Graduate Research Course

Migration: Birds & Monarch Butterfly

Sensors, biophysics, biochemistry — from radical-pair cryptochromes to 11 000-km non-stop godwit flights, from monarch cardenolide toxins to oyamel-fir overwintering.

Migration Atlas: Distance by Species

Annual migration distance, log-km axis — bars coloured by taxon. Spans 4 orders of magnitude.

The Arctic tern (Sterna paradisaea) is the animal-kingdom distance champion at ~70 000 km/yr — nearly twice the Earth’s circumference. Three insects (globe skimmer dragonfly, painted lady, monarch) achieve continent-scale migration through multi-generational relay, each individual flying only a fraction of the full path. The gray whale holds the mammal record at 20 000 km between Baja lagoons and the Chukchi Sea.

Altitude & Depth: Migration in the 3rd Dimension

Vertical extent of migration routes — from 9000 m bar-headed goose crossings to 1200 m bluefin-tuna dives.

Rüppell’s vulture once struck a jetliner at 11.3 km altitude — the highest confirmed bird flight. The bar-headed goose crosses the Himalayas at 9 km with hemoglobin variant αA that has elevated O₂ affinity (Scott 2010). At the other extreme, leatherback turtles and bluefin tuna dive routinely to −1.2 km during ocean-crossing migrations; sperm whales hunt giant squid at −2.2 km.

Climate Constraint

Migration Under Climate Change

Every migratory species faces a chain of climate-linked constraints between where it is, where it is going, and where it stops to refuel. The constraints are not independent — a shift at any single stage can unravel the entire journey:

1. Phenological mismatch. Arrival timing decouples from resource peaks. Pied flycatcher caterpillar-food now peaks 2 weeks before chicks hatch (Both 2006). Population declines of 90% in mismatched regions.

2. Stopover-site loss. Yellow Sea wetland drainage removed 65% of shorebird refueling capacity (Studds 2017). Red knots lose 30% body mass on longer detours.

3. Breeding-ground mismatch vs. wintering. Bar-tailed godwit Alaska breeding warming 3× wintering rate. Arctic tern ice-retreat at both poles simultaneously.

4. Heat-stress mid-migration. Wet-bulb T_w > 35 °C during stopover = lethal. Albright 2017 projects desert-crossing bird mortality spikes by 2050.

5. Altered wind regimes. Jet-stream meandering changes historical tailwind corridors. Loonin 2023 modeled 9% greater energy cost for trans-Atlantic migrants by 2060.

6. Monsoon-phenology decoupling. Indian monsoon delays or early onsets shift breeding of baya weaver, Sarus crane, paradise flycatcher — cross-links Climate M14.

7. Monarch overwintering collapse. Oyamel fir Abies religiosa dies below 3000 m; cold snaps in 2002 & 2016 killed 80% of overwintering butterflies. Milkweed loss along US migration cuts female fecundity (Pleasants 2013).

8. Elevational refugia exhaustion. Tropical montane species (Andean tanagers, Himalayan warblers) run out of uphill habitat. Freeman 2018 observed 42% range-edge uplift 1985-2017.

9. Magnetic-field drift. Earth’s field declination changes ~0.3°/yr. Inclination-based compasses of birds and turtles re-calibrate each generation; fast drift plus climate-driven coast retreat can move sea-turtle imprint beaches out of magnetic signature (Brothers 2015).

10. Food-web decoupling. Caribou mismatch: plant green-up advances faster than calving (Post 2008). Little auks lose access to lipid-rich Arctic copepods as warming shifts to less-nutritious southern species.

The combined risk is multiplicative: a migrant that survives constraint 1–9 can still starve at its destination from constraint 10. Conservation responses include flyway-scale protection (Yellow Sea intertidal restoration), climate-connectivity corridors(AmericanMidwest milkweed restoration), and assisted colonization of oyamel fir to cooler elevations. SeeM8: Climate & Migration Shifts for quantitative models.

About This Course

A bar-tailed godwit weighing 600 g flies 11 000 km from Alaska to New Zealand without stopping — without food, water, or sleep — over 11 consecutive days. A monarch butterfly the weight of a paperclip traverses 4 000 km across three North American generations to the same Mexican oyamel fir grove used by its great-grandparents. Both rely on sensors we are still decoding: quantum-spin cryptochrome radical pairs, antennal circadian clocks, star-compass memorization, polarized-light E-vectors.

Cross-links: Eagle Biophysics,Emperor Penguin,Climate M14 Monsoon,Climate M5 Phenology.

Nine Modules

Why Migrate?

Evolutionary cost-benefit of migration, partial vs. full, circannual clocks, Berthold genetics of migratory restlessness (Zugunruhe), origin of migration.

ZugunruheEvolutionBerthold

Celestial Compasses

Emlen funnel experiments, star compass rotation learning, polarized-light E-vector detection, sunset polarization cues, Kramer 1957 orientation cage.

EmlenPolarized LightStar Compass

Magnetoreception Biochemistry

Radical-pair cryptochrome (CRY4) model Ritz 2000/Xu 2021 CRY4 in European robin, magnetite iron-based hypothesis, spin-dependent chemistry.

CryptochromeRadical PairXu 2021

Bar-Tailed Godwit: 11000 km

Limosa lapponica Alaska to New Zealand non-stop 11000 km, 11-day flight, Gill 2009 satellite tracks, fat-loading pre-departure, flight-muscle atrophy.

LimosaGill 200911000 km

Passerine Nocturnal Migration

Thrushes, warblers, nocturnal flight call detection, moon-watching, radar ornithology, flight altitudes 500-2000 m, BirdCast nowcast products.

NocturnalRadarBirdCast

Monarch Butterfly Migration

Danaus plexippus multi-generational 4000 km to Mexican oyamel fir forests, Urquhart 1976 discovery, eastern vs. western populations, colony census.

DanausOyamelUrquhart

Monarch Compass & Biochemistry

Reppert time-compensated sun compass, antennal circadian clock, cardenolide sequestration from milkweed, Malcolm 1989 toxin ecology.

ReppertAntennaeCardenolides

Flight Physiology & Fat

Hyperphagia pre-migration (doubles body mass), lipid β-oxidation, heart hypertrophy, muscle glycogen vs. fat economy, Piersma flexible phenotypes.

HyperphagiaLipidPiersma

Climate & Migration Shifts

Visser & Both 2005 pied flycatcher mismatch, arrival-date advance 1-2 days/decade, monarch Ogard & Pleasants 2013 collapse, milkweed loss.

VisserMismatchMonarch Decline

Begin Module 0: Why Migrate? →