02 Oct 2009 Annual Game Census
The 2009 annual game census was successfully completed over the period 27th to 30th September. We were a little concerned that the early green flush of the trees would impede our ability to see animals and preliminary results suggest that this may indeed have been the case. Hence, next year’s count will definitely be done earlier in September.
With Hanno’s departure, Gerhardt Lorist assisted with the count and thoroughly enjoyed the experience, getting to witness the beauty of Welgevonden’s wilderness from the air. Some interesting observations included a lot of Denham’s Bustard, plenty of bushpig on the southern plains and a leopard near Bee-eater pass.
An aerial census is not designed to determine the total number of animals on a property but rather to monitor trends over time. As such, the purpose of conducting a census is not accuracy but rather precision. It is simply not possible to count all the animals on a property. Certain animals are easier to count than others simply due to habitat preferences (e.g. white rhino versus black rhino), time of activity (diurnal vs. nocturnal), size of animal (e.g. kudu vs. klipspringer), herd size (impala vs. bushbuck), choice of shelter (e.g. under a tree or underground) and various other factors.
Hence, an aerial census is primarily designed to monitor trends in populations of medium to large diurnal herbivorous mammals. However, one cannot realistically expect to count all individuals in a population. As the day advances, animals seek shelter under trees and become increasingly difficult to spot. Animals also move from one census grid into another, leading to possible under or overcounting (it is assumed that these balance each other out).
If one looks at the differences between the 2008 and 2009 data, the biggest negative differences are for species that are notoriously difficult to count, i.e. warthog, waterbuck (prefer thick riverine habitat) and reedbuck (prefer long grass in marshy habitat).
In light of the above, management is of the view that the 2009 data are conservative for a number of reasons as follows:
a. The early green flush greatly reduced visibility, particularly along the rivers
b. The week of the census was continuously overcast, which not only affects animal behavior but also reduces visibility due to shadows being less distinct
c. Hanno was replaced by an extremely enthusiastic but new and inexperienced observer
In addition, if one considers that the observed recruitment rate for the prey species on Welgevonden is approximately 15%, the net loss of animals due to predation since the 2008 September count, which took place after the 2008 game introductions, will have been in the region of 600 animals. Also, it is worth noting that our original predation models contemplated 10 killing leopards on the property whereas Lourens’ more recent data suggest that there are up to 30 leopards on the property, 20 of which can reasonably be assumed to be killing leopards. This is a clear demonstration of the importance of ongoing research and monitoring. Given the above considerations, the most important and encouraging aspect of the 2009 census is that the numbers are still progressing towards our medium-term goal of attaining 4000 head of game on the property.
The census data from 1998 to 2009 are presented in the table below.
- Species highlighted in red are those species whose numbers should not/cannot be controlled by management as they should be self-regulating.
- Species highlighted in blue (gemsbok and tsessebe) are those species that can be controlled by management but which management have opted not to control due to poor adaptation to the environment (tsessebe, which is also an extremely expensive animal to buy) or due to their historical range not encompassing the Waterberg (gemsbok).
- Species highlighted in green are those that can be controlled by management but which are either of a lower priority at this point in time (bushbuck, nyala, giraffe) or are doing fine (reedbuck, rhino, waterbuck) or are too expensive to readily manipulate (buffalo).
- Species highlighted in yellow are those species which have been prioritized by management in terms of the establishment of the self-perpetuating grazing lawns and/or predation. Elephant management has been prioritised as the elephant is a keystone species with the potential to change its environment.
Note: Elephant Contraception:
Although only 104 individuals were counted during the recent census, the elephant population on Welgevonden currently stands at 121.
The contraception programme, which has been running since 2006, has been enormously successful so far with no new calves being born in the last two years. As a result of this remarkable success, management took a decision to allow 6 of the breeding cows to breed so as to maintain the social integrity of the herds. Hence, these 6 cows were not inoculated during the 2009 contraception event, which was conducted during the week of the census.