Birds have inbuilt GPS (Global Positioning System)

                                                                                                                               Professor R. S. Sengar and Dr. D. K. Singh

Birds don't use human GPS; they have an amazing biological navigation system, an "inbuilt GPS" using Earth's magnetic field (magnetoreception), the sun (solar compass), stars (stellar compass), and even smells, processed by special brain areas like Cluster N and proteins like cryptochrome in their eyes, allowing them to sense direction and even magnetic intensity for a "map" to find their way over vast distances, switching these senses on/off as needed.

How their internal GPS works:

(1) Magnetic Compass & Map (Magnetoreception):

(i) Mechanism: Birds sense the Earth's magnetic field, using its direction as a compass and intensity for a rough map.

(ii) Eyes (Compass): A protein called cryptochrome (Cry4) in their eyes reacts to magnetic fields (especially with blue light), giving them a visual compass.

(iii) Beak (Map): Iron-based receptors (magnetite) in their beaks might detect magnetic intensity, acting like a position-finding tool.

(iv) Brain: A region called Cluster N processes this magnetic data, allowing them to "turn it on/off".

(2) Solar Compass: They use the sun's position, even detecting polarized light patterns on cloudy days, to know direction and time.

(3) Stellar Compass: Nocturnal migrants learn star patterns and the Earth's rotation to orient, using fixed points like the North Star.

(4) Olfactory Map (Smell): Homing pigeons use familiar smells in their environment to find their way home, a sense we often overlook.

Combining the Cues:

Birds integrate these different senses (magnetic, solar, stellar, scent, visual landmarks) to create a highly effective, redundant navigation system, allowing them to pinpoint locations and follow complex migratory routes.

In essence, birds don't have a tiny satellite device, but rather a sophisticated biological system that processes multiple environmental cues, especially the Earth's magnetic field, to create a comprehensive "internal GPS" for incredible migration feats.

पक्षियों का प्राकृतिक GPS

पक्षियों में प्राकृतिक GPS उनकी मस्तिष्क की क्षमता और शारीरिक संवेदनशीलता से आता है, जहाँ वे पृथ्वी के चुंबकीय क्षेत्र, सूर्य, तारों और गंध का उपयोग करके दिशा तय करते हैं, इसे 'स्विच की तरह' चालू-बंद कर सकते हैं; जबकि वैज्ञानिक छोटे जीपीएस टैग या जियोलोकेटर का उपयोग करके उनके प्रवास पैटर्न और व्यवहार का अध्ययन करते हैं, जिससे संरक्षण में मदद मिलती है।

The protein in bird eyes associated with a "chrome" in its name is cryptochrome (specifically Cry1a and Cry4 isoforms), which is believed to be the primary light-sensitive receptor enabling birds to sense the Earth's magnetic field for navigation.

Mechanism in the Avian Eye

The proposed mechanism, known as the radical-pair mechanism, works as follows:

Light Activation: When blue light enters the bird's eye, it is absorbed by a flavin adenine dinucleotide (FAD) chromophore within the cryptochrome protein, exciting an electron.

Radical Pair Formation: The excited electron is transferred to a nearby tryptophan amino acid, creating a pair of molecules with single, unpaired electrons (a "radical pair").

Magnetic Sensitivity: The spins of these two electrons are quantum entangled. The Earth's magnetic field influences the balance between their possible spin states (singlet and triplet).

Signal Transduction: This magnetic field-dependent change in the radical pair's spin state affects the duration and yield of the subsequent chemical reactions. This ultimately creates a visual pattern or "magnetic filter" across the bird's visual field, allowing the bird to "see" the magnetic field lines and use them as a compass.

Location: These cryptochrome proteins are primarily located in the outer segments of the ultraviolet (UV) or violet-sensitive cones in the retina, positioning them optimally for this light-dependent magnetic sensing.

Key Cryptochrome Isoforms:

Cry1a: Was initially considered the most likely candidate magnetoreceptor due to its location in the UV cones, but recent findings suggest it may not be inherently photosensitive enough to be the primary receptor.

Cry4: Current evidence strongly points to cryptochrome 4 (specifically Cry4a in migratory species) as the pivotal protein in this compass. Its expression levels are constant throughout the day (unlike other cryptochromes involved in the circadian clock) and are significantly upregulated during migratory seasons, suggesting a dedicated role in navigation.

पक्षियों का प्राकृतिक GPS

(1) चुंबकीय संवेदन: पक्षियों की चोंच में मैग्नेटाइट (एक चुंबकीय चट्टान) और आँखों में विशेष कोशिकाएँ होती हैं, जो उन्हें पृथ्वी के चुंबकीय क्षेत्र को महसूस करने और दिशा जानने में मदद करती हैं।

(2) आंतरिक स्विच: उनके दिमाग का एक खास हिस्सा (क्लस्टर एन) चुंबकीय जानकारी को संसाधित करता है, जिसे वे आवश्यकतानुसार 'चालू' या 'बंद' कर सकते हैं।

(3) दृश्य संकेत: वे सूर्य और तारों की स्थिति देखकर भी दिशा का पता लगाते हैं, खासकर रात के प्रवास के दौरान।

(4) गंध की भावना: गंध भी उन्हें अपने रास्ते खोजने में महत्वपूर्ण भूमिका निभाती है, जो अक्सर हमें महसूस नहीं होती।

लेखकः डॉ0 आर. एस. सेंगर, निदेशक ट्रेनिंग और प्लेसमेंट, सरदार वल्लभभाई पटेल कृषि एवं प्रौद्योगिकी विश्वविद्यालय मेरठ।