Oil spills can have devastating effects on seabirds and other wildlife. When oil spills into the ocean, it forms a thin slick across the surface of the water. This oil coating can cause serious problems for birds that come into contact with it. Over 250 species of birds are affected by oil spills each year. Understanding what happens to birds during an oil spill is important so we can try to mitigate the damage and provide the best possible care for impacted wildlife.
How do birds get exposed to oil during a spill?
Seabirds are most directly impacted by oil spills. These birds spend most of their time floating on the surface of the water where oil slicks form after a spill. Diving seabirds that swim underwater and feed on fish and other marine life often resurface into the slick and become coated with oil. Shorebirds walking along contaminated beaches can also pick up oil on their feathers.
As birds try to preen and clean their feathers, they often ingest the oil. This can poison the birds and cause serious internal damage. Even small amounts of oil can be detrimental over time. Just a few drops rubbed into a bird’s feathers can destroy their insulating and waterproof properties.
What are the effects of oil exposure on birds?
Oil has an immediate and dramatic effect on a bird’s feather structure and function. Feathers are made up of tiny barbs that zip together like zippers to create a waterproof barrier. When feathers come into contact with oil, these barbs start to mat and separate. This damages the intricate structure of the feathers and causes them to stick together in clumps. Birds lose both their waterproofing and their ability to regulate their body temperature.
Without insulation from the cold ocean water, hypothermia quickly sets in. Birds exposed to oil will start shivering uncontrollably as their body loses heat. They frequently die from this temperature shock within a few hours.
Ingested oil causes internal damage and interferes with digestion. Oil-coated birds spend more time trying to clean themselves and less time feeding. Without proper nutrition, they become weak and emaciated. Oil’s harmful effects on their digestion can also lead to anemia, organ damage, and reproductive issues.
How does oil impact seabirds over the long-term?
Oil pollution has numerous chronic effects that impact birds over longer time scales. Even small amounts of oil can impede a bird’s flight and swimming abilities. Without clean feathers, diving and soaring become much more energy intensive. This means birds have to spend more time resting and less time feeding and migrating.
Reproducing also becomes more difficult for oiled birds. Oil contamination lowers hatching success by interfering with egg development and causing lethal birth defects. Adult birds that ingest oil frequently experience damaged organs that make breeding less successful.
These long-term impacts severely disrupt local bird populations. After major spills, some colonies of seabirds completely collapse. Other bird populations take many years to recover as ongoing pollution continues to hamper reproduction. Protecting birds from chronic oil pollution is key to sustaining healthy numbers.
What happens when seabirds encounter oil spills?
Here is a general overview of what typically occurs when seabirds get coated by spilled oil:
Direct contact with oil
– Birds floating on the water surface directly encounter the oil slick. Diving birds resurface through the oil, coating their bodies.
– Oil sticks to feathers immediately, matting and separating barbs. Insulating and waterproofing properties are lost.
Hypothermia and exhaustion
– In just a few hours, birds can no longer maintain proper body temperature and start to succumb to hypothermia.
– Fatigue sets in as birds attempt to stay warm while swimming and flapping vigorously. Birds rest more and spend less time foraging.
Ingestion of oil
– While preening, birds ingest oil that further weakens them through internal tissue damage.
– Fish and invertebrates contaminated by the spill are also consumed, increasing oil toxicity.
Dehydration and starvation
– Damaged feathers become waterlogged, reducing buoyancy. Birds must work harder to stay afloat.
– Weakened birds have difficulty diving and catching prey. Lack of food leads to starvation.
Reproductive failure
– Breeding adults exposed to oil may not nest or fail to hatch healthy chicks.
– Oil-coated eggs suffocate developing embryos. Hatchlings are frequently malformed or non-viable.
Colony desertion
– Entire colonies may abandon heavily oiled nesting sites that chicks can’t traverse. Birds won’t return for years.
Death
– Most oiled birds die within days primarily due to hypothermia, starvation, and organ damage. Carcasses get consumed by scavengers and sink beneath the waves.
Key statistics on oiled birds after spills
Here are some key statistics and estimates on how oil spills typically impact seabird populations:
Number of birds killed
– Exxon Valdez spill (1989): 250,000 – 500,000 seabirds killed
– Prestige spill (2002): Over 200,000 seabirds estimated dead
– Deepwater Horizon spill (2010): More than 1 million birds impacted
Species affected
– Species most affected are those that float on the water surface: cormorants, grebes, loons, murres, puffins.
– Diving birds are also vulnerable when surfacing: penguins, auks, shearwaters, pelicans.
– Wading birds using sandy beaches and intertidal areas are also at risk.
Population impacts
– Common murre colonies declined up to 70% after Exxon Valdez spill. Still listed as “recovering” 30+ years later.
