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Home , African fish eagle, Balaenicipitidae, Clarias, Clarias gariepinus, Goliath heron, Shoebill

Journal of Science 45(2): 131-143, 2019 ISSN 0856-1761, e-ISSN 2507-7961 © College of Natural and Applied Sciences, University of Dar es Salaam, 2019

Kleptoparasitism of Balaeniceps rex by African Haliaeetus vocifer in Western Tanzania

Jasson RM John1* and Woo S Lee2 1Department of Zoology and Wildlife Conservation, College of Natural and Applied Sciences, University of Dar es Salaam, P. O. Box 35064, Dar es Salaam, Tanzania. 2Department of Forest Sciences, College of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea. *Corresponding author E-mail: [email protected]

Abstract Kleptoparasitism is a specialised form of foraging interference occurring throughout the kingdom and especially is well documented among including African fish Haliaeetus vocifer. However, only one record is reported between fish eagle and Balaeniceps rex despite their habitat overlap and it remains undescribed. This paper documents kleptoparasitism of shoebills by fish eagles in Malagarasi , western Tanzania. Kleptoparasitism was highly seasonal occurring in the dry season, especially at low floods. Both adults and non-adult eagles stole prey from shoebills, with non-adults initiating attacks at shorter distances than adults perhaps because of the lack of experience. The shoebill preys were comparatively larger than those from fish eagle own fishing and required long preparation time which provided the opportunities to kleptoparasites. Shoebill’s long prey handling time (6.90 ± 4.48 min) may have provided benefits to fish eagles as all kleptoparasitism attempts (n = 138) were successful. Moreover, it seemed likely that an attacking fish eagle posed significant danger to the shoebill and given the fact that shoebill lacks structures such as pointed bill to defend from kleptoparasitic attack it opted not to retaliate. Perch availability and habitat openness in the study sites could also have facilitated kleptoparasitic behaviours.

Keywords: Balaeniceps rex, Haliaeetus vocifer, handling time, kleptoparasitism, Malagarasi- Muyovozi Ramsar Site

Introduction openness (Paulson 1985), large concentrations Kleptoparasitism is a specialised form of of hosts (Brockmann and Barnard 1979), foraging interference (Perrins and Birkhead large/visible food items or prey (Brockmann 1983) occurring throughout the animal and Barnard 1979, Dekker et al. 2012) and kingdom (Iyengar 2008), and especially is shortage of food from self-foraging (Oro well documented among birds (Brockmann 1996). Moreover, age of kleptoparasites and and Barnard 1979). It is particularly common hosts as well as the distance between them; in waterbirds (Furness 1987) and in have also been hypothesized to play (Morand-Ferron et al. 2007) significant roles in avian kleptoparasitism especially eagles; notably the African fish (Broom and Ruxton 1998, Dekker et al. 2012). eagle Haliaeetus vocifer (Sumba 1989, Distances between the hosts and Kasoma 1995) and bald eagles Haliaeetus kleptoparasites not only affect the chances of leucocephalus (Dekker et al. 2012). observing kleptoparasitic opportunities but Several studies have suggested ecological also increases the cost of attempting conditions that relate to the of kleptoparasitism as kleptoparasites expend kleptoparasitism; they include habitat energy when travelling to the hosts. This 131 http://journals.udsm.ac.tz/index.php/tjs www.ajol.info/index.php/tjs/

