Threats to Wildlife: Habitat Loss, Poaching, Invasive Species, Disease, Pollution and Climate Change

Wildlife populations are under more pressure today than at any point in human history. WWF’s Living Planet Report 2024 found that monitored vertebrate populations had declined by an average of 73 percent since 1970. Understanding the causes is the first step towards solutions. This module summarises the main threats, how they work and who is most at risk.

What you will learn

The main direct threats to wildlife
How threats interact and reinforce each other
Which traits make species vulnerable
The underlying drivers behind the threats

1. Habitat loss, degradation and fragmentation

Converting natural habitats to farmland, plantations, pasture, mines, roads and cities is the single largest threat to wildlife on land. Examples include oil palm and pulp plantations replacing lowland rainforest in Borneo and Sumatra, soy and cattle pasture replacing the Cerrado and parts of the Amazon, and farmland and settlements replacing grasslands and savannas worldwide. Even where habitat remains, it may be degraded (by logging, overgrazing, altered fire regimes or pollution) or fragmented into small, isolated patches (Ecology Module 10).

2. Overexploitation: hunting, fishing and trade

Commercial poaching for high-value products: elephant ivory, rhino horn, tiger bones, pangolin scales, bear bile, totoaba swim bladders.
Bushmeat hunting: snares set for meat kill millions of animals a year in Central African, West African and Southeast Asian forests, and increasingly in savannas. In parts of Southeast Asia, industrial-scale snaring has created “empty forests” where habitat remains but large animals are gone.
Live animal trade for pets: parrots, songbirds, reptiles, primates and ornamental fish.
Overfishing and bycatch: sharks, rays, sea turtles, dolphins and seabirds caught in nets and longlines. Bycatch in gillnets has pushed the vaquita to the brink.

3. Invasive species

Species introduced by people outside their natural range can prey on, compete with or bring diseases to native wildlife. Invasive species are a leading cause of recorded extinctions, particularly on islands. Examples include rats, cats and stoats on islands from New Zealand to the Galápagos, cane toads poisoning predators in Australia, Burmese pythons in Florida’s Everglades, and the brown tree snake, which wiped out most of Guam’s native forest birds.

4. Disease

New diseases can devastate wildlife, especially when spread by people or trade:

Chytrid fungus (Batrachochytrium dendrobatidis) has contributed to declines in hundreds of amphibian species and the extinction of dozens, one of the largest recorded losses of biodiversity attributed to a disease.
White-nose syndrome has killed millions of bats in North America since 2006.
Highly pathogenic avian influenza (H5N1) has killed wild birds and marine mammals on every continent except Oceania since 2021, including sea lions and elephant seals in South America.
Devil facial tumour disease in Tasmanian devils and canine distemper in lions, wild dogs and Amur tigers.

5. Pollution

Pesticides: DDT thinned the eggshells of eagles and falcons; diclofenac, a veterinary drug in livestock carcasses, killed tens of millions of vultures in South Asia in the 1990s and 2000s; neonicotinoids are linked to declines in insects and insect-eating birds.
Poisoning: carcasses laced with poison to kill predators kill vultures in large numbers.
Plastics: entanglement and ingestion affect seabirds, turtles and marine mammals.
Lead from ammunition and fishing tackle poisons eagles, condors and swans.
Light and noise: artificial light disorients turtle hatchlings and migrating birds; ocean noise disrupts whales.
Nutrients: fertiliser run-off creates oxygen-poor dead zones.

6. Climate change

Rising temperatures, changing rainfall, sea-ice loss, ocean acidification and more extreme weather affect wildlife directly and by changing habitats and food (Ecology Module 12). Climate change increasingly interacts with other threats, for example making fragmented populations less able to move.

7. Infrastructure

Roads kill huge numbers of animals and fragment habitat; power lines electrocute and collide with large birds such as bustards, cranes, vultures and storks; dams block fish migrations and change rivers; wind turbines can kill raptors and bats if poorly sited; fences block migrations of wildebeest, zebra and saiga.

How threats interact

Threats rarely act alone. A road into a forest brings loggers, then hunters, then settlers; fragmented populations are more vulnerable to disease, inbreeding and fire; climate change can make invasive species spread faster. Conservation plans must address combinations of threats.

Which species are most vulnerable?

Species tend to be at higher risk if they are large-bodied and slow-breeding (elephants, great apes, rhinos, whales, sharks); specialists with narrow diets or habitats (giant pandas, koalas, many island birds); restricted to small ranges, especially islands and mountains; valuable in trade; wide-ranging carnivores that come into conflict with people; or migratory species that depend on several sites across countries.

Underlying drivers

Behind the direct threats lie indirect drivers: rising consumption, population growth, global trade, weak governance and corruption, poverty, and economic systems that do not account for the value of nature. Long-term solutions therefore involve policy, markets and development, not only fieldwork.

Case study: the vulture crisis in South Asia

In the 1990s, populations of three vulture species in India, Nepal and Pakistan crashed by over 95 percent. Scientists eventually identified the cause in 2004: diclofenac, an anti-inflammatory drug given to cattle, was lethal to vultures that fed on treated carcasses. Veterinary diclofenac was banned in India, Nepal and Pakistan in 2006, and a safe alternative, meloxicam, was promoted. Nepal created “vulture safe zones” and vulture restaurants supplying drug-free carcasses. Declines have slowed and some populations have stabilised, but related drugs remain a threat. Losing vultures also had human costs: more rotting carcasses and more feral dogs, linked to increased rabies risk.

Try it yourself

Choose one threatened species from our animal profiles. List its threats in order of importance using the categories in this module. Which threats interact, and which single action would help it most?

Key terms

Overexploitation: harvesting wildlife faster than it can recover.
Bycatch: animals caught unintentionally in fishing gear.
Invasive species: introduced species that spread and cause harm.
Empty forest syndrome: intact-looking forest emptied of large animals by hunting.
Indirect drivers: social and economic forces behind direct threats.

Threats to Wildlife