SABAP2 RANGE CHANGE MAP FOR BLUE CRANES IN THE OVERBERG & SWARTLAND
Posted on the 28th June 2010
(This great news regarding Blue Cranes numbers in the Overberg and Swartland was first published by the Animal Demography Unit (ADU) - visit www.sabap2.adu.org.za. - Ed.)
Blow your vuvuzela, the national bird, the Blue Crane, is increasing in the Overberg and Swartland. This range change map is for the Blue Crane, and focuses on two regions where the species is known to be increasing, the Overberg and Swartland districts of the Western Cape. Each square is a quarter degree grid cell, as used for SABAP1. The number in the top of each square is the reporting rate from SABAP1. The lower number in each square is the SABAP2 reporting rate, calculated by pooling together all the checklists received so far for pentads in that quarter degree grid cell. The reporting is the ratio (number of checklists with the species)/(total number of checklists).
The dominant colour in this map is green. In these cells, the SABAP2 reporting rate is larger than the SABAP1 reporting rate. Often, it is far larger. In the Swartland, on the west coast, there are cells where the reporting rate has increased from below 5% to above 30%. In the cells coloured blue, the species was not recorded in SABAP1 but has been recorded in SABAP2. So the range has continued to expand. The ADU's CAR project, which is based on actual counts of Blue Cranes, shows large increases in the abundance of this species across the Swartland and Overberg, and it is pleasing that SABAP2, which is based only on records of the presence or absence of species in a checklist, is able to show the same patterns.
In the orange cells, the SABAP2 reporting rates are lower than the SABAP1 reporting rates. But in almost every case, the change is small. It is therefore unlikely that the abundance of Blue Cranes in these cells has really decreased. There are seven red cells in which Blue Cranes were reported in SABAP1, but not yet in SABAP2. In all except one, the SABAP1 reporting rate was less than 5%. The one with a reporting rate of 14.1% was quarter degree grid cell 3321CD (Sandkraal), and there were only seven SABAP1 checklists, with Blue Crane reported on one (and 1/7=14.1%). There are only three SABAP2 checklists for this cell so far, and all are for only one of the nine pentads within the cell. The bottom line is that, for these comparisons to be really strong, we need lots and lots more checklists for SABAP2 pentads!
Sadly, the overall picture for Blue Crane is not as good as it is in the Overberg and Swartland, and the reporting rates across the northern provinces of South Africa mainly show declines. We will put the range change map for the entire SABAP2 region onto the website soon.