Natures wonders: migration factors theory (Introduction)

by David Turell , Thursday, October 06, 2022, 18:11 (568 days ago) @ David Turell

A complex study of migration types:

https://ecoevocommunity.nature.com/posts/predicting-how-inexperienced-migratory-animals...

"///we know that many migrants cross continents, timing their departures to reach more favourable climes, and typically dividing their journeys into multiple daily or nightly flight-steps. Thanks to advanced tracking and computational methods, we can now accurately predict and monitor the density of migration across species and geographical ranges, including of agriculturally-important insects.

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"Many migratory bird species have access to a sun compass, star compass, or geomagnetic compass. We are getting ever closer to understanding the sensory mechanisms underlying magnetoreception. Experienced (adult) bird migrants, similarly to their oceanic counterparts, can assimilate map-like information to reach previously-known migratory goals. Contrastingly, many naïve migrants are thought to complete the bulk (long-distance phase) of their inaugural migrations based on inherited migratory compass headings, often termed clock-and-compass migration. The resultant compass courses vary with choice of primary compass cue (e.g., sun, stars or geomagnetic), and according to how headings are derived from the primary cue. Star compass and geomagnetic compass courses maintain constant headings relative to their North-South axes, whereas magnetoclinic and sun compass headings typically shift increasingly Southward, particularly for the time-compensated sun compass, where migrants account for the sun’s diurnal arc.

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"While it is well known that juvenile bird migrants are particularly prone to being displaced by wind, some displacement experiments indicate that they can partially self-correct for such displacements. But how might that be possible without a map sense? It turns out, that partial correctional shifts would be feasible if migrants’ directional responses to the stars or sun is time-compensated to account for their rotation. The star compass of migrating birds does not seem to work in this way, but the sun compass has not been analogously tested.

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"As a result, sun compass courses performed best – and most closely resembled – the daytime migration routes of the monarch butterfly (Danaus plexippus) and the longest nocturnal routes such as willow warblers (Phylloscopus trochilus yakutensis) migrating 13,000 km from East Siberia to East Africa. Constant-heading star or geomagnetic courses (loxodromes) performed best across short to medium distances, like for the common rosefinch (Carpodacus erythrinus) migrating from South-East Europe to India. The gradually-shifting magnetoclinic compass was found to be over-sensitive to imprecision and untenable for longer-distance and East-West oriented migration routes. Based on simulations of the nine modelled species for biologically-relevant error scenarios (0-60° expected error among flight-steps), we could predict > 97% of variability in compass course performance among the species tested based on three factors – number of flight-steps, a spherical geometry factor and (daily or nightly) flight-step distance.

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"Our study supports twilight sun-compass orientation being key to many high-latitude and long-distance inaugural migrations. However, this does not exclude geomagnetic compass use by long-distance migrants, not least among night-migratory species (given that stars are often obscured). To test the possibility of time-compensated sun compass use and self-correction, we recommend controlling for inner clock updates in experiments testing orientation among real or virtually displaced migrants. Our modelling framework can be extended to assess how inherited migratory orientation can facilitate exploitation of favourable migratory habitats. For example, in the simplest case, our models could include migratory detours, with a second migratory heading triggered by geomagnetic or other environmental factors. While the jury is still out regarding the ubiquity of inherited compass headings by naïve migrants (e.g., as opposed to gradient-based navigation), our study suggests that clock-and-compass migration can provide a basis to reach restricted destinations, illustrating how simple rules can potentially explain complicated patterns observed in nature."

Comment: this may explain the migratory mechanisms but does not explain the initial steps. A bird or an insect had to suddenly decide to cross an ocean looking for a warmer climate. How does a concept like that appear in a tiny brain? To go wherever and back? God has to be involved.