– Atlantic puffin populations dropped by more than 60% following the Prestige spill and took over a decade to rebound.
– Western grebes and common loons suffered losses of 30-45% of their populations after the Exxon Valdez spill.
– After the Deepwater Horizon spill, laughing gull populations decreased by 25% and only saw marginal recovery 5 years later.
Rehabilitation statistics
– Only around 2% of oiled birds survive after rehabilitation efforts. Most die before reaching care.
– During rehabilitation, studies show that <50% of heavily-oiled birds survive even with extensive treatment. - Time is critical - birds arriving at rehabilitation centers within 1-3 days have the highest chance of survival. - On average, only 10-15% of oiled birds are ever recovered, treated, and released back to the wild after spills.
Detailed impacts of oil on seabird feathers
To understand why oil is so dangerous for seabirds, it helps to look closely at how oil specifically damages their feather structure and function. Here are some of the main ways oil degrades feathers:
Matting
– Oil causes feathers to stick together into clumps, destroying their intricate interlocking structure.
– Barbules that allow feathers to zip together are glued into unusable mats.
Loss of waterproofing
– Feathers soaked in oil can no longer repel water. The bird gets waterlogged, which pulls feathers apart further.
– Diving birds lose crucial waterproofing needed to plunge into ocean after prey.
Plumage separation
– Normally feathers form a cohesive, flexible coat. Oil causes entire feathers to detach from the skin.
– Bald patches open up, allowing cold ocean water to touch the skin and cause dangerous heat loss from the body core.
Soiling
– Oil smears all over feathers, turning them from light and fluffy to a dark, heavy mass.
– With feathers matted and soaked, birds can no longer fly or even walk.
Increased heat loss
– The thick layer of smeared oil eliminates the feather’s ability to trap warm air against the skin.
– Without insulation, birds rapidly become hypothermic as body heat dissipates into the cold ocean waters.
Increased buoyancy
– Normally feathers trap air to optimize floating ability. When matted down with oil, feathers lose trapped air bubbles.
– Birds have to work harder paddling and flapping to stay at surface, quickly becoming fatigued.
Unique vulnerabilities of different seabird species
While all seabirds are detrimentally impacted by oil, some species face greater challenges depending on their sizes, feeding behaviors, migration habits, and other life history traits.
Penguins
– Small surface area relative to body size means oil clings thickly rather than shedding off.
– Tend to live in large colonies, enabling oil to affect thousands of birds at once.
– Breed in burrows, causing adults and chicks to traverse oiled beaches repeatedly.
Albatrosses
– Forage over huge ocean distances, increasing exposure to sporadic oil slicks.
– Plunge diving to catch prey causes oiling of underparts as well as upper feathers.
– Highly philopatric, returning to same breeding sites annually, even if still oiled.
Shearwaters
– Often migrate extremely long distances, up to 10,000 miles roundtrip.
– Normally only return to breeding colonies after several years to nest. Oil impacts can persist.
– Feed on ocean surface and perform aerial diving, increasing contact with slicks.
Auks
– Nest in extremely dense groups on cliffsides, with constant physical contact.
– One oiled bird will spread oil rapidly throughout entire breeding colony.
– Pursuit diving to depths over 100 feet exposes auks to any subsurface oil.
Grebes
– Winter in flocks of hundreds of thousands of birds on concentrated estuaries.
– Tend to enter torpor while roosting, which may inhibit escape from quickly approaching slicks.
– Plumage is less dense compared to other waterbirds, providing less insulation.
How oil impacts the breeding success of seabirds
Oil pollution doesn’t just kill adult birds – it also cripples their ability to successfully reproduce by reducing fertility, embryo mortality, and chick survival. Here are some of the main ways oil hinders seabirds from breeding:
Reduced fertility
– Oil can interfere with egg formation in breeding females. Exposure is correlated with smaller eggs and lower hormone levels.
– Courtship displays and pair bonding are disrupted when birds are oiled. Mates may fail to breed at all.
Altered incubation
– Adults may take longer breaks from incubation duties after becoming oiled. More exposed and cooled eggs don’t hatch.
– Oil transfer between nesting birds can coat the exterior of eggs and impede oxygen exchange.
Higher embryo mortality
– Oil penetration into the eggs smothers and poisons developing chicks before hatching.
– Studies show chick mortality increases to over 50% when breeding birds are exposed to oil.
Birth defects
– Embryos that survive exposure may develop heart, limb, and other deformities that prevent survival after hatching.
– Oil contamination is linked with physical and cognitive developmental issues in hatchlings.
Abandonment
– Heavily oiled nesting colonies are often deserted as birds are too weak to tend nests. Breeding efforts for the year fail.
– Incubating adults have to choose between self-preservation and caring for eggs after becoming oiled.
