Journal of Mammalogy, 88(2):427–435, 2007
AGE-SPECIFIC FERTILITY AND FECUNDITY IN NORTHERN
FREE-RANGING WHITE-TAILED DEER: EVIDENCE FOR
REPRODUCTIVE SENESCENCE?
GLENN D. DELGIUDICE,* MARK S. LENARZ,
AND
MICHELLE CARSTENSEN POWELL
Forest Wildlife Populations and Research Group, Minnesota Department of Natural Resources, Grand Rapids,
MN 55744, USA (GDD, MSL)
Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, St. Paul, MN 55108, USA (GDD)
Section of Wildlife, Minnesota Department of Natural Resources, Forest Lake, MN 55025, USA (MCP)
Key words:
age-specific fertility, fecundity, Odocoileus virginianus, pregnancy, reproduction, senescence, white-tailed deer
Aspects of deer reproduction have received intense study,
including relations of nutrition, body condition, range quality,
weather conditions, and human handling to fertility, fecundity,
and productivity (Barron and Harwell 1973; Cheatum and
Severinghaus 1950; DelGiudice et al. 1986; McCaffery et al.
1998; Mech et al. 1987; Nelson and Mech 1990; Verme and
Ullrey 1984); reproductive physiology and endocrinology
(Harder 2005; Harder and Moorhead 1980; Harder and Woolfe
1976; Plotka et al. 1977, 1980; Rhodes et al. 1992); and
increasingly, neonate survival and reproductive success
(Carstensen Powell 2004; Heugel 1985; Kunkel and Mech
1994; Langenau and Lerg 1976; Ozoga and Verme 1986). As
was true until recently for studies of deer survival, age class
(i.e., fawn, yearling, and mature adult during breeding) has
been the most common frame of reference for investigations of
reproduction, with relatively little attention focused on senescence of adults (Eberhardt 1985; McCaffery et al. 1998;
Rhodes et al. 1992). However, long-term studies of other
Population performance of white-tailed deer (Odocoileus
virginianus) is driven largely by survival and reproduction.
Increasingly, study of various ungulates has shown that hazard
functions (i.e., instantaneous probability of death) and survival
over their life cycles are related to age from birth through
senescence (Caughley 1966; DelGiudice et al. 2002, 2006;
Eberhardt 1985; Festa-Bianchet et al. 2003; Gaillard et al.
2000; Loison et al. 1999; Siler 1979). Given that age distributions of populations vary, knowledge of age-specific reproduction would enhance our understanding of population
performance and dynamics relative to intrinsic factors, regulatory mechanisms, and their interaction with extrinsic factors.
* Correspondent: glenn.delgiudice@dnr.state.mn.us
Ó 2007 American Society of Mammalogists
www.mammalogy.org
427
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Population performance of white-tailed deer (Odocoileus virginianus) is driven largely by survival and
reproduction. Knowledge of age-specific reproduction would enhance our understanding of population
performance and dynamics relative to intrinsic factors, regulatory mechanisms, and their interaction with
extrinsic factors. From 1991 to 2002, we examined serum progesterone as an indicator of pregnancy in freeranging white-tailed deer (0.5–15.5 years old), age-specific fertility and fecundity, and the potential effect of
reproductive senescence on population change. We did not detect relationships between serum progesterone
concentrations and Julian date, age, or body mass at capture in 41 confirmed-pregnant, adult (1.0-year-old)
does. Serum progesterone concentrations of 284 females ranging in age from 0.5 to 15.5 years were distributed
bimodally with a narrow peak at 0.0–0.4 ng/ml (composed of samples from 46 of 50 fawns) and a broad peak
centered at about 3.6 ng/ml. Only 1 (1.8%) of 55 fawns was pregnant, whereas pregnancy rates were 96.6% (112
of 116) for 2.5–7.5 year olds and 98.5% (64 of 65) for 8.5–15.5 year olds. Among adults, the lowest pregnancy
rates occurred in yearlings (87.5%), not in the oldest does. Mean estimated fecundity was 1.3 fetuses per doe in
yearlings and was 1.8 fetuses per doe in 2.5–15.5 year olds. We observed no evidence of senescence relative to
fertility and fecundity in adult female white-tailed deer up to 15.5 years old. Because older does comprise
a relatively small proportion of the population, fecundity rates of these females have little impact on population
change (k); however, their ultimate value to the population may be in their life-long reproductive success and
associated genetic contribution.
