Researcher: Mike and Ann ScottRegion: Etosha National Park, Namibia
BackgroundPopulation size in Etosha National Park was estimated at 80 birds in 1989 but by 1994 this tiny population had declined to only 60 birds, comprising 49 adults and 11 juveniles. Apart from an isolated high count of 138 birds in July 1976, there are no further records of the population size ever exceeding 100 birds.
The species as a whole does not seem to migrate far, and Namibian birds are known to move locally only within the Etosha NP area, where the birds have been observed to descend in the evening from high level to waterholes, where they roost. The fact that there are very few records of movements from elsewhere suggests that Etosha is probably a closed system.
Blue Cranes occur primarily in dry grassland habitat where water regularly occurs. In the arid grasslands of Etosha the favoured areas are the perennial springs around the pan edge and isolated waterholes in grassy plains. Nests occur on the ground in open grassy areas, not far from water, so that chicks may be led to water to drink and escape predators. The cranes feed on seeds and flowers from grasses, and frogs, reptiles and fish; in Etosha they regularly turn over elephant and ungulate dung to consume dung beetles and other insects.
Isolated and small populations can be prone to inbreeding effects if genetic heterogeneity has been lost; this could apply to Etosha’s cranes, given the small breeding population estimated at just 24 pairs, and their apparent genetic isolation (M Wink in litt.). This, disease and catastrophic events such as severe drought under global climate change could push such a small population to extinction within a generation or two.
ObjectivesBlue Cranes (Anthropoides paradiseus) are the world’s most range-restricted crane species and occur mainly in South Africa, with three discrete sub-populations. However, a curious and highly isolated breeding population of these cranes also occurs in Namibia, over 1 000km north of any other population. The birds occur within Etosha National Park and on the grasslands to the north, and pose a genetic and conservation puzzle – how does this particular population survive without mixing with South African birds and in particular, within the predator-rich Etosha National Park?
From a conservation point of view they are classified as Critically Endangered in Namibia because of their tiny population size and the 25% decline in numbers since the late 1980s. This project assesses conservation and ecological factors that have shaped this population and compares them with what is known about South Africa’s Blue Cranes, as a basis for a conservation strategy for the Blue Crane population in Namibia.
This two-year study aims to determine the reasons for the small and possibly declining population of Blue Cranes through population size monitoring, and identify the factors critical in the ecology and life-history of these birds in Namibia. Two students will benefit from training and supervision, and a Species Management Plan for the cranes will be one of the outcomes, along with some papers in scientific journals on this critically endangered species.
MethodologyThe current size and age composition of the Namibian Blue Crane population is being addressed by means of a national survey of the species. It began in March 2007 with an aerial survey by the Namibia Crane Working Group to determine any breeding areas – followed up by ground observations and includes an estimate of the adult: juvenile ratio. A second survey of all likely waterholes, through a coordinated ground count by volunteers and MET staff, will take place at the height of the dry winter season.
Habitats used by Blue Cranes in the Etosha area on a seasonal basis are being investigated and include the use of space during the breeding season as opposed to during the winter (dry) season, as well as limiting factors in terms of breeding habitat, in relation to predators and diet and use of nearby water.
Behaviour and breeding success is being investigated, for example timing, nest site selection, feeding behaviour and survival. This project is collaborating with a comprehensive study being undertaken to compare Namibian and South African Blue Crane genetic samples by collecting blood samples. Genetic sampling will be informative as to whether this population is inbred and thus something of its immediate history.
The participation of all crane workers and supporters in Namibia (including the Ministry of Environment and Tourism) and elsewhere will be promoted through the Namibia Crane Working Group – headed by coordinators Ann and Mike Scott, who also have longstanding links with the Overberg Crane Group, Western Cape; the EWT South African Crane Working Group; and the International Crane Foundation. One of the aims of the project is to build capacity for Namibian conservationists.
A Species Management Plan will be formulated once the results from this two-year survey are available.
Our annual wet-season combined aerial/ground crane census at Etosha National Park and northwards took place from 17-24/3/12. This survey is part of a biannual series started in 2006. The census yielded a total count of only 18 adults and two chicks (all within the Park) – a further decrease in adult numbers for the wet season from 32 in April 2010 and 24 in April 2011. However, this figure is not regarded as the maximum count for 2012…
The rains were again excellent this year and there was a considerable amount of water in the Pan, especially the eastern parts, while Lake Oponono was still flooded. Our aerial survey area started at Namutoni and Andoni, then ran westwards across the Oshigambo River to the Ekuma River where we turned northwards and criss-crossed the Lake Oponono area. From here we turned south into the Park again and westwards to Ozonjuitji m’Bari, then back eastwards via Okaukuejo. As with previous surveys in March/April, we found a smallish flock of non-breeding Blue Cranes at Fischer’s Pan, in this case only seven birds. Three Crowned Cranes (18° 15’S 15° 45’E) and two Wattled Cranes (18° 15’S 15° 45’E) were recorded in the Lake Oponono area, but no Blue Cranes were seen outside the Park.
