Sedimentary biomarkers and bone specimens reveal a history of prehistoric occupation on Somerset Island (Arctic Canada).

Archaeological studies of pre-historic Arctic cultures are often limited to artefacts and architecture; such records may be incomplete and often do not provide a continuous record of past occupation. Here, we used lake sediment archives to supplement archaeological evidence to explore the history of Thule and Dorset populations on Somerset Island, Nunavut (Canada). We examined biomarkers in dated sediment cores from two ponds adjacent to abandoned Thule settlements (PaJs-3 and PaJs-13) and compared these to sediment cores from two ponds without past human occupation. Coprostanol and epicoprostanol, δ15N measurements, sedimentary chlorophyll a and the ratio of diatom valves to chrysophyte cysts were elevated in the dated sediment profiles at both sites during Thule and Dorset occupations. Periods of pronounced human impact during the Thule occupation of the site were corroborated by 14C-dated caribou bones found at both sites that identified intense caribou hunting between ca 1185 and 1510 CE. Notably, these sediment core data show evidence of the Dorset occupation from ca 200 to 500 CE at sites where archaeological evidence was heretofore lacking. We highlight the utility of lake sediments in assisting archaeological studies to better establish the timings, peak occupations and even lifestyle practices of the Dorset and Thule Arctic peoples.

A 2200-year record of Andean Condor diet and nest site usage reflects natural and anthropogenic stressors.

Understanding how animals respond to large-scale environmental changes is difficult to achieve because monitoring data are rarely available for more than the past few decades, if at all. Here, we demonstrate how a variety of palaeoecological proxies (e.g. isotopes, geochemistry and DNA) from an Andean Condor (Vultur gryphus) guano deposit from Argentina can be used to explore breeding site fidelity and the impacts of environmental changes on avian behaviour. We found that condors used the nesting site since at least approximately 2200 years ago, with an approximately 1000-year nesting frequency slowdown from ca 1650 to 650 years before the present (yr BP). We provide evidence that the nesting slowdown coincided with a period of increased volcanic activity in the nearby Southern Volcanic Zone, which resulted in decreased availability of carrion and deterred scavenging birds. After returning to the nest site ca 650 yr BP, condor diet shifted from the carrion of native species and beached marine animals to the carrion of livestock (e.g. sheep and cattle) and exotic herbivores (e.g. red deer and European hare) introduced by European settlers. Currently, Andean Condors have elevated lead concentrations in their guano compared to the past, which is associated with human persecution linked to the shift in diet.

Linking 19th century European settlement to the disruption of a seabird's natural population dynamics.

Recent estimates indicate that ∼70% of the world's seabird populations have declined since the 1950s due to human activities. However, for almost all bird populations, there is insufficient long-term monitoring to understand baseline (i.e., preindustrial) conditions, which are required to distinguish natural versus anthropogenically driven changes. Here, we address this lack of long-term monitoring data with multiproxy paleolimnological approaches to examine the long-term population dynamics of a major colony of Leach's Storm-petrel (Hydrobates leucorhous) on Grand Colombier Island in the St. Pierre and Miquelon archipelago-an overseas French territory in the northwest Atlantic Ocean. By reconstructing the last ∼5,800 y of storm-petrel dynamics, we demonstrate that this colony underwent substantial natural fluctuations until the start of the 19th century, when population cycles were disrupted, coinciding with the establishment and expansion of a European settlement. Our paleoenvironmental data, coupled with on-the-ground population surveys, indicate that the current colony is only ∼16% of the potential carrying capacity, reinforcing concerning trends of globally declining seabird populations. As seabirds are sentinel species of marine ecosystem health, such declines provide a call to action for global conservation. In response, we emphasize the need for enlarged protected areas and the rehabilitation of disturbed islands to protect ecologically critical seabird populations. Furthermore, long-term data, such as those provided by paleoecological approaches, are required to better understand shifting baselines in conservation to truly recognize current rates of ecological loss.

Author Correction: A pre-Inca pot from underwater ruins discovered in an Andean lake provides a sedimentary record of marked hydrological change.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Striking centennial-scale changes in the population size of a threatened seabird.

Many animal populations are under stress and declining. For numerous marine bird species, only recent or sparse monitoring data are available, lacking the appropriate temporal perspective needed to consider natural, long-term population dynamics when developing conservation strategies. Here, we use a combination of established palaeoenvironmental approaches to examine the centennial-scale dynamics of the world's largest colony (representing approx. 50% of the global population) of the declining and vulnerable Leach's Storm-petrel (Hydrobates leucorhous). By reconstructing the last approximately 1700 years of the colony's population trends, we corroborate recent surveys indicating rapid declines since the 1980s. More surprisingly, however, was that the colony size was smaller and has changed strikingly in the past, even prior to the introduction of human stressors. Our results challenge notions that very large colonies are generally stable in the absence of anthropogenic pressures and speak to an increasingly pressing need to better understand inter-colony movement and recruitment when inferring range- and species-wide trends. While the recently documented decline in storm-petrels clearly warrants conservation concern, we show that colony size was consistently much lower in the past and changed markedly in the absence of major anthropogenic activity. In response, we emphasize the need for enlarged protected area networks to maintain natural population cycles, coupled with continued research to identify the driver(s) of the current global seabird decline.

