Physiological-theoretical consideration of the effects of rising temperatures and increased hydrogen and water vapor concentrations in the atmosphere on the flight physiology of birds

1. Introduction

Global temperature increases change the chemical and physical composition of the atmosphere. In particular, the rising water vapor content and the secondary increase in concentrations of light gases such as molecular hydrogen (H₂) influence the density, humidity content, and thermal dynamics of the air layers. These changes have a direct impact on flying animal species, especially birds, whose physiological performance and aerodynamic efficiency depend heavily on air density and oxygen partial pressure.

2. Atmospheric Changes

As global warming increases, the evaporation rate increases. For every Kelvin increase in temperature, the maximum water vapor absorption of the atmosphere increases by about 7% (Clausius-Clapeyron relationship).
The increased water vapor content lowers the average air density, since H₂O molecules (M = 18 g/mol) displace lighter components such as N₂ or O₂ (M = 28-32 g/mol).
In addition, in warmer zones, geochemical and biological processes can produce increased amounts of hydrogen, which also contributes to lowering the air density.

3. Physiological Effects on Birds

3.1. Reduced lift efficiency
Decreasing air density results in lower lift force for the same wing area. Birds must avoid higher wingbeat frequencies or higher flight altitudes to compensate for energy losses. This leads to reduced flight range and increased energy consumption per distance.

3.2. Altered oxygen partial pressure
With increasing temperature and humidity, the relative oxygen content per unit volume of air decreases. This impedes alveolar oxygen supply, especially in species whose lungs are already physiologically stressed by thin high-altitude air (e.g., migratory birds).

3.3. Respiratory Physiological Stress
High humidity reduces diffusion efficiency in the parabronchi of the avian lungs. Oversaturated air also promotes condensation in the respiratory tract, which increases the risk of inflammation. A rapid rise in temperature overwhelms adaptive regulatory mechanisms such as mucosal adaptation, capillary constriction, or changes in hemoglobin affinity.

4. Inflammatory Tendency and Adaptation Limits

Increased humidity and thermal stress lead to microedema, oxidative stress, and local hypoxia. Insufficient genetic adaptation leads to chronic irritation and inflammation of the respiratory epithelium.
In humans, similar mechanisms show an increased prevalence of respiratory diseases in hot, humid climates. Applied to birds, this means increasing morbidity, especially in species with thin-walled air sacs and high metabolic rates.

5. Summary

Rising temperatures and increasing water vapor content change flight physiology through:

• Reduced air density → lower lift

• Reduced oxygen availability → higher work of breathing

• Increased humidity → inflammatory respiratory stress

• Insufficient adaptation rate → long-term population declines

6. Conclusion

The combination of rapid global warming and increasing atmospheric hydrogen/water vapor content is placing physiological stress on avian species. Species with narrow thermophysiological tolerance windows and limited altitude adaptation will be affected first. Too slow evolution or migration, combined with deteriorating flight economics, can lead to a long-term reduction in global bird diversity.

Appendix A: Vaccinations to improve oxygen supply in humans and risks of rapid adaptation in birds

A.1. Hypothetical vaccination strategies in humans

The goal would be a biochemical modulation of oxygen uptake and utilization in order to be better adapted to humid, hot, and oxygen-poor atmospheres. Possible approaches:

1. Hemoglobin affinity modulation:
   Gene-based or protein-modulating vaccines could alter the oxygen binding curve of hemoglobin (e.g., shiftg to the left). Result: more efficient uptake at low O₂ partial pressure, but risk of poorer O₂ delivery in the tissue.

2. Erythropoietin activation (EPO):
   Vaccine-based stimulation of erythropoiesis increases the number of red blood cells. In the short term, this increases O₂ transport capacity. Risks: thrombosis, hyperviscosity, cardiovascular overload.

3. Mitochondrial adaptation vaccinations:
   Experimentally conceivable: activation of HIF-1α regulatory pathways to increase mitochondrial efficiency. This improves hypoxia tolerance, but could lead to uncontrolled cell metabolism or tumor induction in the long term.

A.2. Risks of Rapid Adaptation in Birds

Small animal species such as songbirds or bats have extremely short generation times and high mutation rates. This theoretically allows for rapid physiological adaptation to new atmospheric conditions. The following are problematic:

1. Overadaptation to humid air:
   An excessive shift in respiratory physiology to high humidity can lead to dehydration and lung damage during a sudden dry period.

2. Unstable energy economy:
   Changes in hemoglobin or air sac structures can offer short-term advantages, but destabilize energy balance in the long term (e.g., excessive resting metabolic rate).

3. Incorrect regulatory signals:
   Small organisms react strongly to temperature fluctuations. Accelerated genetic adaptation can override regulatory mechanisms, leading to metabolic instability, tissue damage, or extinction of local populations.

A.3. Summary

Conclusion:
While artificial vaccination or genetic adaptations in humans could be controlled, the rapid natural adaptation of small birds leads to unpredictable physiological overrides. A balance between speed of adaptation and environmental change remains crucial for long-term ecological stability.

Cute little songbird: