The Quantum Needle of the Avian Magnetic Compass

Proc Natl Acad Sci U S A. 2016 Apr 26;113(17):4634-9. doi: 10.1073/pnas.1600341113. Epub 2016 Apr 4.


Migratory birds have a light-dependent magnetic compass, the mechanism of which is thought to involve radical pairs formed photochemically in cryptochrome proteins in the retina. Theoretical descriptions of this compass have thus far been unable to account for the high precision with which birds are able to detect the direction of the Earth's magnetic field. Here we use coherent spin dynamics simulations to explore the behavior of realistic models of cryptochrome-based radical pairs. We show that when the spin coherence persists for longer than a few microseconds, the output of the sensor contains a sharp feature, referred to as a spike. The spike arises from avoided crossings of the quantum mechanical spin energy-levels of radicals formed in cryptochromes. Such a feature could deliver a heading precision sufficient to explain the navigational behavior of migratory birds in the wild. Our results (i) afford new insights into radical pair magnetoreception, (ii) suggest ways in which the performance of the compass could have been optimized by evolution, (iii) may provide the beginnings of an explanation for the magnetic disorientation of migratory birds exposed to anthropogenic electromagnetic noise, and (iv) suggest that radical pair magnetoreception may be more of a quantum biology phenomenon than previously realized.

Keywords: magnetic compass; magnetoreception; migratory birds; quantum biology; radical pair mechanism.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animal Migration / radiation effects*
  • Animals
  • Birds / physiology*
  • Computer Simulation
  • Cryptochromes / chemistry*
  • Cryptochromes / physiology
  • Cryptochromes / radiation effects
  • Dose-Response Relationship, Radiation
  • Homing Behavior / radiation effects
  • Magnetic Fields*
  • Magnetometry / methods
  • Models, Biological*
  • Models, Chemical
  • Quantum Theory*
  • Radiation Dosage
  • Signal Transduction / radiation effects


  • Cryptochromes