John and Lee- Kleptoparasitism of shoebills by African fish eagles in Western Tanzania could be more important for raptorial Nahonyo and Msuya (2008) registered one kleptoparasites such as fish eagles that perch incidence of kleptoparasitism on a shoebill by on top of trees or emergent vegetation fish eagles in Malagarasi wetlands but the overlooking hosts. interaction remains undescribed. Specifically, Kleptoparasitised individuals may in addition to documenting this challenge or retaliate, escape with food to kleptoparasitic interaction, this research cover, reduce handling time (including hypothesized that; (1) the rate of switching to smaller prey) or remain passive kleptoparasitic attack would be higher in (Stillman et al. 1997). Stillman et al. (1997) driest months when fish eagles may be hypothesized that kleptoparasitism should be precluded from catching prey and it is during flexible, with aggression only occurring when this period when shoebills become restricted benefits of this action outweigh the costs. to fewer and wetter locations which may Sirot (2000) suggested that kleptoparasitism attract kleptoparasites, and (2) the prey size and aggressiveness should increase when food and handling time would differ between hosts patches are harder to locate. Using ideal free foraging under pressure of kleptoparasites and distribution (IFD) model, Hamilton (2002) those that foraged in areas without found that kleptoparasitism increases with kleptoparasites. increasing difference in searching efficiency, increasing difference in fighting ability, Materials and Methods increasing handling time while decreases with Study sites increasing resource input rates, increasing Field work was conducted between June ownership advantage and increasing fighting 2011 and February 2012 within the central time. In general, when payoff for drainage of the Malagarasi-Muyovozi Ramsar kleptoparasitism is low, individuals switch to Site (3–6°S, 30–32°E), and largely within a searching for prey (Stillman et al. 1997, Smith swamp located in southern part of Lake et al. 2002). Nyamagoma around the village of Kasisi This paper both qualitatively and (5°03'05"S, 30°57'14"E) (Figure 1). The quantitatively describes kleptoparasitic water levels in the lake and adjacent interactions between shoebills Balaeniceps floodplains can fluctuate widely on an annual rex and fish eagles. The two are large basis depending on rainfall and inflow waterbirds in sub-Saharan where in (Nkotagu and Ndaro 2004); annual flooding some large wetlands (e.g., in , Tanzania, beginning in November and peaking between and ) they share habitats April and May. Large and small open water (Brown et al. 1982). However, despite the channels around this lake variously open and habitat overlap between the two , there close depending on currents and water volume. is no mention of kleptoparasitism in The vegetative swamp surrounding the edges (Gould 1851, Hagey of the lake is largely comprised of grasses and et al. 2002), of which shoebill is the only sedge species. member, in published reviews (Brockmann At Kasisi village, the miombo and Barnard 1979, Morand-Ferron et al. 2007, Brachystegia woodland which is mixed with Iyengar 2008) and in shoebill foraging studies Borassus palm (Borassus aethiopum) (Figure in Sudan, Uganda and Zambia (Guillet 1979, 2a, b) bordering the swamp on one side. In Möller 1982, Mullers and Amar 2015). The between the tall vegetative swamp and most recent extensive review of woodland, there are extensive open glades of kleptoparasitism in birds being that of short vegetation dominated by Eleocharis- Morand-Ferron et al. (2007) where 33 Leersia plant species forming dense floating families were noted to be involved in vegetation platforms (John and Lee 2012). interspecific kleptoparasitism. Moreover, These floating platforms sometimes contain

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Tanz. J. Sci. Vol. 45(2), 2019 small natural surface water openings (pools), by shoebills to hunt for air-breathing fish that which are supplemented by those made by become sparse, especially as water recedes. humans and the antelope Sitatunga (Tragelaphus spekii). These ‘pools’ are used

Figure 1: Map showing the study area at Kasisi Village, South of Lake Nyamagoma, within Malagarasi-Muyovozi Ramsar Site.

Study species eastern sub-Saharan Africa from Sudan to The is a widespread Zambia (Feduccia 1977, Hancock et al. 1992) raptor in Africa occurring at many water and therefore classified as ‘vulnerable’ by bodies containing fish except in arid areas IUCN (BirdLife International 2019). Most of (Brown et al. 1982). As its name suggests, it the shoebill habitats are treeless remote chiefly feeds on fish, although other prey such floodplains and permanent swamps (Hancock as , waterbirds and reptiles are et al. 1992). The shoebill is a rare (e.g., < 500 occasionally consumed (Stewart et al. 1997). mature individuals survive in Tanzania) It is, however, the most known kleptoparasitic specialist large (John et al. 2012). raptor in Africa (Sumba 1989, Kasoma 1995). The shoebill has extremely long toes (Gould The shoebill has a narrow and disconnected 1851) to support its weight (≈ 7 kg) when distribution along major water basins in walking on floating vegetation platform

