Chapter 2 · Try it yourself

Red Knot Refuel

A red knot lands on Delaware Bay in mid-May skinny from a flight up from South America. It has about two weeks to nearly double its weight on horseshoe crab eggs before the last hop to the Arctic. You control the crabs, the bait harvest and the weather. The bird does the eating.

1. Female horseshoe crabs in the bay

2. Bait harvest

3. May weather

100 g
Day 1 · May 14
Beach scene. Day 1 · May 14 Bay water 15 °C Chart of the bird’s weight. 180 g: ready for the Arctic Bird’s weight (g) Eggs on the beach surface (index)
  • Bird’s weight
  • Departure weight, about 180 g
  • Egg supply bars
  • Eggs (green dots on the sand)

The flyway

Map of the red knot’s spring flyway from Tierra del Fuego at the tip of South America, with stopovers in Brazil, north to Delaware Bay, about 10,300 kilometers in a straight line, then about 2,900 kilometers to the Canadian Arctic near Southampton Island. EquatorTierra del FuegoBrazil stopoversDelaware BayCanadian Arctic(Southampton Island)≈10,300 km≈2,900 km

Simplified outlines. Straight-line distances; the birds fly farther. The whole one-way trip is more than 15,000 km (9,300 miles), one of the longest migrations of any bird.

Bird’s weight today
100 g

  • Gained today+0 g
  • Eggs eaten today0
  • Egg supply0 of 100
  • Still needed80 g

Day-by-day numbers (table)
Day-by-day stopover numbers for the current settings
DayWater °CEgg supplyGain (g)Weight (g)

Simplified, illustrative model, not a population forecast. Crab numbers echo recent estimates of mature females in the Delaware Bay region (about 5 million in 2003–2012; about 8–19 million in 2024 depending on the method, ASMFC). Today’s bait rule is males only, capped at 500,000 crabs a year for 2026–2027 (ASMFC); males lay no eggs, so this barely touches the egg supply. Crabs spawn once bay water passes roughly 15 °C (59 °F). Knots can only reach eggs near the surface, brought up when crowds of crabs dig up earlier nests, so eggs rise faster than crab numbers. Bird numbers follow studies: arrival often near or under 100 g; departure at about 180 g or more (Baker and others 2004; Atkinson and others 2007); average gains of about 4–5 g a day, with some birds gaining far more; knots eat on the order of 20,000 eggs a day at full speed. The model’s first days are slow while the bird regrows a shrunken gut. Recent counts put the stopover population at roughly 40,000–55,000 red knots (2023–2025).