Reality Check: Most King Penguin Populations Have Been Increasing, Not Declining

The world’s second-largest penguin colony situated on islands in the Southern Ocean has collapsed in just a few decades, falling from half a million breeding pairs in the 1980s to just tens of thousands in 2017. The researchers have no conclusive explanation for the colony’s decline. However, the population crash is in sharp contrast to most other populations of King Penguins that have increased significantly in recent decades (see papers below). Breeding populations of King Penguins have increased at all sites at very high rates, but because populations sizes are at some point limited by environmental and density-dependence factors, researchers assume that the carrying capacity has been or soon will be reached.

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

King Penguin populations increase on South Georgia but explanations remain elusive

Foley, C.M., Hart, T. & Lynch, H.J. Polar Biol (2018) 41: 1111.

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.

Full paper

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.

Full paper

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.

Full paper

The post Reality Check: Most King Penguin Populations Have Been Increasing, Not Declining appeared first on The Global Warming Policy Forum (GWPF).

via The Global Warming Policy Forum (GWPF)

August 1, 2018 at 05:04AM

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