Ornithology Lecture Notes 1 - Introduction to Birds & …
Figure 13. a, European Robins with a damaged cluster N that were tested in a planetarium simulating the local starry sky (STN, star north)
oriented in the typical north-northeast spring migratory direction). b, Birds with cluster N damage could not orient using their magnetic compass
(MPW, magnetic pole). c, Birds with cluster N damage could also orient during sunset using their sun compass (From: Zapka et al. 2009).
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Figure 24. Orientation of displaced White-crowned Sparrows. A-G, adults; H-N, juveniles. Control birds and those tested at
a location west of the capture location on the breeding grounds typically oriented to the east or southeast in the general direction
of their wintering area. Sparrows transported in an icebreaker east of the capture site tended to oriented to the west or northwest, a
direction that would lead them back to the breeding area or their typical migration route (From: Åkesson et al. 2005).
A study where White-crowned Sparrows were displaced longitudinally across distances ranging from 266 to 2869 kilometers provides some additional possible clues about how magnetic cues might be used by birds (Åkesson et al. 2005). Both young and adult White-crowned Sparrows were captured on their breeding area in the Northwest Territories, Canada, towards the end of the breeding season and shortly before they would normally begin fall migration (15 July to 10 August). One group of sparrows (15 adults and 15 juveniles) were transported (on an icebreaker) to unfamiliar sites along a northeasterly route to the magnetic north pole (79.0° N, 105.1° W) and then further southeast (Figure 23). A control group (5 adults and 39 juveniles) was transported a short distance west of the capture site. Using Emlen funnels (Figure 6 above), the directional orientation of both groups of sparrows was determined, with the experimental group tested at nine different locations (including their breeding area; site 1 in the Figure 23B). Sparrows in the control group generally oriented to the southeast (Figure 24), the general direction of their presumed wintering area.
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The use of the sun for orientation by birds was first demonstrated by Kramer (1950). He used a test apparatus where mirrors altered the apparent position of the sun and found that European Starlings altered their directional preference accordingly. The avian sun compass is based on the sun’s azimuth (the point on the horizon directly below the sun), with the sun’s altitude being irrelevant. Because the sun moves across the sky during the day, the use of a sun compass requires an internal clock because it is the sun’s azimuth at a particular time of day that provides directional information.
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Figure 2. Example of the difference between true navigation and vector navigation by a hypothetical songbird migrant in Europe
with a fall migration route from Norway to Spain (thin solid arrow). In this hypothetical experiment, migrants en route are captured
and displaced (dashed arrow) from their traditional migratory path to a distant, unfamiliar site in eastern Europe and then released.
True navigation (the thick solid arrow to Spain) would require the ability to determine the ‘new’ location and adjust the migratory
route to compensate for the displacement and still end up at the over-wintering site in Spain. Because vector navigation (the thick solid
arrow to Italy) is only the ability to continue moving in a particularly direction for a certain distance or time, there would be no
compensating to take into account the ‘new’ location. So, migration would continue along the some orientation and for the same distance,
but the hypothetical migrant would end up in Italy rather than Spain (From: Bingman and Cheng 2005).
Official journal of the Human Behavior and Evolution Society.
Omnidirectional and nondirectional are very similar, but they emphasize different things. If I say something is omnidirectional, I'm emphasizing the fact that all directions are equal. For example, I could be in front of, behind, to the right or left, on top of, or underneath an omnidirectional microphone and it could pick up sound just as equally from any of those directions. On the other hand, nondirectional carries a connotation that direction isn't that important—a sidewalk is nondirectional because I can walk either way without coming upon restriction, but there's no reason to emphasize the fact that I could walk any which way I wanted to.1