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JOURNAL OF MAMMALOGY
MATERIALS AND METHODS
Study area.— We conducted our winter capture of deer 0.5
years old on a 791-km2 area, described elsewhere (DelGiudice
1998; DelGiudice et al. 2002), and located along the southeastern boundary of Chippewa National Forest in north-central
Minnesota (468529N–478159N and 938459W–948079W). Inclusion of spring–summer–autumn ranges, where captures of
neonates occurred, expanded the study area to 1,865 km2
(468499N–478159N
and
938359W–948209W—Carstensen
Powell et al. 2005). The uplands were dominated by deciduous
and mixed deciduous–coniferous stands, whereas conifers were
prevalent on the lowlands (Doenier et al. 1997).
Mean weekly snow depth varied from 0 to 88 cm, and monthly
mean minimum temperatures ranged from 288C to 78C during the January–March trapping periods, 1991–2002 (DelGiudice
et al. 2005). During June–October 1991–2002, the range of
monthly mean maximum temperatures was 6–288C (National
Oceanic and Atmospheric Administration 1991–2002).
Deer capture, handling, and monitoring.— We captured deer
primarily by Clover traps (Clover 1956) during January–March
1991–2002, but augmented these efforts with captures by
rocket-net (2%) and net-gun (3%—DelGiudice et al. 2005).
Details of handling are reported elsewhere (DelGiudice et al.
2005), but generally, we physically restrained, blindfolded,
and chemically immobilized female deer with 75–100 mg
of xylazine HCl (Xyla-ject; Phoenix Scientific, St. Joseph,
Missouri) and 300–400 mg of ketamine HCl (Keta-ject;
Phoenix Scientific) during 1st captures. We administered
chemical boosters as needed to maintain immobilizations.
We collected blood samples by venipuncture of the jugular
vein into a 5-ml ethylenediaminetetraacetic acid vial and into
two or three 10-ml serum tubes. Deer were routinely catheterized for urine, weighed to the nearest 0.5 kg, ear-tagged,
and physically examined; rectal temperature was monitored
(DelGiudice et al. 2001); morphological measurements were
made; a 4th incisor was extracted for age determination by
cementum annuli (Gilbert 1966); and a very high frequency
(Telonics, Mesa, Arizona) or global positioning system
(Advanced Telemetry Systems, Isanti, Minnesota) radiocollar
was fitted. Commonly, pregnancy was determined by dop-tone
ultrasound (Pocket-Dop II; Imex Medical Systems, Golden,
Colorado). Certain techniques were employed during handling
less consistently over the full study period as required by shortterm companion studies (e.g., fitting of vaginal implant
transmitters—Carstensen et al. 2003; Carstensen Powell
2004). Before release, each deer was injected intramuscularly
with 1,500,000 international units of a broad-spectrum antibiotic (Dual-Cillin; Phoenix Scientific). We reversed anesthesia
with an intravenous injection of 15 mg of yohimbine (Sigmal
Chemical Co., St. Louis, Missouri—Mech et al. 1985). We
chemically immobilized and handled female deer during recaptures only when 14 days had elapsed since their most recent
previous capture, chemical immobilization, and handling. Male
deer were either physically restrained or only lightly immobilized with xylazine and ketamine, ear-tagged, reversed with
yohimbine, and released. Animal capture and handling
protocols were approved by the University of Minnesota’s
Institutional Animal Care and Use Committee and meet the
guidelines recommended by the American Society of Mammalogists (Animal Care and Use Committee 1998).
During springs 1997 and 1999–2002, 41 known-pregnant
(confirmed by dop-tone ultrasound), adult (1.5 years old)
radiocollared does, with serum progesterone concentration
measured during the previous winter, were monitored during
the fawning season so that we could capture, radiocollar, and
release their neonates for study of their movements and survival (Carstensen et al. 2003; Carstensen Powell 2004;
Carstensen Powell et al. 2005). Twins rather than singletons
were most common in does 2.5 years old entering winter
(M. S. Lenarz, Minnesota Department of Natural Resources
[MNDNR], in litt.); however, when only 1 neonate of a dam
was captured in spring, it was typically not known with
certainty whether a twin existed.
