The telescope is set up on its tripod and turned to medium power. In the clear circle of light there is a grey, fluffy, and rather comical-looking head, poking above the edge of the nest.
A moment later another head rises behind it, another chick: there are three in all, and they have just become aware of the return of one of their parents. Reducing the magnification, we are just in time to include within the circle the adult heron as it arrives, ruffles and then sleeks its plumage. Zoom in again, to maximum power, and we see the adult bird lean over and open its bill.
All three chicks strain upwards to be fed, but only one is selected, either through the discretion of the parent, sharing the food out equally, or because the chosen chick is more pushy than the others and does not scruple to take the food intended for its fellows.
With a gulping motion the parent bird regurgitates the contents of its crop and passes to the chick a semi-digested mash of fish, with a leavening of frogs, perhaps, or a rat or water-vole – delicious for baby herons and, for the moment, the chief interest of their lives. The parent has spent an hour or two collecting it, at any distance up to twelve miles from the colony, but probably no further away than the adjoining lakes and streams.
Only in recent years have herons begun to nest locally again. Several decades ago there was said to be a small heronry at Charlotte’s Vale, near Grove Mill at Watford, but otherwise the only nest-site was at Marsworth Reservoir, Tring. Then, in the seventies, herons began to take an interest in Broadwater, a large flooded gravel-pit near Denham.
Before excavation took place, the contractors agreed plans to leave a specified number of islands in the lake. The largest group of these, in the southern end, has now become covered with alders, birches, and willows, and provides a sanctuary for a variety of breeding and roosting birds.
For years the herons were to be seen hanging about the islands during the breeding season. Finally, after a number of false starts, some nests were constructed and the colony began. By now there are twenty or more nests to be seen every spring: bulky platforms of sticks, lined with twigs and other bits of vegetation, sometimes built from scratch, but more often based on the previous year’s and enlarged. The female does the building work, while the male provides the materials.
The breeding season begins early, for the heron is a large bird and its young take a long time to grow. The eggs, normally three to five in number, are laid in February or March, and are incubated for about twenty-five days. The young are ready to leave the nest about seven or eight weeks later.
By the end of May or early June, the young herons, wearing the drab grey plumage of the juvenile, have flown the nest. Some remain at Broadwater, loafing about on the islands or shore or perched on the colony trees, but the rest disperse quite widely over the surrounding district.
The colony at Broadwater has proved a great success, and an offshoot has now been established among the wooded islands and gravel strands at Stocker’s Lake, a couple of miles to the north.
As a result, the heron, once noteworthy away from its recognized haunts in the Colne Valley, is now becoming a frequent visitor to many sites where previously it was virtually unknown.
While they show no sign of breeding again at Charlotte’s Vale, the herons have adopted one particular field there as a daytime roost. Here they wait, digesting their food, until darkness falls and it is safe for them to return to the streams and rivers which, during the hours of daylight, are prone to human disturbance.
The field is broad, sloping, and roughly triangular, bounded on one side by Grove Mill Lane, on another by a narrow strip of woodland beside the River Gade, and on the third by more extensive woods adjoining the golf-course. On a high part of the slope is a single large cedar of Lebanon; the herons either perch on its branches, or on the ground elsewhere in the field – often beside the wire fence parallel with the river. As many as fourteen birds congregate here during the day from September to March, although four or five is a more usual number.
By late January most of the breeding birds have already returned to the Colne Valley to stake their territories among the trees and repair the nests in readiness for another generation of young.
Gravel workings such as these at Broadwater are often criticised for the damage they cause to the environment, and certainly much has been lost here – the botanically rich Harefield Moor has been virtually destroyed. None the less, there are compensations, of which the heronry is one of the most interesting and exciting.
On this cloudy afternoon at the end of March, the colony is in full swing, with as many nests occupied out of sight as are in plain view. The air above the trees is full of parent birds coming and going, and it looks as if a bumper crop of chicks is again to be brought off this year.