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Do Female Pumas (Puma concolor) Exhibit a Birth Pulse?Author(s): John W. Laundré and Lucina HernándezSource: Journal of Mammalogy, 88(5):1300-1304. 2007.Published By: American Society of MammalogistsDOI: http://dx.doi.org/10.1644/06-MAMM-A-296R.1URL: http://www.bioone.org/doi/full/10.1644/06-MAMM-A-296R.1

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DO FEMALE PUMAS (PUMA CONCOLOR) EXHIBIT ABIRTH PULSE?

JOHN W. LAUNDRE* AND LUCINA HERNANDEZ

Instituto de Ecologia, A.C., Durango Regional Center, Km 5 Carr. A Mazatlan, C.P. 34100, Durango, Durango, Mexico

Female pumas (Puma concolor) give birth in all months of the year with a possible birth pulse in July–

September. This pulse is proposed to be timed to provide increased survival probabilities to young born during

these months. We tested data on birth dates from 8 different studies for a birth pulse. We also compared survival

rates for young born in July–September to those for young born outside of these dates during a 17-year study in

Idaho and Utah. The distribution of litters born per month was not uniform, with 41% of births occurring in July–

September. Survival rates of young born in July–September were equal to those in other months of the year

(0.774 6 0.006 versus 0.779 6 0.004). We conclude that there was a propensity for higher numbers of litters to

be born in July–September. However, we rejected the hypothesis that young born in July–September had greater

survival than young born at other times of the year. We suggest that rather than there being a survival advantage

to pumas born in July–September, perhaps there is a survival disadvantage to those born in January–February

(4.5% of 484 litters). However, there were insufficient data to test this alternate hypothesis.

Key words: birth pulse, Idaho, Puma concolor, survival of young, Utah

A high degree of synchrony (¼ degree of coordination—

Sinclair et al. 2000) in births in temperate zone herbivorous

mammals is relatively common (Berger and Cain 1999;

Hungerford et al. 1981; O’Gara 1978) and is considered an

antipredator adaptation (Ims 1990; Rutberg 1987; Sinclair et al.

2000). The phenology or timing of these birth pulses is thought

to be associated with seasonal forage abundance (Bunnell

1982; Linnell and Andersen 1998). Many predator species also

show a high degree of annual synchrony in births whose

phenology is often associated with that of their prey (Bekoff

1977; Mech 1970; Persson et al. 2006). In all cases, birth

phenology and synchrony are considered adaptive traits to

enhance the survival chances of offspring (Sinclair et al. 2000).

A notable exception to this pattern of timing and synchrony

in births of predators is the puma (Puma concolor). Females

are known to give birth to young in all months of the year

(Anderson 1983). However, Logan and Sweanor (2001)

proposed that a reported higher than average number of births

in July–September constituted a ‘‘birth pulse’’ or evidence of

a certain degree of birth synchrony. They further hypothesized

that the timing of this birth pulse provided a greater survival

advantage for young born within the pulse (Logan and

Sweanor 2001:90). They argued that females were timing

and synchronizing births to take advantage of ungulate young

born the previous months and possible concentrations of

ungulates during winter months (Logan and Sweanor 2001:90).

Although Logan and Sweanor (2001) did find higher

numbers of litters born in July–September, 59% of the litters

were born outside of this period. Also, others have reported

high numbers of births in May, June, October, and November

(Ashman et al. 1983; Lindzey et al. 1994; Ruth 2004). Thus,

the hypothesis of a pulse in births of pumas needs additional

analysis. To our knowledge, the hypothesis that the timing of

such a pulse is driven by enhanced survival has not been

formally tested.

Investigating the factors that contribute to the timing and

synchrony of offspring is important in understanding the

population dynamics of any species. This is especially the case

for predator species whose parturition patterns can impact their

relationship with their prey (Sinclair et al. 2000). Conse-

quently, it is important to 1st clarify if a birth pulse exists in

pumas, and 2nd to test the hypothesis that young born within

this pulse time have a greater survival than other young.

We present birth data from a 17-year study of pumas in

Idaho and Utah and combined them with published data from

other studies to test if a birth pulse in July–September exists for

pumas. If such a pulse exists, we used data on survival of

young from our study and from the literature to test the

prediction that young born within this birth pulse had a higher

survival rate than young born outside of this period. The results

of these tests could help us better understand what factors drive

the timing of births in pumas.