Determination of pregnancy.— Serum progesterone concentrations of the adult males and known-pregnant does of this
study, and previously published serum progesterone concentrations for pregnant and nonpregnant deer (Abler et al. 1976;
G. D. DelGiudice, MNDNR, in litt.; Gaillard et al. 1992;
Harder 2005; Wood et al. 1986), were used to establish a
threshold concentration indicative of pregnancy (1.6 ng/ml).
Serum tubes from all deer were allowed to clot for ,12 h,
were centrifuged, and serum was decanted and stored frozen
until assayed. Serum progesterone concentrations were determined by solid phase 125I radioimmunoassay (Coat-A-Coat
procedure; Diagnostic Products Corporation, Los Angeles,
California) in our laboratory in Grand Rapids, Minnesota.
Data analysis.— To expand our understanding of serum
progesterone as an indicator of pregnancy, we explored
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ungulates, including red deer (Cervus elaphus), moose (Alces
alces), bighorn sheep (Ovis canadensis), and roe deer
(Capreolus capreolus) have begun to illuminate the value of
understanding ‘‘life-history trade-offs’’ relative specifically to
how age of females (including senescence) interacts with phenotypic quality (e.g., body mass and condition) during the
reproductive process (Bérubé et al. 1999; Borg 1970; Guinness
et al. 1978a; Heard et al. 1997; Hewison and Gaillard 2001).
What has followed is an enhanced understanding of how agespecific reproduction may affect population performance.
Very little is known about reproductive senescence in whitetailed deer. According to Verme and Ullrey (1984), maximum
productivity occurs in does 3–7 years old, then declines in
older does, but little specific explanation is offered as to how
this decrease in productivity is manifested during the reproductive cycle. Nelson and Mech (1990) reported no difference in productivity in free-ranging female deer 10 years
old (up to 17 years old) compared to younger does. Our longterm (1991–2002) primary objectives were to examine serum
progesterone as an indicator of pregnancy in free-ranging,
female white-tailed deer (0.5–15.5 years old) and potential
influences (e.g., time, age, and body mass) on concentrations;
age-specific fertility and fecundity; and the potential effect of
reproductive senescence on population change.
Vol. 88, No. 2
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DELGIUDICE ET AL.—FERTILITY IN WHITE-TAILED DEER
potential influences of Julian date (January–March), age, and
body mass at capture (independent variables) on progesterone
concentrations of pregnant deer by multivariable regression
analysis (Proc GLM—SAS Institute Inc. 1996). Before fitting
regression models, we ascertained by diagnostics that multicollinearity among independent variables was not a significant
problem (Proc Reg—SAS Institute Inc. 1996).
To assess the influence of age-specific reproduction on population change, we constructed a postbreeding census matrix
model (Caswell 2001; Leslie 1945) by combining iterative
Nelson estimates (INE) of survival (pi—DelGiudice et al. 2002,
2006) with estimates of fecundity (mi) based on road-killed
pregnant does (1972–1981) in northern Minnesota (M. S. Lenarz,
MNDNR, in litt.) and estimates of pregnancy rates from the
study cohort. The basic form of the Leslie matrix model is:
where Nt is a vector of length 16 giving the number of female
deer 0 years of age (i.e., neonates), and deer aged 1–15, just
after the birth-pulse in year t. The matrix A is a population
projection matrix with age-specific values for fecundity f(1,i) in
the top row and survival probabilities p(iþ1,i) in the offdiagonals. We used the birth-pulse form of the model in which
reproduction occurs following survival (Caswell 2001); hence
fi ¼ mipi. The value mi represents the expected number of
female fawns produced by a doe in the ith age class. Values for
pi represent the probability that an individual in age class i at
time t will survive to enter age class i þ 1 at t þ 1.
The model assumes that population dynamics are deterministic (i.e., survival and fecundity rates are constant) and
projects population change as the finite rate of increase (k)
given by the dominant eigenvalue of the matrix (Caswell
2001). As such, the model provides a means to determine sensitivity of k to changes in fecundity and survival schedules.
