Background information and definitions
Oil spills at sea can kill large numbers of seabirds and have the potential to wipe out entire populations where these are small or localised. Oil can stick to birds’ feathers, making them lose their water-proofing and potentially leading to hypothermia. When birds try to clean their feathers they ingest oil and are likely to become poisoned.
Birds can be taken in and cleaned, but this is an expensive operation, with the cleaning operations after the Treasure oil spill in South Africa in 2000 costing an estimated $100/bird (Whittington 2003). In addition, whereas cleaning may prevent adults from dying, there is evidence that the offspring of rehabilitated birds have lower survival than normal (Barham et al. 2008). This means that the hand-rearing of offspring may be an important intervention after oil spills (Barham et al. 2008, see ‘Artificially incubate and hand-rear birds in captivity’).
In addition to the direct effects described in the studies below, one study (Ryan 2003) estimated that the population of African penguins Spheniscus demersus was 19% larger than it would have been without rehabilitation efforts (approximately 163,000 adults, compared to 137,000).
Barham, P.J., Underhill, L.G., Crawford, R.J.M. & Leshoro, T.M. (2007) Differences in breeding success between African penguins (Spheniscus demersus) that were and were not oiled in the MV Treasure oil-spill in 2000. Emu, 107, 1–7.
Barham, P.J., Underhill, L.G., Crawford, R.J.M., Altwegg, R., Mario Leshoro, T., Bolton, D.A., Dyer, B.M. & Upfold, L. (2008) The efficacy of hand-rearing penguin chicks: evidence from African Penguins (Spheniscus demersus) orphaned in the Treasure oil spill in 2000. Bird Conservation International, 18, 144–152.
Ryan, P.G. (2003) Estimating the demographic benefits of rehabilitating oiled African penguins, pp. 25–29 in eds. Nel, D.C. & Whittington, P.A. Rehabilitation of oiled African Penguins: a conservation success story. BirdLife South Africa and Avian Demography Unit, Cape Town.
Whittington, P.A., (2003) Post-release survival of rehabilitated African penguins, pp. 8–17 in eds. Nel, D.C. & Whittington, P.A. Rehabilitation of oiled African Penguins: a conservation success story. BirdLife South Africa and Avian Demography Unit, Cape Town.
Supporting evidence from individual studies
A replicated controlled study in Canada and the USA (Sharp 1996) found that ringed seabirds that were oiled, cleaned and released (‘treated’) were found dead (recovered) much sooner than birds that were not oiled (between six and 111 days before 98 treated birds were recovered vs. 216-1,019 days for 700 non-oiled birds). In addition, estimated survival rates of oiled common guillemots Uria aalge were just 13% over 20 days (resulting in negligible annual survival), much lower than the 90-95% annual survival for adults (20-40% for juveniles) commonly seen.Study and other actions tested
A replicated study of African penguin Spheniscus demersus survival between 1994 and 1996 following a 1994 oil spill near Cape Town, South Africa (Underhill et al. 1999) found that 65% of 4,076 penguins collected, cleaned, banded and released were re-sighted within two years of release. The majority of these (73%) were seen in the first year but new sightings continued until the end of the study period. The number of dead birds reported (24 from monitoring teams, 25 by the public) was very close to the number expected from previous studies and the authors argue that large-scale mortality of penguins was unlikely to have occurred.Study and other actions tested
Referenced paperUnderhill L.G., Bartlett P.A., Baumann L., Crawford R.J.M., Dyer B.M., Gildenhuys A., Nel D.C., Oatley T.B., Thornton M., Upfold L., Williams A.J., Whittington P.A. & Wolfaardt A.C. (1999) Mortality and survival of African penguins Spheniscus demersus involved in the Apollo Sea oil spill: an evaluation of rehabilitation efforts. Ibis, 141, 29-37.
