| African Fish Eagle | |
| Haliaeetus vocifer | |
| Status: | Vulnerable |
| Range: | All mesic habitats in southern Africa |
| Area of occupancy: | 75,238 km2 including 2,074 km of border rivers |
| Population estimate in Namibia: | 600 individuals |
| Population trend: | Stable to decreasing |
| Habitat: | All perennial rivers and dams and pans when wet |
| Threats: | Over-fishing, pesticide abuse, degradation of riverine habitat |
Distribution and abundance
 Click to see distribution map |
Found mainly in border areas of Namibia along the perennial rivers (Boshoff 1997). Densities vary greatly depending on aridity, which probably influences fish populations and number of tall trees available for breeding. Occurs much more sparsely inland where it is found on inland dams, particularly the larger dams, and pans when they are wet. Vagrant to the coast and usually only at the estuaries of the Orange and Cunene where they meet the Atlantic. Namibia has 2,074 km of perennial river (Mendelsohn et al. 2002) and Fish Eagles occur along most sections. It occupies about 75,000 km2 in Namibia of which 15% lies within protected areas (Jarvis et al. 2001).
Highest densities occur along the tropical perennial rivers and the lowest along the perennial desert rivers. Average linear densities recorded over a 10 year period were 6.0 birds/10 km on the Kwando River, followed by 3.6 birds/10 km (Chobe), 3.1 birds/10 km (Zambezi), 2.3 birds/10 km (Kavango, when people are absent), 1.6 birds/10 km (Orange) and 1.3 birds/10 km on Cunene River (RE Simmons unpubl). The highest concentration of birds is found in the Mahango Reserve, just before the Kavango River flows south into Botswana, where an average 9 birds have been recorded in the past 10 yr but up to 23 birds sometime occur (M. Paxton & L. Sheehan unpubl).
The global breeding population was estimated by Brown et al. (1982) at 100,000 to 200,000 prs. Namibia's population is estimated at a surprisingly small 530 individuals based on the density estimates above and inland dams and pans. Populations may fluctuate with water levels in impoundments; thus with annual rainfall trends generally declining and evaporation rates in Namibia always exceeding the precipitation (Mendelsohn et al. 2002), we can expect reduced numbers on inland dams in future years.
Ecology
Intimately tied to water bodies, flowing or stationary, this species catches mainly fish but also takes waterbirds, small birds, terrapins, snakes and carrion, and known to pirate other species of their prey (Steyn 1982, Brown et al. 1982). Birds perch hunt from, and nest in, large trees overlooking rivers and dams. In Namibia the majority of the population (c. 530 birds) are found on perennial rivers and the remainder (c. 8%) occur on inland dams (RE Simmons unpubl). Breeds from June to July (egg-laying, 8 records) with young in the nest from July (2 records) through August (3 records) to November (1 record) (Jarvis et al. 2001). These records are similar to egg-laying dates in southern South Africa (Boshoff 1997), but elsewhere in southern Africa it breeds slightly earlier in Zimbabwe, egg-laying from April-June, and May-June in both Botswana and the former Transvaal (Tarboton & Allan 1984, Boshoff 1997). Nothing is know of the breeding success or factors that limit this species populations in Namibia. Over-fishing however contributes to its demise on one n Namibian river (below).High densities on some rivers in other parts of Africa give this species the distinction of higher breeding densities than any other large eagle in Africa. This and other aspects of the African Fish Eagle's biology in southern Africa are given by Steyn (1982) and Simmons (2005).
Threats
A recently identified and quantified threat is intense over-fishing by humans driving away birds from otherwise suitable rivers. Most rivers in arid regions support dense human populations in Namibia (Mendelsohn et al. 2002), particularly the Kavango River. In the 10 year period prior to 1999, no Fish Eagles were recorded in wetland counts along short sections of the Kavango River, east of Rundu. This was confirmed by DG Allan (unpubl.) along 52 km of river. However, as people moved away from the river following guerilla activity after 1999, eagles immediately returned and began breeding. The density rose in one intensively monitored area from 0 to 2.25 birds/10 km within months of resident people leaving (Simmons 2003). Since large fish concurrently returned (C Hay unpubl) the cause for low eagle populations was probably the absence of prey of adequate size. Nets including mesh as small as mosquito net size are used daily and consequently remove virtually all fish and fry from the river (M. Paxton unpubl). Degradation of wetlands especially rivers such as the Okavango (Hay et al. 1996) has negatively impacted fish eagle populations elsewhere in similar waterways (Douthwaite 1992).
