Oil spills have a devastating effect on marine wildlife. Marine birds are exquisitely sensitive to changes in their environment. Even small oil spills can cover vast amounts of water and affect countless birds. Different species of marine birds are affected in different ways by oil spills, those that spend most of their life at sea and only come ashore for short periods of time (e.g. guillemots) , are more likely to be seriously affected by an oil slick compared with birds that spend more time on land or in the air. Birds that respond to stress and fear by diving are more likely to end up with more oil coating their feathers than birds that rather than fly away from dangerous/stressful encounters. The long-term effects of oil differ among marine bird species; birds with high reproductive rates will rapidly re-populate an area that has lost a large proportion of its population to oil pollution, in contrast birds from a species with lower reproductive rates and smaller clutch sizes will take longer to recover from oil pollution losses. (Alonso-Alvarez, C. et al. 2007)(Balseiro, A. et al. 2005)

Heavily Oiled Bird © Tom Pearman

Oil spills first form a thick layer of oil on the surface of the water, then over time the oil disperses forming a thin film that can coat miles of sea. Birds that are caught in the spill will quickly become heavily coated in thick oil. This oil will weigh them down and cause them to beach or drown rapidly.(Tully Jnr, T.N. Lawton, M.P.C. Dorrestein, G.M. 2000 Ch 15 pg 339)

Lightly Oiled Bird © Irish Seal Sanctuary

Once the oil has dispersed however, birds may become coated with a minute volume of oil. This will not impede them physically as the oil slick would, instead it disrupts their waterproofing and buoyancy predisposing them to developing hypothermia and slowly they become emaciated and hypoglycaemic.(Briggs, K.T. 1996)(Briggs , K.T. 1997)

Understanding the effect of differing types of oiling allows veterinarians to predict the different consequences for the individual casualty. Heavily oiled birds will present with such immediate problems as: ingestion of large volumes of a toxic substance and exhaustion from the physical weight of the oil coating their feathers. Lightly oiled birds will present with: emaciation; low PCV and TS; chronic exposure to toxic substance. Different presenting conditions require slight alterations in the standard approach to treating an oiled bird.(Tully Jnr, T.N. Lawton, M.P.C. Dorrestein, G.M. 2000 ch 15 pg 339) (Keeble, E.2003)

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Waterproofing

Body Condition and Weight

Ingestion

Stress

Haemolytic Anaemia

Waterproofing

Percentage oil coverage does not correlate with level of waterproofing. Even a tiny patch of oil on the bird’s feathers will disrupt the air-water barrier and allow water to penetrate the warm air layer that lies next to the skin. The presence of oil on the birds feather’s will stimulate them to preen, this spreads the oil over more feathers so even though the bird may appear clean it can still be oiled. Lightly oiled birds are not weighed down physically by the oil. This allows them to survive longer before they beach. (R.S.P.C.A. 2001)(Briggs et al. 1997)

Once the waterproof barrier created by the interlocking feathers is disrupted the insulating layer of warm air that lies close to the bird’s skin is lost. Cold seawater can then penetrate through the feathers and reach the bird’s skin. Water conductors heat much more efficently than air. Once the water has reached the skin the bird looses huge amounts of body heat to the water. Birds are unlike marine mammals in that they don’t have an insulating layer of fat under their skin. Instead they rely on the layer of trapped air. Rapid diffusion of body heat into the surrounding environment and no back-up form of insulation triggers fast onset of hypothermia.(Tseng, F.S. 1997)

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Body Condition and Weight

During the time between the loss of insulation and beaching the bird’s metabolic rate will have to increase dramatically to generate enough heat to maintain normal body temperatures and counteract the developing hypothermia. Any increase in metabolic rate must coincide with an increase in feed intake or the body will move into a state of catabolism to obtain the necessary energy requirements. Oiled seabirds therefore have above average nutritional requirements. Loss of insulation however prevents them from spending as much time as is necessary at sea to catch fish to meet these elevated energy requirements. Their diving abilities are reduced. Decreasing feed intake with increased metabolic rate results in sudden weight loss. Often oiled birds presented at rehabilitation centres are extremely emaciated and in very poor body condition score. This does not correspond with poor prognosis. Provided that they receive the necessary supportive care these birds usually respond very well to treatment in the rehabilitation facility.(Tully Jnr, T.N. Lawton, M.P.C. Dorrestein, G.M. 2000) (Keeble, E.2003)

