Barn swallows time their nests

The air above Shukkeien Garden carries the quick calls of barn swallows as they cut through the warming afternoon. Their flight paths crisscross the open spaces between the pine groves and ornamental ponds, each bird tracing tight arcs and sudden dives. If you watch closely, you can see the mud pellets they carry in their beaks, dark against their white throats.

Barn swallows build their cup-shaped nests from hundreds of these mud pellets, mixed with grass stems and lined with feathers. The timing matters. Late spring brings the sustained warmth that keeps mud workable and the insect abundance that makes raising young possible. Each pair needs to collect nearly a thousand beakfuls of mud to complete their nest, pressing each pellet into place while it remains soft. They choose sheltered spots under eaves, bridges, or pavilion overhangs where rain cannot dissolve their work.

The swallows synchronize their nesting with the emergence of flying insects. Late spring in Hiroshima brings midges, mosquitoes, flying ants, and small beetles into the air column where swallows hunt. A single barn swallow catches hundreds of insects each day, and a pair feeding nestlings may capture over a thousand. They hunt in layers, sometimes skimming just above the water surface for emerging midges, sometimes climbing thirty meters up to chase flying ants on their nuptial flights. The swallows' wide gape and flexible neck allow them to snatch prey while maintaining their flight path. When insects are dense, you might see several swallows working the same thermal, each bird claiming a different altitude.

The young hatch after two weeks of incubation, naked and helpless. For the next three weeks, both parents shuttle between nest and hunting grounds, each return trip bringing a throat pouch full of compressed insects. The nestlings grow quickly on this protein-rich diet, their flight feathers emerging in precise sequence. By the time they fledge, the late spring insect emergence has peaked, giving the young swallows the best possible start. Listen for their calls now, sharp and conversational, carried on air that still holds the day's warmth. Somewhere above you, a swallow turns on a wingtip, following the insects upward into the gathering dusk.