* Correspondent: launjohn@hotmail.com

� 2007 American Society of Mammalogistswww.mammalogy.org

Journal of Mammalogy, 88(5):1300–1304, 2007

1300

MATERIALS AND METHODS

Study area.—The study area was located in southern Idaho

and the extreme northwestern corner of Utah. The total area of

2,400 km2 contained approximately 1,700 km2 of puma habitat

within 5 small, semi-isolated mountain ranges (65–760 km2)

with elevations ranging from 1,830 to 3,151 m above sea level.

Mule deer (Odocoileus hemionus) were the principal prey

species of pumas, with only a remnant (, 50) elk (Cervuselaphus) population. Other species preyed on occasionally by

pumas during the study period included coyotes (Canislatrans), bobcats (Lynx rufus), and porcupines (Erethizondorsatum).

Mountain ranges were internally fragmented into open and

forested habitat patches that varied in size. Forested patches

consisted of various mixes of Douglas-fir (Pseudotsugamenziesii), subalpine fir (Abies lasiocarpa), juniper (Juniperusosteosperma and J. scopulorum), pinyon pine (Pinus edulis),

quaking aspen (Populus tremuloides), and curl-leaf mountain

mahogany (Cercocarpus ledifolius). Dominant shrubs in open

areas included big sagebrush (Artemisia tridentata), gray

rabbitbrush (Chrysothamnus nauseosus), bitterbrush (Purshiatridentata), and buffaloberry (Shepherdia rotundifolia). Climate

was characterized by hot, dry summers (208C–358C) and

cold, windy winters (�258C–48C). Humidity rarely exceeded

40%, and precipitation was sporadic with an annual average

of 30 cm.

Data sources and analysis.—We used data on estimated

birth dates of puma litters during the 17 years of our study. We

collected these data during our intensive winter capture efforts

and summer monitoring of radiocollared females (Laundre

et al. 2007). When we captured young, we took standard body

measurements and body mass and estimated birth dates with

formulas we developed for our study area (Laundre and

Hernandez 2002). Through our capture and monitoring efforts

we were able to determine whether the majority of the young

we captured survived to or died before independence. Our field

procedures followed guidelines of the American Society of

Mammalogists (Animal Care and Use Committee 1998) and

were approved by the Animal Welfare Committee of Idaho

State University.

In addition to our field data, we found data on the timing of

births of puma litters from 10 other sources: 5 published studies

(Lindzey et al. 1994; Logan and Sweanor 2001; Robinette et al.

1961; Ross and Jalkotzy 1992; Spreadbury et al. 1996), 2

technical reports by Ashman et al. (1983) and Anderson et al.

(1992), 2 summaries provided by Robinette et al. (1961) and

Anderson (1983), and data reported by Ruth (2004). Sample

sizes ranged from 6 litters (Spreadbury et al. 1996) to 135

litters (Ashman et al. 1983). We included data from all studies

to examine general trends of births but limited our statistical

analysis of birth timing to the 7 data sets with �30 litters.

To test the prediction that higher than expected numbers of

litters were born in any given month, we conducted chi-square

analyses on each individual data set and a heterogeneity chi-

square analysis among the data sets (Zar 1999). We assumed an

equal distribution of litter births over the 12 months to calculate

expected frequencies. We did not group births into 3-month

blocks, that is, length of the proposed birth pulse, because of

the arbitrariness of grouping months outside of the proposed

pulse months (July–September). We reasoned that if there were

higher than expected births during these months, the monthly

comparisons should detect this difference.

To test the prediction that survival of young born from July

to September was different than young born outside of this

period, we used MICROMORT analyses (Heisey and Fuller

1985). In this analysis we were interested in the survival rate of

young from birth to age of independence rather than annual

survival rates. Thus, we pooled individuals within the 2 cohorts

of interest, all young born within and outside of July–

September, and entered them together at the beginning of the

time interval, that is, birth. We found average age to inde-

pendence in our study to be 16.1 months 6 0.26 SE (n ¼ 56) so

we used an interval length of 490 days. We only used young

that we were able to monitor from birth to either death or

independence. We tested for differences between cohorts born

within and outside of the July–September period with the Z-

statistic for a normal approximation, which we then compared

with critical values of the t-statistic for large sample sizes

(Bangs et al. 1989; DeYoung 1989; Zar 1999). We report all

means 6 SE and set alpha at 0.05.