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John and Lee- Kleptoparasitism of shoebills by African fish eagles in Western Tanzania unlike other large wetland birds which have to ambushing of surfacing prey, a phenomenon wade. The foraging behaviour of the shoebill that Guillet (1979) described as ‘collapsing’ resembles that of many Ardeidae, i.e., ‘stand- (Figure 2c). The shoebill is a non-social and-wait’ and ‘walk slowly’ (Guillet 1979, forager (Möller 1982) but may form loose Mullers and Amar 2015), but in shoebill this groups at good foraging sites. is usually followed by a pronounced

(a) (b)

(c) (d) Figure 2: (a) An adult African fish eagle (Haliaeetus vocifer) perched on tall sedge clump attending the shoebill (Balaeniceps rex) for food stealing, (b) A Shoebill in floating mats, in the background is the Miombo woodland intermixed with Borassus palms which provided perches for African fish eagles when attending shoebills for kleptoparasitism, (c) The shoebill plunging for prey, a process described as ‘collapsing’ by doing this it is likely to attract kleptoparasites to prepare for attack, (d) The Shoebill with a prey accompanied by herbage debris which is likely to increase prey preparation time before swallowing.

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Data collection Independent foraging birds Host-kleptoparasite interaction A search for fish eagles and shoebills Host-kleptoparasite interaction was foraging independently was conducted after studied by using a method described by Mock the break of the host groups and reduction of and Mock (1980), whereby several birds (i.e., kleptoparasitic attacks in January and the entire study system; 1-10 for hosts, 1-6 for February. This part intended to establish the kleptoparasites) were kept under simultaneous prey type and size consumed by both fish and continuous observations for several hours eagles and shoebills and handling time for up to 9 hours between sunrise (06:30 h) and shoebill in to compare with those that sunset (19:30 h). Shoebills foraging (prey foraged in areas with kleptoparasites. Prey capture) bouts are longer (Möller 1982) and items were identified whenever possible to use in-between periods for resting (Mullers species level and the size of prey was and Amar 2015) and thus foraging events for estimated in relationship to the length of the < 2 birds could be studied by a continuous for shoebill (beak length; 22 cm, Brown watch. We used binoculars (Bushnell: 8 x 42 et al. 1982, Hancock et al. 1992, Collar 1994) FOV430') for studying birds. and tarsus for fish eagle (tarsus; 8.5 cm, Although the study birds appeared not to Brown et al. 1982). Fish eagles use talons to be disturbed by human presence up to a fish and/or carry their prey to safe points distance of 70 m, observers, nonetheless, used usually in top of the trees. Capture success for neighbouring woodland and tall Miscathidium each species was determined by dividing the grass as natural blinds. The distance between number of successful strikes or collapsing original perches of kleptoparasites and (shoebill) by the total number of shoebills was visually estimated by a single strikes/collapsing. observer throughout the study period. Age classes of both the host and kleptoparasites Statistical analysis were grouped into adults and non-adults Data were managed using Microsoft based on types according to Buxton Excel and SPSS for Windows Release 16.0 et al. (1978) for shoebills and Brown and (SPSS Inc., Chicago, Illinois). Data are Cade (1972) for fish eagles (non-adults, < reported as mean and standard deviation 4years). Total number of both hosts and (mean ± SD). Mann-Whitney U test was used kleptoparasites for each species was estimated to determine differences between means for by averaging the number of birds present at prey size for both eagles and shoebills. Mann- start and end of each observation. Rates of Whitney U test was also used to compare the attacks in each continuous observation were distances attained by non-adults and adult estimated by dividing the number of attacks kleptoparasites during kleptoparasitic attacks. by total observation time (h). Spearman rank correlation was used to A total of 777.2 observation-hours were determine the effect of the group size of conducted over 100 days (7-13 days/month) kleptoparasites and hosts on attack rates over with a mean range of 6.22-9.54 h/day of the study period, and the dependent observation. Observation time period from correlation coefficients (r) between eagles, June 2011 to January 2012 did not vary shoebills and attack rates were tested by using significantly (Kruskal-Wallis H test: H = t-statistics (Chen and Popovich 2002) where 12.44, df = 7, P = 0.087), less time (56 h) was critical value was obtained from Natrella spent in February 2012 because shoebills (2012). Results were considered significant at became scarce and, when present, they P < 0.05 (all two tailed). changed foraging locations frequently and quite often disappeared from the observers’ view.