The age structure at k is a ‘‘stable age distribution’’ (i.e., the
proportion in each age class is constant) and is a function of the
survival and fecundity schedules (Caswell 2001). PopTools
software (version 2.6.2, G. M. Hood, 2004, http://www.cse.
csiro.au/poptools) was used for all calculations and does not
require an age structure Nt in its projection of k.
Survival probabilities and fecundity are measured on
different scales; survival cannot exceed 1, whereas fecundity
is not limited. For this reason, elasticity analysis (Caswell
2001) was used to determine model response to proportional
rather than absolute (sensitivity analysis) perturbations. Using
this analysis it is possible to determine the contribution of each
element in the matrix to k.
Finally, we conducted a sensitivity analysis relative to our
serum progesterone threshold. We reduced the progesterone
concentration indicative of pregnancy from 1.6 to 0.8 ng/ml,
which results in a net increase in the proportion of pregnant
females. We then recalculated the matrix model and examined
the effect of this change on k.
RESULTS
Known pregnancies.— Mean serum progesterone concentration was 4.0 ng/ml, but varied widely (range ¼ 1.6–6.6 ng/ml;
Fig. 1) for 41 known-pregnant, adult does monitored during
springs 1997, 1999, and 2000–2002 for fawn capture.
Concentrations for all but 2 deer were .2.0 ng/ml. Mean age
at winter capture was 5.6 years (range ¼ 1.5–14.5 years, n ¼
39); 74.4% of these were 7.5 years old. We did not detect
a relationship of serum progesterone concentration to Julian
date, age, or body mass at capture (P 0.209). At least 6
(60%) of 10 dams 10.0 years old gave birth to twins,
resulting in a minimum productivity of 1.6 fawns per pregnant
doe (16:10). Minimum fawn productivity of all knownpregnant does was 1.4 fawns per pregnant doe.
Total female capture and pregnancy rate.— We captured,
aged, and collected blood from 284 female deer ranging from
0.5 to 15.5 years old (77% 7.5 years old; Fig. 2). Serum
progesterone concentrations were distributed bimodally with
a pronounced narrow peak at 0.0–0.4 ng/ml, comprised almost
exclusively of fawns (46 of 50 fawn values), and a broad peak
centered at about 3.6 ng/ml (Fig. 1). There was little difference
¼ 0.3,
in mean serum progesterone concentrations of fawns (X
95% confidence limits [CL] ¼ 0.2, 0.4 ng/ml), adult females
¼ 0.7, 95% CL ¼ 0.4, 1.1 ng/ml),
assessed as nonpregnant (X
and adult males (X ¼ 0.3, 95% CL ¼ 0.2, 0.4 ng/ml—G. D.
DelGiudice, MNDNR, in litt.) as opposed to values observed
¼ 4.0, 95% CL ¼ 3.6, 4.4
in the known-pregnant adults (X
ng/ml). Again, we detected no relationships between serum
progesterone concentrations of pregnant females and Julian
date, age, or body mass at capture (P 0.215).
Less than 2% (1 of 55) of fawns, but 87.5% (42 of 48) of
yearlings were pregnant. Pregnancy rates were 90.5–95.7% in
2.5, 3.5, 6.5, and 10.5 year olds; however, notably lower
sample sizes than for yearlings likely contributed to the modest
variation observed in these age classes (see Fig. 2). Pregnancy
rates were 100% in all remaining yearly age classes, where
again samples were smaller than for fawns and yearlings,
particularly for the 8.5–15.5-year olds (Fig. 2). Overall,
pregnancy rates were 96.6% (112 of 116) and 98.5% (64 of
65) in 2.5–7.5 year olds and 8.5–15.5 year olds, respectively.
Lowering the threshold serum progesterone concentration to
0.8 ng/ml increased the pregnancy rates of yearlings from
87.5% to 91.7%, but pregnancy rates of all annual age classes
2.5 years old, except 6.5 year olds (unchanged at 95.0%),
increased to 100%.
