987), it has rarely b e e n verified. O n l y H o d g m a n and others
(1997) found 1 case of raptor predation in
Maine, F r e d r i c k s o n (1990) found 1 case in N e w f o u n d l a n d , a n d T h o m p s o n (1994) found 1 marten killed by a great h o r n e d owl in Ontario.
No o t h e r s t u d i e s h a v e d o c u m e n t e d bobcats
as the p r e d o m i n a n t p r e d a t o r of martens. Red
foxes p r e y e d o n m a r t e n s in N e w f o u n d l a n d
( F r e d r i c k s o n 1990; D r e w and Bissonette 1997)
a n d in O n t a r i o ( T h o m p s o n 1994). Foxes a n d
c o y o t e s w e r e p r e d a t o r s in W y o m i n g (L. E Ruggiero, R o c k y M o u n t a i n R e s e a r c h Station, Missoula, MT; pers. c o m m . ) , a n d coyotes and fishers in M a i n e ( H o d g m a n a n d o t h e r s 1997). T r a p p i n g a c c o u n t e d for 90% of the m a r t e n m o r t a l i t y
in an i n t e n s i v e l y t r a p p e d m a r t e n p o p u l a t i o n in
M a i n e ( H o d g m a n a n d o t h e r s 1994). O b s e r v a tions in C a n a d a a n d M a i n e s u g g e s t that other
p o p u l a t i o n s h a v e intraspecific p r e d a t i o n such
as w e o b s e r v e d . S t r i c k l a n d a n d D o u g l a s (1987)
r e p o r t e d t r a p p e r s w h o f o u n d f r e q u e n t scarring
on m a l e m a r t e n pelts b u t n o n e o n female pelts.
H o d g m a n a n d o t h e r s (1997) f o u n d 2 m a r t e n s
killed by o t h e r m a r t e n s .
The lack of p r e d a t i o n w e o b s e r v e d d u r i n g the
w i n t e r was s u r p r i s i n g b e c a u s e o t h e r studies rep o r t e d h i g h e r m o r t a l i t y in w i n t e r in M a i n e
( H o d g m a n a n d o t h e r s 1997) a n d in N e w f o u n d l a n d ( F r e d r i c k s o n 1990). In Maine, the h i g h e s t
m o r t a l i t y o c c u r r e d w h e n the d e c i d u o u s trees
lacked leaves a n d p r o v i d e d less cover. A p r e y
s h o r t a g e in N e w f o u n d l a n d p r o b a b l y contribu t e d to the p o o r s u r v i v a l of m a r t e n (Fredricks o n 1990). T h e lack of w i n t e r p r e d a t i o n on m a r tens in o u r s t u d y m a y h a v e b e e n a result of
their r e d u c e d a c t i v i t y in the w i n t e r , p a r t i c u l a r ly d u r i n g d a y l i g h t hours, a n d their e x t e n s i v e
use of rest sites u n d e r the s n o w (Bull and Heater 2000). The r e d u c e d a c t i v i t y w e o b s e r v e d
c o u l d h a v e b e e n i n f l u e n c e d by t h e r m o r e g u l a tion a n d p r e y availability a n d vulnerability, as
w e l l as risk of p r e d a t i o n (Zielinski, in press).
P r e d a t i o n was the m a j o r cause of m o r t a l i t y in
the p o p u l a t i o n w e i n v e s t i g a t e d , and p r e d a t i o n
of f e m a l e s b e f o r e w e a n i n g kits r e s u l t e d in low
i
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SI'RIN~.; 2001
BULl. , \ N I l I l E A l I-R: .SURVIVAL A N D RI/I't-~(/I)UCIION IN ~],,\I(IF:N
r e p r o d u c t i v e rates. A d d i t i o n a l research is w a r r a n t e d to d e t e r m i n e i f r e p r o d u c t i o n e x c e e d s
m o r t a l i t y o v e r the l o n g t e r m a n d if a v i a b l e
p o p u l a t i o n is b e i n g m a i n t a i n e d in m a r t e n p o p u l a t i o n s in n o r t h e a s t e r n O r e g o n .
ACKNOWI+EDGM t'~NTS
E G. C u l v e r assisted with field work. A g e determ i n a t i o n s were m a d e by G. M a t s o n at Matson's Laboratory, Milltown, MT. F u n d i n g was p r o v i d e d by the
Pacific N o r t h w e s t Research Station; National Wildlife Federation; National A u d u b o n Society; O r e g o n
D e p a r t m e n t of Fish a n d Wildlife; La G r a n d e R a n g e r
District; a n d Forest Service, Pacific N o r t h w e s t Region, Fish a n d Wildlife. A n earlier d r a f t of the m a n u s c r i p t w a s r e v i e w e d by J. A. Bissonette, S. W. Buskirk, D. J. H a r r i s o n , M. G. Raphael, L. E R u g g i e r o , J.
E S h e p h e r d , M. D. Snider, a n d W. J. Zielinski.
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