Population Size and Trends. The Grey Crowned Crane was considered the most common crane in Africa in 2004 with the population estimated at 50,000 to 64,000 individuals (Xxxxxxxx et al. 2007). It has, however, been experiencing a steady long term decline across much of its range. When this species was uplisted from Least Concern to Vulnerable in the 2009 Red List update, there was some evidence to suggest that declines may have exceeded a rate of 50% during the past three generations or 45 years (Xxxxxxxx et al. 2007), but data were regarded as patchy and an overall decline of 30-49% was considered a more reasonable estimate. With the addition of more complete data, overall estimates suggest that the species’ global population has declined by over 50% in 19 years, and when these data are extrapolated to a period of 45 years, assuming an exponential trend, the calculated rate of decline is c.65-80%. This sharp decline, together with the fact that the issues causing this decline have been in existence since the 1960’s and are showing no signs of abating, has led to the uplisting of Grey Crowned Cranes from Vulnerable to Endangered in the 2012 Red List update (Birdlife International 2012). The Southern African Grey Crowned Crane is also listed in Column A, categories 1b and 1c and the East African Grey Crowned Crane in Column A, categories 1b and 3c of the AEWA Table 1a/. The status of the Grey Crowned Cranes sub-species was defined as follows in the Rwandan workshop: East African sub-species: Significant long-term population decline with fragmenting range and rapidly contracting area of occupancy. Southern African sub-species: Declined population with fragmenting range and contracting area of occupancy. Grey Crowned Cranes are most abundant in Kenya, South Africa and Uganda, albeit that Kenya and Uganda have and continue to suffer significant declines in population. South Africa currently has the most stable and viable population on the African continent and the large floodplains of Zambia support a substantial and increasing population. Burundi, Mozambique, Rwanda, Tanzania and Zimbabwe all have relatively smaller, but still viable populations of between 100 and 2000 birds each. Botswana, Malawi and Namibia have very few Grey Crowned Cranes remaining, and the status of the species in the Angola and the Democratic Republic of Congo is largely unknown. Of note is that Southern Sudan has recently reported sightings of Grey Crowned Cranes, a new species for the country, but still in ve...
Population Size and Trends. Astragalus proimanthus is currently known from three extant occurrences worldwide, two of which were newly discovered or relocated after more than 50 years during surveys in 2000. These occurrences consist of six extant subpopulations that can be further subdivided into 25 colonies (colonies are defined as discrete population segments located within 0.5 miles of other segments and not isolated by major breaks in habitat). An additional subpopulation reported by Whiskey Basin Consultants (1981) from 4-4.25 miles east of Sweetwater County Highway 1 and north of the Henry’s Fork River has not been relocated since 1981 and may be Figure 5. Habitat of Astragalus proimanthus on gentle south-facing slopes of clay-rich soil derived from the Green River Formation along the slopes on the south side of the BLM road paralleling the Henry’s Fork River (Occurrence # 007). Note the small gray mats of A. proimanthus in the foreground. extirpated. Individual colonies range in size from 0.1 to over 40 acres and may number from less than one dozen plants to over 3200 (Table 3). Population estimates for Precocious milkvetch have varied widely over the years, reflecting survey intensity. Xxxx and Xxxx (1980) estimated the population at 400 plants in 2 main colonies on either side of Sweetwater County Highway 1. Xxxxxx Xxxxxxx and associates conducted the first intensive survey in May 1981 and estimated the total population to be approximately 22,000 individuals, based on extrapolations from subsamples of 12 major colonies in 5 subpopulations (Whiskey Basin Consultants 1981). Marriott (1989) resurveyed this area in May-June 1989, focusing on identifying new populations and initiating a monitoring program, rather than a quantitative census. Her population estimate is significantly higher, ranging from 25,000-40,000 individuals in 19 colonies. Marriott estimated each major subpopulation to contain 5000-10,000 plants based on ocular estimates of habitat quality. Xxxxx Xxxx and Xxx Xxxxxxx counted 2644 individuals at 11 colonies in June 2000 and estimated the total population at these sites (representing all three known occurrences) at 5500-7000 plants. Extrapolating from these figures, the current total population of Astragalus proimanthus is estimated at a minimum of 10,500-13,000 individuals. Trend data are difficult to determine for these populations because of differences in survey methodology, the lack of baseline data for occurrences 004 and 007, and the drought conditions p...
Population Size and Trends. Information on population size, reliability of the estimates and the statistical analyses of the trends. Graph of trends over time with associated statistical parameters.
Population Size and Trends. From 1955 until the mid-1970s, population size was estimated at 10,000 individuals or fewer (Xxxxxx 1959, Xxxxxxxxx 1977, Xxxxxxxx-Xxxxxx 1975, 1981) In the mid-1970s, the population was thought to comprise 9,000–10,000 or even 13,000 individuals (Mullié & Poorter 1977, Poorter 1981), rising to 16,000-17,000 by the mid-1980s (Xxxxxxx et al. 1985, Monval & Pirot 1989, Xxxxxxx et al. 1991). A dramatic increase in numbers occurred during the late 1980s and early 1990s; 25,800 birds were recorded in January 1990 and 29,000 in January 1995 (Xxxxxxx 1997). However, the most recent estimate of the NW European Bewick’s Swan population, derived from coordinated international counts made in mid-winter, was only 21,500 individuals in 2005 (Xxxx & Xxxxxxx 2010, Xxxxxxx et al., in prep.) following a decline since the mid-1990s (Xxxxxxx 1997, Xxxxxx et al. 1999, Xxxxxx & Xxxxx 2006, Wetlands International 2008). 35000 30000 25000 20000 Swan Counts IWC (imputed) 15000 10000 5000 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
