Researchers have documented the first ever confirmed case of a freshwater fish preying on a bird in mid-flight. The team reported their astonishing findings in the Journal of Fish Biology, substantiating longstanding rumors that African tigerfish (Hydrocynus vittatus), quite incredibly, hunt down birds in flight. This rumor, which was perpetuated back in the 1940s, was never definitively verified until recently.
African Tigerfish Hunt H. rustica
Aquatic animals are known to hunt down birds around their habitats; this ferocious behavior has been witnessed in a number of predatory fish, as well as marine sharks. Although these predatory pursuits are rare in freshwater fish, there are reports of bass species, eels, piranhas and pike that infrequently prey on birds. Such behavior is characterized by fish attacking floating and swimming birds, along with stationary birds that lie close to the water’s edge.
Nico Smit, the director of the Unit for Environmental Sciences and Management at North-West University in Potchefstroom, in South Africa, explained that the previous “anecdotal reports” never truly convinced his team. In light of this, researchers from the Water Research Group of North West University, South Africa, elected to study the migration of the creatures, alongside their habitat use in the Mapungubwe National Park – an African lake, located close to the Botswana-Zimbabwe border.
Although the researchers’ primary intention was not to observe fish flying from the surface of the lake, what they did witness was a source of great shock. The group claim they encountered as many as 20 successful attacks launched by fish, every day. The African tigerfish would perform attacks against barn swallows (Hirundo rustica) along the lake’s surface.
In 1960, other studies reported on the possibility that barn swallows were being snatched from the skies by the African tigerfish of the Ndumu Game Reserve, in South Africa. However, direct observations of swallow predation by tigerfish was yet to be made; instead, the study merely drew a relationship between the disappearance of H. rustica from the waters and the large population of African tigerfish in the area.
The Hunting Strategies
During 2003, the African tigerfish population was established in the Schroda Dam – a small storage lake that was constructed in the Limpopo River catchment of Mapungubwe National Park. Previous studies showed – during the day – the tigerfish swam in deep waters, where their activity was markedly decreased. However, in the summer of 2011, a daily, mid-morning increase in activity was noticed, among five radio-tagged H. vittatus individuals, between the hours of 8 a.m. and 12 p.m. This shift in behavioral pattern was identified in an open-water region of the dam that did not correspond with conventional shelter or feeding areas; however, the change was correlated with migrant barn swallows that fed and drank while flying over the lake’s surface.
During the 15-day survey, the team established that the African tigerfish used two different hunting strategies. Firstly, the fish would perform “surface or subsurface pursuits,” before performing an aerial strike. Secondly, they were also capable of launching direct aerial attacks from deeper waters, at depths of over 0.5 meters. Ultimately, the former strategy worked least effectively, with a success rate of one in seven; direct strikes from deeper waters, however, offered a much-improved success rate of one in three.
Over the course of the entire study, around 300 barn swallows were preyed upon by the African tigerfish, suggesting the tactic of plucking low-flying birds direct from the skies was not as uncommon as initially suspected. In explaining the basis for this unorthodox behavior, the authors suggest that it may have been “… born out of necessity due to food availability limitations.” However, they also reflect on the possibility that, in resorting to this method of predation, African tigerfish could become the prey of larger avian predators, such as the African fish eagle (Haliaeetus vocifer) – an eagle found throughout sub-Saharan Africa, resembling the aesthetic of the Bald Eagle.
The authors of the latest research study call for further investigation into the conservation implications attributed to the predation pressure that H. vittatus exerts on H. rustica. In summarizing his thoughts on the ability of the African tigerfish to pluck barn swallows from mid-flight, Smit had the following to say:
“We hope that our findings will really focus the attention on the importance of basic freshwater research, and specifically fish behaviour.”
By James Fenner