During the past 5 years (2008-2012) I have been photographing and studying the Great Crested Grebes at Ranworth Broad. During that time many aspects of their behaviour have been revealed and there always seems to be another behavioural trait from one year to the next, previously unseen
The following account in photographs and narrative, is a personal view of the grebes breeding ecology in 2012, with references to the four preceding years.
Bathing & Preening
Feather maintenance is important to all birds and the Great Crested Grebe is no exception. Being an aquatic hunter means that 'bath time' occurs on a regular basis and what tends to follow a few dives in search of prey is a 'shaking' routine to expel excess water. However, on occasions, but observed very infrequently, the whole bathing routine is utilised (see slideshow) with flapping of wings pushing water over the whole body in a kind of shower routine, not unlike duck species.
Mating & Displaying
One of the highlights of grebe behaviour, must be the 'penguin dance'. This is where both birds dive and re-appear with aquatic plants and then paddle quickly across the water to meet up with the vast majority of their bodies above the water. What follows is some head shaking, where some of the 'gift' of plants is lost and mostly ends up around the grebes necks, or in the water.
At other times, during the breeding season, pair bonding takes place. Unlike the 'penguin dance' this involves a 'coming together', which is followed by head shaking. This has also been witnessed happening after a territorial encounter with other pairs or single grebes, cementing the bond between the pair.
In 2012 an element of new behaviour was witnessed when a grebe was either delivering a threat display or displaying to attract a mate. It did this by raising its wings above its body and exposing the white wing patch, which the majority of grebes possess. It is more likely that this behaviour was the latter of the two, as normal threat display is indicated by out-stretching the body lateral to the water surface. A similar behaviour has been witnessed by a Little Grebe, but in that instance the wings were not only raised but 'fluttered'. This may well explain the presence of the very visible white wing panel on grebes, as a measure of fitness, as it does not appear to full-fill any other purpose and certainly not as some form of camouflage, particularly in flight.
The basis of the nest usually consists of a branch either just under the water or above, which acts as an anchor for the plants that follow, to raise the nest above water level. Twigs and branches are dragged across the water by both grebes, with some items obviously too big or on occasions still attached to a tree!
More 'softer' material follows with aquatic plants acting as the interior nest substrate, on which the eggs are laid.
In 2011 one pair were attempting to build a nest on a lateral branch, approximately one foot above the water. The result was a 'clothes line' of aquatic plants, which the grebes eventually gave up on.
Maintenance of the nest continues even after the eggs are layed. The tidal nature of Ranworth broad saw several nests washed away, built by what must have been inexperienced pairs, as in the case of the 'clothes line'.
Shaking to expel excess water
Great Crested Grebes are highly territorial, defending their territories with aggression, against any would be intruders. The usual stance is that of neck out-stretched parallel to the water, with vocalisation. Diving under the water and coming up near the intruder is also utilised, if the initial threat display has not worked. If all else fails, then a no-holds barred fight will ensue, until one bird has successfully driven off the other.
Threat display or mating display?