Chinstrap and macaroni penguin diet and demography at Nyrøysa, Bouvetøya

Abstract

Knowledge regarding interactions between predators and their prey is fundamental for understanding underlying links between climate change and ecosystem responses, including predator demographics, in the Southern Ocean. This study reports data on reproductive performance, total population size and diet composition for macaroni and chinstrap penguins breeding at Nyrøysa on Bouvetøya during the summers of 1996–97, 1998–99, 2000–01 and 2007–08. The breeding populations of these two species at Nyrøysa decreased significantly over the study period, with an 80% decline for chinstraps and a 50% decline for macaroni penguins, despite relatively high levels of chick production. During this period macaroni penguins at this site ate a diverse diet, dominated by myctophid fish and two krill species, whereas chinstrap penguins were Antarctic krill specialists. The population changes are probably primarily due to the expanding Antarctic fur seal population, and also to landslides that are the result of increased melting on the island which have destroyed penguin breeding sites. Additional impacts from global warming of the ocean might also be playing a role and could exacerbate the decline in these penguin populations if krill and other prey are negatively impacted in the future in this region. The local chinstrap penguin population would probably be most heavily affected given its narrow feeding niche and small current population size.

Temporal variation in trophic relationships among three congeneric penguin species breeding in sympatry

“…This pattern was somehow moderated in chinstrap penguins, whose isotopic niches showed lower overlap with the other species’ isotopic niches in both years. The reliance of all species on the same trophic level, presumably predominantly on krill (Niemandt et al., ; Ratcliffe & Trathan, ), was clear in the present study for both years. At nearby breeding sites in the South Orkney Islands, some studies have found that krill dominates the diet of Adélie and chinstrap penguins, with estimated contributions generally over 90%, while fish seem to dominate in the diet of gentoo penguins (Lynnes, Reid, & Croxall, ; Rombolá, Marschoff, & Coria, ; White & Conroy, ).…”

“…Irrespective of the species, δ 15 N measured in this study were generally moderately high, which is consistent with the contribution of prey of higher trophic level to the diet (e.g., fish or squid; Negrete et al., ) compared to that measured in other studies and areas. For example, stomach content analysis on chinstrap penguins from Bouvetøya described a diet composed of <1% fish during three nonconsecutive sampling years (Niemandt et al., ). Conversely, in the South Shetland Islands, Polito et al.…”

“…Penguins are a monophyletic group in which many species are found breeding sympatrically at several sites in the sub-Antarctic islands (Forcada, Trathan, Reid, Murphy, & Croxall, 2006; Fagan, Naveen, Trivelpiece, & Trivelpiece, 2012;Niemandt et al, 2016;Paterson, Wallis, Kennedy, & Gray, 2014;Trathan, Croxall, & Murphy, 1996). The co-occurrence of these closely related species has long raised questions regarding what degree of competition takes place and how these species successfully coexist (Lynnes, Reid, Croxall, & Trathan, 2002;Trivelpiece & Volkman, 1979;White & Conroy, 1975).…”

Temporal shift in the isotopic niche of female Antarctic fur seals from Bouvetøya

“…During the breeding seasons of 1996/97, 1997/98 and 2001/02, krill was the main prey found in scats and stomach contents of AFS on Bouvetøya (Klages et al 1999;Kirkman et al 2000;Hofmeyr et al 2010), which is consistent with the low d 13 C and d 15 N measures for 1997. Krill was also the dominating prey item in the diet of chinstrap penguins (Pygoscelis antarctica) for all years (1997, 1999 and 2001) in which diet has been studied at Bouvetøya (Niemandt et al 2016). In contrast, the macaroni penguin (Eudyptes chrysolophus) breeding at Bouvetøya relied heavily on myctophid fish during the breeding seasons of 1997, 1999 and 2001, but crustaceans, mostly krill, dominated their diet in 2008 (Niemandt et al 2016).…”

“…Krill was also the dominating prey item in the diet of chinstrap penguins (Pygoscelis antarctica) for all years (1997, 1999 and 2001) in which diet has been studied at Bouvetøya (Niemandt et al 2016). In contrast, the macaroni penguin (Eudyptes chrysolophus) breeding at Bouvetøya relied heavily on myctophid fish during the breeding seasons of 1997, 1999 and 2001, but crustaceans, mostly krill, dominated their diet in 2008 (Niemandt et al 2016). The concurrent Fig.…”