Possible Clues:

• Wanting energy, fires up — that provides energy
• Staying-power
• The ability to sustain prolonged effort
• Fires up lacking energy and strength
• Unflagging vigour provides way to get a bird
• Shackleton's first volunteers had a short time in Endurance
• Ability for sustained effort
• Mostly remain with chatty bird, showing capacity for endurance
• Street dictator with a capacity for carrying on
• Mark article about male perseverance