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Results floating vegetation would entangle within the Food stealing fish eagle’s talons making it difficult to fly A total of 234 and 359 independent with the prey. Over 50% of the stolen prey observations were made on fish eagles and items were either intra-kleptoparasitised or shoebills, respectively. During the study shared by a group of two or more fish eagles, period, shoebills made a total of 317 strikes which sometimes involved fierce contests and for prey of which 295 (93%) were successful chases but non-adult fish eagles were usually and yet of these successful strikes, 138 (47%) tolerated. Non-adult eagles joined the food were stolen by eagles. Fish eagles swooped stealing from September onwards; this was down with their feet extended forward and suspected to be a post breeding period of fish talons outstretched and landed within 5 m to eagles in the area. Fish eagles, irrespective of give time for shoebill to relinquish its prey. their age classes, were 100% (n = 138) Most prey (fish) were disabled during the successful in stealing food items from shoebill strikes and were therefore unlikely to shoebills. Despite the fact that other large escape the kleptoparasitic eagles; the dense fish-eating wading birds were occasionally floating vegetation platform also reduced the foraging near the kleptoparasitised shoebills probability of the fish sliding back into water. (Table 1) fish eagles did not attempt to steal In all kleptoparasitic events the shoebill did prey from them. However, non-adults eagles not retaliate; typically, it would move a few attended the host or initiated attacks at a steps away from the relinquished prey and shorter distance (103.79 ± 57.41 m) than did continue to preen and stretch its wings (these adults (441.67 ± 250.81 m) (Man-Whitney U were however, common behaviours after any test: U29,48 = 89.50, P < 0.0001). Adult ‘collapsing’ whether successful or not). kleptoparasites usually perched either in the Thereafter it changed hunting location by top of tall emergent trees or tall grass/sedges either stalking or making short flights. On one adjacent to the floating platform while non- occasion a shoebill tried to evade a fish eagle adults used floating vegetation platforms as by flying with prey dangling in its beak but it close as 20 m from the shoebill (Figure 2) and was too slow for an adult eagle. Non-adult were usually in a group of at least two. Even shoebills were rare (n = 19, ≈ 5%) and when at this close proximity to a kleptoparasite, the present did not stay at one point unlike adults shoebills did not attempt to escape or change which lurked at water openings for longer hunting spots once established and continued periods. to try to hunt. Stolen food items were consumed by fish eagles on the ground presumably because the

Table 1: Large fish-eating birds that foraged near the kleptoparasitised shoebills but fish eagles did not attempt to steal prey from them Species Distance (m) from Frequency of kleptoparasitised shoebill Prey strikes Black-headed ( melanocephala) 127.86 ± 98.60 21 Saddle-billed (Ephippiorhynchus 132.50 ± 127.44 24 senegalensis) Grey heron (Ardea cinerea) 150.50 ± 107.63 20 Great egret (Ardea alba) 175.00 ± 140.64 14 (Ardea goliath) 179.44 ± 137.44 14

