A Heron is often the first bird that a non-birdwatcher notices when they visit Tring Reservoirs; herons waiting motionless on the edges of the canals and reservoir banks as they patiently wait for a fish to come within striking distance.
At this time of year the herons are hunting for food to feed their young chicks and as well as fish they will take frogs, small mammals and insects and occasionally other small birds and even worms.
The heronry at Wilstone is one of the largest in Herts and contains 25 - 30 nests most years i.e. up to 60 adult birds, and in a good year maybe another 60 young herons will fledge. Most pairs at Tring have between one and three chicks. In broods of three (or more), one chick is usually smaller than the others and will not survive if there is a shortage of food. Young birds are also at risk of falling out of the nest; as they get bigger they start standing up in the nest flapping their wings to exercise them and if they fall out of the nest at this stage, especially at Wilstone where they nest over water, they will probably die. However, once the young birds are safely grown and out of the nests, they can look forward to a long life.
One sharp-eyed birdwatcher has managed to read the ring numbers of two herons at Tring reservoirs. Tring Ringing Group ringed one of the birds as a chick in the nest at Wilstone on 18/4/1992. The other was found to have been ringed at Earls Barton gravel pit in Northants in 1988, which makes it 17 years old. This bird can be recognised by its deformed right foot that it rests on its 'knuckles'.
Most herons disperse upon fledging then return to their natal colony to breed but this bird must be breeding here at Tring and has travelled considerably further than the 28km median natal dispersal distance based on BTO ringing data.
We have seen this heron fishing along the canal at Marsworth, possibly he or she followed the canal network from Northamptonshire.
The BBC programme Countryfile on 18/4/04 reported on herons at Beesthorpe nature reserve in Notts. Here ringers found heron chicks with serious deformities and broken limbs, and for the last 18 months scientists have been testing nestlings for a range of toxins. (Tring was selected as one of the healthy populations against which the Beesthorpe birds were compared.) PCBs were the only toxin that was found to be higher in the affected birds. These chemicals, used in transformers and electrical goods, were banned 30 years ago but are still present in the environment, in the ground, in water and in us. The scientists are now trying to discover where the PCBs found in the Beesthorpe herons are coming from and will track birds to their feeding grounds using a mobile radar tracking station.
Over the last few winters, Little Egret has been seen regularly roosting with the grey herons at Wilstone and on Tringford reservoir. Little egrets often nest colonially with other herons on the continent, how long before we have Little Egrets competing for nest space in those flimsy willows?
Lynne
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