The major decline in African penguin numbers in the 20th century can be initially attributed to harvesting of eggs for food (outlawed in 1967) and guano for the fertilizer industry. Like the Humboldt penguin, the African penguin relied heavily on burrows excavated in the meter thick guano deposits, formerly found at many nesting sites, to protect eggs and young from predators and direct sunlight. The guano is particularly important when penguins nest in sparsely vegetated rocky areas where little other protection may be found. Chick mortality can be high during periods of hot weather since the chicks do not have the option of cooling themselves in the sea until they have moulted for the first time and obtained waterproof feathering. Numerous chicks apparently died at Foxy Beach (Boulders) in 2008 as a result of prolonged direct exposure to intense sunlight and high temperatures. This affected progeny of penguins nesting in the open on the beach rather than those in the dense vegetation behind. Today, the population density of African Penguins is largely regulated by prey availability. Competition for food by commercial fisheries is also thought to have contributed to the decline in numbers. This is discussed in the section on Feeding above. When food levels are critically low, penguins may either not start to breed, or, after breeding has started, foraging trips may be so long that penguins abandon their nests before the foraging partner returns. Mass abandonment of nests was observed at Dyer island in 1991 and is attributed to food shortage (Crawford and Dyer, Ibis 137, p.329-339 (1994)) Pollution, in particular oil spillages, poses a major threat to African Penguins as to other seabirds. Even small spillages can cause the oiling of many birds, possibly due to the fact that fish may be found concentrated under oil slicks, thus drawing predators such as penguins to the affected areas (Kerley et al., 1987. S. Afr. J. Wildlife Res. 17(4), p.128-130). Oil causes feathers to clump together and allows water to seep in between, thus exposing the birds to the elements. Further, affected birds tend to ingest oil as they preen their oiled plumages. Ingestion of oil leads to petrochemical poisoning which may manifest itself by internal ulceration or loss of sight. Several major oil spills have affected the African Penguin populations. In 1968, about 3000 penguins were oiled following the grounding of the Esso Essien, and in 1994, about 10000 penguins were oiled after the sinking of the Apollo Sea (Underhill et al., 1999. Ibis 141(1), p.29-37). The worst incident so far occurred on June 23, 2000, when the bulk ore carrier MV Treasure sank between Dassen and Robben Islands, which host the 1st and 3rd largest breeding colonies of African Penguins, respectively. 1300 tonnes of bunker oil were spilled, leading to the oiling of 19000 penguins, mainly on Robben Island. This triggered the biggest bird rescue operation in history, coordinated by SANCCOB (S. African Foundation for the Conservation of Coastal Birds), IFAW (International Fund for Animal Welfare) and IBRRC (International Bird Rescue Research Center). The oiled birds were collected and transferred mostly to a rehabilitation facility hastily set up in an old railway yard in the Salt River area of Cape Town. Over 90% of these birds could be released after they had been stabilized, cleaned and gradually rehabilitated over a period of several months. A further unoiled 20000 penguins were evacuated by helicopter or fishing boats from Dassen Island, which was in the projected path of the oil slick, and transported overland to the Port Elizabeth area, where they were released. Several of these birds were tracked using transmitters, and were found to swim straight back towards their home colonies (Barham et al., 2006. Ostrich 77(3/4), p.202-209)). However, in the 2 weeks it took them to do so it was possible to clean up much of the oil. The African Penguins in the Cape Town area today are a living tribute to the many staff and volunteers who assisted in the rescue effort. A detailed report on the penguin rescue efforts following the Treasure oil spill can be found on the IBRRC website. Even in years with no major oil spills, many oiled penguins are found. For example, in 2001 and 2002 a total of 991 oiled penguins were admitted to the SANCCOB rehabilitation center (Parsons and Underhill, African. J. of Marine Sci., 27(1), p.289-296 (2005)). Most of these admissions were in winter when the prevailing winds blow oil (often illegally washed from ships bilge tanks) near to the shore. Fortunately, over 85% of these birds could be released. Knowledge on survival and subsequent breeding success of rehabilitated oiled birds is of major importance for conservation purposes, so that resources can be optimally channelled when the next major incident is encountered. It has been found that breeding pairs including at least one oiled bird rehabilitated after the Treasure oil spill have