Prey

 

The fish identified being caught and devoured by the grebes at Ranworth are Perch, Roach, Ruffe and Bleak.  Smaller fry are also taken, but defy identification, as they are very quickly swallowed, even when feeding the young.

One grebe was seen to catch and devour a Roach, weighing approximately three quarters of a pound, followed by a Perch of about the same weight, within approximately 30 minutes of each other (see Prey slide show).  When devouring, what are large items of prey, the head and neck are positioned vertically to allow the prey to be swallowed.  Sometimes and in the case of the aforementioned Perch, the larger prey are taken under the water after capture, before being consumed.  The said Perch was taken under twice and it is hypothesised that this may be to reduce the oxygen supply over the gills by swimming at speed under water, making a fish like a Perch, armed with a spiky dorsal fin easier to handle and then consume.  After consuming the Perch, the grebe was seen to drink on two occasions immediately afterwards.

In the case of Ruffe, where one is found there are generally others and I have witnessed a grebe catching one after another from under the floating visitor centre.  Again, these are fish are armed with protective dorsal fins, but are sometimes favoured by grebes, when there is a small accessible shoal and therefore energy values out way handling time (E/H values).

Roach were caught on several occasions, but unlike Perch did not prove so difficult to devour, likewise Bleak, the fish caught the majority of the time, during the breeding season.

P11 P11 (9)

Young

 

The highest amount of fledged young in a single brood in 2012 was three, with other broods of 1 and 2 young.  Up until 2012 the productivity on the broad was very low, with only 2 young being seen, but in 2012 there were at least 12 young produced.  While there may be various reasons for this, eliminating the number present (which has always been at least 20 grebes), it is most likely that the grebes now had more experience of successful nest building (see nest building paragraph 3).

Up until 2012, the only fish species observed fed to the young was Bleak and it may have been the case that this fish was both plentiful and easily caught, at the time the young were present.  However, in 2012 as well as plentiful Bleak; Ruffe, perch and roach were being fed to the young, along with unidentified small fish.

On one occasion the male was bringing very small fry to the young, but the female caught a relatively large Bleak (approximately 5 inches).  The fish was passed to each of the three young several times, failing on each occasion to swallow the fish and eventually, after about 15 minutes the female devoured the fish herself, albeit with some difficulty.

As well as their diet of fish, the young are presented with breast feathers plucked from the parent.  This is thought to line the crop and give some internal protection from the scales, bones and fins of the prey.

Another piece of behaviour, never seen before was of two young pair-bonding.  The two young carried out the usual head shaking routine and whether this is innate or learned behaviour remains up for debate, as it could be either or.

Egg-laying after young hatch!

 

Bearing in mind that very soon after hatching the young are taken out on the water by the female (when small, carried onboard the female's back) and then fed and cared for by both parents, a very unusual piece of behaviour was witnessed in 2012.

The first nest to produce young was just to the right of the visitor centre, where there were also two other nests (as in 2011).  Three young were successfully raised, but did not follow the usual course of events and go on board or with the parents out on the water.  Instead, both parents engaged in nest maintenance and the female laid a further four eggs, whilst the young were still around the nest!  The four eggs were subsequently predated, possibly by a Carrion Crow, which was seen in close proximity to the nest.  Despite having to care for the initial three young, the female grebe laid yet another single egg and the pair were still maintaining the nest. The egg was subsequently washed away and any more attempts at raising young and rearing another brood were then abandoned.  A very interesting piece of behaviour, nonetheless!

Y+e Y+e (2) Y+e (3)

Association with boat

 

On the 17th July 2012, yet another piece of grebe behaviour not seen before occurred, when a grebe began to follow the boat, during boat trips around the broad.

Sometimes the grebe would 'pick the boat up' at the bottom of the broad.  At this point during the first instances of this behaviour, the boat was slowed down and then speeded up to make sure the grebe was actually utilising the boat for a particular purpose.  The grebe reacted to this and also later to the noise of the electric motor-diving when the motor speed was increased, when it was some way behind after going slow on the trip and then catching the boat up, sometimes following 2- 3 feet behind the boat.  On other occasions the grebe would swim alongside the boat and then dive under the boat and on occasions catch a fish.

The boat is moored next to the floating visitor centre and as described in 'Prey' (paragraph 3) a grebe was often seen diving under the centre or the boat, associating the floating objects as a source of potential prey.  It is therefore believed that even when the boat was mobile the association with the boat and a food source was still associated and hence the following learnt behaviour, which ensued and continued during the Summer.

G96 (80) G96 (81) G96 (82)

With Perch

Entering the water

Young begging

Young plus eggs!

Following the boat

Great Crested Grebe Photo Diary 2012 (2)

Young Young (8) Young (7) Young (9)