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Overall, the rates of food piracy were October-November (end of dry season), and significantly correlated with the number of declining afterwards (Figure 3). Figure 3 hosts present; Spearman rank correlation: rs = shows a pronounced bell-shaped pattern with nd 2 0.577, and kleptoparasites, rs = 0.382 (all P shoebills (polynomial 2 order equation: r = values < 0.0001). The increase of shoebills at 0.8076, y = –0.277x2 + 2.6116x – 0.9038) and 2 2 the study sites attracted more fish eagles (rs = the rate of attack (r = 0.7841, y = –0.019x + 0.275, n = 100, P = 0.006). The dependent 0.1908x – 0.1848) than in fish eagles (r2 = correlation coefficients with rate of attack 0.7948, y = –0.0954x2 + 1.1233x – 0.2345). were significantly higher for hosts than Shoebills dispersed to shallower areas as the kleptoparasites (t-statistic: tDifference = 2.0165, swamp started to flood during the rainy df = 97, P < 0.05). For pooled monthly data, season from December to February, but this the rate of food pirating and number of hosts did not cause a sharp decline in fish eagles showed a bell-shaped pattern over the study because territorial eagles did not move. months increasing from July peaking around

Figure 3: Monthly trends of host-kleptoparasite interaction from June 2011 to February 2012 in the Malagarasi wetlands.

Prey type, size and handling time 99 cm, fish eagle prey; 28.42 ± 14.26 cm, 8.5- Shoebills preyed on two species of fish 68 cm, U32,35 = 354.000, P = 0.009, Figure 5). but predominantly on the African lung fish, Kleptoparasitic pressure did not affect the aethiopicus (> 60%) while fish prey size consumed by shoebills as prey size eagle preyed on six species of fish but largely of shoebills foraging in areas with fish eagles on C. gariepinus and (Tilapia rendalli) (39.33 ± 17.75 cm) did not differ significantly 2 (x = 37.000, df = 5, P < 0.0001, Figure 4). (U35,146 = 2373.500, P = 0.506) from those Shoebills foraged on larger prey than fish preyed by shoebills foraging in areas without eagles (shoebill prey; 41.800 ± 19.39 cm, 11- fish eagles (41.800 ± 19.39 cm). Large prey 137

John and Lee- Kleptoparasitism of shoebills by African fish eagles in Western Tanzania

(> 60 cm) were usually cut into sections by length (in areas without kleptoparasites; rs = shoebills and swallowed at intervals. The 0.673, P < 0.0001, with kleptoparasites; rs = entire process from scooping to swallowing 0.582, P < 0.0001) and handling time did not ranged from 2 to 30 minutes (6.90 ± 4.48 differ for shoebills foraging with and without min) depending on the size of the prey. Prey the kleptoparasitic pressure (U35,146 = 2260, P handling time by shoebill increased with prey = 0.285).

Figure 4: Diet prey compositions for shoebills and fish eagles. In addition to and , fish eagles fed on Tilapia rendalli, Schilbe mystus, Marcusenius stanleyanus and Oreochromis sp.

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Figure 5: Distribution of fish total length in the diet of shoebills and fish eagles.

Discussion a potentially learned behaviour of fish eagles Food stealing that prey was likely captured by their hosts, Kleptoparasitism in African fish eagles is were visible from a long distance. These well documented whereby it steals food habitat qualities may explain why pirating mainly from egrets and (Sumba 1989, from shoebills is not common elsewhere. Kasoma 1995). However, this is the first time What is surprising in this study is the a detailed ecological investigation on fish large (150 cm tall) stork-like bird, the shoebill, eagles stealing food from shoebills is did not retaliate nor escape when attacked by described. The environmental characteristics the fish eagles. This could be due to the lack in the study area were unique and likely of particular physical traits such as pointed important in facilitating kleptoparasitic beak (shoebill has a huge shoe-like bill) behaviour in this eagle species. For example, which could inflict pain to the fish eagles and the dense floating platforms of vegetation, was not agile enough to chase an eagle when which prevented fish eagles from hunting, it escaped with a prey. It is therefore not made it more accessible for them to steal prey surprising that other large waterbirds with captured by their hosts, the shoebill. Unlike in spear-like bill were not kleptoparasitised by the Malagarasi-Muyovozi Ramsar Site, fish eagles. Sumba (1989) reported that in habitat openness and presence of perching Uganda saddle-billed storks and goliath locations for avian kleptoparasites that favour defended their prey successfully food piracy (Paulson 1985) are usually against fish eagles and in fact saddle-billed lacking in most shoebill habitats (Hancock et stork could stab a fish eagle with its bill to al. 1992). Openness provided two benefits to death (Mock and Mock 1980). It could also be facilitate kleptoparasitism (see also Paulson that shoebills may be expending much energy 1985): (1) several shoebills could be under during ‘collapsing’ and may be temporarily continuous surveillance by fish eagles from exhausted immediately after collapsing events high perches, (2) shoebill ‘collapsing’ events,

