Wednesday, March 01, 2023

Woodcocks have the brightest white feathers ever measured

IMPERIAL COLLEGE LONDON

Woodcock in flight — IMAGE: WOODCOCK IN FLIGHT view more
CREDIT: JEAN-LOU ZIMMERMANN

The mainly brown woodcock uses its bright white tail feathers to communicate in semi-darkness, reflecting 30% more light than any other known bird.

These surprise findings, by a team led by an Imperial College London scientist, suggest there is much to learn about how birds that are most active at night or at dawn and dusk communicate.

Birds that are most active during the day often have colourful plumages, which they use to communicate information with each other. Birds that are most active at dawn and dusk or at night (‘crepuscular’), such as nightjars and woodcocks, tend to have less showy plumage, as while sleeping during the day they need to be camouflaged to avoid predators.

Rather than using showy plumages, it was thought that birds active during low light conditions instead used sounds or chemicals to communicate. However, many have bright white patches, which could be used in environments with very little natural light for communication if these are reflective enough.

The Eurasian woodcock, Scolopax rusticola, is primarily mottled brown, but has patches of white feathers on the underside of its tail. This means it only shows these patches when raising its tail or during courtship display flights.

However, as they are crepuscular, and so most active during low light, these white patches need to reflect as much light as possible to attract attention. To investigate how they might do this, the team studied the white tail feathers of Eurasian woodcock specimens from a collection in Switzerland.

They used specialised microscopy to image feather structure, spectrophotometry to measure the light reflectance, and models to characterise how photons of light interact with structures inside the feather. They were surprised to find the reflectance measurements showed the feathers reflected up to 55% of light – 30% more light than any other measured feather. The results are published today in Royal Society Interface.

Lead researcher Jamie Dunning, from the Department of Life Sciences (Silwood Park) at Imperial, said: “Bird enthusiasts have long known that woodcocks have these intense white patches, but just how white they are and how they function has remained a mystery. From an ecological perspective the intensity of the reflectance from these feathers makes sense – they need to hoover up all the light available in a very dimly lit environment, under the woodland canopy at night.”

Individual feathers are made of a central stem with protrusions called rami forming the bulk of the structure. The rami are held together by round Velcro-like ‘barbules’.

The team found that in the woodcock’s white tail feathers the rami are thickened and flattened, which both increases the surface area for light to bounce off, while also making it less likely light will pass between the feather barbs without being reflected.

There are two main ways surfaces are reflective. ‘Specular’ reflection is when light bounces off a smooth surface, like a mirror. ‘Diffuse’ reflectance scatters light rays in different directions. The thickened rami were found to be made up of a network of keratin nanofibers and scattered air pockets. This creates lots of interfaces that can scatter light, increasing the feathers’ diffuse reflectance.

Analysis of the feathers showed one final trick up the woodcock’s sleeve: the rami and barbules in the white woodcock feathers are arranged to create a venetian-blind-like effect that further enhances the surface area, by sitting at the optimum angle for light reflectance.

Principal Curator of Birds at the Natural History Museum Dr Alex Bond said: “This research is a brilliant combination of using museum specimens and cutting-edge tools to try and understand this phenomenon. Being able to see whether closely related species or species with similar ecology also had these incredibly white feathers was a key bit of figuring out the story.”

Optical microscopy image of the white tail region

SEM image fo the white feather tips

CREDIT

Liliana D’Alba

JOURNAL

Journal of The Royal Society Interface

DOI

10.1098/rsif.2022.0920

ARTICLE TITLE

How woodcocks produce the most brilliant white plumage patches among the birds,

ARTICLE PUBLICATION DATE

1-Mar-2023

Flamingos form cliques with like-minded pals

Peer-Reviewed Publication

UNIVERSITY OF EXETER

An aggressive Caribbean flamingo — IMAGE: AN AGGRESSIVE CARIBBEAN FLAMINGO DISPLACES TWO OTHER BIRDS view more
CREDIT: PAUL ROSE

Flamingos form cliques of like-minded individuals within their flocks, new research shows.

Scientists analysed the personalities and social behaviour of Caribbean and Chilean flamingos.

Birds of both species tended to spend time with others whose personality was similar to their own.

The study, by the University of Exeter and the Wildfowl & Wetlands Trust (WWT), reveals the complex nature of flamingo societies and could help in the management of captive flocks.

“Our previous research has shown that individual flamingos have particular ‘friends’ within the flock,” said Dr Paul Rose, from WWT and Exeter’s Centre for Research in Animal Behaviour.

“In this study, we wanted to find out whether individual character traits explain why these friendships form.

“The answer is yes – birds of a feather flock together.

“For example, bolder birds had stronger, more consistent ties with other bold birds, while submissive birds tended to spend their time with fellow submissive flamingos.”

The “personality” of flamingos was assessed by measuring consistent individual differences, such as aggressiveness and willingness to explore.

“Like humans, flamingos appear to carve out different roles in society based on their personality,” said Fionnuala McCully, now at the University of Liverpool, who collected data for the study during an MSc Animal Behaviour course at the University of Exeter.

“For example, we observed groups of aggressive birds which attempt to dominate rivals and tend to get in more fights.

“Meanwhile, the role of submissive birds may be more complex than simply being lower down the pecking order – they may be using a different approach to get what they need.

“The various different personality groups provide social help to their members, for example by supporting each other in the many squabbles that take place in flamingo flocks.”

In the Caribbean flamingos, birds of a certain personality type had a particular role within the group overall, but this was not found in the Chilean flock. The reasons for this are unclear, and it’s possible that a larger study of wild birds would find such a pattern.

