07. Observations of Eagle congregations at a Redbilled Quelea colony in the Kruger National Park Duan Biggs University of South Africa, PO Box 392, Unisa, 0003, duanbiggs@freemail.absa.co.za On 15 and 16 January 2001, observations were made at a Redbilled Quelea Quelea quelea colony in the Kruger National Park (KNP). Observations were made predominantly on foot on walks into the colony, as well as from a vehicle from a nearby road. The colony was situated along the Mhlambamadube stream about 15 km south of Skukuza restcamp. (The junction of the S112 and the H3 is a good landmark.) The colony was dispersed in sections of suitable habitat along the Muhlambamadube stream and its tributaries. The full extent of the colony was not established but, judging from the activity of the eagles and other birds of prey feeding at the colony, it was probably spread out along the stream over a distance of up to 6 km. The sub-colonies were situated in thorn-thickets, which occur near the valley bottoms, and the tree species that appeared to be favoured for nesting were Sickle Bush Dichrostachys cinerea, Buffalo Thorn Ziziphus mucronata and Acacia spp. The trees used for nesting were mainly fairly small, seldom reaching over 6 m in height. To estimate the number of nests per tree, the number of nests in a few trees were counted and the figure obtained was 50–60 nests per tree. During the time of observations, the chicks were ‘branching’; with an average brood size of three (Maclean 1993), there were sometimes as many as 100–150 chicks clambering around the branches of the trees used for nesting. ‘Branching’ refers to the period when young birds are not yet able to fly properly and spend their time practising, out of the nest, in the tree in which they bred out. Predators at the colony Counts were made of the number of eagles at the colony. As the colony and hence the eagle activity was spread out, it was difficult to estimate the total number of eagles present. At times large numbers of eagles were soaring on thermals and this was the best opportunity to count the number of eagles present. The counts varied between 300 and 550 but, judging from the extent of the colony and from observations by other observers, it is estimated that there may have been over 1000 eagles present at the colony. Lesser Spotted Eagle Aquila pomarina was the predominant species at the colony, making up 60–80% of the eagles present. There were at least 50–100 Steppe Eagles A. nipalensis present, of which the majority were immature birds, as well as at least 20–50 Tawny Eagles A. rapax and 5–10 Wahlberg’s Eagles A. wahlbergi. There was a pair of Wahlberg’s Eagles breeding along the Mahlambamdube, close to one of the sub-colonies. The pair of eagles called continuously and the extent to which they were disturbed by the large number of other eagles at the colony is an interesting question. Also present at the colony were at least 20–40 Whitebacked Vultures Gyps africanus, 5–10 Hooded Vultures Necrosyrtes monarchus and 2–5 Whiteheaded Vultures Trigonoceps occipitalis. A single juvenile African Hawk Eagle Hieraaetus fasciatus was observed. Smaller raptors included a small flock of Eastern Redfooted Kestrels Falco amurensis, a single Lanner Falcon F. biarmicus and Steppe Buzzard Buteo buteo. There was a small number of Marabou Storks Leptopelis crumeniferus present. Numbers of Yellowbilled Tockus flavirostris and Redbilled Hornbill T. erythrorhynchus were recorded in the colony and were likely also feeding on quelea chicks. Of the non-avian predators, little activity was observed besides a Leopard Panthera pardus encountered in one of the subcolonies and a small number of Rock Monitors Varanus exanthematicus. Discussion Most of the Redbilled Quelea colonies in KNP occur in the basaltic grassland savannas in the eastern half of the park (Sinclair & Whyte 1991). Pienaar (1969) stated that during the period 1956–1969, Redbilled Quelea colonies were recorded on only three occasions south of the Sabie River. The colony was active in January whereas the majority of colonies in KNP have been reported during the months of February and March (Pienaar 1969). This reflects the good early rains in the 2000/2001 rainy season, as well as the abundant rains of the previous season. Concentrations of large numbers of Lesser Spotted Eagles at abundant food sources during the non-breeding season have been reported previously (Kemp in press). Pienaar (1969) reported large congregations of eagles at quelea colonies between 1956 and 1969 in KNP, with 1000–1250 eagles present at a colony in February 1967. Lesser Spotted Eagles represented the majority of eagles present at a quelea colony just north of Gudzani-East windmill, north-east of Satara restcamp, KNP, where there were over 1000 eagles present (Kemp in press). At that colony there were a small number of Tawny