Potential for redistribution of post-moult habitat for Eudyptes penguins in the Southern Ocean under future climate conditions

Abstract

Anthropogenic climate change is resulting in spatial redistributions of many species. We assessed the potential effects of climate change on an abundant and widely distributed group of diving birds, Eudyptes penguins, which are the main avian consumers in the Southern Ocean in terms of biomass consumption. Despite their abundance, several of these species have undergone population declines over the past century, potentially due to changing oceanography and prey availability over the important winter months. We used light-based geolocation tracking data for 485 individuals deployed between 2006 and 2020 across 10 of the major breeding locations for five taxa of Eudyptes penguins. We used boosted regression tree modelling to quantify post-moult habitat preference for southern rockhopper (E. chrysocome), eastern rockhopper (E. filholi), northern rockhopper (E. moseleyi) and macaroni/royal (E. chrysolophus and E. schlegeli) penguins. We then modelled their redistribution under two climate change scenarios, representative concentration pathways RCP4.5 and RCP8.5 (for the end of the century, 2071-2100). As climate forcings differ regionally, we quantified redistribution in the Atlantic, Central Indian, East Indian, West Pacific and East Pacific regions. We found sea surface temperature and sea surface height to be the most important predictors of current habitat for these penguins; physical features that are changing rapidly in the Southern Ocean. Our results indicated that the less severe RCP4.5 would lead to less habitat loss than the more severe RCP8.5. The five taxa of penguin may experience a general poleward redistribution of their preferred habitat, but with contrasting effects in the (i) change in total area of preferred habitat under climate change (ii) according to geographic region and (iii) the species (macaroni/royal vs. rockhopper populations). Our results provide further understanding on the regional impacts and vulnerability of species to climate change.

Keywords: Subantarctic penguins; climate change; habitat preference models; migration; overwinter; species redistributions.

FIGURE 1

Distribution of breeding sites of the five focal Eudyptes penguin taxa across the Southern Ocean: eastern rockhopper penguins, macaroni/royal penguins, northern rockhopper penguins and southern rockhopper penguins.

FIGURE 2

Methodology of the process used to make future predictions of the redistribution of preferred habitat under future climate change scenarios (adapted from Hindell et al., 2020).

FIGURE 3

Habitat model response curves for sea surface height and sea surface temperature for the five focal Eudyptes penguin taxa: eastern rockhopper (E. filholi), macaroni (E. chrysolophus)/royal (E. schlegeli) penguins, northern rockhopper (E. moseleyi), and southern rockhopper (E. chrysocome). Positive predicted probability of preference suggests higher preference for those ranges of that environmental variable and negative predicted probability of preference suggests the animals actively do not select those ranges of the environmental variables. The higher the positive predicted probability of preference is, the more those ranges of the environmental variable are actively selected. Orange gridlines are for references: Horizontal lines are 0.0; vertical lines for sea surface heights are STF = 0.5 m (Subtropical Front), SAF = 0.128 (Subantarctic Front), PF = −0.634 (Polar Front) and SACCF = −1.09 (Subantarctic Circumpolar Current Front); and sea surface temperature is the 5°C point. Definitions for the front locations according to sea surface heights taken from Orsi et al. (1995) and Venables et al. (2012).

FIGURE 4

Relative habitat preferences, showing top 10 percentile, for five taxa of Eudyptes species: eastern rockhopper (E. filholi), macaroni (E. chrysolophus)/royal (E. schlegeli) penguins, northern rockhopper (E. moseleyi) and southern rockhopper (E. chrysocome) with the mean generalized major oceanographic frontal zone locations as defined by Orsi et al.,  (Southern Antarctic Circumpolar Frontal Zone = SACCFZ, Antarctic Polar Frontal Zone = PFZ, Subantarctic Frontal Zone = SAFZ, Subtropical Frontal Zone = STZ; using the Orsi Fronts). The purple layer is above the other colour layers.

FIGURE 5

Changes in habitat preference for five taxa of Eudyptes penguin under climate change predicted conditions. The figures represent polar projections of current important habitat for: eastern rockhopper (E. filholi), macaroni (E. chrysolophus)/royal (E. schlegeli) penguins, northern rockhopper (E. moseleyi), and southern rockhopper (E. chrysocome), and predicted habitat changes under Representative Concentration Pathway RCP4.5 (which assumes global temperatures increasing by 1.1–2.6°C and a mean sea level rise of 0.47 m, by the year 2100) and RCP8.5 (which assumes global temperatures increasing by 3.0–12.6°C and a mean sea level rise of 0.62 m, by the year 2100 (Sabine, 2014), which correspond to medium and high radiative forcing, respectively. RCP4.5 and RCP8.5 scenarios depict: Habitat that could remain important (blue), habitat that could be potentially gained (green) and habitat that could be lost (orange).

FIGURE 6

Percentage change in habitat area per region (using the Marine Ecosystem Assessment for the Southern Ocean defined regions) for the eight different climate representation (ACCESS1.0, BCC‐CSM1.1, CanESM2, CMCC‐CM, EC‐EARTH, GISS‐E2‐H‐CC, MIROC‐ESM, and NorESM‐M: grey points) for eastern rockhopper penguins (ERHP), macaroni/royal penguins (MRP), northern rockhopper penguins (NRHP) and southern rockhopper penguins (SRHP) under Representative Concentration Pathways RCP4.5 (red) and RCP8.5 (blue) scenarios. Percentage change for the eight climate change representations is shown by the dots. The boxes indicate the 25th–75th percentiles.