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John and Lee- Kleptoparasitism of shoebills by African fish eagles in Western Tanzania putting it at a disadvantage of winning the activities in open waters (fish eagles can only contest and so deciding to be passive. fish in open waters) during the dry season, Non-adult fish eagles appeared at the may have, encouraged kleptoparasitism. study swamp during post breeding and Studies have shown that kleptoparasites often participated in food stealing. These non-adults steal food during poor conditions for foraging were tolerated by adult fish eagles unlike (Oro 1996, Varpe 2010) which explains the other adults joining the meal where fierce increased rates of kleptoparasitic attack contests always occurred. It is assumed that during low flood period. As the swamp these non-adults were related to the adults became flooded from January following the (territory owners) and thus tolerance may onset of rains in October, fish eagles altered have been related to familial relationship. their behaviour towards active hunting Familial tolerance has also been reported in independently, perhaps due to their increased other raptor species such as crested caracara foraging sites/success and the difficulties of Polyborus plancus (Rodríguez-Estrella and accessing shoebills. Shoebills changed from Rivera-Rodríguez 1992). Fish eagles are ‘stand-and-wait’ to ‘walking slowly’ foraging territorial and adult tend to remain resident in strategy following flood rise (see also John their breeding areas but some proportion of and Lee 2012). the young disperse (Brown and Cade 1972, Brown and Hopcraft 1973). Non-adults, Prey type, size and handling time which may include progeny of the resident The shoebill’s chief food, African lung eagles as well as dispersing from elsewhere fish and catfish, are both piscivorous, air were probably less efficient than adults in breathers and also show a degree of obtaining food independently and so they cannibalism (Smith 1931, Willoughby and compensated for this by robbing prey from Tweddle 1978, Guillet 1979, Möller 1982, shoebills (see Fischer 1985 for Bald eagles H. van der Valk 2012, Mullers and Amar 2015) leucocephalus). This was also reflected in the which may reduce abundance of smaller fish shorter approach distances attained by non- in shoebill foraging sites especially in dense adult fish eagles as compared to adults when floating vegetation platforms with few surface stealing food from shoebills. openings. Moreover, the larger prey favours In the Malagarasi wetlands, as water kleptoparasitism as they require long draws back into the main channels and ponds, processing periods (Kushlan 1978, Mock and food resources (especially fish) become Mock 1980). This can also explain why fish concentrated in these places thereby eagle did not attempt to steal prey from other influencing the distribution of that waterbirds (such as egrets and herons) around depend on them. In addition, human activities because they prey on smaller food items than (fishing, grazing, burning and even shoebills (Kasoma 1995). For example the excavation of aestivated lungfish) also largest of all, goliath heron feeds mostly on intensify towards the end of the dry season prey of ≈30 cm while those of > 50 cm are (i.e., during the low floods) (Nahonyo and voluntarily rejected (Mock and Mock 1980). Msuya 2008). During this period, shoebills Smaller prey items are usually consumed are forced to search for good foraging sites rapidly and provide little reward for which unfortunately become limited resulting kleptoparasitism (Barnard et al. 1982, Kellner in the formation of loose groups at few and Cooper 1998). The Shoebill prey size and locations. Aggregated hosts may imply good handling time were not affected by conditions for kleptoparasitism (Brockmann kleptoparasitic pressure from fish eagles and Barnard 1979, Vickery and Brooke 1994), because the shoebill does not have the chance for instance because of short flight distance to to select prey. Instead, it feeds by ambushing hosts (Thompson 1986). Increased human any surfacing organisms and then scooping of

