One of the birds I see most regularly here in southern England is the Eurasian coot Fulica atra. This is another of those oh-so-familiar animals that we see so often that we normally pay it little attention. Stop and look properly, and you’ll discover something pretty incredible. While at Kew Gardens recently I took a number of photos of co-operative coots, and that’s why we’re here.

Eurasian coots occur wherever there are lakes, ponds, and marshes, and they also occur in estuaries, deltas, coastal wetlands and bays of the sea. They’re omnivores, eating everything from invertebrates and bird eggs to fruit, seeds, leaves and submerged algae. The birds shown here were grazing – bending their heads to the side to snip grass from a lawn.

Coots are rails (that is, member of the core gruiform group Rallidae). 11 extant species are recognised, as are several recently extinct island endemics. The Eurasian coot – also called the Common coot, and typically just ‘The Coot’ across much of its range – is not unique to Eurasia, also occurring across Africa and Australia. It has recently colonised New Zealand.

Coots are obviously similar to gallinules (Gallinula): in terms of skeletal and integumentary morphology, the only obvious differences are a narrower, longer pelvis and more compressed leg bones in coots and far wider lobes on the toes. The toe lobes are remarkably big – they seem to be an alternative solution to webbing, increasing the surface area of the foot substantially yet allowing the toes to be tightly compressed such that the foot remains narrow and blade-like during part of the swimming and walking cycle. Similar lobed toes in grebes have been shown to form a slotted hydrofoil during swimming (Johansson & Lindhe Norberg 2001) but I haven’t checked to see if similar work has demonstrated hydrodynamic benefits in coot feet. Incidentally, there don’t seem to be any obvious indications from bony anatomy that these lobes are present.

As far as morphology goes, it essentially seems that coots are large, heavy-bodied gallinules with a number of diving specialisations and wing proportions that are in keeping with their greater wing-loading (Olson 1973). Or, maybe gallinules and coots are best imagined as sister-groups (Livezey 1998).

The Eurasian coot is a very widespread, adaptable bird that occurs from subtropical regions to far northern ones, preferring to avoid freezing conditions (but sometimes enduring them nonetheless) and often wintering in coastal locations. In fact, some populations are regularly associated with the sea where they are clearly able to cope with windy, turbulent waters – this is all quite remarkable for a member of a group otherwise associated with marshes and still pools. Coots are actually unusual relative to other rallids in being so highly aquatic – they are almost certainly the most aquatic of all rallids in the Western Palaearctic, and they are regular divers. Many populations are resident while others are migratory. Migrating coots do their flying at night.

Eurasian coots are black, with the head and neck often being noticeably blacker than the rest of the animal. A white frontal shield is continuous with the bill tissue. This shield is larger in older birds, in territory holders, and during the breeding season. It’s seemingly using when assessing competitors (Visser 1988); that of males is slightly larger than that of females but the female shield apparently has an ornamental role too. Certain other coot species have ornamentations on the shield, like red nodules.

Coots are sexually monomorphic (that is, males and females look about the same, bar those differences just mentioned), highly territorial and pugnacious, but gregarious in the winter. Intraspecific nest parasitism is common in Eurasian coots (that is, many females lay eggs in the nests of neighbours) (Samraoui & Samraoui 2007) and has also been documented in several other species. Some studies indicate that as many as half of all nests are parasitized by other coots, and the fact that eggs are often rejected from nests suggests that some individuals are able to recognise this parasitism and eject the eggs that aren’t their own.

Coots have a famously harsh method of raising offspring. For whatever reason, it seems that they produce broods that are too large to support, and the chicks compete vigorously for parental attention. The parents respond to this in aggressive fashion, attacking their own chicks, often picking them up and shaking them when they beg for food, and definitely favouring some over others. This behaviour is termed tousling (the phenomenon of preferring some chicks over others is termed parental favouritism) and it results in the eventual killing of the weaker ones and the reduction of the brood down to a far smaller number. Whether this has evolved as a method of ensuring the survival of only the toughest (read: fittest) chicks is the big question. [Photo below by Böhringer Friedrich.]

This behaviour is almost certainly linked to the presence of the weird, elaborate head plumes present on the chicks of American coots F. americana: parents prefer and preferentially pay attention to certain chicks over others on the display of their display plumes, and these attractive chicks are the ones that survive (Lyon et al. 1994). In other words, we seem to have social selection influencing the evolution of ornamentation, not sexual selection, in this particular case (Lyon & Montgomorie 2012). Notably, however, the ornaments concerned are not carried through into adults.

There’s certainly a lot more to say about coots. But I must stop there – and this was meant to be but a brief showcasing of photos.

For previous Tet Zoo articles of interest, see...

Refs - -

Johansson, L. C. & Lindhe Norberg, U. M. 2001. Lift-based paddling in diving grebe. The Journal of Experimental Biology 204, 1687-1696.

Livezey, B. C. 1998. A phylogenetic analysis of the Gruiformes (Aves) based on morphological characters, with an emphasis on the rails (Rallidae). Philosophical Transactions of the Royal Society of London B 353, 2077-2151.

Lyon, B. E., Eadie, J.M. & Hamilton, L. D. 1994. Parental choice selects for ornamental plumage in American Coot chicks. Nature 371, 240-242.

Lyon, B. E. & Montgomerie, R. 2012. Sexual selection is a form of social selection. Philosophical Transactions of the Royal Society B 367, 2266-2273.

Olson, S. L. 1973. A classification of the Rallidae. The Wilson Bulletin 85, 381-416.

Samraoui, F. & Samraoui, B. 2007. The reproductive ecology of the Common coot (Fulica atra) in the Hauts Plateaux, northeast Algeria. Waterbirds 30, 133-139.

Visser, J. 1988. Seasonal changes in shield size in the Coot. Ardea 76, 56-63.