Fur seal pups hauling out with dry and wet fur.

<p>(A) Pup with dry fur. The hairs are curled, but constitute a continuous surface. (B) Pup with wet fur, 5 min after leaving the water. The guard hair is divided into strands, opening gaps through which the light grey under fur is visible.</p

T_body, T_skin, T_fur and T_surface of the pups with wet and dry fur.

<p>Minimum (T_min), maximum (T_max) and mean (T_mean) temperatures of the pups' fur surface, air inside the fur, skin and body core along with temperature range, standard deviation (s.d.) and number of measurements (N). Total includes the data of all investigated pups with dry and wet fur. Beneath the data of all pups are sorted by wet or dry fur conditions.</p

Cape fur seal pups hauling out under intense solar radiation.

<p>The pups, aged 18 and 28 days, hauled out in the sun for 1.5 h, T_air  = 31.3°C. T_surface increased up to 78.7°C on their backs.</p

Reduction of T_surface on hauled out pups by wind forced convection.

<p>Pups hauling out under solar radiation with sudden appearance of a light breeze of wind force 1–2 (Beaufort), corresponding to 0.2–3.3 m/s. (A) Pup with T_max = 61.2°C on the surface, T_air = 17.3°C. (B) Decreased T_surface after light breeze for 5 s to T_max = 58.8°C (3.9%). (C) Pup with T_max = 72.3°C on the surface, T_air = 23.8°C. (D) After 42 s of light breeze T_surface decreased to T_max = 47.3°C (34.6%).</p

T_body and T_skin of the pups with wet and dry fur.

<p>T_body with dry fur (green diamonds, green regression line, N = 23) and wet fur (turquoise filled circles, N = 3) as well as T_skin with dry fur (red circles, red regression line, N = 279) and wet fur (blue circles, blue regression line, N = 28) against T_air. Mean T_skin with dry fur is 38.4±1.7°C, mean T_skin with wet fur is 35.8±1.3°C, which is significantly lower than with dry fur (<i>p</i>≤0.0001). T_body is constant with no significant difference between wet and dry fur. The slope of regression of T_body is with 0.002 again practically constant, while the regressions of T_skin ascend by 0.32 (dry fur) and 0.13 (wet fur).</p

Accuracy of heading perception of a harbor seal.

<p>The harbor seal's ability to detect deviations of the cross from the FOE (in %) is plotted as a function of the angular distance between FOE and cross (in deg). The threshold of heading perception, defined as the angular distance between FOE and cross (delta phi) that could be detected with a performance of 50%, was interpolated by fitting an exponential function to the data (black curve; r² = 0.99). The resulting threshold of 0.6 deg is indicated by a black arrow pointing to the x-axis. Numbers at the data points indicate the number of trials per angular distance. The seal's false alarm rate of 21.7% (N = 351) is indicated at an angular distance of 0 deg (closed circle).</p

Optic flow projection.

<p>A three dimensional cloud of dots was presented to the harbor seal on an underwater projection screen. The FOE of the optic flow field (white dot, dot not shown during experiments) could occur on 28 positions all covered by a ring-shaped mask (grey circle). A cross was superimposed on the optic flow field at a pre-programmed angular distance (delta phi) to the FOE and could either match (“no go”-trial) or deviate from the FOE (“go”-trial, illustrated in this figure).</p

Experimental setup for the determination of the threshold of heading perception from virtual optic flow and response behavior of the harbor seal.

<p>A The computer generated optic flow field was back-projected by a projector and via a mirror system onto an underwater projection screen installed inside a projection chamber. For a high-quality underwater projection, the water surface was calmed by an acrylic frame, and the experimental area in front of the projection chamber was shaded by a black curtain. Inside this area, the animal was stationing underwater in a hoop station with the eyes at 1.5 m distance to the projection. During trials, the experimenter (not displayed) stayed outside the experimental area in order to avoid giving secondary cues. Scale 0.5 m. B In a “no go”-trial, in which the superimposed cross matched the FOE, the animal had to touch the cross with its snout in order to be rewarded. C In a “go”-trial (compare with <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0103555#pone-0103555-g002" target="_blank">Figure 2</a>), in which the cross deviated by a pre-programmed angular distance from the FOE, the seal had to turn away from the projection screen and touch the hoop station with its snout.</p

Experimental Feeding Platform.

<p>A. Feeding platform in place in the enclosure. B. Harbor seal feeding from feeding apparatus.</p

Representative Kinematic Profiles of Suction vs. Biting.

<p>A. Frame from video during in-water suction feeding trial with overlaid spatial model stick figure. B. Plot of Gape (cm) for a single suction feeding trial. C. Plot of Gular Depression (cm) for a single suction feeding trial. D. Plot of Maximum Gape Angle (degrees) for a single suction feeding trial. E. Plot of Gape Angle Velocity (degrees/s; opening and closing) for a single suction feeding trial. F. Frame from video during on-land biting feeding trial with overlaid spatial model stick figure. G. Plot of Gape (cm) for a single biting feeding trial. H. Plot of Maximum Gape Angle (degrees) for a single biting feeding trial. I. Plot of Gular Depression (cm) for a single biting feeding trial. J. Plot of Gape Angle Velocity (degrees/s; opening and closing) for a single biting feeding trial.</p