Learning target: I can use evidence from a reading to explain how losing a scavenger disrupted an ecosystem service, tell a correlation from a cause, and compare the solutions people tried to bring the service back.
Read the whole passage once for the story. Then read it again with a pencil: number the paragraphs 1 to 7, underline each cause, and circle each piece of evidence (a number, a study or a comparison). Answer every question in complete sentences and name the paragraph your evidence comes from.
You will need: This worksheet, Pencil, Highlighter (optional)
[1]In much of India, cattle that die of old age or illness are not eaten. For centuries, the bodies of cows and buffalo were hauled to the edge of a village or to a dump and left in the open. Within hours, dozens of vultures would glide down from the sky, and a large flock could strip a carcass to bare bone in well under an hour. Nobody paid these birds, and few people thought of them as workers, yet they were doing a job that kept towns cleaner and safer.
[2]In the 1990s, bird scientists noticed something alarming. Three kinds of vultures that had been among the most common large birds of prey on Earth were vanishing. Surveys repeated over about fifteen years showed that their numbers had dropped by more than 95 percent, and one species had lost more than 99 percent. They tested ideas such as a new infection, a shortage of food and poisoning by crop pesticides, and none of those explanations fit the evidence.
[3]The answer came in the early 2000s from studies in Pakistan and then India. Veterinarians had begun treating sick or injured cattle with diclofenac, an inexpensive drug that eases pain and swelling. The drug does cattle no harm. But when a vulture feeds on an animal that died within a few days of a dose, the leftover drug damages the bird's kidneys, and the vulture can die within days. Only a tiny fraction of carcasses needed to contain the drug to cause the crash, because each vulture feeds on many carcasses over its life.
[4]With the vultures gone, the carcasses did not disappear. They rotted slowly, and other animals moved in to eat them. Rats and feral dogs, dogs that live on their own without owners, suddenly had extra food. One study estimated that the number of feral dogs in India grew by millions during the years the vultures declined. That mattered for people, because dog bites cause nearly all human rabies cases in India. Rabies is a deadly infection of the brain, and sales of rabies vaccine rose as more people were bitten.
[5]Here a careful reader should slow down. A graph showing vultures falling while dogs rose does not, by itself, prove that one change caused the other. Dog numbers might also have grown because towns were growing and making more garbage. To test the idea, economists in a 2024 study compared districts of India that had been home to many vultures with districts where vultures had always been rare. After diclofenac came into wide use, human death rates rose by more than 4 percent in the former vulture districts but not in the others. Because both kinds of districts went through the same national changes, the difference points to the loss of vultures, and the poorer sanitation that followed, as a cause. Rabies was probably one pathway; germs from rotting carcasses washing into water may have been another.
[6]India and its neighbors tried several solutions. In 2006 the governments of India, Pakistan and Nepal banned diclofenac for use in animals. Scientists tested other painkillers on vultures in captivity and found that one, meloxicam, did not harm them, so veterinarians could switch to it. Conservation groups built breeding centers where vultures are raised safely and later released, and some regions set up vulture safe zones where farmers are helped to use only safe drugs. Each solution has limits. Some people kept giving cattle diclofenac made for humans after the ban, and other livestock painkillers were later found to be dangerous to vultures too.
[7]Recovery is slow. A pair of these vultures raises at most one chick a year, and young birds take about five years to begin breeding, so numbers can climb only gradually even when the food is safe. Recent surveys suggest the steep declines have slowed or stopped in some areas, but the populations remain a small fraction of what they once were. The vultures' story shows how a service that no one counted, cleaning up dead animals, can turn out to be worth a great deal once it is gone.
| What happened at this step |
|---|
| Step 1: cattle |
| Step 2: vultures |
| Step 3: carcasses |
| Step 4: dogs and rats |
| Step 5: people |
| What it does | One strength | One limit |
|---|---|---|
| Banning diclofenac for animals | ||
| Switching to meloxicam | ||
| Captive breeding and release | ||
| Vulture safe zones |
Before answering, write one short label in the margin beside each paragraph: 1 the job, 2 the mystery, 3 the cause, 4 the chain of effects, 5 testing the cause, 6 the solutions, 7 recovery. When a question names a paragraph, go back to that label and reread just that paragraph. For q6, look for the words 'does not, by itself, prove' and 'compared'.
The 2024 study compared places that lost vultures with places that never had many. Design a similar comparison for a different question: does losing turkey vultures in part of California change how long roadkill stays on the road? Describe which places you would compare, what you would measure, what other differences between the places could fool you, and what result would support the idea that vultures provide a cleanup service there.