Cooperative feeding of Common Mergansers

 September 2022

Common mergansers (Mergus merganser), also known as Goosanders are diving ducks who mainly eat small fishes. Their daily requirement of fishes is around 400 g. Mergansers have different strategies of hunting them. They fish individually, but also cooperatively in small or large flocks.

Fishing in flocks is a very impressive strategy. Their aim is to target a fish, or better a fish school, and push it together to shallow shore water where fishes can be easily caught. Mergansers are usually firstly moving slowly in loose formation, looking in short intervals under water surface for prey.

When the fishes are located, the chase begins: birds rush rapidly on the water and drive fishes to the shore.

In short distance runs, Mergansers have wings folded, but in distances more than few meters, they run with the aid of their wings. During this chasing run, Mergansers pack into a dense formation.

When the fishes are pushed to the shallow water, some Mergansers dive repeatedly in pursuit of fishes and the other members of the group continue with the fish chase on the water surface. After a while they can switch roles.

Mergansers are continuing until one or more of them catch a fish. Neck-stretching and wing-flapping after surfacing can help them to swallow the fish.

Merganser with a fish

 

Merganser wing-flapping
 

Postures of Mergansers during feeding (Anderson et al. 1974)
 

During the chase, some individuals can be distracted by spotting another fish and chasing it separately. These individual hunts are often less successful compared with flock fishing.

Cooperative fishing in other animals

Cooperative fishing is also common in aquatic mammals – Common dolphins (Delphinus delphis) and Killer whales (Orcinus orca). They practise “carousel” feeding, meaning they push the school of fishes to the water surface by making a circle around the fishes and doing bubbles underwater. Moreover, dolphins do wall formation by driving a fish school towards another group of dolphins. Another method is line-abreast, in which dolphins follow the school of fishes in line side by side.

Flock of Mergansers was seen on the beautiful lake Saimaa in Finland on 18.08.2022.

References:

• Anderson, B. W., Reeder, M. G., & Timken, R. L. 1974. Notes on the feeding behavior of the Common Merganser (Mergus merganser). The Condor 76: 472–476.
• Burgess, E. A. 2006. Foraging ecology of common dolphins (Delphinus sp.) in the Hauraki Gulf, New Zealand: a thesis presented in fulfilment of the requirements for the degree of Master of Science (Zoology), Massey University, Albany, New Zealand (Doctoral dissertation, Massey University).
• Kajtoch, Ł., Lešo, P., Matysek, M., Kata, M., Gacek, S., Zontek, C., Bisztyga A. & Gwiazda, R. 2017. Do flocks of great cormorants and goosanders avoid spatial overlap in foraging habitat during the non-breeding season?. Aquatic Ecology 51: 473–483.
• Mills, D. 1962. The goosander and red-breasted merganser in Scotland. Wildfowl 13: 79–92.
• Neumann, D. R. & Orams, M. B. 2003. Feeding behaviours of short-beaked common dolphins, Delphinus delphis, in New Zealand. Aquatic Mammals 29:137–149.
• Newson, S. E., & Hughes, B. 1998. Diurnal activity and energy budgets of Goosander Mergus merganser wintering on Chew Valley Lake, North Somerset: influence of time of day and sex. Wildfowl 49: 173–180.
• Sjöberg, K. 1988. Food selection, food‐seeking patterns and hunting success of captive goosanders Mergus merganser and red‐breasted mergansers M. serrator in relation to the behaviour of their prey. Ibis 130: 79–93.
• Wood, C. C., & Hand, C. M. 1985. Food-searching behaviour of the common merganser (Mergus merganser) I: functional responses to prey and predator density. Canadian Journal of Zoology 63: 1260–1270.