SkarpChapter 1 of 1
How Experience Rewrites a Migration Route
Compare a young bird following an inherited direction-and-time program with an experienced adult correcting after displacement. See how first journeys can build learned maps and why species, environments and available cues produce different results.
1. Two Navigation Problems
First journey
A juvenile has not visited its wintering area. It can nevertheless use an inherited seasonal program: maintain a broadly appropriate direction for an appropriate duration.
Vector navigation
Vector navigation resembles an arrow on a map: "fly southwest for this long." It can move a young bird far without telling it exactly where it is.
Experienced correction
An experienced adult may locate itself relative to a goal or route and change course after displacement. This flexible ability is called true navigation.
2. Displacement Reveals the Difference
The test
Researchers transport birds away from an expected route, release them, and track the direction they choose. A correction suggests position-finding, not merely a fixed heading.
White-crowned sparrows
In 2007, adults moved about 3,700 km across the United States corrected their direction rapidly. Juveniles did not show the same response.
Different tasks
Juveniles are not simply poor navigators. They must reach an unfamiliar region; adults can add memories of prior journeys, places, and environmental patterns.
3. What Experience May Build
Map does not mean visual map
A navigational map is a system for estimating location from cues that vary across space. It need not resemble a human road map.
Combine cues
Repeated travel can associate combinations of coastline shape, winds, odors, and magnetic values with a route position or a homeward direction.
A flexible route
Experience can make navigation resilient. When one cue is missing or unreliable, another may help. A migration route is a set of learned relationships, not only a line.
4. A Songbird Can Read Magnetic Position
Compass versus map
Magnetic information can support a compass for direction. Geographic variation in magnetic features can also potentially contribute to a map for estimating position.
Reed warblers
In a 2018 coil experiment, sham-operated Eurasian reed warblers reoriented after a simulated displacement of roughly 1,000 km.
Use precise conclusions
Birds lacking trigeminal input did not compensate in that test. This supports a magnetic-map role in this setting, not one universal mechanism for all birds.
5. Gulls Show Why Smell Matters
Gulls outside the corridor
In 2015, adult lesser black-backed gulls were displaced far from their normal corridor. Intact gulls oriented toward their population-specific route.
Direction remained
Gulls with olfactory nerves sectioned still tended southward, but did not make the same eastward corrective response after a western displacement into unfamiliar surroundings.
Context matters
The result indicates that smell can support correction in this situation. It also shows that familiarity with an area can change which information is sufficient.
6. Seabirds Switch Resources Near Land
Over open water
In a 2015 study, control Scopoli's shearwaters and magnetically disturbed birds oriented homeward efficiently after a displacement of about 400 km.
When smell was impaired
Temporarily anosmic birds initially followed more tortuous paths and did not orient homeward in open sea. Many changed toward home after reaching coastlines.
Cue value is conditional
Topography can become useful near land. Species, experience, displacement scale, weather, terrain, and cue availability determine which signals a bird can use.
7. Thought Exercise: Choose the Backup
Diagnose the navigation problem
Imagine two displaced adults:
- A gull is released far west of its familiar migration corridor under cloudy skies.
- A shearwater is released over open water, then later reaches a recognizable coastline.
For each bird, ask:
- Which cue could help estimate position first?
- Which cue becomes more useful if the first cue is blocked?
- Would a juvenile with no prior trip likely make the same correction?
The goal is not to name one "best" sense. It is to match a cue to the bird's experience and environment.
8. Check Understanding
One question
Choose the explanation that best connects juvenile migration, adult correction, and sensory cues.
Why might an experienced adult correct after a displacement while a juvenile continues in its original migratory direction?
- The adult may use a learned map built from prior journeys, while the juvenile may be following an inherited direction-and-time program.
- Adults always have stronger muscles, so they can fly directly toward any destination.
- Juveniles cannot detect odors, landmarks, or magnetic fields until their second year.
Show Answer
Answer: A) The adult may use a learned map built from prior journeys, while the juvenile may be following an inherited direction-and-time program.
Adults can combine prior experience with available cues to estimate their position and correct course. Juveniles may have sensory abilities, but without previous journeys they often rely more heavily on an inherited migration vector.
Key Terms
- anosmic
- Unable to use the sense of smell.
- olfaction
- The sense of smell; airborne chemical patterns can provide spatial information for some birds.
- true navigation
- The ability to estimate position relative to a goal and correct course after displacement.
- navigational map
- A system for estimating location from environmental cues that vary across space.
- trigeminal nerve
- A cranial nerve with branches that can carry sensory information; in some bird experiments, its ophthalmic branch is necessary for magnetic-map responses.
- vector navigation
- Migration guided mainly by an inherited direction and duration, rather than by knowing the bird's position relative to a destination.