Eagles (at least 6) and Wahlberg’s Eagles (at least 4) and Steppe Eagles (at least 2). At least 100 Marabou Storks were present. According to Pienaar (1969) the important avian predators at Redbilled Quelea colonies in KNP observed at colonies between 1956 and 1969 were Wahlberg’s Eagle, Tawny Eagle (and possibly Steppe Eagles), Yellowbilled Kites Milvus migrans, Bateleurs Terathopius ecaudatus, African Hawk Eagles and Marabou Storks. The noteworthy absence of Lesser Spotted Eagle in this list is likely due to the fact that identification of large brown eagles during those times was not as precise as it is today and the Lesser Spotted Eagles were probably mistaken for other species. Pienaar (1969) noted that a variety of smaller birds of prey were recorded at quelea colonies in the Kruger National Park between 1956 and 1969 and that the avian predators exerted the greatest pressure on the colonies when the fledglings leave the nests. Other non-avian predators of all types have been recorded at Redbilled Quelea colonies. Pienaar (1969) mentioned that the most important of these were Chacma Baboons. Other predators reported by Pienaar included a variety of snake species. Genets Genetta spp., African Wild Cat Felix lybica, Servals Felis serval and Civets Civetiica civetta tear open nests within their reach. Both Brown Hyena brunnea and Spotted Hyenas Crocuta crocuta have been observed at colonies and at one colony even Lion Panthero leo and Leopard were observed tearing open nests and robbing them of their young. Kemp (in press) estimated that the eagles consumed 25% of their mass each day. This high estimate of intake took into account the easy availability of prey and the need for eagles to lay down reserves prior to migration. The timing of abundant food sources, such as at quelea colonies, may be an important component in the migratory strategy of this and other migrant raptors. The quelea colonies may thus represent an important food source to Lesser Spotted Eagles before their departure in early March (Kemp in press). In South Africa alone, 40–100 million queleas have been killed each year since the 1950s by agriculturists because they are considered pests (Lloyd 1999). The extent to which the extensive agricultural control of queleas annually in sub-Saharan Africa diminishes the number and size of Redbilled Quelea colonies and thus negatively affects the ability of migratory eagles to build up reserves before migration requires further investigation. (In addition, the impact of the poisoning of quelea on non-target species has been widely reported but seldom quantified. – Ed.) The impact of all these eagles and other predators on the breeding success of the queleas is surprisingly low. Kemp (in press) calculated that the estimated 1000 eagles present at the 1600-hectare Gudzani-East colony consumed only 8.75% of the estimated number of quelea chicks available, assuming that each eagle consumed 25% of its body mass each day and that each nest broods three chicks. Pienaar (1969) stated that the extent of predation varies greatly from year to year, and from colony to colony. He estimated predation by observing torn versus intact nests and his estimates varied from 13–60%, but he estimated that it is often over 50%. Lloyd (1999) reported that 80–90% of Redbilled Quelea nests fledge young. With a 9–10 day incubation period and a 11–13 day nestling period, in combination with their huge numbers and their highly synchronized breeding, the predators are simply swamped with more food than they can use. Acknowledgements I would like to thank Abbey Legari, the Skukuza section ranger, for giving permission to make observations in the colony and for providing me with an excellent game guard in the form of Jairos Chiloane. Johann Knobel and Robert Bryden contributed valuable information and assisted with observations. Kemp A. In press. Concentration of non-breeding Lesser Spotted Eagles Aquila pomarina at abundant food: a breeding colony of Redbilled Quelea Quelea quelea in the Kruger National Park. Acta ornithooecologica. Lloyd P. 1999. Queleas. Africa – Birds & Birding 4(4): 52–61. Maclean G.L. 1993. Roberts’ Birds of Southern Africa. John Voelcker Bird Book Fund, Cape Town. Pienaar U. de V. 1969. Observations on the nesting habitats and predators of breeding colonies of Redbilled Queleas Quelea quelea lathami (A. Smith) in the Kruger National Park. Bokmakierie 21(3) suppl.: xi–xv. Sinclair J.C. & Whyte I. 1991. Field guide to the birds of the Kruger National Park. Struik Publishers, Cape Town. Fig. 1. Lesser Spotted Eagles Aquila pomarina perched at the edge of the quelea breeding colony early in the morning, with a flock of Redbilled Queleas flying past. Fig. 2. Crowded quelea nests in one of the trees in the colony.

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Document posted: 24-Aug-2001