Dr Rose said: “Our findings need further investigation, both to help us understand the evolution of social behaviour and to improve the welfare of zoo animals.

“But it is clear from this research that a flamingo's social life is much more complicated than we first realised.”

The findings are based on observations of captive flamingos at WWT Slimbridge.

The paper, published in the journal Scientific Reports, is entitled: “Individual personality predicts social network assemblages in a colonial bird.”

JOURNAL

Scientific Reports

METHOD OF RESEARCH

Observational study

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

“Individual personality predicts social network assemblages in a colonial bird.”

ARTICLE PUBLICATION DATE

1-Mar-2023

Pink + pink = gold: hybrid hummingbird’s feathers don’t match its parents

Peer-Reviewed Publication

FIELD MUSEUM

Hybrid hummingbird with parent species — IMAGE: THE GOLD-THROATED HYBRID, CENTER, WITH ITS PARENT SPECIES H. BRANICKII (LEFT) AND H. GULARIS (RIGHT), IN THE FIELD MUSEUM’S COLLECTIONS. view more
CREDIT: KATE GOLEMBIEWSKI, FIELD MUSEUM

The Pink-throated Brilliant hummingbird, Heliodoxa gularis, has, unsurprisingly, a brilliant pink throat. So does its cousin, the Rufous-webbed Brilliant hummingbird, Heliodoxa branickii. When scientists found a Heliodoxa hummingbird with a glittering gold throat, they thought they might have found a new species. DNA revealed a different story: the gold-throated bird was a never-before-documented hybrid of the two pink-throated species.

John Bates, the senior author of a new study in the journal Royal Society Open Science reporting on the hybrid, first encountered the unusual bird while doing fieldwork in Peru’s Cordillera Azul National Park, which protects an outer ridge on the eastern slopes of Andes mountains. Since the area is isolated, it would make sense for a genetically distinct population to emerge there. “I looked at the bird and said to myself, ‘This thing doesn’t look like anything else.’ My first thought was, it was a new species,” says Bates, a curator of birds at Chicago’s Field Museum.

When Bates and colleagues gathered more data about the specimen in the Field Museum’s Pritzker DNA Lab, however, the results surprised everyone. “We thought it would be genetically distinct, but it matched Heliodoxa branickii in some markers, one of the pink-throated hummingbirds from that general area of Peru,” says Bates. If it was H. branickii, it didn’t make sense for the bird to have gold throat feathers; in the hummingbird family, it’s rare for members of the same species to have dramatically different throat colors.

The initial run of DNA sequencing looked at mitochondrial DNA, a type of genetic material that only gets passed down through the mother. That mitochondrial DNA gave a clear result matching H. branickii; the researchers then analyzed the bird’s nuclear DNA, which includes contributions from both parents. This time, the DNA showed similarities to both H. branickii and its cousin, H. gularis. It wasn’t half branickii and half gularis, though-- one of its ancestors must have been half-and-half, and then later generations mated with more branickii birds.

The question remained how two pink-throated bird species could produce a non-pink-throated hybrid. The study’s first author, Field Museum senior research scientist Chad Eliason, says the answer lies in the complex ways in which iridescent feather colors are determined.

“It’s a little like cooking: if you mix salt and water, you kind of know what you're gonna get, but mixing two complex recipes together might give more unpredictable results,” says Eliason. “This hybrid is a mix of two complex recipes for a feather from its two parent species.”

Feathers get their base color from pigment, like melanin (black) and carotidnoids (red and yellow). But the structure of feathers’ cells and the way light bounces off them can also produce something called structural color. Color-shifting iridescence is a result of structural color.

The researchers used an electron microscope to examine the throat feather structure on a subcellular level, and an analytical technique called spectroscopy to measure how light bounces off the feathers to produce different colors. They found subtle differences in the origin of the parents’ colors, which explain why their hybrid offspring produced a totally different color.

“There's more than one way to make magenta with iridescence,” says Eliason. “The parent species each have their own way of making magenta, which is, I think, why you can have this nonlinear or surprising outcome when you mix together those two recipes for producing a feather color.”

While this study helps explain the strange coloration of one unusual bird, the researchers say that it opens the door to more questions about hybridization.

Separate species are generally defined as lineages that are genetically distinct and don’t interbreed with each other; hybrids break that rule. Sometimes hybrids are weird one-offs or are sterile, like mules; in other cases, hybrids can form new species. It’s not clear how common hummingbird hybrids like the one in this study are, but the researchers speculate that hybrids like this one might contribute to the diversity of structural colors found across the hummingbird family tree.

“Based on the speed of color evolution seen in hummingbirds, we calculated it would take 6-10 million years for this drastic pink-gold color shift to evolve in a single species,” says Eliason.

Co-author Mark Hauber at the University of Illinois Urbana-Champaign adds that “this study gives us clues about the nanostructural basis of evolutionary shifts in color.”

This study was contributed to by Bates’s and Eliason’s Field Museum colleagues Jacob Cooper (now at the University of Kansas), Shannon Hackett, Erica Zahnle, Dylan Maddox, and Taylor Hains, as well as Tatiana Paqueño Saco (Peruvian Ministry of Natural Resources) and Mark Hauber (University of Illinois, Urbana-Champaign).

The gold-throated hummingbird hybrid in the Field Museum’s collections.

The gold-throated hybrid, center, with its parent species H. branickii (left) and H. gularis (right), in a drawer the Field Museum’s collections.