The bison of Yellowstone National Park

Abstract

Records from live-trapping operations in 1964-66 provided sex and age structure information. The records suggested that female survival was favored during the calf year, but that male survival was favored the next 3 years of life, after which differential survival could not be distinguished from the records. Adult bulls outnumbered adult cows, but this could be attributed to earlier reductions. Age classes of the wintering population in the Mary Mountain area in 1964-65 were: calves, 16%; yearlings, 11%; 2.5-year-olds, 6%; 3.5-year-olds, 5%; and adults, 62%. These may change somewhat after a period with no reductions. Observed spring calf percentages of mixed herd numbers for 3 of 5 years were 19-20%. Percentages of total population were approximately 11%. These percentages may also change if reductions are not made. Significant mortality of calves at birth or just before or after was suggested by limited data. Thereafter, little mortality occurred during the first year. Nearly half the calves which survived into their first winter died before 2.5 years of age. Recruitment into the population occurred with survival to 3 years of age. Population trends suggested that increases in the population were often very slow. Reductions by man apparently were not the sole factor which caused population decreases nor retarded increases. Parasites, diseases, predation, and emigration were not important. Environmental factors culminating in usual and more-than-usual winter mortality appeared important. Herd groups followed definite patterns of seasonal movement. Spring migrations to summer ranges, occurring by the second week of June, appeared to be influenced by weather patterns and temperatures rather than snow melt or vegetation changes. Temporary fall movements occurred in conjunction with fall storms at higher elevations; final movements to winter ranges occurred by mid-November. Bull movements were somewhat more irregular. Movements and distribution on summer range areas appeared more influenced by the presence of biting flies than by possible factors of breeding activity and vegetation changes. A species of Symphoromyia of the Rhagionidae was implicated. Mixing and interchange between population subunits resulted in designation of three herds according to their use of winter range areas. These three subunits formed two breeding populations in summer. Little contact occurred between members of these two populations at any time. The limited neckband information on marked adult cows suggested that they have an affinity for a given winter range regardless of summer movements. Temporary shifts of population segments from one winter range to another have occurred. Thus, although no population segment is isolated from another, the three exist as fairly separate entities in terms of winter range. This may explain the lack of population emigration to and reestablishment on unoccupied ranges either within or outside the park since historic times. Analysis of 22 rumen samples showed that sedge was the most important forage item. S...

Bisoniana LXXII. The behaviour of wisent and bison in larger enclosures

“…For the wisent, Krasiński (1967) writes that mature bulls are in the herds only during the mating season; they join the herds from late July until the beginning of October and migrate independently from the herds during the rest of the year. Also Mohr (1952) On the other hand, Meagher (1973) says that in the bison »mature bulls were commonly seen in the mixed groups at all seasons«. Heck (1968) only mentions that the bison bulls live somewhat apart from the herds during calving time (April-June), but according to Lott (1974) the bulls live solitary except during the mating season (July-August), although the bulls may join the herds in other times of the year as well.…”

“…Migrations are necessary, as they normally live in large herds, which soon brings about a scarcity of food at one spot. As mentioned, Meagher (1973) sees biting insects as an important cause. Roe (1972) discusses flies as a cause of wallowing; this behaviour by the way was seldom seen in the »Amsterdamse Bos« animals.…”

“…Little has been published yet about day rhythm of the bison. As for the annoying flies, mentioned by Mohr (1952), it should be noted that Meagher (1973) refers to »biting insect populations« as an important cause for large migrations of wild bison herds. Table 5 shows the number of times an animal was seen in each of the sections on one day (average of seven observation days); this frequency was expressed in percentages, and an impression of these frequencies may be gained from Fig.…”

Observations of Wood Bison Swimming across the Liard River, Northwest Territories, Canada

“…May 2003). Although accidents are not usually considered as a substantial mortality factor, bison population dynamics are often punctuated by mass "accidental deaths" when entire groups of animals are lost (Meagher, 1973). Before the damming of the Peace River, major spring drownings of Wood Buffalo Park bison were not uncommon; 3000 animals were lost in one year (Fuller, 1966;Carbyn et al, 1993).…”

“…Drowning is a source of mortality for other bison populations such as those in Wood Buffalo National Park, Yellowstone National Park, and Mackenzie (Meagher, 1973;Carbyn et al, 1993;Damien Joly, pers. comm.…”