Why a Messy City Lake Holds More Bird Species Than a Tidy Park

Bare mud at a lake's edge is not a sign of neglect. It is foraging habitat. Waders such as the common sandpiper and little ringed plover work the exposed margins for invertebrates buried a centimetre or two down, and they need soft, uncompacted ground to do it. A concrete promenade or a mown grass slope to the waterline removes that layer entirely. The birds move on before a visitor has unzipped their binocular case.

Emergent vegetation, the patchy reeds, the stands of bulrush, the floating mats of water hyacinth that lake-cleaning drives target, serves a different function. Purple swamphens nest in it. Baya weavers hang their flask-shaped nests from the stems. Little grebes dive under it and surface three metres away. Remove the vegetation and you remove the structure that makes those behaviours possible. A clean open sheet of water is ecologically closer to a swimming pool than to a functioning wetland.

The organic material that accumulates at neglected urban lakes, leaf litter, decomposing aquatic plants, fish that have died near the surface, drives an invertebrate community that most park designers do not consider and most birders underestimate. Chironomid midges breed in the sediment. Aquatic beetles colonise submerged debris. Dragonfly larvae spend up to three years in the muck before emerging. Each of these is a food source, and the birds that eat them follow the supply.

Barn swallows and wire-tailed swallows quarter low over the water because the midge hatch is densest there, not because they prefer urban lakes aesthetically. Cattle egrets and intermediate egrets stand at the margins because the disturbed sediment around a partially clogged inlet releases invertebrates into the water column. The rubbish that catches the eye, a plastic bag snagged on a reed stem, a tyre half-submerged at the edge, coexists with biological richness that the rubbish did not cause and that cleaning campaigns often damage by destroying the substrate alongside the litter.

A tidy urban park typically offers two habitat types: mown grass and ornamental planting. A scrubby city lake in reasonable ecological health offers six or seven within a hundred-metre walk: open water, floating vegetation, emergent reeds, mudflat, rank grass, shrub edge, and the ecotone where each meets the next. Species partition these zones. The Indian pond heron stands motionless at the reed edge. The black-winged stilt wades the open shallows. The white-throated kingfisher perches on a dead branch over the water. The pied kingfisher hovers above the open surface. None of these birds uses the same microhabitat, and none of them would find what they need in a park designed for human recreation.

The gradient also matters seasonally. Winter brings migratory ducks, gadwall, northern pintail, common teal, that need open water and undisturbed margins for roosting. They do not stay where there is heavy foot traffic or where the shoreline has been hardened. The same lake that looks like an eyesore in October may be holding forty species by December, including birds that have flown from Central Asia or Siberia to get there.

The productive approach is to arrive early, move slowly along the least-disturbed margin, and spend time at the edge where one habitat type meets another. Ecotones concentrate activity because they put multiple food sources within reach of a single perch. A dead tree standing in shallow water at the reed edge is worth ten minutes of patient watching: it offers a hunting perch for kingfishers, a loafing spot for cormorants, and a potential nest cavity for mynas or parakeets.

Sound is often the better guide at a dense reed bed. The zitting cisticola's repetitive single note, the bubbling call of a hidden purple swamphen, the sharp alarm of a watercock, these locate birds that will not show themselves in open water. Learning five or six calls specific to wetland species transforms a visually impenetrable reed margin into a readable habitat.

The species count at an urban lake is also not fixed. It responds to water level, season, disturbance patterns, and what is growing at the margins. A lake that held twelve species in a dry April may hold thirty in a wet November. The mess is not static, and neither is what lives in it.