Sense of smell

Procellariiforms (e. g. petrels and albatrosses) search their prey by smelling it. Procellariiforms are able to fly and are closely related to penguins (see Evolution). Both penguins and procellariiforms prey on fish, krill and squid and they use the same areas for foraging. But do they also use the same senses for foraging?

Are penguins able to smell?

Procellariiforms have well developed olfactory bulbs. So, it is supposed that they use their sense of smell for foraging. Penguins use visual cues to scent out their prey. They are emmetropic despite the different refractive indices of water and air (see chapter Sight). There has been nothing known about the sense of smell in penguins for a long time. It was even expected that penguins are not able to smell.

Investigation of the sense of smell in penguins

Penguins do not smell their prey directly

In order to investigate the sense of smell in penguins there were some experiments. Firstly, researchers found out that penguins did not react on the smell of their prey directly. In this experiment African Penguins could choose between blended fish and water which has no smell. But there was no preference for one of the offered odors, the penguins chose one option randomly. That is why it is assumed that penguine cannot smell their prey directly.

Perception of dimethyl sulphide

In other experiments which were done on land firstly was observed that penguins react on the chemical substance dimethyl sulphide (DMS). African Penguins that were tested showed an obvious preference for this substance. They approached the source of DMS and stayed there for some time.

Dimethyl sulphide as evidence for prey

DMS is produced by phytoplankton in little amounts. It is released in greater amounts when animals prey on phytoplankton. This animals are for example krill or fish and these in turn are the prey of penguins. Where many DMS is released there should be a lot of prey for penguins. So, the perception of DMS could be an advantage for penguins in foraging.

Range of the sense of smell

Thereafter, experiments at sea were done. The results were the same: More penguins were observed when the researchers put slicks with the odor of DMS in the water than at control slicks which had another odor.
It is assumed that penguins can smell the substance at a distance from up to two kilometers because most penguins were observed at the slicks after 20 to 30 minutes (African Penguins commute at 1,2 meters per seconds).

Penguins do not react on fish oil

Procellariiforms can perceive some substances by smelling, for example fish oil and other substances that are associated with krill or phytoplankton. In this way they can find their prey more effectively. In the experiments at sea the penguins did not react on fish oil. An explanation could be that procellariiforms also eat dead or damaged fish, but penguins only eat fish that is alive. Damaged fish release fish oil and that is why penguins do not react on fish oil.

Sense of smell in social context

The meaning of the sense of smell in social context is not known yet. It has to be cleared how the odor of the partner or the offspring influences the relationships. In experiments with the odor of feces it was investigated that in African Penguins the females chose the faeces of other penguins and avoided own faeces. In contrast, males did not avoid their own faeces. An explanation of this behaviour is not given yet.

References:

Cunningham, G. B., Strauss, V., & Ryan, P. G. (2008). African penguins (Spheniscus demersus) can detect dimethyl sulphide, a prey-related odour. Journal of Experimental Biology, 211(19), 3123-3127.
Cunningham, G. B., & Strauss, V. (2009). Further studies investigating the behavioral responses of African penguins (Spheniscus demersus) to olfactory stimuli.
Wright, K. L., Pichegru, L., & Ryan, P. G. (2011). Penguins are attracted to dimethyl sulphide at sea. The Journal of experimental biology, 214(15), 2509-2511.