RESULTS

We verified the presence of 61 litters (148 young) during

17 years of our study. Average litter size for the 61 litters was

2.4 6 0.08 young. Forty-eight (79%) of the 61 litters were of

collared females. We were able to determine birth months for

42 litters (Fig. 1a). Births occurred in 10 months, primarily

from June to November with a peak in August, which

represented 24.1% of total litters born. Forty-eight percent of

the litters were born in the July–September time interval (Fig.

1a). For the 7 data sets with �30 litters, we found the

percentage of litters born in the July–September interval varied

from 35.4% (Ruth 2004) to 56.7% (Ross and Jalkotzy 1992).

Combined with our data, the average percentage of young born

in the July–September time interval was 41.8% 6 2.4%. When

we combined the data for all 11 studies, we found births

occurring in every month of the year (Fig. 1b) and 40.5% of the

births occurring in July–September.

For 7 of the 8 data sets, the distribution of litters being born

over the year was not uniform (Table 1). However, the

distributions of individual studies differed significantly (v2 ¼118.8, d.f. ¼ 7). In 5 of the studies with a nonuniform

distribution, high numbers of litters born in different months

(June, July, August, and October) seem to contribute to the lack

of uniformity (Table 1). However, in the other 2 studies, the

low occurrence of litters born in January and February

contributed the most to the nonuniformity (Table 1). When

we combined the data from all 11 studies, the distribution of

the number of litters born also was not uniform (Table 1). For

the combined data, high numbers of litters born in July and low

numbers born in January and February contributed to the

nonuniformity (Table 1).

October 2007 1301LAUNDRE AND HERNANDEZ—TIMING OF REPRODUCTION IN PUMAS

Survival rates.—Of the 42 litters in our study, we had

survival data on 84 young (51 males and 33 females). Fifty-six

of these young (32 males and 24 females) reached inde-

pendence at an average age of 16.1 6 0.26 months. The

MICROMORT-estimated survival rate to independence of the

84 young was 0.72 6 0.005, or 72% survived to independence.

Thirty-four of the young were born in the July–September

period and had an estimated survival rate to independence of

0.774 6 0.006. The estimated survival rate of the other 50

young born outside of the July–September period was 0.779 6

0.004. These survival rates are essentially identical.

DISCUSSION

Examination of our data on birth dates, like that reported by

others, indicated that pumas can give birth to young in every

month of the year (Lindzey et al. 1994; Logan et al. 1986;

Logan and Sweanor 2001; Ross and Jalkotzy 1992; Spreadbury

et al. 1996). As with other studies, we also found a high

number of births in August (10) but also an almost equal

number (9) in October. When we combined the data from the

various studies we also found high numbers of litters (.10%/

month) born from June to October, with the most litters (69)

being born in July. Logan and Sweanor (2001) proposed that

these high number of litters born, especially in July–September

represented a peak or pulse of births. For most mammals with

synchronized births, including predators, the majority of

parturitions (.80%) occur within a relatively short, , 1- to

2-month, period (Berger and Cunningham 1994; Bowyer 1991;

Henriksen et al. 2005; Sinclair et al. 2000). Although births of

pumas were not concentrated in such a restrictive time frame,

births were not uniformly distributed over the year and almost

half of them occurred in the proposed pulse period (Fig. 1b).

Logan and Sweanor (2001) suggested possible geographical

adjustment of the birth pulse for differing local factors of prey

abundance, for example, the phenology of fawn production.

However, in studies from Alberta (Ross and Jalkotzy 1992),

southern Idaho (our data), to southern New Mexico (Logan and

Sweanor 2001), the largest number of litters was born in

August. Thus, the higher than expected number of births during

the proposed pulse period seems prevalent over a wide

geographical region.

Although there does seem to be support of a birth pulse in

July–September, we did not find evidence in our study that

young born during these times had a survival advantage over

ones born outside of this period. Ross and Jalkotzy (1992:421)

reported an average age to independence in their study of

15.2 6 0.5 months (n ¼ 36, 95% confidence interval [95%

CI]¼ 14.2–16.2 months, our calculations). Based on the mean

estimate of independence, young born in July–September in

their study would reach independence in October–December of

the subsequent year. Of 42 young that reached independence, 9

(21.4%) did so in October–December. If we use the 95% CI for

age to independence (14.2–16.2 months), 95% of the young

born in July–September would reach independence between

September and January. Ross and Jalkotzy (1992; Fig. 1)

reported 13 (30.9%) of the 42 young reached independence

during this time period and 19 (45.2%) young reached inde-

pendence in March–May. Based on 14- to 16-month age to

independence, these individuals would have been born outside

of the July–September period. Thus, the data of Ross and

Jalkotzy (1992) also did not indicate a higher survival ad-

vantage of young born within July–September.

