Every choice a breeding bird makes carries a price. Time spent guarding a nest is time not spent foraging; energy poured into one clutch is energy unavailable for the next; a meal delivered to a chick is a meal the parent didn't eat. These tradeoffs reflect a constant balancing act between current reproduction, future reproduction, and the parent's own survival.
How birds may balance self-care vs. parental responsibilities was recently studied in the Nazca Booby, a large (wingspan 1.55 meters), long-lived (average lifespan 23 years) pelagic seabird that nests in colonies on the Galapagos Islands. They forage exclusively offshore, hunting fish from high in the air. Females are heavier and stronger than males and are known to engage in extra-pair copulations (EPCs) 🥰, so males guard females to ensure offspring are exclusively theirs. But spending more time onshore means less food in their bellies. The research team studied the birds’ parenting tradeoffs by tracking when individuals attended the colony before, during, and shortly after egg-laying. They found that males consistently spent more nights at the colony than females in the weeks before and during egg-laying, reducing foraging time in exchange for attracting mates, holding nest sites, and guarding paternity. With one exception: on the night between the fertilization windows of a potential first and second egg — a brief paternity-risk-free window — most males abandoned the colony for one night of offshore hunting. Passing on their genes was a priority, but they knew when to sneak out for a risk-free nosh.