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Tanz. J. Sci. Vol. 45(2), 2019 prey includes intake of dead herbage debris Knappe for English translation of the German (Figure 2d). As a result, this probably reduces shoebill article. IdeaWild provided additional the chances for smaller prey to slip back into field equipment. Stephen Clark and W.D. water, but it would increase prey preparation Newmark commented on earlier drafts of this time because smaller prey may sometimes be manuscript. difficult to separate from vegetation debris. The difference in diet composition between References shoebills and fish eagles is a result of prey Barnard CJ, Thompson DBA and Stephens H behaviours. For example, preys hunted by fish 1982 Time budgets, feeding efficiency and eagles (Figure 4) tend to feed in open waters flock dynamics in mixed species flocks of where they form schools at water surface lapwings, golden plovers and . Behav. (Bruton 1979, Stewart et al. 1997). 80: 44-69. BirdLife International 2019 Species factsheet: Conclusion Balaeniceps rex. Retrieved 21 January Although this study was not able to 2019, from http://www.birdlife.org. estimate the sizes of the prey stolen by fish Brockmann HJ and Barnard CJ 1979 eagles, there is little doubt that they were as Kleptoparasitism in birds. Anim. Behav. large as those taken by shoebills and hence 27(2): 487-514. provided incentives for theft. The habitat Broom M and Ruxton GD 1998 characteristics in the study area, non- Evolutionarily stable stealing: game theory retaliatory behaviour of shoebills, and large applied to kleptoparasitism. Behav. Ecol. prey that require long handling time also 9(4): 397-403. favoured kleptoparasitism. Moreover, the Brown LH and Cade TJ 1972 Age classes and shoebill inhabits inaccessible and often population dynamics of the Bateleur and remote swamps. Thus there is a possibility African fish eagle. Ostrich 43(1): 1-16. that kleptoparasitism, in addition to being Brown LH and Hopcraft JBD 1973 seasonal, may have gone unnoticed. Population structure and dynamics in the Kleptoparasitism is likely to increase and African Fish Eagle Haliaeetus vocifer interfere with the foraging of the shoebills if (Daudin) at , . Afr. J. human activities in wetlands are not Ecol. 11(3-4): 255-269. controlled or regulated. In future, Brown LH, Urban EK and Newman K 1982 kleptoparasitic interactions between shoebills The birds of Africa. Volume I. London and fish eagles will also be influenced by the Academic Press. changing climate due to changes in flooding Bruton MN 1979 The breeding biology and cycles. early development of gariepinus (Pisces: Clariidae) in Lake Sibaya, South Acknowledgements Africa, with a review of breeding in Ministry of Natural Resources and species of the subgenus Clarias (Clarias). J. Tourism provided research permit. Financial Zool. 35(1): 1-45. support came from Mohamed bin Zayed Buxton L, Slater J and Brown LH 1978 The Species Conservation Fund Project No. breeding behaviour of the shoebill or 0925790, Tampa’s Lowry Park Zoos and whale-headed stork Balaeniceps rex in the SNU-Environmental Leadership Program Bangweulu Swamps, Zambia. Afr. J. Ecol. Alumni Scholarship. Field logistical support 16(3): 201-220. was greatly offered by O. Msangi, I. Nkuwi, Chen PY and Popovich PM 2002 Correlation: C. Nahonyo, A. Lameck, F. Mwalle and the Parametric and nonparametric measures. Kasisi village government. Authors are also CA: Sage: Thousand Oaks. indebted to all the field assistants and S.

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