Although mature females produced from 3 to 7 calves, none produced calves in alternate years. Nonlactating females produced equal numbers of male and female calves. Manipulation of age structure in bison should have little effect upon calf production unless a substantial proportion of adult females reach age Meagher suggested that a preponderance of aged females could reduce calving rates. Halloran concluded that calving rates in the Wichita Mountains were influenced by a tendency of individual females to produce calves in alternate years, a pattern that he attributed to superior condition of nonlactating females. Rutberg reported that 25 of 29 nonlactating females at the National Bison Range carried male fetuses, compared with 26 of 53 male fetuses in lactating females.
Maternal investment and sex ratio adjustment in American bison calves
Bison Producers of Alberta :: Calving Patterns Among American Bison
The human sex ratio is the number of males for each female in a population. This is a list of sex ratios by country or region. The table's data is derived from The World Factbook ,  except when otherwise indicated. It shows the male to female sex ratio as estimated by the United States' Central Intelligence Agency. However, there are differences between the estimates by The World Factbook and numbers reported by the census offices of respective countries. For example, The World Factbook in reported Switzerland's sex ratio at birth as 1.
Calving Patterns Among American Bison
As stated previously, the Yellowstone bison of the present derive from two subspecies: plains bison from Montana Pablo-Allard herd and Texas Goodnight herd , introduced in , and a remnant of the original wild population of mountain bison. Skinner and Alcorn summarize the introduction, numbers, and subsequent management practices pertaining to the introduced herd at the Buffalo Ranch in Lamar. Population numbers are from that source and other official reports.
Please take this quick survey to tell us about what happens after you publish a paper. Behavioral Ecology and Sociobiology. Cow-calf behavior was observed in American bison Bison bison to determine if mothers invested differentially in sons and daughters. Cows nursed sons significantly longer than they did daughters in their first three months of life.