Chick mortality
– Newly hatched chicks have higher mortality when being fed by oiled parents. Chicks die from oil toxicity, hypothermia, or starvation.
– Chicks unable to fledge from the nest because of oiled feathers and reduced parental care.
Different ways oil can impact seabirds after spills
Here is a table summarizing the various pathways oil takes to exert both lethal and sub-lethal effects on seabirds:
| Exposure Type | Effects on Seabirds |
|---|---|
| External oil coating feathers | – Loss of waterproofing and insulation |
| – Hypothermia | |
| – Inability to fly or forage | |
| Ingestion during preening | – Organ damage |
| – Digestive issues | |
| – Physiological impairment | |
| Ingestion through food chain | – Toxicity from contaminated prey |
| – Reduced fitness and survival | |
| Exposure at nesting colonies | – Eggs coated with oil |
| – Embryo mortality | |
| – Nest abandonment |
rehabilitation processes and success rates for oiled birds
When oiled birds are recovered, they go through intensive rehabilitation aimed at removing oil, restoring the feather structure, and stabilizing the bird. Here is an overview of this process and why it often has low success rates:
Stabilization (1-3 days)
– Address critical medical issues – rehydrate, increase body temperature, administer drugs.
– Without stabilization, most birds die quickly from shock. Success rates for this stage approach 90%.
Washing (1-2 weeks)
– Use warm water, detergents, and elbow grease to remove oil from feathers and skin.
– Prevent further damage of feathers and skin through careful washing protocols.
– Success rates drop to 50% as harsh detergents and handling stress take toll.
Rinsing (2-3 days)
– Thoroughly rinse detergents which can compromise waterproofing if left in feathers.
– Eyes, nares, mouth are carefully flushed to remove oil ingested internally.
– Survival rates remain around 50% during this relatively low-stress stage.
Drying (2-4 weeks)
– Use cage dryers to fully dry the feathers and restore natural oils.
– Ensure feathers are drying properly and properly aligned.
– Some birds cannot be fully restored and have to be euthanized. Success rates drop to 35%.
Conditioning (2+ weeks)
– Strengthen and waterproof feathers through swimming sessions.
– Build up muscles through flight training so birds can return to the wild.
– Survival rates increase to 50% again during this pre-release conditioning period.
Release
– Only about 20% of recovered birds are successfully returned to the wild after rehabilitation.
– However, released birds face much higher mortality rates than normal. Only 2% survive over the long term.
Potential secondary effects of oil spills on seabirds
Oil spills can impact seabirds even without coming in direct contact through these secondary effects:
Decline of food sources
– Oil toxicity kills fish, invertebrates and other prey species that birds rely on.
– This creates food shortages forcing birds to work harder to find adequate nutrition or fail to thrive.
Habitat degradation
– Breeding colonies and migratory stopover sites can be fouled with oil and abandoned.
– Some habitat degradation persists even decades after the visible oil is gone.
Increased predation
– Weakened oiled birds fall victim more frequently to predators.
– Some predators target seabird colonies where oil weakens nest defenses.
Altered migration patterns
– Birds avoid traditional routes that take them through or near oiled areas.
– Forced to use unfamiliar routes, birds can become exhausted and emaciated.
Compromised resilience
– Exposure to oil makes seabirds more vulnerable to environmental fluctuations, disease, and pollution.
– Their typical ability to bounce back from disruptions declines after oiling.
Conclusion
Oil spills subject seabirds to a wide array of lethal and sub-lethal effects. Direct feather soiling causes the majority of mortality through hypothermia, drowning, and starvation. Birds that escape immediate death face disrupted breeding, organ damage, and food shortages that continue to take a toll. Though rehabilitation efforts help some oiled seabirds, most ultimately perish due to persistent impairments and damaged habitat.
Even small spills can have disproportionately large ecological impacts. Seabirds tend to congregate in dense colonies, so a single event can affect entire populations. Since many species are slow to reach sexual maturity and have low reproductive rates, their numbers take years to recover after heavy losses. Some colonies have deserted traditional nesting sites permanently due to chronic oil contamination.
Prevention remains the best long-term solution. Improved shipping standards, phase outs of oil transportation in sensitive areas, and increased preparedness for responding quickly to spills can help mitigate damages. But until society transitions away from a dependence on oil, seabirds will remain at risk. More research and monitoring of how both large and small spills impact different species can help inform conservation priorities in the future.
With proactive policies and appropriate funding, some seabird populations have bounced back after major disasters. But we will only stem losses if society takes a hard look at our chronic dependence on oil and how it threatens vulnerable species and ecosystems. Though individual birds succumb quickly during spills, responsible stewardship and conservation action can give future generations of seabirds the protection and clean waters they deserve.