Using fetuses per pregnant doe from a 10-year survey of
road-killed deer (M. S. Lenarz, MNDNR, in litt.), and agespecific pregnancy rates of our study cohort, mean estimated
fecundity in our study cohort ranged from 1.3 in yearlings to
2.2 in 10.5 year olds (Fig. 3). Mean estimated fecundity in does
2.5–15.5 years old was 1.8 fetuses per doe (range ¼ 1.5–2.2
fetuses per doe), with twins being most common at all ages and
triplets being relatively rare (Fig. 3). Consequently, we found
no evidence of reproductive senescence related to pregnancy or
fecundity in the free-ranging, female, white-tailed deer in this
study. Lowering the progesterone threshold of pregnancy to 0.8
ng/ml had only a very modest increasing effect on estimated
fecundity of yearlings and 2.5, 3.5, and 10.5 year olds (1.4, 2.1,
1.7, and 2.1 fetuses per doe, respectively, compared to original
estimated fecundities given in Fig. 3).
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Nt ¼ A Nt1 ;
429
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Vol. 88, No. 2
JOURNAL OF MAMMALOGY
There was no difference in body mass between pregnant
¼ 64.7, 95% CL ¼ 63.6, 65.8 kg, n ¼ 141) and nonpreg(X
¼ 60.9, 95% CL ¼ 54.0, 67.9 kg, n ¼ 5) females
nant (X
2.5 years old; however, body mass tended to be greater in
¼ 66.4, 95% CL ¼ 64.7, 68.2 kg,
does 8.5–15.5 years old (X
¼ 63.5, 95% CL ¼
n ¼ 54) compared to 2.5–7.5 year olds (X
62.2, 64.9 kg, n ¼ 92). Body mass was lower in nonpreg ¼ 48.4, 95%
nant yearlings than in pregnant yearlings (X
¼ 55.1, 95% CL ¼ 52.7,
CL ¼ 45.1, 51.7 kg, n ¼ 6 versus X
57.4, n ¼ 30).
Our Leslie matrix model analysis indicated that the high
pregnancy and fecundity rates of the older does in our study
cohort would have little impact on k. At stable age distribution,
females aged 8–15 years represented only 5.8% of all does in
the age structure. The sum of the elasticity values for f8 to f15
(fecundity values for does in this study aged 8–15 years) was
only 0.022, which is ,4% of the elasticity value for adult
survival (p1 to p15, survival values of does in this study aged
1–15 years). In fact, the sum of the elasticity values for p0 to
p7 (survival of neonates to 7 years old) was 0.76 (on a scale
of 0 to 1). This implies that in general, k is much more sensitive
to perturbations in survival probability of younger does than it
is to fecundity.
When we reduced the progesterone threshold indicative of
pregnancy by 50%, it increased pregnancy rates primarily in
the younger age classes. Pregnancy increased in only 1 age
class for does 8–15 years old. In response to this change, k
increased 1.3%.
DISCUSSION
Pregnancy has been accurately determined in white-tailed
deer, roe deer, elk (Cervus elaphus), bighorn sheep, and
domestic ungulates using threshold progesterone concentra-
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FIG. 1.—Serum progesterone concentrations of A) 41 free-ranging, confirmed (by dop-tone ultrasound and neonate capture)-pregnant, adult
(1.5 years old) white-tailed deer; and B) the entire study cohort (n ¼ 284) of free-ranging, female white-tailed deer (0.5–15.5 years old) livecaptured during January–March 1991–2002, in north-central Minnesota.
April 2007
DELGIUDICE ET AL.—FERTILITY IN WHITE-TAILED DEER
FIG. 2.—Age distribution of 284 free-ranging, female white-tailed
deer (0.5–15.5 years old) live-captured during January–March 1991–
2002, in north-central Minnesota.
other northern cervids where the seasonal variation of nutrition
is most dramatic. Pregnancy rates have ranged up to 74% in
more southerly, agriculturally dominated areas where growing
seasons are longer and crops of greater nutrient quality are
more available (Cheatum and Severinghaus 1950; Friedrich
and Hill 1982; Haugen 1975; Ingebrigtsen 1988; McCaffery
et al. 1998; Morton and Cheatum 1946; Severinghaus 1946;
Verme and Ullrey 1984).
