1. Sep, 2021

The fabulous scent of seabirds

Birds have large wings, but a light body. Despite their walnut-sized brains, they do have the reputation of being pretty smart. This holds not only for singing birds that produce amazingly complex songs, but also corvids (members of  the crow family) and parrots. Avian biologists have been puzzled for a long time how intelligent and complex behavior of birds can be produced by such tiny brains. Avian brains may not have large,  but highly compact brains many of these neurons are located in the forebrain, the area  that is connected with cognition in humans. They also found that parrots and corvids have forebrain neuron counts equal to or greater than primates with much larger brains.

The amazing quality of seabirds is their ability to navigate over the immense oceans using their smell as their major tool. This holds in particular for Procellariiformes,  an order of tube-nosed seabirds that comprises four families: the albatrosses, shearwaters, fulmars, and 2 families of storm petrels (Hydrobates pelagicus). All species are accomplished long-distance foragers, and many undertake long trans-equatorial migrations. They have elongated tubes or nostrils on their thick upper beaks that probably contribute to their enhanced ability to smell prey in the open ocean (see insert).  But more importantly perhaps is that these birds have olfactory tissues in the brain that take up about 37% of total brain volume (as compared with the 3 % of songbirds).

Until Gabrielle Nevitt  from the University of California, Davis, came along, no one had fully explored how seabirds use their elaborate nose gear to track their prey over vast ocean expanses. How do they do it? One chemical in particular called dimethyl sulfic (DMS) seems to play a crucial role. DMS is generated when zooplankton (krill) devours phytoplankton. For us, DMS  may smell like oysters on a half shell , or the seashore. DMS forms odor plumes, like puffs of cigarette smoke, that drift over the ocean surface and are picked up by the birds, zigzagging and continuously sniffing until zeroing in on their prey. Storm petrels are especially good at detecting the chemicals at a great distance.  In addition,  albatrosses may cover thousands of kilometers in a single foraging trip. Their survival thus depends on finding the proverbial needle in the haystack on a daily basis, often in dark and cloudy conditions within very limited visibility.

Sources.

Nevitt, C.A. (2008). Sensory ecology on the high seas. The odor world of the procellariiform seabird. J. Exp Biology, 211,  (2008).1706-1713.

Ackerman, J., The Bird way,  Chapter four.  The scent of sustenance.  Penguin Books. 2021.