The case of the waterfowl killers could be written in an espionage novel or murder mystery, with its fuzzy, innocent little victims, an invisible murder weapon, and diligent government scientists scrambling to discover whodunit.
The evidence of death, naturally, would be spelled out in the first chapter: More than 200 dead ducks have turned up in the northwestern suburbs in the last two weeks.
A prime suspect is the midge larva, the offspring of a mosquito-like insect and a favorite cuisine for ducks. A dead midge can carry a form of botulism that doesn`t harm humans but can fell a duck in a matter of hours.
The killer stalks storm-water retention ponds, such as man-made lakes built to hold storm water at apartment complexes and lend some country ambiance to the rapidly developing suburbs.
Trudi Goodman`s son David, 22, apparently reported the first signs of carnage Labor Day on Lake Edwin, a retention pond at the Triumvera condominium complex, west of Glenview, where they live.
About 15 ducks floated on their sides. Several others wobbled on land.
The next day, Goodman learned that about 30 ducks had turned up dead in a pond at Ridgewood Cemetery in nearby Des Plaines.
In Arlington Heights, health officials had begun finding the first remains of 190 ducks that died on a retention basin in Hasbrook Park.
The three findings touched off an investigation at the National Wildlife Health Laboratory in Madison, Wis., where scientists confirmed what they suspected all along: A natural, everyday food chain had prompted a botulism epidemic in the suburban duck world.
Though the epidemic has startled some animal lovers, biologists treated it routinely. For years, retention ponds at many apartment complexes have been veritable petri dishes growing a toxic substance, Type C botulism, and turning the northwestern suburbs into a Death Valley for ducks.
It is not unusual to see mass killoffs of ducks in some Western states, said Christopher Brand, an epizootiologist with the national laboratory who diagnosed botulism in a duck from Arlington Heights. ``But you do see cases in Illinois, and for some reason the northwest suburbs, around Palatine and Arlington Heights, are repeat offenders.``
The massive duck kills in the Western states are caused by toxins growing in wetlands. But the suburbs have been rough on ducks because of the shallow man-made lakes.
Retention ponds are likely places for the toxin that produces botulism because their shallow water is heated by the sun, creating the warm, oxygen-free conditions in which the toxic germination thrives. As the water in the ponds recedes, it can create muddy banks that strand the larvae and make them easy prey for ducks.
``The northwest suburbs have a lot of these ponds because that`s a high-density area,`` said Scott Garrow, a district wildlife biologist for the Illinois Department of Conservation. ``That`s why you`re seeing the problem out there.``
The food chain that appears so benign when ducks dip their bills into the water to feast on insects becomes like an espionage-novel version of germ warfare when examined closely.
Microscopic, nontoxic botulinum spores are consumed by small aquatic invertebrae, such as the midge larva. But when the invertebrae die and begin to decompose, the spores germinate and produce the toxin that causes botulism. If enough of the decomposing larvae are eaten by a duck, the animal will die from paralysis within a day.
Many of the ducks drown when the paralysis affects their ability to float. Those that make it ashore die when they lose control of their respiratory systems.
When the paralyzed duck dies, flies descend on the carcass to lay eggs, which hatch maggots. Other ducks are then drawn to the carcass for a feast.
``There`s nothing another duck likes better than a bunch of maggots,``
Brand said. ``It`s good protein.``
It may be good protein, but it can create an epidemic.
Scientists say that most ducks avoid the fate because they change feeding grounds often. But well-meaning humans armed with bread crumbs may inadvertently lure ducks to their death.
``If the birds linger in one place, there`s more of a chance to ingest a lethal dose,`` Garrow said. ``When people feed them in an area, the birds just don`t leave. The well-intended snacks are actually making them more susceptible to disease.``
Few people realize the potential danger of duck feeding. ``That is what upsets us most, when we heard it blamed on people feeding the ducks,`` said Mary Cunningham, property manager at Triumvera.