Pesticides, particularly DDT, continues to be a threat where it enters the water system, thinning egg shells, and causing reproductive failure of breeding eagles. The effect appears to be localised (Douthwaite 1992, CJ Brown unpubl) and may occur where pesticide-filled barrels are illegally emptied or spraying equipment cleaned in the rivers, causing massive fish die-offs (M. Paxton pers obs). There is no firm proof, however, that organochlorines have limited populations in southern Africa (Davies & Randall 1989). One reason may be that persistent toxic chemicals entering Namibia's hot environment, especially pans, appear either to be denatured by the high temperatures or evaporate under the intense sun (CJ Brown unpubl).
Conservation status
This species is classified as Vulnerable because of its surprisingly small total population in Namibia of less than 600 birds. Given that most of its population occurs on rivers that are heavily utilised by man in arid regions, the species continues to face threats such as the over-fishing identified on the Kavango River. Thus we can expect declines to occur where stringent measures are not enforced to prevent over-fishing. It is presently under little threat at inland dams and sewage works but smaller dams may be less likely to hold eagles in future years if rainfall decreases and temperature increases under climate change scenarios. It does not feature in any other red data book and is rarely found in Namibia's Ramsar sites (Etosha, Walvis Bay, Sandwich Harbour, Orange River mouth). However it is well represented in the protected areas of Caprivi.
Actions
Strictly control over-fishing through in-appropriate net sizes on all northern rivers. Create river-based conservancies with fishing-free zones, allowing fish to spawn and grow and thus disperse into areas where they can be used by man and eagle. Protect large riverine trees through legislation. Strictly control pesticide spraying near water bodies and particularly the practice of washing and even emptying toxic chemical containers and spraying equipment in rivers or any water bodies. Monitor breeding attempts (only 13 currently on record in Namibia) and where appropriate collect unhatched eggs for pesticide analysis.
From: Simmons RE & Brown CJ 2006. Birds to watch in Namibia: red, rare and endemic species. National Biodiversity Programme, Windhoek, Namibia
References
Boshoff AF 1997. African Fish Eagle Haliaeetus vocifer. In: Harrison JA, Allan DG, Underhill LG, Herremans M, Tree AJ, Parker V, Brown CJ (eds). The Atlas of Southern African Birds. Vol. 1: 205-207. BirdLife South Africa, Johannesburg.
Brown LH, Urban E, Newman K 1982. The Birds of Africa Vol 1. Academic Press, London.
Brown CJ [no date] Pesticides in the environment in northern Namibia. Unpublished MS.
Davies RAG, Randall RM 1989 Historical and and geographical patterns in egg shell thickness of African Fish Eagles Haliaetus vocifer in relation to pesticide use within southern Africa. In: Meyburg B-U & Chancellor RD (eds). Raptors in the modern world Pp 501-513. WWGBP, Berlin.
Douthwaite R 1992 Effects of DDT on the Fish Eagle Haliaetus vocifer population of Lake Kariba in Zimbabwe Ibis 134: 250-258.
Hay CJ, van Zyl BJ Steyn GJ 1996. A quantitative assessment of the biotic integrity of the Okavango River, Namibia, based on fish Water SA 22: 263-284.
Jarvis A, Robertson A, Brown CJ, Simmons RE 2001 Namibian Avifaunal database. National Biodiversity Programme. Ministry of Environment & Tourism, Windhoek.
Mendelsohn JM, Jarvis A, Roberts C, Robertson A. 2002. Atlas of Namibia: a portrait of the land and its people. Ministry of Environment & Tourism, David Phillip.
Paxton, Mark ornithologist - naturalist Okavango River (shamvura@iway.na)
Simmons R 2003. Carmine Bee-eaters taking stick: man's heavy toll on Namibian riverine life. Africa Birds & Birding Feb/Mar: 14-15.
Simmons RE 2005 African Fish Eagle In: Hockey PAR, Dean WRJ, Ryan PG, (eds.) Roberts Birds of Southern Africa, 7th ed. John Voelcker Bird Book Fund, Black Eagle Publishing, Cape Town.
Simmons, Rob Dr, ornithologist, FitzPatrick Institute University of Cape Town, (harrier@botzoo.uct.ac.za)
Steyn P 1982. Birds of Prey of southern Africa, David Philip, Cape Town.
Tarboton WR, Allan DG 1984. The status and conservation of Birds of Prey in the Transvaal. Tvl Museum Monogr 4, Pretoria.