Reality Check: Most King Penguin Populations Have Been Increasing, Not Declining
“Numbers of king penguins have increased throughout the Southern Ocean over the past 50 years.”
These stunning aerial images of a King Penguin colony in South Georgia show thousands of penguins instinctively herding their recently born young into giant huddles to stop them freezing to death
According to a new study, the world’s second-largest penguin colony situated on islands in the Southern Ocean has progressively declined in just a few decades, falling from half a million breeding pairs in the 1980s to 60.000 pairs in 2017. The researchers have no conclusive explanation for the colony’s decline.
The authors of the new paper point out, however, that the reported population decline is in sharp contrast to most other populations of King Penguins that have increased significantly in recent decades. They write:
“Numbers of king penguins have increased throughout the Southern Ocean over the past 50 years. This increase has been interpreted as a recovery from historical exploitation in the 19th century or change in the functioning of trophic food webs. However, their numbers may fluctuate extensively in response to large-scale climatic (sic) events such as the Sub-Tropical Indian Dipole and El-Niño Southern Oscillation.”
Some scientists have even linked global warming to the growth of King Penguin populations:
“Local anomalies in sea surface temperature have increased in parallel with King Penguin population growth rate, suggesting that climate forcing may contribute to colony growth…” (Foley et al. 2018)
Other have predicted that limits to carrying capacity and over-population may cause decline.
“Until recently, breeding populations of king penguins have increased at all sites at very high rates, but because populations sizes are at some point limited by extrinsic (environmental) and/or intrinsic (density-dependence) factors, we may assume that the carrying capacity has been or soon will be reached. Consequently, we expect the rate of increase of king penguin populations to stabilize or decrease.” (Delord et al., 2004)
Whatever the cause of the reported decline of the king penguin colony at Ile aux Cochons, it would appear that this is a localised event that stands in sharp contrast to the good health of other king penguin populations in the Southern Oceans.
King Penguin populations increase on South Georgia but explanations remain elusive
Foley, C.M., Hart, T. & Lynch, H.J. Polar Biol (2018) 41: 1111. https://doi.org/10.1007/s00300-018-2271-z
While dramatic increases in populations of King Penguins (Aptenodytes patagonicus) have been documented throughout their range, population changes on the island of South Georgia have not been assessed. We reconstructed time series of population size for six major colonies across South Georgia using historical data stretching back to 1883 and new population estimates derived from direct on-the-ground censuses and oblique, high-resolution digital photographs. We find evidence for a significant increase in the population of King Penguins at all colonies examined over the 124 years of available survey data. We discuss our findings in the context of four established hypotheses explaining King Penguin population growth: (1) favorable changes in the pelagic food web; (2) climate forcing; (3) greater availability of breeding habitat; and (4) the cessation of harvesting. While we do find evidence that glacial retreat may have increased suitable breeding habitat at some colonies and facilitated population expansion, glacial retreat is not associated with all of South Georgia’s growing populations. Local anomalies in sea surface temperature have increased in parallel with King Penguin population growth rate, suggesting that climate forcing may contribute to colony growth, but a complete explanation for the island’s rapidly growing King Penguin population remains unclear.
Population development and historical occurrence of king penguins at the Falkland Islands
P.A. Pistorius et al. (2012) Antarctic Science 24(5):435-440
Abstract: After an extended period of sporadic sightings of small numbers of king penguins at the Falkland Islands, they established themselves on Volunteer Point, situated at the north-east of the islands, by the late 1970s. By 1980, a small breeding population was present which yielded some 40 fledglings during that same year. Since 1991, the population has been monitored annually and the resulting fledgling counts analysed to assess population trends. The population demonstrated a significant increase over the past three decades, at about 10% per annum, with time explaining 75% of the variation in count data. The current population is estimated to be 720 breeding pairs. Despite several authors having alluded to the existence of a large colony of king penguins at the Falklands prior to human exploitation, we found no evidence in
support of this. We furthermore found no evidence in the literature in support of exploitation for king penguin oil during the 19th century. Unlike at other breeding sites, increasing numbers of king penguins at the Falklands is consequently unlikely to be a recovery response following exploitation, but rather an indication of either increased immigration or of improved feeding conditions.
[…] In recent years, king penguin numbers have increased throughout most of their range (Van den Hoff et al. 1993, Williams 1995, Woehler et al. 2001, Crawford et al. 2003, Weimerskirch et al. 2003, Delord et al. 2004, Van den Hoff et al. 2009), after more than a century of decline as a result of exploitation for penguin oil (Williams 1995). In the absence of supporting evidence (as discussed below), a similar history has tenuously been claimed for the Falklands population, which was reportedly subjected to exploitation during the 1800s with total extermination by 1870 (Williams 1995, Woods & Woods 1997, Clausen & Huin 2003). The aim of this paper is to report on growth of the king penguin population at the Falkland Islands over the past three decades and to review the historical occurrence of this species at this location.
Long-term trends in the population size of king penguins at Crozet archipelago: environmental variability and density dependence?
