Take action on behalf of grizzly bears and their habitat
GRIZZLY TIMES MAPS & GRAPHS
This section of Grizzly Times features maps, graphs, and associated extended captions that illustrate key aspects of history, environmental change, future prospects, and current challenges. Most of what you find here will not be found in publications or other resources produced by government researchers and managers, although every map and graph is based on publicly available information and data either in scientific publications or management reports. The emphasis throughout this section is on providing a comprehensive and integrated view of the context that has shaped the past and present as well as future prospects of grizzly bears in the U.S. Northern Rocky Mountains.
The maps and graphs are organized by major themes identified in the tabs below. To go to these sections, just click on the tab.
Yellowstone Population Trend 1959-2016
This figure shows all estimates of size made for Yellowstone's grizzly bear population, 1959-2016. This period spans the ground-breaking study by Frank & John Craighead as well as the tenure of the Interagency Grizzly Bear Study Team. Briefly, the gray dots represent estimates of minimum population size, which is essentially a rock-bottom estimate of numbers of bears in the population. The dark burgundy dots or lines denote estimates of total population size, with the light burgundy vertical line or band around each estimate the extent of uncertainty. Estimates of population size since 2006 have been based on the so-called Chao2 adjustment, using two different estimated ratios of independent males to independent females in the population, which explains the higher and lower burgundy trend lines during recent times. The gray diamonds and standard errors for 1959-1980 are the results of a population simulation by Larry Roop for the period spanning closure of dumps in Yellowstone and listing of the population in 1975.
The take-away points from this graph are: (1) using comparable estimates of total size, the population has probably doubled since listing; (2) contrary to claims made by agency spokespeople comparing minimum population estimates from 1975 to total population estimates recently, the population did not quintuple in size; and (3) agency spokespeople have been distorting information on long-term population trend by comparing figurative apples with figurative oranges.
Yellowstone Population trend 2004-2016
Population trend 2014-2016
These graphs contain the same information as the figure immediately above, but differ by focusing on more recent periods of time. The figure at left shows trend between 2004-2016 based on four different--largely incommensurate--methods. I explained three of the methods above. The fourth, mark-resight, consistently produces a higher population estimate, but with much greater uncertainty, as denoted by the relatively large uncertainty intervals. The basic point, though, is that all methods are consistent in showing little or no increase for the Yellowstone grizzly bear population during this span of time. The graph above right focuses on the three most recent years, including 2015 and 2016, during which we saw record grizzly bear mortality. The population almost certainly declined during the last three years leading up to the 2017 removal of Endangered Species Act protection for Yellowstone's grizzly bears.