Proceedings of the Seventh Mountain Lion Workshop

MODELING OFFSPRING SEX RATIOS AND GROWTH OF COUGARS
DIANA M. GHIKAS, Department of Biological Sciences, University of Calgary, 2500
University Drive N.W., Calgary, AB T2N 1N4, Canada, email: dghikas@ucalgary.ca
MARTIN JALKOTZY, Arc Wildlife Services Ltd., 3527-35th Avenue S.W., Calgary, AB T3E
1A2, Canada, email: martin_jalkotzy@nucleus.com
IAN ROSS, Arc Wildlife Services Ltd., 3527-35th Avenue S.W., Calgary, AB T3E 1A2, Canada
RALPH SCHMIDT, Arc Wildlife Services Ltd., 3527-35th Avenue S.W., Calgary, AB T3E
1A2, Canada
SHANE A. RICHARDS, Department of Biological Sciences, University of Calgary, 2500
University Drive N.W., Calgary, AB T2N 1N4, Canada
Abstract: We further examined data from the Sheep River cougar study conducted in southwest
Alberta from 1981-94. We asked is there evidence of an equal or constant offspring sex ratio, or
do sex ratios vary over time, as a function of the mother's age, geographic location or population
size. Logan and Sweanor (2001) analysed offspring sex ratios as a function of mother's age and
found that sex ratios of first litters were significantly different from subsequent litters and 1:1.
Logan and Sweanor (2001) suggested that offspring sex ratios might be influenced by the
mother's physical state (i.e., young mothers produce less-costly females so energy can be
allocated to growth). We investigated possible relationships between offspring sex ratios and
cougar growth, and whether growth varied by sex and geographic location. The study area was
divided into east and west locations based coarsely on prey abundance and cougar mortality.
Probabilistic models were formulated for the sex-ratio analysis. A deterministic model based on
the flexible Richards curve (Maehr and Moore 1992) was used to predict mass growth. Model
predictions that were the most parsimonious with the data were identified using corrected Akaike
Information Criterion. Parameters were estimated using maximum log-likelihood. The most
parsimonious model predicted that offspring sex ratios vary yearly. Evidence was not strong for
sex ratios varying as a linear function of mother's age. The growth model predicted that females
attain 91-92 % of adult mass by 25-26 mos, indicating that growth is largely completed prior to
first reproduction ( x =30.0 ± 1.8 mos SE, Ross and Jalkotzy 1992). In years with poor resource
conditions, the mother's physical state may result in more female offspring being reared than
male. Predicted mean mass at age of independence for male and female offspring was 48.8 kg
and 34.1 kg, respectively, inferring males are more costly to rear. The growth model that varied
by sex only had the highest weight of evidence; adding geographic location did not result in a
more parsimonious model. All growth models were unable to accurately estimate birth mass,
which was also found by Maehr and Moore (1992).
LITERATURE CITED
Logan, K. A., and L.L. Sweanor. 2001. Desert Puma: Evolutionary ecology and conservation of an enduring carnivore. Island
Press, Washington.
Maehr, D.S., and C.T. Moore. 1992. Models of mass growth for 3 North American cougar populations. J. Wildl. Manage. 56:
700-707.
Ross, P.I., and M.G. Jalkotzy. 1992. Characteristics of a hunted population of cougars in southwestern Alberta. J. Wildl.
Manage. 56: 417-426.
PROCEEDINGS OF THE SEVENTH MOUNTAIN LION WORKSHOP
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