No abstract

We excavated active and abandoned Ade ´lie Penguin (Pygoscelis adeliae) colonies at Seymour Island and Hope Bay, Antarctic Peninsula, to determine an occupation history for this species at these sites. Previous research at Hope Bay has indicated an occupation there since the middle Holocene, based on a sediment record from Lake Boeckella. Excavations revealed only shallow and relatively fresh ornithogenic soils in the active colonies at the two localities. At least 53 abandoned pebble mounds were located at Hope Bay of which nine were excavated and four were sampled by probing to recover organic remains to determine their age. Radiocarbon dating of egg membrane, feather, and bone from both sites revealed a young occupation dating to less than *600 years after correcting for the marine carbon reservoir effect. The mismatch in the geologic record of Ade ´lie Penguin occupation in the northern Antarctic Peninsula, including Lake Boeckella sediments and geologic deposits and lake sediments on King George Island, with more direct evidence of breeding colonies from ornithogenic soils from active and abandoned colonies is hereby referred to as the 'northern enigma' as it does not occur in other regions of Antarctica including the southern Antarctic Peninsula, East Antarctica, or the Ross Sea, where the penguin record extends to the early to middle Holocene and matches well with the geologic record of deglaciation and penguin occupation. As yet, there is no convincing explanation for the 'northern enigma'.

The food delivered to chicks by their parents may be influenced by many factors, such as changes in food availability, the status of dominance of parents or changes on their ability or opportunity to get different kinds of resources. Changes in the nutritional requirements due to chick growth, as well as their acquisition of the ability to feed on new kinds of food and larger meals can also lead to variations in the food delivered to chicks (

Mercury (Hg) is a pervasive environmental contaminant that accumulates in the organs and tissues of seabirds at concentrations capable of causing acute or long-term adverse health effects. In the present study, Hg concentrations in Adélie penguin (Pygoscelis adeliae) egg membranes and chick feathers served as a proxy for Hg bioavailability in the marine environment surrounding the northern Antarctic Peninsula. Stable isotopes were measured in conjunction with Hg to infer information regarding feeding habits (δ 15 N, diet/trophic level; δ 13 C, foraging habitat). The Hg concentrations were low relative to toxicity benchmark values associated with adverse health effects in birds and ranged between 0.006 and 0.080 µg g -1 dry weight (n = 65) in egg membranes and 0.140 to 1.05 µg g -1 fresh weight (n = 38) in feathers. Egg membrane δ 15 N signatures suggested that females from different breeding colonies had similar diets consisting of lower and higher trophic prey prior to arrival to breeding grounds. In contrast, δ 15 N signatures in feathers indicated that chick diet varied by colony. The Hg concentrations demonstrated significant positive relationships with δ 15 N, providing support for the hypothesis of Hg biomagnification up the food chain. The δ 13 C signatures in both tissue types provided evidence of foraging habitat segregation among populations. The differences in Hg exposure and foraging ecology suggest that each colony has localized foraging behaviors by breeding adults that warrant additional investigation.

The Adélie penguin (Pygoscelis adeliae)is an indicator species of the state of the Antarctic marine environment and this is reflected in the size of its reproductive populations. The mean number of breeding pairs of the Adélie penguin on Penguin Point, Marambio / Seymour Island, east of the Antarctic Peninsula, in the Weddell Sea, increased by 32.4% (λ = 1.01) from 1985/1986 to 2014/2015. Although in intermediate counts, there were fluctuations in the number of couples. Variations in Adélie penguin populations may be due to natural variables such as the extent of sea ice; quantity and quality of food; winter survival of adults and juveniles; predation; among others, or due to human activities such as commercial fishing. Our study attempts to contribute to the current estimates of the reproductive population of the Adélie penguin in the region and may also contribute to the negotiations for the implementation of the marine protected area proposed in the sector.