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Ingestion

Ingestion of oil is a common problem seen in oiled seabirds. The amount of oil ingested can vary greatly. If the bird is only lightly oiled it may have only ingested a small volume of oil from preening. However if the bird is heavily oiled it will most likely have ingested a larger volume of oil - in heavily oiled birds oil may even be visible in the mouth. The first place of the alimentary canal the oil affects is the oral mucosa, oil is highly irritant and will cause hyperaemia and if corrosive can cause bleeding. When a bird is presented first, at either the on-site first-aid station or the rehabilitation centre, washing the bird’s beak and mouth with warm saline solution helps remove any traces of oil remaining in the mouth and decreases the amount of oil ingested from then on.

Oil causes severe damage as it moves through the GIT. Rapid passage throught the GIT decreases the length of time the oil is in contact with the gut wall. Oral fluids facilitate swift movement of the oil through the GIT, the faster the transit time the smaller the volume of oil that will be absorbed. This is why it is recommended that birds not be fed immediately on capture. Food in the GIT slows elimination of oil and enhances absorption.(Briggs et al 1997)

Irritation of the intestinal epithelium ranges from mild to severe depending on the type of oil and the volume ingested. Mild damage may simply irritate the villi and microvilli; this will decrease absorption of nutrients from the gut lumen. More severe irritation due to a more toxic type of oil or ingestion of a larger volume of oil will cause irreparable damage to the epithelial lining resulting in necrosis of the villi and damage to the submucosa. Severe epithelial damage will prevent nutrient absorption until the epithelium has been regenerated. Damage to the submucosa means the Gut-Associated-Lymphoid-Tissue will be disrupted. This is one of the mechanisms by which ingestion of oil causes immunosuppression in oiled seabirds. Massive numbers of lymphocytes are located in these regions and provide an important protective barrier against pathogenic and opportunistic bacteria in the gut. Unable to defend themselves against bacterial invasion the bird will now be at risk of septicemia, bacteremia and endotoxemia.(Leighton, F.A. et al 1983)(Briggs, K.T.et al 1996)

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Stress

Ingestion of toxic substances, loss of buoyancy, decreased ability to dive and swim along with sudden hypothermia are highly stressful to marine birds. Some species are more susceptible to stress than others e.g. Auks. As in mammals, when stressed birds release corticosteroids from the adrenal glands. Corticosteroids decrease the immune response and induce hypoglycaemia.

(Briggs, K.T. et al 1997) Briggs has studied how stess develops and causes problems in seabirds that have become coated in oil and are captured for rehabilitation. Follwing capture stress levels increase further. By the time an oiled seabird is presented for examination at the veterinary clinic it is often severely hypoglycaemia and it is for this reason that immediate gavaging /IV administration of fluids with high glucose content is recommended.

Stress undoubtedly predisposes marine birds to development of secondary infections during rehabilitation as their immune system is severely compromised. Many factors precipitate stress in seabirds and the aim of rehabilitation should be to clean the birds and release them while minimising stress levels. This involves determining what processes during rehabilitation are most likely to cause stress (handling, washing, and unusual environment) and then looking at ways to minimise these potential stressors.

Several studies have been carried out to determine what if any effect petrochemical ingestion and stress have on the immune system of seabirds.

Briggs et al 1997

"Among oiled seabirds leucocyte numbers (especially lymphocytes) are depressed in circulation and in the major lymphoid organs...bone marrow hypercellularity with an emphasis on erythropoesis, suggests an adaptive shift from white cell to red cell production in response to haemolytic anaemia."

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Haemolytic Anaemia

Several journal articles have been published documenting the development of haemolytic anaemia in marine birds following ingestion of oil.

Review of a journal article "Haematological changes and anaemia associated with captivity and petroleum exposure in seabirds."

A study was completed in California, U.S.A by Newman, Mazet, Ziccardi et al. 1999. Haematological changes and anaemia associated with captivity and petroleum exposure in seabirds. They looked at a range of haematological parameters in marine birds that were captive or captive and exposed to petroleum by ingestion. Several previous studies had concluded that haemolytic anaemia in oiled birds presented at rehabilitation centres was caused by the ingestion of petroleum. This is a article shows that captivity alone has a negitive effect on the PCV irrespective of oil ingestion. It also shows that a single injection of iron dextrose has a postive impact on the PCV. (Newman, Mazet, Ziccardi et al. 1999)

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