A pre-Inca pot from underwater ruins discovered in an Andean lake provides a sedimentary record of marked hydrological change.

Pre-Hispanic artifacts and sacred architecture were recently discovered submerged in a large lake (Laguna Sibinacocha) in the Peruvian Andes. The underwater ruins indicate a dramatic shift in the region's hydrology but the timing and triggers of this shift remain unknown. In a novel approach blending archaeology and paleoecology, we analyzed a sediment sequence from within one of the recovered artifacts, specifically a pot from the Late Intermediate Period (~1000-1400 CE). Radioisotopic dating of discrete sediment intervals sampled from the pot show a stratigraphically intact profile that preserves a history of change at this site. The pot's basal sediment age places the timing of lake-level rise at ~1600 CE, which post-dates the end of the Inca Empire (1400-1532 CE) by several decades. The ubiquity of planktonic algae throughout the sediment profile suggests water levels remained high above the pot since its submergence. Paleoclimate data from the nearby Quelccaya ice core records indicate lake flooding followed a pronounced wet period beginning ~1520 CE. These data show the permanence of mean state changes in climate on the region's hydrology, with clear implications for the study site (an important water resource for ~500,000 people) and other lakes in the rapidly warming Andes.

Sterols and stanols as novel tracers of waterbird population dynamics in freshwater ponds.

With the expansion of urban centres in the mid-twentieth century and the post-1970 decrease in pesticides, populations of double-crested cormorants (Phalacrocorax auritus) and ring-billed gulls (Larus delawarensis) around Lake Ontario (Canada and USA) have rapidly rebounded, possibly to unprecedented numbers. Along with the use of traditional palaeolimnological methods (e.g. stable isotopes, biological proxies), we now have the capacity to develop specific markers for directly tracking the presence of waterbirds on nesting islands. Here, we apply the use of lipophilic sterols and stanols from both plant and animal-faecal origins as a reliable technique, independent of traditional isotopic methods, for pinpointing waterbird arrival and population growth over decadal timescales. Sterol and stanol concentrations measured in the guano samples of waterbird species were highly variable within a species and between the three species of waterbirds examined. However, cholesterol was the dominant sterol in guano, and phytosterols were also high in ring-billed gull guano. This variability highlights a specialist piscivorous diet for cormorants compared to a generalist, omnivorous diet for gulls, which may now often include grain and invertebrates from agricultural fields. A ratio that includes cholesterol and sitosterol plus their aerobically reduced products (cholestanol, stigmastanol) best explained the present range of bird abundance across the islands and was significantly correlated to sedimentary δ15N. Overall, we demonstrate the use of sterols and stanols as a direct means for tracking the spatial and temporal presence of waterbirds on islands across Lake Ontario, and probably elsewhere.

Tracking the History and Ecological Changes of Rising Double-Crested Cormorant Populations Using Pond Sediments from Islands in Eastern Lake Ontario.

In the Laurentian Great Lakes region, the double-crested cormorant (Phalacrocorax auritus) has seen a thousand-fold population increase in recent decades. These large colonies of birds now often conflict with socioeconomic interests, particularly due to perceived competition with fisheries and the destruction of terrestrial vegetation in nesting habitats. Here we use dated sediment cores from ponds on islands in eastern Lake Ontario that receive waste inputs from dense colonies of cormorants and ring-billed gulls (Larus delawarensis) to chronicle the population rise of these species and assess their long-term ecological impacts. Modern water chemistry sampling from these sites reveals drastically elevated nutrient and major ion concentrations compared to reference ponds not influenced by waterbirds. Geochemical tracers in dated sediment cores, particularly δ15N and chlorophyll-a concentrations, track waterbird influences over time. Fossil diatom assemblages were dominated by species tolerant of hyper-eutrophic and polluted systems, which is in marked contrast to assemblages in reference sites. In addition to establishing long-term ecological impacts, this multi-proxy paleoecological approach can be used to determine whether islands of concern have been long-term nesting sites or were only recently colonized by cormorant or ring-billed gull populations across the Great Lakes, facilitating informed management decisions about controversial culling programs.

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

Numerous environmental pressures have precipitated long-term population reductions of many insect species. Population declines in aerially foraging insectivorous birds have also been detected, but the cause remains unknown partly because of a dearth of long-term monitoring data on avian diets. Chimney swifts (Chaetura pelagica) are a model aerial insectivore to fill such information gaps because their roosting behaviour makes them easy to sample in large numbers over long time periods. We report a 48-year-long (1944-1992) dietary record for the chimney swift, determined from a well-preserved deposit of guano and egested insect remains in Ontario (Canada). This unique archive of palaeo-environmental data reflecting past chimney swift diets revealed a steep rise in dichlorodiphenyltrichloroethane (DDT) and metabolites, which were correlated with a decrease in Coleoptera remains and an increase in Hemiptera remains, indicating a significant change in chimney swift prey. We argue that DDT applications decimated Coleoptera populations and dramatically altered insect community structure by the 1960s, triggering nutritional consequences for swifts and other aerial insectivores.