K. Delord et al., Polar Biol (2004) 27: 793–800
Penguins are often at, or close to, the top of the food chain in the Southern Ocean, and the population dynamics of such apex predators are often sensitive indicators of the effects of environmental change in ecosystems (e.g. Aebischer et al. 1990; Furness and Greenwood 1993; Ainley 2002; Gjerdrum et al. 2003; Voigt et al. 2003). King penguins (Aptenodytes patagonicus) represent a major component in terms of biomass and energy flux in the sub-Antarctic marine ecosystem (Woehler 1995). A high number of king penguins were slaughtered by sealers during the nineteenth century on sub-Antarctic islands (Rounsevell and Copson 1982). Since then, there has been a long recovery process, possibly resulting from density-dependence effects at low numbers, and all breeding populations for which long-term data are available have showed a dramatic increase during the twentieth century (Conroy and White 1973; Lewis Smith and Tallowin 1979; Rounsevell and Copson 1982; Gales and Pemberton 1988; Weimerskirch et al. 1992; Woehler and Croxall 1997; Woehler et al. 2001). Until recently, breeding populations of king penguins have increased at all sites at very high rates, but because populations sizes are at some point limited by extrinsic (environmental) and/or intrinsic (density-dependence) factors (Newton 1998), we may assume that the carrying capacity has been or soon will be reached. Consequently, we expect the rate of increase of king penguin populations to stabilize or decrease. However, until now, there has been no clear evidence of colonies being over-populated and possibly stabilizing since the early 1990s.
Massive decline of the world’s largest king penguin colony at Ile aux Cochons, Crozet
King penguins (Aptenodytes patagonicus Miller) are major consumers in the Southern Ocean. The colony at Ile aux Cochons, Iles Crozet, in the southern Indian Ocean was known in the 1980s as the largest king penguin colony and the second largest penguin colony in the world. However, there have not been any recent estimates of this colony. Aerial photographs taken from a helicopter, and satellite images were used to report on changes in the colony and population sizes over the past 50 years. The colony has declined by 88% over the past 35 years, from c. 500 000 pairs to 60 000 pairs. The possible causes of this decline were explored but no plausible explanation for such an unprecedented decrease in penguin populations was found. The study highlights the use of satellite imagery as a non-invasive technique for population monitoring, and stresses the need for further research on the causes of this alarming trend in this colony. […]
[…] Several hypotheses might explain the massive decline in this colony. First, the decline occurred from the late 1990s, coinciding with the strong Dipole event in 1997 that affected the foraging capacities of king penguins on Ile de la Possession, the second most important island of Iles Crozet for breeding king penguins, with negative consequences for breeding performance and colony size (Bost et al. 2015). The 1997 event may have affected the population of Ile aux Cochons more severely than other colonies because of stronger density-dependent effects, and the population has not recovered, as has been observed on Ile de la Possession (Delord et al. 2004, Bost et al. 2015).
Second, the decline may have resulted from the partial relocation of the colony. King penguins are relatively faithful to their birthplace and first breeding site (Saraux et al. 2011) and it seems unlikely that adults and young individuals from Ile aux Cochons have a different behaviour than those from other colonies. However, observations from helicopter flights in 2016 noted a smaller colony nearer to the beach, on the penguins’ access route to the large colony. This colony was recorded for the first time on the 2005 satellite images, and was still present in the 2015, 2016 and 2017 satellite images. This colony was not present in 1962 (Bauer 1963) or during ground observations in 1974 and 1982 (Derenne et al. 1976, Voisin 1984). It was not mentioned in 1988, but the Spot images focused on the Morne du Tamaris colony (Guinet et al. 1995). However, the size of this new colony (17 000 pairs) can account for the relocation of only a small fraction of the original colony.
Third, feral cats (Felis catus L.) and house mice (Mus musculus L.) are present on Ile aux Cochons (Derenne & Mougin 1976, Derenne et al. 1976). Cats apparently occurred in small numbers in the 1970s (Derenne et al. 1976) and neither species is known to be a predator of king penguin chicks. However, the behaviour of these two introduced species towards native fauna has changed during recent years on other sub-Antarctic islands, as shown by observations on Gough and Marion islands of mice attacking albatross chicks, causing the decline of at least some populations (Wanless et al. 2007, Davies et al. 2015, Dilley et al. 2016), or at Kerguelen, where cats have been observed to attack wandering albatross (Diomedea exulans L.) chicks, reducing breeding success (Weimerskirch unpublished data).
Fourth, diseases or parasites can seriously affect seabird populations, reducing breeding success, survival of adults and population growth rates (Weimerskirch 2004, Cooper et al. 2009). There are no data available about the occurrence of any such diseases on Ile aux Cochons. Tick infestations also affect seabird populations, and have been found to be a vector of Lyme disease in king penguins (Gauthier-Clerc et al. 1999), but again a massive tick infestation appears to be unlikely compared to the situation recorded on Ile de la Possession. The extent of the decrease of the colony of Morne du Tamaris would be unprecedented if it were a result of disease outbreak, but previous large mortalities of king penguins (although not to the same extent as in the Ile aux Cochons colony) have been reported in 1992–1993 on Marion Island (Cooper et al. 2009), at the time of the rapid decline described here.
Finally, a catastrophic event seems unlikely to have occurred. The colony is well inland and therefore should not be impacted by a tsunami, and there is no evidence of a volcanic eruption on the satellite images or recent helicopter photographs. Furthermore, the progressive decline of the extent of the colony suggests a gradual, long-term decrease in this colony.
In conclusion, the cause of the massive decline of the colony remains a mystery, and needs to be resolved. Although the decline started at least 20 years ago, it appears to be ongoing, and the causes of the decline may still be active. Ile aux Cochons is rarely visited, and the use of satellite images has allowed the detection of this unexpected phenomenon. However, to be able to understand the cause of the decline, it is necessary to study the colony on land and at sea. The last visits ashore were in 1974 and 1982. It would be of considerable importance to examine the foraging ecology (including at-sea distribution) of individuals from this colony to detect potential adverse trophic conditions, and make observations on the conditions that occur on land today, such as the possible presence of diseases and parasites, and the effects of native or introduced predators.