Ornithology Lecture 14

Definition of Migration

  • Migration: Defined as a predictable and cyclical movement between non-overlapping home ranges within a single year.

  • Importance of predictability and reproducibility in migration behavior of species.

Adaptations for Migration

  • Birds require adaptations for:

    • Effective and accurate orientation and navigation.

    • Distinction between orientation (direction) and navigation (specific location).

Orientation vs. Navigation

  • Orientation:

    • The position of a migratory flight in the correct direction (e.g. South in autumn, North in spring).

    • Appears to be genetic since inexperienced juvenile birds can orient properly.

  • Navigation:

    • Finding one's way to a specific location; accuracy can vary (coarse scale vs. local scale).

    • Pigeons and breeding shorebirds exhibit fine-scale navigation.

Experimental Evidence of Migration

  1. White-Crowned Sparrows:

    • Breeding in the north (Alaska/Yukon) and wintering in southern US.

    • Experiments showed birds transported from California to Louisiana and Maryland returned to California the following winters, indicating high fidelity in migration routes.

  2. Manx Shearwater:

    • Example of a shearwater tracked after being transported to Boston; returned to breeding grounds in Ireland (3,200 miles in 12.5 days).

    • Highlights remarkable navigation across large distances without prior experience.

  3. Lyall's Albatross (Wisdom):

    • Breeding primarily on two Hawaiian islands, individual tracked flying from Washington State at a rate of 350 miles per day back to breeding islands.

Historical Context of Bird Navigation

  • Homing Pigeons:

    • Domesticated rock doves used for message delivery historically since ancient Rome.

    • Established reliable mail systems in the past, used in wars for messaging when other forms of communication failed.

Experiments on Learning Migration Behavior

  • Albert Perdic's Experiments on Starlings:

    • Captured 10,000+ starlings near migration stopovers.

    • Adults navigated accurately while juveniles followed previous migratory orientation even when translocated, indicating genetic factors and experience importance.

Orientation Mechanisms

Cues Used by Birds:

  1. Visual Cues:

    • Use of landmarks and geographical features (coastlines, big land features) for guidance.

  2. Solar Compass:

    • Birds use the sun's position for navigation, adjusting for time.

    • Studies showed directionality in restless behavior correlating with sun position.

  3. Star Navigation:

    • Experience helps juvenile birds learn to navigate using patterns of stars.

  4. Olfactory Cues:

    • Birds can smell different environments, aiding navigation (e.g. differences in scents of pine vs. onion farms).

  5. Geomagnetic Cues:

    • Birds may sense Earth's magnetic fields to aid orientation during migration, particularly in long-distance travelers.

    • Experiments involving robins and pigeons showed dependence on geomagnetic fields for navigation.

Physiological Mechanisms

  • Magnetite: Iron oxide found in the beaks of some birds that could be sensitive to magnetic fields.

  • Cryptochromes: Specialized retinal pigments that may help detect magnetic fields to orient longitudinally and latitude-wise.

Conclusion

  • Birds utilize a combination of genetic orientation, learned navigation through experience, and multiple environmental cues (visual, olfactory, solar, magnetic) for successful migration.

  • Understanding bird migration contributes to knowledge about conservation and environmental changes affecting migratory patterns.