Logan and Sweanor (2001) reported that of 12 females born

in their study area and recruited as breeding adults, equal

numbers were born within and out of the proposed pulse period

of July–September. Additionally, these 2 groups of 6 females

each produced approximately equal numbers of successful

litters within and outside of the pulse period (Logan and

Sweanor 2001). Thus, the data of Logan and Sweanor (2001)

tend to refute the hypothesis that birth of litters in July–

September resulted in a survival advantage to those young.

It is possible that if abundance of ungulate prey during these

3 studies was low, survival of young regardless of when they

were born would be similar. However, Ross and Jalkotzy

(1992) reported ungulates as common during their study and

mule deer abundance was high during 5 of the 8 years of the

FIG. 1.—Distribution of births of puma (Puma concolor) litters over

the year for a) the study in Idaho and Utah and b) combined data from

11 published and unpublished sources.

1302 JOURNAL OF MAMMALOGY Vol. 88, No. 5

study by Logan and Sweanor (2001). During our study,

abundance of mule deer was high the first 8 years then declined

55% and remained low during the last 9 years (Laundre et al.

2007). However, it was only during the year when deer

declined and 2 years after that survival of young differed from

the 1st years of the study (Laundre et al. 2007). Once puma

numbers adjusted downward to the lower prey abundance,

overall survival rates of young returned to predecline levels

(Laundre et al. 2007). Thus, most of the data on survival comes

from periods of apparently sufficient prey abundance.

Although there seemed to be no survival advantage to litters

born in July–September, the fact remains that the birth of litters

was not uniform. In trying to explain this pattern, perhaps we

should consider a birth hiatus rather than a birth pulse. If we

look for periods with low numbers of births rather than peaks, it

becomes obvious that there is a major lack of births in January

and February (22 of 484 litters reported or 4.5%; Fig. 1). The

lack of litters born in these months contributed to the

significant nonuniformity of births in 2 studies as well as in

the combined data (Table 1). We suggest that having immobile

and energy-demanding (because of lactation) young (Laundre

2005) at this time could be a significant survival disadvantage.

In January and February in more northern areas, deer are

concentrated and thus locally more abundant. However, if deer

shift their range use during this period, as we have observed in

our study (J. W. Laundre and L. Hernandez, pers. comm.),

a female puma with immobile young would have to travel

further to hunt. In doing so, she would have to expend more

energy, possibly exacerbated by the cold temperatures, and be

away from her young longer. During her absence, the young

could be more vulnerable to the cold temperatures and

predation or cannibalism from male pumas (Logan and

Sweanor 2001) and consequently have a lower survival rate.

This hypothesis could be tested by comparing survival rates of

young born in January–February with that of young born in

other times of the year. However, because of the low number of

litters born at these times, we currently lack the data to test this

hypothesis. We could also test this hypothesis by comparing

timing of births of pumas from southern South America, where

weather patterns would be reversed. We predict high numbers

of births in January–March. At this time, there are insufficient

published data to test this prediction.

ACKNOWLEDGMENTS

This project began in 1985 as a long-term study of puma ecology,

behavior, and conservation conducted under the auspices of Idaho

State University and the Northern Rockies Conservation Cooperative.

We thank the following organizations for supporting the fieldwork

used for the basis of this analysis: ALSAM Foundation, Boone and

Crockett Club, Earthwatch Institute, Fanwood Foundation, Idaho State

University, National Rifle Association, The Eppley Foundation,

United States Bureau of Land Management, Northern Rockies

Conservation Cooperative, Idaho Department of Fish and Game,

Mazamas, Merrill G. and Emita E. Hasting Foundation, Patagonia,

Inc., SEACON of the Chicago Zoological Society, William H. and

Mattie Wattis Harris Foundation, Utah Division of Wildlife, and

Wiancko Charitable Trust for financial and logistic support. We thank

the many Earthwatch volunteers without whose help this work would

not have been accomplished. We also thank K. Jafek, K. Allred,

J. Loxterman, B. Holmes, K. Altendorf, C. Lopez Gonzalez, L. Heady,

and S. Blum for their help in the field. We extend special thanks to

C. Patrick and G. Ordway for their support. Finally, we thank H. Shaw

and J. Linnell for their helpful comments on this manuscript.

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1304 JOURNAL OF MAMMALOGY Vol. 88, No. 5