Research ArticleECOLOGY

Foraging behavior links sea ice to breeding success in Antarctic penguins

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Science Advances  24 Jun 2020:
Vol. 6, no. 26, eaba4828
DOI: 10.1126/sciadv.aba4828
  • Fig. 1 Sea-ice conditions and penguin behavior.

    Scenes around the penguin colony studied (yellow line) photographed in (A) January 2012, when sea ice was extensive, and (B) January 2017, when sea ice was nearly absent (Photo credit: Y.Y.W., National Institute of Polar Research). Typical foraging trips of penguins recorded in (C) ice-covered January 2012 and (D) ice-free January 2017, showing distance from nest and dive depth. Penguins traveled by walking and swimming in 2012 and 2017, respectively, during the periods denoted by gray bars. The scales of both the x and y axes are matched in (C) and (D) to facilitate comparison. (E to H) All foraging trips recorded by GPS loggers for each season. Yellow circles represent the colony.

  • Fig. 2 Interannual variability in penguin performance.

    (A) Trip duration, (B) trip distance (i.e., the maximum distance from nests reached during the trips), and (C) the number of krill captured in a dive, standardized for a 100-s dive duration, plotted on a log scale. Body mass of adult (D) females and (E) males, (F) chick growth rates, and (G) the number of fledglings per nest, plotted on a linear scale. In box plots, the 25th percentile, the median, and the 75th percentile are shown by boxes, the 10th and 90th percentiles are shown by error bars, and the data points outside the 10th and 90th percentiles are shown by small circles.

  • Fig. 3 Penguin diving behavior.

    Typical krill-feeding dives recorded in (A) January 2013, when sea ice was extensive, and (B) December 2016, when sea ice was nearly absent. In ice-covered seasons, penguins slowed ascending speeds down at the end of each dive to search for cracks in the ice for breathing [red arrows in (A)]. (C to G) Relationships between dive depth and dive duration of krill-feeding dives for each season, with the ordinary least-squares regression lines (2010/11, Y = 1.30 × X + 66.6, R2 = 0.57, N = 531; 2011/12, Y = 1.36 × X + 69.7, R2 = 0.20, N = 485; 2012/13, Y = 1.19 × X + 77.3, R2 = 0.49, N = 1119; 2016/17, Y = 1.01 × X + 55.7, R2 = 0.60, N = 2275).

  • Table 1 Foraging and breeding performance of Adélie penguins in four seasons.

    Values shown are estimates (with 95% confidence interval) based on linear mixed-effect models for foraging behavior and means ± SD or single observations for others.

    2010/112011/122012/132016/17
    Sea-ice coverYesYesYesNo
    Foraging behavior
      Trip duration (hours)19.3 (15.9–23.7)19.7 (12.4–31.4)15.0 (9.0–25.1)11.8 (7.6–18.4)
      Trip distance (km)2.1 (1.6–2.7)2.4 (1.4–4.3)2.4 (1.3–4.5)6.9 (4.1–11.9)
    (N = 91 trips from 15 birds)(N = 92 trips from 28 birds)(N = 64 trips from 17 birds)(N = 260 trips from 27 birds)
      Dive duration intercept (s)*69 (58–80)74 (48–100)81 (56–106)54 (30–79)
    (N = 531 dives from 8 birds)(N = 485 dives from 9 birds)(N = 1119 dives from 15 birds)(N = 2275 dives from 19 birds)
      No. of krill captured in a
    100-s dive
    4.1 (2.8–6.1)3.6 (1.4–9.2)5.2 (2.2–12.6)5.4 (2.2–13.2)
    (N = 443 dives from 8 birds)(N = 374 dives from 9 birds)(N = 996 dives from 15 birds)(N = 1211 dives from 12 birds)
    Body condition
      Adult female body mass (kg)3.8 ± 0.4 (N = 21 birds)4.0 ± 0.4 (N = 18 birds)4.2 ± 0.3 (N = 29 birds)4.4 ± 0.5 (N = 42 birds)
      Adult male body mass (kg)4.4 ± 0.3 (N = 21 birds)4.2 ± 0.4 (N = 28 birds)4.6 ± 0.4 (N = 42 birds)4.9 ± 0.5 (N = 31 birds)
    Breeding status
      Chick growth rate (g day−1)67 ± 14 (N = 14 birds)69 ± 20 (N = 15 birds)76 ± 16 (N = 33 birds)102 ± 8 (N = 18 birds)
      No. of nests (in late
    December)
    70109181108
      No. of fledglings (in early
    February)
    3788219143
    Stomach content
      Prey composition by mass†Krill 38 ± 46%Krill 37 ± 46%Krill 91 ± 19%Krill 94 ± 14%
    Fish 62 ± 46%Fish 63 ± 46%Fish 9 ± 19%Fish, 6 ± 14%
    Krill composition by massE. superba 32 ± 24%E. superba 73 ± 42%E. superba 81 ± 34%E. superba 100%
    E. crystallorophias 68 ± 24%E. crystallorophias 27 ± 42%E. crystallorophias 19 ± 34%
    (N = 10 birds)(N = 10 birds)(N = 11 birds)(N = 8 birds)

    *Intercept of dive duration as a function of dive depth (i.e., dive duration of a hypothetical 0-m dive).

    †In addition to krill and fish, a few amphipods (<1% by mass in most birds) were often found.

    Supplementary Materials

    • Supplementary Materials

      Foraging behavior links sea ice to breeding success in Antarctic penguins

      Yuuki Y. Watanabe, Kentaro Ito, Nobuo Kokubun, Akinori Takahashi

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