Ravens that look identically black absorb heat at measurably different rates

Research by the Natural History Museum of Los Angeles County, UCLA, Indiana University, and Cal State University Dominguez Hills. Published in Integrative Organismal Biology, 2026.

Two black ravens, two thermal profiles

To human eyes, a common raven is black. Every common raven is black. But when researchers at the Natural History Museum of Los Angeles County and UCLA measured how raven feathers interact with infrared radiation, the sameness disappeared. Subspecies from different geographic regions absorbed near-infrared radiation - the heat from sunlight - at significantly different rates. Birds that looked identical to every observer who has ever watched them were, thermally speaking, distinct.

This finding emerged from the first study ever to measure mid-infrared reflectance in bird feathers - the portion of the electromagnetic spectrum that governs how much heat a bird radiates away from its body. Published in Integrative Organismal Biology, the research represents a collaboration between material engineers at UCLA, ornithologists at the Natural History Museum of Los Angeles County, biologists at Indiana University and Cal State University Dominguez Hills, and museum collections holding specimens from across North America.

The spectrum birds cannot see either

Color, as biologists typically study it in birds, covers two ranges of the electromagnetic spectrum: the visible wavelengths that humans perceive and the ultraviolet wavelengths that birds can see but we cannot. Both play well-documented roles in mate selection, camouflage, and species recognition. But the spectrum extends in the other direction too - into infrared wavelengths that neither humans nor birds can see.

Infrared splits into two functionally different regions for living organisms. Near-infrared corresponds to heat absorption - how much solar thermal energy a feather soaks up. Mid-infrared corresponds to heat emission - how much thermal energy a bird's body radiates outward. The physics here is governed by the same principles that engineers use when designing radiative cooling materials: surfaces that efficiently emit mid-infrared radiation shed heat into the cold vacuum of space, even in warm environments.

This is not a metaphor. Any object warmer than its surroundings radiates heat, and if it has a clear view of the sky, that radiation ultimately escapes into space, where the effective temperature is just a few degrees above absolute zero. Engineers working on passive cooling technologies have exploited this physics to create surfaces that stay cool without electricity. The question this study asks is whether bird feathers have evolved to do the same thing.

Five species, three habitats, one surprise after another

The research team examined museum specimens of five North American bird species: the great horned owl, Northern bobwhite, Steller's jay, song sparrow, and common raven. For each species, they selected specimens from geographically diverse areas representing different regional subspecies. They measured reflectance across four spectral ranges: visible, ultraviolet, near-infrared, and mid-infrared.

The standout finding involved the Northern bobwhite. Among the five species, bobwhites showed the most variation in mid-infrared emittance - the rate at which their feathers radiate heat. The researchers suggest this tracks with habitat. Bobwhites prefer open prairies and grasslands where they are constantly exposed to the sky. A bird sitting in a treeless field has an unobstructed radiative pathway to space. Under those conditions, mid-infrared properties of feathers could have a meaningful effect on thermoregulation.

Forest-dwelling species, by contrast, spend much of their time under canopy that blocks the sky view. For them, mid-infrared emittance may be less important because the radiative pathway to space is interrupted by leaves and branches that absorb and re-emit thermal radiation at ambient temperatures. The selective pressure to evolve feathers optimized for radiative cooling would be weaker.

The raven paradox: same color, different thermal behavior

The raven results add another layer. When the researchers divided common raven specimens by subspecies, they found statistically significant differences in near-infrared absorptance - the amount of solar heat the feathers take in. These are birds that appear uniformly black across their entire range. Whatever structural or chemical differences exist in their feathers are invisible to the eye and to standard ornithological analysis, but they produce measurable thermal consequences.

This suggests that feather evolution operates on dimensions that conventional color-based studies have missed entirely. Two populations of ravens might face different thermal challenges depending on their latitude, altitude, or habitat openness, and their feathers may have diverged in response - but only in the infrared, where no one was looking.

Engineering meets ornithology in the spectrometer

The study required instruments that biology departments do not typically have. Measuring mid-infrared reflectance demands specialized spectrometers designed for materials science research. UCLA's engineering department provided the equipment and technical expertise. As Dr. Allison Shultz, Curator of Ornithology at the Natural History Museum, noted, getting access to such instruments is difficult - and many engineers are understandably reluctant to put biological specimens into precision optical equipment.

This interdisciplinary barrier has likely contributed to the complete absence of mid-infrared data in ornithological research until now. Biologists lacked the instruments; engineers lacked the biological questions. The collaboration that produced this study bridged that gap, but it required building trust across disciplinary cultures.

Small sample, large implications, many unknowns

The study examined five species - a tiny fraction of the roughly 10,000 known bird species. Whether the patterns observed here generalize across the class Aves is entirely unknown. The sample sizes within each species were also small, limited by museum specimen availability and the labor-intensive measurement process. Statistical significance with small samples should be interpreted cautiously.

The measurements were performed on museum specimens - preserved feathers that may not perfectly replicate the infrared properties of feathers on living birds. Preservation techniques, age of specimens, and desiccation could all alter reflectance properties. The researchers acknowledge this but argue that museum specimens are currently the only practical way to access geographically diverse material.

The connection between mid-infrared feather properties and actual thermoregulatory benefit in living birds remains theoretical. Demonstrating that feathers can emit mid-infrared radiation is different from demonstrating that this emission meaningfully affects a bird's body temperature in the field. Wind, humidity, posture, feather fluffing, and behavioral thermoregulation (seeking shade, panting) all complicate the picture.

The broader promise of this work cuts two ways. For conservation, understanding how birds manage heat loads could help predict which populations are most vulnerable to rising temperatures - especially open-habitat species like bobwhites that may already be operating near their thermal limits. For engineering, bird feathers represent millions of years of evolutionary optimization for multi-functional surfaces that manage light, heat, water, and structural demands simultaneously. Both fields stand to gain from a spectral dimension that, until this study, no one had measured.