Stable isotopes reveal Holocene changes in the diet of Adélie penguins in Northern Victoria Land (Ross Sea, Antarctica)

Abstract

Adélie penguin (Pygoscelis adeliae) modern and fossil eggshells and guano samples collected from ornithogenic soils in Terra Nova Bay (Victoria Land, Ross Sea) were processed for carbon and nitrogen isotopic ratios with the aim of detecting past penguin dietary changes. A detailed and greatly expanded Adélie penguin dietary record dated back to 7,200 years BP has been reconstructed for the investigated area. Our data indicate a significant dietary shift between fish and krill, with a gradual decrease from past to present time in the proportion of fish compared to krill in Adélie penguin diet. From 7,200 to 2,000 years BP, δ(13)C and δ(15)N values indicate fish as the most eaten prey. The dietary contribution of lower-trophic prey in penguin diet started becoming evident not earlier than 2,000 years BP, when the δ(13)C values reveal a change in the penguin feeding behavior. Modern eggshell and guano samples reveal a major dietary contribution of krill but not a krill-dominated diet, since δ(13)C values remain much too high if krill prevail in the diet. According to the Holocene environmental background attested for Victoria Land, Adélie penguin dietary shifts between fish and krill seem to reflect penguin paleoecological responses to different paleoenvironmental settings with different conditions of sea-ice extension and persistence. Furthermore, Adélie penguin diet appears to be particularly affected by environmental changes in a very specific period within the breeding season, namely the egg-laying period when penguin dietary and feeding habit shifts are clearly documented by the δ(13)C of eggshell carbonate.

Eco-environmental implications of elemental and carbon isotope distributions in ornithogenic sediments from the Ross Sea region, Antarctica

“…d 13 C org and C/N in the five sediment profiles and environmental media ( Fig. 4) indicate that guano has very low d 13 C at about À30&, which is similar to the data of Adélie penguin guano reported in the neighboring Northern Victoria Land (Lorenzini et al, 2010) and Antarctic Peninsula (Liu et al, 2006b;Zhu et al, 2009). Algae in Antarctica usually has d 13 C org values at about À29&, significantly lower than the dissolved carbon source in the water column due to the strong isotopic fractionation effects during photosynthesis (Doran et al, 2000), but our samples yielded a much higher d 13 C org , reaching À10&.…”

“…Emslie and Patterson (2007) used carbon isotope values in eggshells of Adélie penguins (Pygoscelis adeliae) to infer a possible historic shift in their diet. Lorenzini et al (2009Lorenzini et al ( , 2010 investigated d 13 C in both eggshells and guano to reconstruct the paleo-diet of Adélie penguins in Northern Victoria Land. d 13 C in bat guano deposited in caves was well studied for the historical change in vegetation of the surrounding area (dominance of C 3 over C 4 plants or vice versa), and further insights into climate change in the past (Mizutani et al, 1992;Bird et al, 2007;Wurster et al, 2008).…”

Lichen response to ammonia deposition defines the footprint of a penguin rookery

“…?13.4 ± 4.2 % (n = 6), guano (Mizutani and Wada 1988) ?21.9 to ?24.5 % (n = 2), guano (0-20 cm depth) (Zhu et al 2009) ?31.8 ± 4.2 % (n = 8), rookery soil (0-5 cm depth) (Mizutani and Wada 1988) ?32.2 ± 3.5 % (n = 6), rookery soil (0-5 cm depth) (Mizutani et al 1986) ?28.6 %, organic N from rookery soils (Wada et al 1981) ?8.0 ± 1.2 % (n = 6), fresh excreta (Lorenzini et al 2010) ?8.0 ± 0.4 % (n = 4), fresh excreta (Mizutani and Wada 1988) Ammonia gas ?6.9 % ?4.7 % (n = 2), bat cave, Mexico (McFarlane et al 1995) ?2.4 ± 0.8 % (n = 6), cape fur seal colony, Namibia (Crittenden et al unpublished data) -10.0 ± 3.1 % (n = 20) royal penguin rookery, Macquarie Island (Erskine et al 1998) U. sphacelata -15.5 to -2.0 % -17.8 to ?10.4 % U. decussata and Usnea antarctica (Cocks et al 1998) U. decussata -17.5 to -10.0 % -18.2 to ?7.5 % U. decussata and Usnea antarctica (Huiskes et al 2006) -15.3 to -7.8 % Usnea antarctica (Lee et al 2009) X. borealis -0.9 to ? 9.0 % ?20.6 ± 0.7 (n = 6), Caloplaca eudoxa, Cape fur seal colony, Namibia (Crittenden et al unpublished data) Biogeochemistry (2015) A key assumption in the calculation of F NH 3 is that d…”

Historical pesticide applications coincided with an altered diet of aerially foraging insectivorous chimney swifts

“…However, insectivory is a feature common to all aerially foraging insectivores, and it is therefore probable that historical changes in prey populations had a role in delimiting populations of these birds. Data on historical diets of many bird species are unavailable, but a variety of proxy approaches have been used to obtain this information, including examination of fossilized eggshell deposits [9], lake and pond sediments [10,11], guano deposits [9,12,13] and tissue biochemistry [14]. Such studies provide insight into past evolutionary and environmental conditions; however, none have yet elucidated how specific dietary shifts in recent decades might be associated with changing pesticide use.…”