This page is your map. Each entry is a doorway into one piece of how a bar-tailed godwit's body remakes itself for flight, twice a year. The substance lives in conversation with Gazza.
Piersma & Lindström (1997)
Rapid reversible changes in organ size as a component of adaptive behaviour · Trends in Ecology & Evolution 12(4)
The paper that named phenotypic flexibility. Until the late 1990s, vertebrate biology treated organ size in adults as essentially fixed. Piersma and Lindström pulled together evidence to argue something different: organs rescale rapidly, repeatedly, reversibly across the lifespan.
The conceptual pivot. Once you accept that a vertebrate liver, gut, kidney or pectoral muscle can change size by 30–70% in days, the entire migratory-bird literature reorganises around it.
💬Discuss with Gazza
Piersma (1998)
Phenotypic flexibility during migration: optimization of organ size · Auk 115(1)
The 1998 follow-up that turned the 1997 idea into a measured hypothesis. Organ size, the paper argued, is optimised across the migration cycle — not maximised at any single stage.
The pre-flight bird is not the same body as the post-flight bird, and neither is the same body as the fuelling bird. Three optimisations across one annual cycle.
💬Discuss with Gazza
Piersma & Gill (1998)
Guts don't fly: small digestive organs in obese bar-tailed godwits · Auk 115(1)
The empirical confirmation. Bar-tailed godwits caught at Alaska pre-flight had massively reduced digestive organs alongside enormous fat reserves. Body composition told the story.
Pre-flight godwits carry roughly half the gut mass of fuelling birds, while body fat may exceed 50% of total mass. The bird shrinks what it doesn't need to keep the fuel airborne.
💬Discuss with Gazza
Battley, Piersma, Dietz, Tang, Dekinga & Hulsman (2000)
Empirical evidence for differential organ reductions during trans-oceanic bird flight · Proc Royal Society B 267
The first hard data on what happens inside a godwit during a trans-oceanic flight. Birds caught in NZ on arrival from Alaska, measured against birds about to leave. The contrast is stark.
30–70% reduction in liver, kidney, gut and gizzard mass post-flight. Heart and pectoral muscle protected. BMR down 42%. The bird that arrives is not the bird that left.
💬Discuss with Gazza
Landys-Ciannelli, Piersma & Jukema (2003)
Strategic size changes of internal organs during migration · Functional Ecology 17(2)
The paper that demonstrated the rescaling is genuinely strategic — different organs change at different points in the cycle, in coordinated patterns, in response to the demands ahead.
The order matters: muscle hypertrophy before fat-loading; gut reduction late; rebuild begins almost immediately on arrival. Phenotypic flexibility is a sequence, not a state.
💬Discuss with Gazza
Piersma, Gill, Ruthrauff, Guglielmo, Conklin & Handel (2021)
Physiomorphic transformations in extreme migration · Frontiers in Ecology and Evolution 9
The 2021 synthesis. Twenty-five years on from the 1997 paper, what does the field know about the body remade for flight? The paper sets out the empirical map and the open questions.
The transformation is mainstream physiology now — but the open question remains: what's the upper limit, and where does individual variation come from? The B6 record sits inside this question.
💬Discuss with Gazza
Conklin, Ruthrauff, Valcu, Verkuil, Johnson & Kempenaers (2026)
Post-hatch first migration: a 116-day-old godwit's 13,391 km flight · recent journal article 2026
The B6 paper. A juvenile bar-tailed godwit, hatched in Alaska, made its first-ever migration — 13,391 km, 11 days, Alaska to Tasmania, alone, at approximately 116 days of age. The current world record for longest non-stop bird migration.
13,391 km · 11 days · juvenile first attempt · ~116 days old · October 2022 · black flag right tibia. The record holder is identifiable individual baueri.
Source: Search Conklin et al. (2026) post-hatch godwit migration.
💬Discuss with Gazza