Adapted Catfish: The Pigeon-Grabbers
Animals use numerous foraging strategies to capture their prey – many even find ways to obtain prey that lie outside their ecosystem boundaries. Recently, scientists discovered a freshwater catfish population intentionally beaching themselves to catch and consume birds.
Many species of ceteceans intentionally beach themselves for various reasons. Intentional beaching in killer whales (Orcinus orca) is carried out to capture prey such as seals, and is a skill developed through conspecific imitation.
Each killer whale calf tends to associate strongly with a female adult, and with her will participate in beaching play over several years, intentionally stranding when no prey is present. Eventually, the calf grows skilled and confident enough to perform intentional stranding on its own. Findings suggest that at around 6 years old, calves may successfully capture their first pup (Guinet and Bouvier, 1995).
A Discovery is Made
2 years ago, similar behaviour was discovered in freshwater catfish! The European catfish (Silurus glanis) is the third largest catfish in the world. At the Tarn River in Southwestern France (where the catfish were introduced in 1983), a group of French scientists observed how the catfish used beaching to capture pigeons (Columba livia Gmelin), then returned to the river and swallowed them. Gulp! What is really exciting about this behaviour is that it is entirely adaptive, having been unobserved in the native range of this species.
The causes that triggered this unusual behaviour are still unknown, but are conjectured to be: 1. increased intraspecific competition, or 2. high energy returns counterbalance the costs (learning, risk of being stranded). Ultimately, the catfish took hold of this new ecological opportunity and “increase[d] the diversity of trophic resources available” to them. (Cucherousset et al., 2012).
Their behaviour is an example of how an introduced species can display ecological and evolutionary adaptations in a new environment!
Cucherousset, J., S. Boulêtreau, F. Azémar, A. Compin, M. Guillaume, et al., 2012. “Freshwater Killer Whales”: Beaching Behavior of an Alien Fish to Hunt Land Birds. PLoS ONE 7(12): e50840. doi:10.1371/journal.pone.0050840
Guinet, C. & Bouvier, J., 1995. Development of intentional stranding hunting techniques in killer whale (Orcinus orca) calves at Crozet Archipelago. Canadian Journal of Zoology, 73:27-33.
“Figure 1. European catfish displaying breaching behaviour to capture land birds,” by Cucherousset et al. PloS ONE, 2011. URL: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0050840#s1 (accessed on 6 April 2012).
“Orca beaching to attack sea lion,” by Sylvain Cordier. Biosphoto, [date unknown]. URL: http://www.arkive.org/orca/orcinus-orca/image-A19731.html#src=portletV3we (accessed on 6 April 2012).