A replicated study in Tasmania, Australia (Giese et al. 2000), in the 1995-6 and 1996-7 breeding seasons found that pre-fledging masses of chicks from rehabilitated oiled little penguins Eudyptula minor were significantly lower than those from non-oiled birds (approximately 700-800 g for chicks from 65 pairs with rehabilitated birds vs. 850-900 g for 167 un-oiled pairs). Hatching success did not differ between groups but the number of chicks produced/egg and fledging success were significantly lower among rehabilitated birds in 1995-6, especially for nests that had a rehabilitated female (with 22% lower fledging success), and laying date was also delayed (eggs in nests from early October for un-oiled birds, but first appeared on the 4 November for rehabilitated birds). These differences were not apparent in 1996-7.Study and other actions tested
A replicated, controlled study in the Western Cape, South Africa, in 1994-9 (Whittington 2003), found that average annual survival of African penguins Spheniscus demersus that were oiled, cleaned and released following four oil spills birds was estimated at 79%, compared with 81% for non-oiled birds, a non-significant difference. Between 40 and 87% of rehabilitated birds were recorded back at their breeding colonies after being released (with between 101 and 2,962 birds rehabilitated each time). The low number of birds recorded for one spill (40% after four years) may have been due to penguins being found a long way from their colonies and therefore released in an inappropriate place (72% of birds that were seen were recorded at a different colony). This study also discusses the survival of hand-reared penguins, orphaned by oil spills, described in ‘Artificially incubate and hand-rear birds in captivity’.Study and other actions tested
A replicated, controlled study on Dassen Island, Western Cape, South Africa (Wolfaardt & Nel 2003), found that at least 60% of African penguins Spheniscus demersus that were rehabilitated following the 1994 Apollo Sea oil spill had bred within six years of the spill. Productivity of these birds was no different from un-oiled birds (0.32 chicks/egg for 599 oiled birds vs. 0.30 for 558 un-oiled) and their chicks showed identical growth patterns. However, the authors note that during some periods of stress, the rehabilitated birds had significantly lower productivity than un-oiled birds. Of 2,744 birds rehabilitated after the Treasure spill in 2000, 75% were seen two years later, but only 17% had bred. Rehabilitated birds were more likely than controls to change breeding partners (67% keeping mates vs. 80-94%), but this difference appeared to be temporary. This study is also discussed in ‘Relocate birds away from oil spills’.Study and other actions tested
Referenced paperWolfaardt A.C. & Nel D.C. (2003) Breeding productivity and annual cycle of rehabilitated African penguins following oiling. Pages 18-24 in: D.C. Nel & P.A. Whittington (eds.) Rehabilitation of oiled African Penguins: a conservation success story. BirdLife South Africa and Avian Demography Unit, Cape Town.
A controlled, replicated study on Robben Island, South Africa, between 2001 and 2005 (Barham et al. 2007), found that African penguin Spheniscus demersus pairs with at least one parent that had been oiled and rehabilitated (i.e. cleaned and returned to the wild) following an oil spill in 2000 had significantly lower fledging success, compared either to pairs without rehabilitated birds (control pairs), or those with birds banded either for research or following rehabilitation from earlier oil spills (43% of 321 chicks fledging from pairs with rehabilitated birds vs. 61% of 170 from controls and 61% of 114 from previously-banded pairs). Hatching success and clutch size were not significantly different between groups and the differences in fledging success were due to high levels of mortality in older chicks from rehabilitated pairs.Study and other actions tested
A small study in South Africa (Barham et al. 2008) examined the survival and reproduction of hand-reared African penguins Spheniscus demersus orphaned after the Treasure oil spill in 2000. This is discussed in ‘Artificially incubate and hand-rear birds in captivity’.Study and other actions tested
Referenced paperBarham P.J., Underhill L.G., Crawford R.J.M., Altwegg R., Leshoro T.M., Bolton D.A., Dyer B.M. & Upfold L. (2008) The efficacy of hand-rearing penguin chicks: evidence from African penguins (Spheniscus demersus) orphaned in the Treasure oil spill in 2000. Bird Conservation International, 18, 144-152.
A small study in Victoria, Australia, in 2003-6 (Weston et al. 2008) found that two hooded plovers Thinornis rubricollis that were oiled following an oil spill in 2003 and captured, cleaned and released, survived for at least two years, bred and raised at least one chick, which also bred. This study is also discussed in ‘Use signs and access restrictions to reduce disturbance at nest sites’.Study and other actions tested