Secrets of Endurance: How Birds “Eat” Their Organs to Survive

Longtailed Shorefish: A Master of Metabolic Plasticity

The best example of this phenomenon is the long-tailed shorebird. These birds undertake some of the longest migratory flights in the world, covering up to 15,000 kilometers each way between their Arctic breeding grounds and southern wintering grounds. Such a journey requires not only the accumulation of significant fat reserves (fuel) but also maximum weight savings. Physiologists have discovered that immediately before and during continuous migrations, shorebirds reduce the volume of their digestive system, specifically their stomach muscles, liver, and kidneys.

Not “eating” but controlled regression: The science of the phenomenon

The term “eating” internal organs is a metaphor. In reality, what’s happening is a process called controlled organ atrophy or regression. This isn’t self-cannibalism, but a highly precise biological mechanism. At the cellular level, this process is often associated with autophagy-the “self-consumption” of cellular components, where the cell disassembles and recycles its old or unneeded parts to obtain energy and building blocks. However, at the level of the entire organ, we’re talking about a reduction in its mass.

• Energy conservation: Reducing the mass of internal organs not actively used during flight reduces the bird’s overall metabolic cost.

• Resource redistribution: Freed proteins and amino acids from regressing organs are used to fuel the extremely active flight muscles that require constant support.

• Weight reduction: Every gram counts on a long-distance flight. Reducing the stomach and intestines by 25-30% significantly reduces the bird’s weight, increasing aerodynamic efficiency and migration range.

Two scenarios of physiological changes in birds

Physiological changes in birds occur in accordance with the current needs of the body, which are usually divided into two opposite but interrelated states: the “flight state” and the “feeding state”.

1. “Flight State”: Ease and Efficiency

Before beginning its extensive migration, the bird accumulates fat, which can account for up to 50% of its total mass. After takeoff, the digestive system, which is not yet needed since the bird is not eating, shrinks. This allows the shorebird to survive for weeks without food. Smaller organs require less blood and oxygen, allowing the body to direct these resources to the muscles that power flight.

2. “Feeding State”: Rapid Recovery

After successfully completing a flight and landing at a stopover or wintering site, a bird must replenish its energy reserves as quickly as possible. Its digestive tract regenerates at an astonishing rate, sometimes within 4-7 days. This allows it to efficiently process large volumes of food, replenishing lost protein and accumulating new fat for the next leg of the journey. This is a striking example of avian metabolic plasticity.

Energy Benefit: The Economics of Long-Distance Migration

The costs of flight are exponential: the heavier the object, the more energy is required to lift it and keep it aloft. Scientists have calculated that by reducing the size of their internal organs, the long-tailed bat saves approximately 3-5% of its energy per hour of flight. Considering that these birds can fly nonstop for 6-8 days, this savings amounts to hundreds of dollars if we measured the cost of energy in human equivalents. This small change in organ size is critical for covering thousands of kilometers.

This energy-saving principle in birds is so effective that similar, albeit less pronounced, changes are observed in other species. For example, some reptiles, such as snakes, significantly increase the size of their digestive system after a large meal, which then decreases once the food is digested. This highlights the universality of this evolutionary strategy for survival through adaptive physiology.

Expanding Knowledge: New Ornithological Discoveries

Modern ornithological discoveries using miniature geolocators and radio transmitters allow scientists to more accurately track migration routes and their impact on the body. Research shows that birds’ ability to shrink organs is not limited to the digestive tract. In some cases, temporary changes in the size and structure of leg muscles are observed: they can atrophy due to inactivity, while the wing muscles become very powerful.

The ability of Calidris canutus and other migrants to undergo such radical internal physiological changes is a reminder that biological plasticity has far broader limits than we previously imagined. This isn’t just a unique fact about the amazing adaptations of birds, but a fundamental principle of survival in extreme conditions: to survive a long journey, one must sacrifice less essential parts of oneself. These evolutionary survival strategies are crucial in the face of climate and habitat change, when the survival demands of migratory birds increase.

Birds reduce their internal organs, demonstrating biological perfection, where metabolism and morphology are adapted to the requirements of avian flight physiology.