Module 2

Emperor II: Breeding & Fasting

Emperor penguins breed in the most extreme environment any bird raises young. Males incubate the single egg for 65–75 days while fasting through the Antarctic winter, losing ~45% of body mass. Coordinated pair-switching at hatch, specialised brood-pouch anatomy, and colony-level synchrony make it possible.

1. The Breeding Calendar

Adults arrive at fast-ice colonies in March (austral autumn). Pair bonds form in April; a single 450–470 g egg is laid in May. The female transfers the egg to the male’s feet/brood pouch and returns to open water to feed. Males incubate through winter (May–July, ~65 days) and hatch the chick alone; females return with fish for the chick in August. Both parents then alternate foraging trips until the chick fledges in November–December.

2. Brood Pouch Physiology

The egg rests on the male’s feet, covered by a specialised featherless skin flap (the brood pouch) that maintains egg temperature at ~36 °C even when external air is below −40 °C. Heat flux through the pouch is actively regulated via vasodilation; the small hatchling stays in the pouch for weeks post-hatch. Groscolas 1990 measured the thermal properties and the corresponding male metabolic cost.

3. Three-Phase Fasting

Groscolas divided the male fast into three biochemical phases: Phase I (1–10 days) burning intake-derived glycogen + residual fat; Phase II (10–100 days) steady-state lipid mobilisation from subcutaneous fat; Phase III (100+ days) protein catabolism signalled by rising plasma urea and falling ketones, at which point the male must abandon the egg to feed. Extension of Phase II by even a few days — via huddle energy savings — is the difference between successful and failed incubation.

Simulation: Mass, Metabolism, Pouch T

Python

script.py48 lines

import numpy as np, matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt

# Male emperor 4-month fast during egg incubation
days = np.arange(0, 130)

# Mass loss: 35 kg -> 20 kg (Groscolas 1990 three-phase fasting)
mass = 35 - 0.12*days - 0.003*(days-60).clip(0)**1.2
mass = np.clip(mass, 18, 35)

# Daily metabolic rate (Ancel 1997): drops to ~40% BMR in huddle
dmr = 120 - 0.4*days
dmr = np.clip(dmr, 60, 200)

# Egg + brood-pouch temperature
t_brood = 36.0 + 0.3*np.sin(2*np.pi*days/30)

fig, axes = plt.subplots(1, 3, figsize=(17, 5), facecolor='#0a0a1a')
for ax in axes:
    ax.set_facecolor('#111827'); ax.tick_params(colors='#cbd5e1')
    for s in ax.spines.values(): s.set_color('#334155')
    ax.grid(True, color='#334155', alpha=0.3)

axes[0].plot(days, mass, color='#38bdf8', lw=2.6)
axes[0].axvline(60, color='#fbbf24', ls=':', label='Phase II begins')
axes[0].set_xlabel('Fast day', color='#cbd5e1')
axes[0].set_ylabel('Body mass (kg)', color='#cbd5e1')
axes[0].set_title('Male fast 35 -> 20 kg', color='#bae6fd', fontweight='bold')
axes[0].legend(facecolor='#1e293b', edgecolor='#334155', labelcolor='#cbd5e1')

axes[1].plot(days, dmr, color='#fbbf24', lw=2.6)
axes[1].set_xlabel('Fast day', color='#cbd5e1')
axes[1].set_ylabel('Metabolic rate (W)', color='#cbd5e1')
axes[1].set_title('Huddle-reduced daily metabolic rate',
                  color='#bae6fd', fontweight='bold')

axes[2].plot(days, t_brood, color='#dc2626', lw=2.6)
axes[2].axhline(36, color='#60a5fa', ls=':', label='Target egg T')
axes[2].set_xlabel('Fast day', color='#cbd5e1')
axes[2].set_ylabel('Brood-pouch T (C)', color='#cbd5e1')
axes[2].set_title('Egg thermal regulation', color='#bae6fd', fontweight='bold')
axes[2].legend(facecolor='#1e293b', edgecolor='#334155', labelcolor='#cbd5e1')

plt.tight_layout()
plt.savefig('output.png', dpi=120, bbox_inches='tight', facecolor='#0a0a1a')
print('Male emperor fasts ~115 days, losing ~45% body mass')
print('Brood pouch maintained at 36 C even at -40 C air')

Click Run to execute the Python code

Code will be executed with Python 3 on the server

Key References

• Groscolas, R. (1990). “Metabolic adaptations to fasting in emperor and king penguins.” In Penguin Biology, Academic Press.

• Ancel, A. et al. (1997). “Energy saving in huddling penguins.” Nature, 385, 304–305.

• Prevost, J. (1961). “Écologie du manchot empereur Aptenodytes forsteri.” Actual. Sci. Ind., 1291, 1–200.

• Stonehouse, B. (1953). “The emperor penguin.” FIDS Scient. Rep., 6, 1–33.

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