Among the adults, yearlings, not old does, had the lowest
pregnancy rate (87.5%) and the lowest fecundity (1.31 fetuses
per doe); proportionately, twins were notably less common
than for adults 2.5 years old, and no triplets were observed in
yearlings. The pregnancy rate in yearlings in this study was
very similar to that of yearling white-tailed deer (85%) in the
central forests of Wisconsin, yet the associated fecundity of
the latter (1.09 fetuses per doe) was notably lower (McCaffery
¼ 1.82 fetuses per
et al. 1998). Interestingly, the fecundity (X
doe) of adults in this study 2.5 years old at breeding was
similar to that of the same age cohort in forests in central
Wisconsin (1.78 fetuses per doe—McCaffery et al. 1998).
Nutrition has its strongest influence on the fertility and
fecundity of white-tailed yearlings (Verme and Ulllrey 1984),
and a body mass threshold has been reported for primiparity in
a number of other ungulates (Gaillard et al. 1992; Hamilton
and Blaxter 1980; Langbein and Putnam 1992; Saether and
Haagenrud 1983), which is consistent with the lower winter
body masses we observed in nonpregnant compared to pregnant yearlings.
It is most noteworthy that evidence from our long-term
study indicates an absence of reproductive senescence relative
to fertility and fecundity for deer up to 15.5 years old. Rather,
the pregnancy rate was 100% at winter capture for 8.5–15.5
year olds (n ¼ 65), except for the 10.5 year olds (92.3%).
¼ 1.84, 95%
Further, estimated fecundity remained high (X
CL ¼ 1.66, 1.98 fetuses per doe) for these older deer (Fig. 3).
The survival senescence of this female study cohort was more
apparent than reproductive senescence (DelGiudice et al.
2006), which is consistent with reports for other ungulate
species (Bérubé et al. 1999; Eberhardt 1985; Gaillard et al.
1998, 2000; Hewison and Gaillard 2001). However, in a
review, Verme and Ullrey (1984) suggested that white-tailed
does were reproductively prime between 3 and 7 years old,
with fecundity gradually decreasing thereafter, but no data
were presented. In a long-term telemetry study in northeastern Minnesota, Nelson and Mech (1990) reported no difference in the number of fawns accompanying old (10 years
old) does in November compared to younger females. In elk
in Yellowstone National Park aged 4–14 and .14 years,
pregnancy rates were 91% and 50%, respectively; however,
the probability of pregnancy was most directly related to
body condition not age (Cook et al. 2004). A study of moose
in British Columbia led to similar conclusions (Heard et al.
1997). Yet, in monestrous roe deer in Great Britain, senescence
in fecundity via implantation failure occurred in does .7 years
old (Hewison and Gaillard 2001), with similar results being
reported for roe deer in Sweden (Borg 1970). In France,
Gaillard et al. (2003) reported pregnancy rates of 95.6%,
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tions in blood (Gaillard et al. 1992; Ramsey and Sadlier 1979;
Robertson and Sarda 1971; Weber and Wolfe 1982; Wood
et al. 1986). With fertilization, the corpus luteum becomes the
primary source of serum progesterone, the concentration of
which peaks within the first 2 weeks of pregnancy (Harder
2005; Plotka et al. 1977; Verme and Ullrey 1984). The bimodal
distribution of serum progesterone concentrations of our study
cohort (284 deer) was remarkably similar to that reported by
Gaillard et al. (1992) for 410 pregnant and nonpregnant female
roe deer. In the latter study, pregnancy was determined with
98.5% accuracy using progesterone concentrations of 1.1
ng/ml as indicative of pregnancy. Our pregnancy threshold
value for serum progesterone (1.6 ng/ml) was closer to that
reported by Wood et al. (1986—1.8 ng/ml) for white-tailed
deer; pregnancy was detected with 97.0% accuracy in that
study. Further, mean serum progesterone concentrations of the
known-pregnant, free-ranging does in this study (95% CL ¼
3.6, 4.4 ng/ml) and of females of the complete study cohort
assessed as pregnant (95% CL ¼ 3.6, 4.0 ng/ml) were
consistent with the .2 ng/ml of Abler et al. (1976) for
white-tailed deer and close to the ultrasound-verified, mean
3.3 ng/ml 6 0.23 SE of pregnant roe deer (Gaillard et al. 1992).
