Natures wonders: more bird migration discoveries (Introduction)

by David Turell , Tuesday, March 15, 2022, 22:10 (982 days ago) @ David Turell

At the quantum level detecting the magnetic field plus more:

https://www.scientificamerican.com/article/how-migrating-birds-use-quantum-effects-to-n...

"Our experimental evidence suggests something extraordinary: a bird’s compass relies on subtle, fundamentally quantum effects in short-lived molecular fragments, known as radical pairs, formed photochemically in its eyes. That is, the creatures appear to be able to “see” Earth’s magnetic field lines and use that information to chart a course between their breeding and wintering grounds.

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"Migratory birds’ navigational input comes from several senses—mainly sight, smell and magnetoreception. By observing the apparent nighttime rotation of the stars around the North Star, the birds learn to locate north before they embark on their first migration, and an internal 24-hour clock allows them to calibrate their sun compass. Characteristic smells can help birds recognize places they have visited before. Scientists know a great deal about the detailed biophysical mechanisms of the birds’ senses of sight and smell. But the inner workings of their magnetic compass have proved harder to understand.

"First, observations of caged birds exposed to carefully controlled magnetic fields show that their compass does not behave like the magnetized needle in a ship’s compass. A bird detects the axis of the magnetic field and the angle it makes with Earth’s surface, the so-called inclination compass...even though songbirds fly at night under the dim light of the stars, their magnetic compass is light-dependent, hinting at a link between vision and magnetic sensing.

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"When two radicals are created simultaneously by a chemical reaction (this is what we mean by radical pair), the two unpaired electrons, one in each radical, can have either antiparallel spins (⇅) or parallel spins (↑↑), arrangements known as singlet and triplet states, respectively.

"Immediately after a radical pair is created in a singlet state, internal magnetic fields cause the two electronic spins to undergo a complex quantum “waltz” in which singlet turns into triplet and triplet turns back into singlet millions of times per second for periods of up to a few microseconds. Crucially, under the right conditions, this dance can be influenced by external magnetic fields. Schulten suggested that this subtle quantum effect could form the basis of a magnetic compass sense that might respond to environmental stimuli a million times weaker than would normally be thought possible. Research that we and others have carried out in recent years has generated fresh support for this hypothesis.

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"From experiments such as these, it is clear that the magnetic compass sensors are located in the birds’ retinas.

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"Schulten’s hypothesis also predicts that there must be sensory molecules (magnetoreceptors) in the retina in which magnetically sensitive radical pairs can be created using the wavelengths birds need for their compass to operate, which another line of research had identified as light centered in the blue region of the spectrum. In 2000 he suggested that the necessary photochemistry could take place in a then recently discovered protein called cryptochrome.

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"We chose cryptochrome-4a (Cry4a), partly because it binds FAD much more strongly than do some of its siblings, and if there is no FAD in the protein, there will be no radical pairs and no magnetic sensitivity.

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"One more cryptochrome finding deserves mention here. We compared robin Cry4a with the extremely similar Cry4a proteins from two nonmigratory birds, pigeons and chickens. The robin protein had the largest magnetic sensitivity, hinting that evolution might have optimized robin Cry4a for navigation.

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"Many questions about the birds’ magnetic compass remain, including whether the magnetic field effects on robin Cry4a observed in vitro also exist in vivo. We also want to see whether migratory birds with genetically suppressed Cry4a production are prevented from orienting using their magnetic compass. If we can prove that a radical-pair mechanism is behind the magnetic sense in vivo, then we will have shown that a biological sensory system can respond to stimuli several million times weaker than previously thought possible. This insight would enhance our understanding of biological sensing and provide new ideas for artificial sensors."

Comment: to put this together from a design standpoint, I cannot believe these birds figured out how and where to migrate naturally. It is logical to want a warm spot in winter, but birds don't think at that level. And they don't follow maps. They migrate by instructions in their brains, as we know according to the article. The guidance mechanism using the magnetic field is highly complex in design. It could not have developed stepwise or the birds would fly to their deaths. This is irreducible complex and therefore fully designed all at once.