Average Body Mass of Male and Female Moose in Vermont

Amanda Pomeroy

September 14, 2015

Abstract

With our data, we seek to determine if there is a statistical difference between live cow and bull moose masses that are three years or older in the Vermont population. Our biological hypothesis states that male mass would be greater than female mass due to an increase in testosterone. Our null hypothesis states that there would be no difference in mass between the sexes. Our alternative hypothesis states that there will be a difference between the mass of the different sexes. The data was collected through the Vermont Gaming Commission Database at a certain check station for large game permits. All data was of dressed moose weights, and so a multiplier of 1.45 was used to accurately gauge the weight of live moose. The data was analyzed with an ANOVA test for variation within the data of the two different sexes. The statistical difference was determined through the p-value of the test, which was .00125. This indicates that there is a statistical difference, which leads us to reject our null hypothesis and support our alternative. Overall, we concluded that the body mass of live bulls was greater than the body mass of live cows, and ultimately body mass can be used as a characteristic for the determination of the sex of a moose in the 3 year and older age class.

Introduction

Moose are one of the largest mammalian species found in the Northeastern United States, and are the official state mammal in the state of Maine. The population of these animals has been affected by the presence of both environmental and human influences, including winter-kill, parasites, vehicular collisions, and hunting (Musante et al. 2010). The annual kill count of moose due to legal hunting policies has increased from 636 in 1980 to 2,582 in 2011 (Andreozzi et al. 2015). Legal regulations are encouraged to protect the moose populations from any major harvesting damages. Parasitism not only affects the annual death rates of moose, but also plays an important role in the overall size measurements of moose in a population. Andreozzi et al. (2015) has linked the greater presence of parasites to overall smaller bull size. In addition to epizootics, sexual dimorphism has been attributed to environmental seasonality, forage quality, and male to female ratios in a specific population. Generally, greater environmental seasonality and forage quality lead to an increase in sexual size dimorphism, while male body growth decreases as the number of males within a population decreases (Garel et al. 2006). Jarman (1983) noted consistent differences in size, coloring, and shape between male and female moose, with the greatest dimorphisms found in medium sized specimens.

Taking the previous observations into account, our study aimed to determine if there was any significant difference in cow and bull moose body masses for the age group of 3 years and up by analyzing the dressed carcass data from check stations in Vermont. Our biological hypothesis stated that bull mass would be greater than cow mass due to the increased presence of testosterone in the system of male moose. Our null hypothesis stated that there would be no significant difference between the average masses of male and female moose, while our alternative hypothesis stated that male moose would have a greater mass than female moose.

Methods

The study was conducted in the state of Vermont on the east coast of the United States. Our data was collected at one check station that serves a specific region of the state. The weights of 20 moose of each sex were collected from hunting records that represent the dressed carcasses of animals, which means that the internal organs have been removed and the carcass was cleaned in the field. The data was analyzed using an ANOVA variance test to determine if there was any significant difference in male and female moose mass. The hunting record data set was multiplied by 1.45 to account for the weight of the internal organs to better estimate the weight of live moose. These mathematical adjustments were made in the R software program.

Results

Our histogram concerning live female moose mass was relatively uniform, ranging from around 500 to 1200 pounds. The average weight of a cow was calculated to be within the range of 800 to 900 pounds. On the other hand, our data concerning live male moose mass showed a uni-modal graph with a seemingly normal curve.The average weight of a bull was calculated to be within the range of 1,000 to 1,100 pounds. The overlapping histogram of both cow and bull masses showed that overlap existed in the weight ranges of 600 to 1,200 pounds. The box-plot of moose mass by sex shows the average weight of cows is less than the average weight of bulls. The ANOVA test of variance between the cow and bull masses yielded a p-value of .00125.

Discussion

In summary, the average mass of male moose was greater than the average mass of female moose. Generally, this data would support the alternative hypothesis and the biological hypothesis, although the difference in mass cannot be attributed solely to testosterone with the conclusions of this study, as our biological hypothesis suggests. The null hypothesis would be rejected. We can determine this because of the p-value of our ANOVA test. The p-value of .00125 is less than .05, which is a statistically important value. This p-value means that the results of our study are .125% likely to happen if the null hypothesis were true. This low probability gives us the evidence to support the alternative over the null, and our alternative correlates with our biological hypothesis. This also provides us the information to answer the state biologist’s question about significant differences in male and female body weights. Our data suggests there is a significant difference, once again, because of our p-value. This indicates that weight is a useful characteristic for distinguishing among male and female moose that are three years and older.

References

Andreozzi, Haley A., Perkins, Peter J., and Kantar, Lee E. 2015. Analysis of Age, Body Weight and Antler Spread of Bull Moose Harvested in Maine, 1980-2009. Alces 51: 45-55.

Garel, Mathieu., Solberg, Erling J., Saether, Bernt-Erik., Herfindal, Ivar., Hogda, Kjell-Arlid. 2006. The Length of Growing Season and Adult Sex Ratio Affect Sexual Size Dimorphism in Moose. Ecology 87: 747-758.

Jarman, Peter. 1983. Mating System and Sexual Dimorphism in Large Terrestrial, Mammalian Herbivores. Biological Reviews 58: 485-520.

Musante, Anthony R., Perkins, Peter J., and Scarpitti, David L. 2010. Characteristics and Dynamics of a Regional Moose Alces alces Population in the Northeastern United States. Wildlife Biology 16(2): 185-204.