Conversely, serum progesterone values of females assessed as
nonpregnant were well below 1 ng/ml, as reported elsewhere
(Abler et al. 1976; Gaillard et al. 1992; Harder 2005) and
¼ 0.3, 95% CL ¼
similar to those of males in our study area (X
0.2, 0.4 ng/ml—G. D. DelGiudice, MNDNR, in litt.). The
absence of a relationship of age, Julian date (January–March)
during gestation, or body mass with serum progesterone
concentrations supports its use as a relatively simple indicator
of pregnancy. The relative stability of elevated serum progesterone during gestation has been reported for captive
pregnant white-tailed deer (Plotka et al. 1977), elk (Weber
and Wolfe 1982), and a variety of domestic ungulates (Irving
et al. 1972; Short 1958).
The nearly complete absence of pregnancy in the fawns of
our study cohort was consistent with what has been noted for
white-tailed deer in northern forests elsewhere (Cheatum and
Severinghaus 1950; Friedrich and Hill 1982; McCaffery et al.
1998), European roe deer (Borg 1970; Gaillard et al. 1992;
Hewison and Gaillard 2001), moose (Heard et al. 1997), and
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JOURNAL OF MAMMALOGY
Vol. 88, No. 2
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FIG. 3.—A) Estimated age-specific fecundity (fetuses per doe) of free-ranging, adult white-tailed deer (1.5–15.5 years old, n ¼ 229) livecaptured during January–March 1991–2002, in north-central Minnesota; and B) the frequency of singletons, twins, and triplets in pregnant, roadkilled white-tailed deer (1.5–15.5 years old; n ¼ 735), 1972–1981, in northern Minnesota.
91.1%, and 41.7% for prime-aged, primiparous, and .12-year
old roe deer does, respectively, as well as smaller litter sizes
among the older class. Rhodes et al. (1992) observed higher
implantation failure in primiparous white-tailed does (yearlings) compared to prime-age does, but did not explore a potential senescent effect.
Although reproductive senescence relative to reduced
fertility or fecundity was not apparent in our study cohort that
ranged up to 15.5 years old, 5–6 years after the onset of
survival senescence (DelGiudice et al. 2006), reduced body
size of neonates and low early survival may very well have
been the initial manifestation of this life history phenomenon.
¼ 2.3 kg 6
We observed lower mean estimated birth-mass (X
0.2 SE versus 3.0 6 0.1 kg), hind-leg length, and girth in
neonates that died within versus beyond 1 week postpartum,
¼ 8.6 years old 6 1.5 SE) of these nonsurvivors
and dams (X
tended to be older than dams of the survivors (6.3 6 0.5 years
old—Carstensen Powell 2004). Verme and Ullrey (1984)
presented similar mean natal masses of 2.3 and 3.2 kg, associated with 70% and 10% neonate mortality, after harsh and
mild winters, respectively. Similar observations of offspring
size and increased summer mortality have been associated with
old (11 years old) and young (3–6 years old) red deer hinds
compared to prime-age hinds (Guinness et al. 1978a, 1978b).
In bighorn sheep, there was a positive association between
adult body mass, longevity, and reproductive success (Bérubé
et al. 1999). Interestingly, reproductive senescence was
observed in only the long-lived ewes with decreases in lamb
April 2007
DELGIUDICE ET AL.—FERTILITY IN WHITE-TAILED DEER
ACKNOWLEDGMENTS
Our study was supported by the MNDNR, Division of Fisheries and
Wildlife, with supplemental funding provided by the Minnesota
Environmental and Natural Resources Trust Fund, as recommended
by the Legislative Commission on Minnesota Resources; Minnesota
Deer Hunters Association; and the Special Projects Foundation of the
Minneapolis Big Game Club. D. E. Pierce of the MNDNR, the Cass
County Land Department, the United States Forest Service, Potlatch
Corporation, and the Blandin Paper Company provided valuable
cooperation and logistical support. We gratefully acknowledge B. A.
Sampson and D. W. Kuehn for technical assistance in numerous
aspects of the study. R. Nelles, R. Schloesser, and more than 120 field
biology interns provided invaluable assistance with animal capture,
care, and handling. Finally, we thank J. Olson (deceased) and the crew
of Helicopter Capture Services, Inc., for their expert performance in
net-gunning deer. We appreciate J. M. Gaillard’s review of an early
draft of the manuscript and his helpful comments. We thank J. Fieberg
for statistical consultation.
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