Perhaps most worrisome, however, are these "secondary" poisonings, said Keith Bildstein, director of conservation science at the Hawk Mountain Sanctuary in Berks County.
He's now studying "catastrophic declines" in East African vultures, killed when they eat carcasses stuffed with the pesticide carbofuran to limit populations of feral dogs, jackals, and lions.
Just one carcass caused 44 vulture deaths, he said. "These kinds of carcasses are indiscriminant killers."
New Jersey officials keep a log of dead and injured eagles, and leading causes are lead toxicity, car hits, electrocutions from power lines, injuries from combat with other raptors, and other unidentified causes requiring necropsies, the animal equivalent of autopsies.
In the recent Delaware incident, the two eagles were discovered Oct. 21 in a Sussex County field.
Sgt. Gregory Rhodes, a wildlife enforcement officer with the Delaware Department of Natural Resources and Environmental Control, said someone driving by noticed the birds on the ground and called officials.
The live bird was taken to Tri-State Bird Rescue and Research, a nonprofit wildlife rehabilitation group in Newark that is known for its oil-spill response teams.
There, veterinarian Erica Miller said, clinicians immediately suspected poisoning.
They ran a lead-poisoning test, "because we do see that quite frequently in eagles," but it was negative.
The bird's heart rate and other signs were normal as well for most other toxics it would likely encounter.
Because of the paralysis, they suspected DDT. While the pesticide is no longer sold in this country, some people still have it, Miller said.