an about 30% reduced breeding success, in terms of numbers of fledged chicks compared to unoiled birds (Barham et al., 2007. Emu 107, p.7-13). Whilst hatching success was similar and also survival of chicks during the brood / guard phase, mortality of chicks was about 4-fold higher in the creche phase. This is likely because this phase is most demanding on the parents, as it involves the highest food demand by the chicks. Those chicks that survived also took longer to fledge. The reasons for these observations are unclear, although likely a result of the prolonged captivity and / or delay in washing after capture (due to the vast numbers of oiled birds), possibly resulting in higher oil uptake. Lengthy capture may also result in increased disruption of pair bonds. This could reduce breeding success, since pairs that repeatedly breed tend to be more productive. A previous study on birds oiled following the Apollo Sea spill had not found a reduced reproductive success, yet the two spills and ensuing rescue efforts were not entirely comparable, since birds were processed quicker and the oil was of a different type in the latter case (Wolfaardt and Nel 2003. In "Rehab. of Oiled Afr. Penguins". Eds. Nel and Whittington. p.18-24). Following the Treasure oil spill, large numbers (about 2000) of orphaned chicks were also collected and subsequently hand-reared. The subsequent breeding success of these chicks has been monitored (Barham et al., 2008. Bird Cons. Intl. 18, p.144-152). Surprisingly, the eventual breeding success of hand-reared chicks was found to be at least as good as that of naturally reared chicks. This not only shows that hand-rearing is a worthwhile conservation effort, but also suggests that hand-reared chicks, possibly from captive populations, could be used to bolster the wild populations if necessary. Predation may also have a major impact on colonies, either due to the introduction of unnatural predators such as cats or dogs, or due to increases in natural predator numbers as a result of decimation of their natural enemies. This is particularly the case for Cape Fur Seals, numbers of which have increased due to the mainly human-induced decline in Great White Shark numbers. Fur Seals can be observed waiting just offshore in front of penguin colonies and may take penguins leaving or returning to sea. In April 2008, I observed one Fur Seal taking two penguins within 30 min as they returned to Foxy Beach (Boulders) after feeding. The loss of a parent will usually also result in the loss of the chicks. Studies at Dyer Island in 1995-1996 revealed that Seals killed 8.7% of the Penguin population in a single year (Marks et al., Marine Ornithology 25, p.9-12 (1997)). In such cases, culling of the predator is essential to sustain the penguin population. Seal tears penguin apart after catching it as it returned to Foxy Beach At sea, not only Fur Seals are a threat, but also certain sharks and Orcas, although the numbers of these have been declining in recent years. On land, Kelp Gulls and Sacred Ibises as well as Mongooses steal eggs and young chicks from nests. Kelp Gull feeding on penguin egg Plasmodium relictum (an avian malaria parasite) is the main blood parasite that can be detected in African Penguins. Birds with obvious malaria symptoms are not generally seen in the wild, although these may often be removed by predation or death at sea. However, studies on birds admitted to the SANCCOB rehabilitation center reveal a high level of exposure of birds in the Western Cape region to the parasite with over 30% of admitted birds being seropositive upon admission in certain years (Parsons and Underhill, African. J. of Marine Sci., 27(1), p.289-296 (2005)). Malaria primarily affects juvenile birds during the summer months. As in humans, the first exposure to the parasite is the most critical as no resistance has been developed yet. Mortality in captive birds can be high, presumably due to the higher stress that these birds are subjected to resulting in a weaker immune system. In fact, avian malaria is the most common cause of death of captive penguins in open-air colonies (Graczyk et al., J. Parasitology 80(2), p.302-308 (1994)). The extent to which wild-living birds are affected by infection is not known, although it would seem likely that even subclinical infection has a slight impact on the bird's overall health. Avian cholera may also sporadically affect penguin populations. Loss of habitat to humans is a lesser problem since most island colonies are not inhabited by man. Human populations can in fact provide a buffer zone against terrestrial predators thus allowing establishment of mainland colonies as at Boulder Beach. African penguins are highly adaptable and will nest in gardens, under verandas or in drainage systems. The downside of nesting in suburbia is that penguins may be lost in road traffic accidents or may fall victim to uncontrolled or escaped pets. Nest disturbance is also more likely.