The ground count yielded 11 adults (five pairs) and two chicks (Salvadora plains and Namutoni causeway), bringing the total to 18 adults and two chicks. Two more chicks observed previously (Halali seep and Namutoni causeway) do not appear to have survived.
Although this count is disappointing, we still need to wait for the dry season when more of the cranes appear to return to the Park, to obtain a final count for 2012.
Comparing the results from previous counts of Blue Cranes at Etosha and Lake Oponono from 1992-2012, it is clear that their numbers in Namibia have declined. For the full report, please click here.
The Blue Crane is rated as globally Vulnerable, and Critically Endangered in Namibia. The isolation of the small subpopulation and its survival in an arid, predator-rich environment within Etosha and the Lake Oponono wetlands to the north pose a conservation enigma. In 1992, the Namibian population of Blue Cranes was estimated at 80 with an apparent decline to 60 in 1994. As part of the Namibia Crane Action Plan, the Namibia Blue Crane Project was initiated in March 2006, but the dropping numbers, despite conservation efforts, has lead to a reassessment of the project and the development of a five-point action plan in November 2010.
One of the main findings has been that, since a count of 60 in April 2006, total numbers have not exceeded 35 birds. This trend could possibly be related to good rains at Etosha and/or within the Cuvelai catchment in 2006, 2008 and 2009; it is believed that there may be a ‘floating’ population of non-breeding birds that may have found (temporarily) suitable habitat elsewhere – hopefully in a crane-friendly area. However, a combined aerial/ground survey in April 2010 yielded only 30 adults and two chicks; and no Blue Cranes at the flooded Lake Oponono. With mounting concern, we waited until the dry-season survey by the MET in August 2010, when the cranes would be concentrated around water points. This resulted in a total count of only 31 cranes, all at Lake Oponono. This now appears to be the total population of Blue Cranes in Namibia; if so, there has been a decline of 50% in numbers in less than five years.
Consequently in November 2010, the team came up with a five-point Blue Crane Action Plan, namely to collate and analyse existing data, determine where the birds are and how they use the landscape; investigate habitat changes and address human impacts and other threats.
A census was carried out in April, which showed a decline from the year before. For the full report, please click here.
Our census of Blue Cranes at Etosha National Park and Lake Oponono this month yielded a total count of only 30 adults and two chicks. It appears that our maximum figure of 35 cranes from last year is still no higher; and considerably lower than previous estimates of 80 in 1992, 60 in 1994 and 67 in April 2006. We would like to do a follow-up dry-season count in August 2010, when the cranes are more concentrated around the water points, and this should provide a more conclusive figure.
We found no cranes of any species at Lake Oponono during the aerial survey, although a total of 12 Wattled Cranes and Crowned Cranes was recorded here during the Summer 2010 Wetland Bird Counts. During our count we found a still considerable amount of water in this area, and our (subjective) impression was that there could be more human activity and possibly fewer birds in general. We did eventually find a large flock of 18 Blue Cranes at Fischer’s Pan that could have been gathering in preparation for moving off for the dry season.
Only four chicks have been recorded for the 2010 season (2x at Springbokfontein; 1x at Halali seepage; and 1x Chudop/Doringdraai).
While we are still hoping that there may be a splinter group elsewhere (due to the good rainfall in recent years), we also have to continue investigating why Blue Crane numbers have declined. Could it be due to changing environmental conditions? Increased predation? Increasing disturbance outside the Park? We hope to organize a planning meeting after the August 2010 dry-season count to reassess the situation.
The ups and downs of telemetry
Wilferd Versfeld has regularly been obtaining invaluable data from our radio-tracked birds, through persistent and opportunistic monitoring efforts. The first VHF transmitter fitted to a Blue Crane signalled movements of 120 km to Andoni and Lake Oponono.
Two more birds are part of a group of eight that has consistently and regularly been found in the Salva-dora/ Halali area. On 18/5/10, Wilferd reported a signal heard on the Pan from the Springbokfontein causeway. The gravel pits at Halali are drying up and have already dried up at Salvadora so that could have made them move. These data indicate that, in addition to springs/seeps around the edge of the Pan, gravel pits containing relatively fresh rain water also appear to be important for the survival of the cranes.
Two new juveniles fitted with telemetry – but
On 16/1/10 we recorded two adult cranes incubating at Springbokfontein. Exactly a month later two downy chicks were spotted by Ranger Dawid Tsumeb from Halali. When we flew over the same area on 22/4/10, we spotted the family group of four out on the spring area near the edge of the Pan at Springbokfontein.
The good news is that, with Wilferd’s expert assistance and Sageus Garieseb’s tireless running ability through the mud, both chicks were captured on 22/4/2010. We fitted a radio transmitter to one and a satellite tracking device to the other. The chicks looked fine the next morning and the family group was busily occupied with feeding. We had high hopes that, if the chicks fledged in 2-3 weeks’ time, this dual telemetry would supply further critically important insights into crane movements.
Unfortunately the chick with the radio transmitter was killed by a predator and the satellite transmitter from the other chick has stopped moving. We do not know what has happened as we are unable to access the area at present.
We observed two pairs of cranes seemingly changing mates in the last few months. Neither of these has produced a chick yet.