Steve Westerman

Wharfedale Naturalists Society

wharfedale-nats.org.uk

IN the late autumn and winter a small number of Little Grebe (Tachybaptus ruficollis) arrive in upstream areas of the river Wharfe (around Ilkley). They seem to prefer the deeper, slower sections. Sometimes referred to as ‘Dabchicks’, these small diving birds are very timid, well camouflaged, and so can be difficult to spot. They often swim amongst vegetation or in shady areas and, at the slightest provocation, will dive below the surface. Apparently, if sufficiently alarmed, they can then keep their body submerged, with just their head above water, while they check to see whether the danger has passed (‘up periscope’). I haven’t observed this behaviour myself, but perhaps that’s as intended and so not altogether surprising!

Once the weather gets warmer, and the breeding season approaches, the Little Grebes leave the river again. Their nests take the form of anchored ‘rafts’, made from water weeds, and so are more suited to relatively still water, and not rapidly rising and falling rivers, such as the Wharfe.

So, why don’t Little Grebe stay year-round at their breeding sites? For a diving bird, Little Grebe have a fairly eclectic diet. This includes insects, molluscs, and small fish. Nevertheless, in the late autumn and winter months, availability of prey may become problematic at their breeding sites. This could simply be the result of annual life-cycles affecting numbers or distribution of prey, but it could also be due to the still water of their breeding site freezing (preventing, or restricting, the Little Grebes’ access to prey). Consequently, the River Wharfe becomes a useful home from home. When considering the timing of their move, why wait for disaster to strike? Perhaps Little Grebe are genetically ‘programmed’, or have learned, to avoid the possibility of sub-zero conditions, and so take evasive action before the really cold weather sets in.

The photograph shows a Little Grebe, in winter plumage, on the Wharfe. Note the characteristic dumpy shape and ‘fluffy’ rear end. As you would expect, their plumage is less flamboyant in the winter months - dark above, including the top of the head, but otherwise rather buff in colour. In the breeding season this changes and their cheeks and neck/throat become a rich, vibrant chestnut-brown. Of course, you will need to go somewhere else to see that!