Figure 1.
Spatial distribution of foraging areas.
(a) Locations and (b) core areas (50% kernel contours) of 10 Antarctic prions (brown symbols & contours), 12 blue petrels (orange symbols & contours), 9 common diving petrels (blue symbols & contours) and 8 South Georgian diving petrels (green symbols & contours) tracked using geolocators during incubation at Bird Island, South Georgia in summer 2010/11. The white star indicates the position of the colony.
Figure 2.
Incubation period of the four small petrels in Bird Island during austral summer 2010/11.
Antarctic prion (AP), blue petrel (BP), common diving petrel (CDP) and South Georgian diving petrel (SGDP).
Table 1.
Trip duration and diving characteristics (mean and standard deviation) of common diving petrels (CPD), South Georgian diving petrels (SGDP), Antarctic prions (AP) and blue petrels (BP) tracked with TDRs and GLS-immersion loggers during incubation at Bird Island, South Georgia, in summer 2010/11.
Figure 3.
Diving capability descriptors.
Mean and standard deviation of (a) maximum dive depth and bottom dive depth, and (b) maximum dive duration and mean dive duration of 19 common diving petrels (CDP), 6 South Georgian diving petrels (SGDP), 3 Antarctic prions (AP) and 5 blue petrels (BP) fitted with TDRs during incubation at Bird Island, South Georgia in summer 2010/11.
Figure 4.
Example of the diving activity and a dive event of a common and a South Georgian diving petrel.
Diving activity during the entire foraging trip and one dive of common diving petrel [(a) and (b), respectively] and South Georgian diving petrel [(c) and (d), respectively] measured with TDRs during incubation at Bird Island, South Georgia in summer 2010/11. Shaded areas indicate darkness.
Figure 5.
Temporal diving activity patterns.
Diel patterns in dive frequency of birds fitted with TDRs loggers during incubation at Bird Island, South Georgia in summer 2010/11. Shaded areas indicate darkness. Species abbreviations: AP (Antarctic prion), BP (blue petrel), CDP (common diving petrel) and SGDP (South Georgian diving petrel).
Figure 6.
Mean daily percentage of time spent on water ± SE of 12 Antarctic prions (AP), 12 blue petrels (BP), 9 common diving petrels (CDP), and 8 South Georgian diving petrels (SGDP) tracked using immersion loggers during incubation at Bird Island, South Georgia in summer 2010/11. Shaded areas indicate darkness. The mean value of waveform for each species is indicated with a horizontal line (different colour for each species).
Figure 7.
Comparing the relevance of 12 h and 24 h at-sea activity patterns.
The ratio of the power content of the 12 h and 24 h harmonics obtained by Fourier analysis (mean and standard deviation), indicating the relevance of the 12 h activity bout to the 24 h pattern, for (A) Antarctic prion, (B) blue petrel, (C) common diving petrel and (D) South Georgian diving petrel.
Figure 8.
Temporal differences in the main and secondary at-sea activity bouts.
Outputs from Rayleigh z-tests used to evaluate clustering of the times of the main and secondary activity bouts (indicated by triangles and circles, respectively) estimated from waveforms of Antarctic prions (A) and blue petrels (B) or of the main bouts only of common diving petrels (C) and South Georgian diving petrels (D). Tick marks from 0–24 represent the hours of the day, the black semicircle depicts night (sunrise at 4∶00 GMT, sunset at 22∶00 GMT). The dotted circumference defines the threshold value for a significant r vector (p<0.05). The mean vector for individual values is indicated with confidence intervals.
Figure 9.
Mean ± SD of δ15N and δ13C values in red cells of four species of small petrel sampled during incubation at Bird Island, South Georgia in summer 2010/11. Species abbreviations: AP (Antarctic prion), BP (blue petrel), CDP (common diving petrel) and SGDP (South Georgian diving petrel). All n = 15.
Figure 10.
Flight performance descriptors.
Mean ± SD of wing loading and aspect ratio of four species of small petrel measured during incubation at Bird Island, South Georgia in summer 2010/11. Species abbreviations: AP (Antarctic prion), BP (blue petrel), CDP (common diving petrel) and SGDP (South Georgian diving petrel). All n = 15.
Table 2.
Summary of the evidence in the present study for interspecific overlap/segregation in each ecological niche axis between Antarctic prion (AP), blue petrel (BP), common diving petrel (CDP) and South Georgian diving petrel (SGDP).