Four nest rafts have recently been installed at my local birding patch — north-west London’s Brent Reservoir (a.k.a. the Welsh Harp) — to support the lake’s most iconic waterbird, the Great Crested Grebe.
The Great Crested Grebe was almost wiped out in Britain in the late 19th century because of a fashion for using its feathers in millinery and its pelt as a substitute for animal furs in boas and muffs. Campaigns against these trades led to bird protection legislation that ultimately saw the population begin to recover, after dropping to as few as 32 breeding pairs nationally.
In the early 20th century, the Welsh Harp became an important site in the revival of the species, and its presence in significant numbers was a major factor in the reservoir’s designation as a Site of Special Scientific Interest in 1950. The grebe is fittingly featured on the logos of both the Welsh Harp Conservation Group and the Friends of the Welsh Harp.
Because grebes have difficulty moving on land, they usually build their nests close to the water’s edge and barely above water level, which leaves them susceptible to flooding if the water level should fluctuate. Unfortunately, heavy rain frequently leads to a rise in Brent Reservoir’s water level that can overwhelm a grebe’s nest, and the bird’s breeding record has suffered over recent years after peaking at about 50 breeding pairs in 1991. As a regular visitor to the Welsh Harp I have on many occasions witnessed the destruction of nests by flooding.
However, a floating nest site is clearly exempt from the risk of inundation, and the new rafts — developed by Biomatrix Water and installed by the Canal & River Trust — are designed to improve the bird’s breeding success in various other ways too. The modular design provides each raft with a central opening that allows grebes to access the nest site from below the water surface. Tailored vegetation will shield the birds and their nests from potential predators. And a low wire fence around the edge of each raft will prevent other waterbirds from clambering aboard and disturbing the grebes.
A wildlife bonus is that the rafts should also help improve the reservoir’s fish stocks, since the planted vegetation will produce a subsurface forest of roots to provide shelter and feeding grounds for fish. And this micro-wilderness of submerged roots will also create an ideal habitat for micro-organisms that help to purify the water.
Three of the four rafts have been moored in secluded areas of the reservoir, but one has been positioned within view of the Cool Oak Lane footbridge, as a public amenity. The hope is that being able to view this raft will encourage more of the local population to develop an interest in the conservation of the Welsh Harp’s remarkable wildlife.
With fingers crossed, I look forward to the coming spring to find out whether the reservoir’s grebes will welcome this innovation.
Andrew's Birding Stuff 