Jewel scarab beetles look like gold, why?


This video says about itself:

Jewel Scarab in Costa Rica -Chrysina

4 February 2014

Here is a video of a lovely creature I came across during a rain forest exploration. I love insects and this one really took the cake. It’s body was was a like a mirror that reflected all the colors around it.

From the University of Exeter in England:

Secret of why jewel scarab beetles look like pure gold, explained by physicists

‘All that glitters is not gold,’ finds research program into way jewel beetles reflect light

June 15, 2017

The secrets of why Central American jewel scarab beetles look like they are made from pure gold, has been uncovered by physicists at the University of Exeter.

The ornate beetles, which have a brilliant metallic gold colour, are highly valued by collectors. But until now the reasons behind their golden iridescent hue, have not been fully understood.

University of Exeter physicists specialising in colour and light have done experiments exploring the origin of the scarab beetles’ striking metallic golden appearance, showing that the golden beetles have a unique ‘optical signature’. The structure of the beetle and its armour uniquely manipulates the way the light is reflected so that it looks like pure gold.

Their results are published in the Journal of the Royal Society Interface.

Professor Pete Vukusic, a physicist specialising in light and colour, led the research which involved experiments and advanced modelling. He found that the golden appearance is due to the high reflectiveness of the beetles’ exoskeleton, which also manipulates a property of the light called its polarisation: the orientation of the reflected light wave‘s oscillations.

The scientists mapped the optical signature of the beetle’s Chrysina resplendens‘ colour, and found it was unusually ‘optically-ambidextrous’, meaning that it reflects both left-handed and right-handed circularly-polarised light.

Professor Vukusic said: “The brilliant golden colour and distinctive polarised reflection from the scarab beetle Chrysina resplendens sets it completely apart from the hundreds of thousands of other beautiful and brightly coloured animals and plants across the natural world. Its exoskeleton has a bright, golden appearance that reflects both right-handed and left-handed circularly-polarised light simultaneously. This characteristic of Chrysina resplendens appears to be an exceptional and wonderfully specialised characteristic in currently known animals and plants. It will serve as a valuable platform from which bio-inspired optical technologies can spring.”

The golden jewel beetle is prized by collectors because of its resemblance to the precious metal.

Other scarab beetles, valued by ancient cultures such as the Egyptians for use as amulets which were sometimes wrapped in the bandages of mummies, are a jewel-like green and blue colours. The vast majority of brightly-coloured beetles tend to be green and do not reflect polarised light. These beetles, in comparison to the brilliant golden colour of Chrysina resplendens, lack much more specialised aspects of their exoskeleton’s finely detailed structure.

Dr. Ewan Finlayson, research fellow on the project, said: “We were drawn to the study of this jewel scarab not only by its striking metallic golden appearance, but also by its ability to control a less obvious property of the reflected light: the polarisation. We have learned that there is great subtlety and detail to be found in these optical ‘signatures’ and in the elaborate natural structures that generate them.”

The golden jewel scarab beetle Chrysina resplendens, mainly found in the Americas, has evolved an exoskeleton that contains intricate nano-structures that are responsible for its appearance.

The spacing of the repeating layers of the nano-structures is found to vary over a specific range through the exoskeleton — a key property that causes the simultaneous reflection of a range of visible colours. It is this fact that explains the very bright reflection as well as the golden hue.

The nano-structured exoskeleton is composed of natural materials including chitin and various proteins. In addition to their brilliant reflectiveness, these structures are remarkable in the way they manipulate the way polarised light is reflected.

Their nanostructures produce circularly-polarised light, where the orientation of the light’s oscillations rotate as the light travels. The two possible directions of rotation are referred to as left handed and right handed.

The experiments build on the work of an early American scientist called Michelson who, in 1911, looked at the polarised reflection from many different Chrysina beetles, and on the work of Anthony Neville (then at Bristol University) in 1971, who began looking more closely at Chrysina resplendens.

There are around 100 species of Chrysina jewel scarab, which are found exclusively in the New World, mostly in Mexico and Central America. The species Chrysina resplendens is found in Panama and Costa Rica. Chrysina scarabs typically live in mountain forests. The larvae feed on rotting logs of various tree species, while the adults feed on foliage. The larval form lasts for several months to a year, and pupation takes a month or two. After the adult emerges it lives for about a further three months, although this span probably varies between species.

One explanation for the highly-reflective appearance of the beetle exoskeleton is crypsis: the ability of the animal to blend in to its surroundings.

Dr Martin Stevens, Associate Professor of Sensory and Evolutionary Ecology at the University of Exeter and an expert in animal vision, colour change and camouflage, said: “It is not absolutely clear why these beetles are a bright golden colour, but one option is that it somehow works in camouflage under some light conditions. The shiny golden colour could also change how the beetle is seen as it moves, potentially dazzling a would-be predator. There are many species which are iridescent but jewel beetles are one of the most charismatic and brightly coloured, and their colour might be used in mating. However, it is not clear how other beetles see the gold colour and reflected light. Many small mammals would not be able to distinguish the golden colour from reds, greens, and yellows, but a predatory bird would likely be able to see these colours well.”

Golden-cheeked warbler video


This is a golden-cheeked warbler video.

These birds nest only in Texas in the USA, wintering in Mexico and Central America.

Green heron video


This is a green heron video.

These North and Central American birds are rare vagrants in Europe.

I saw them in Costa Rica.

Reddish egret video


This video says about itself:

Reddish Egret

20 July 2016

Video by Kris Wiktor/Shutterstock.

Reddish egrets live in north and central America.

Saving agami herons


This is an agami heron video from Ecuador.

From BirdLife:

First-ever conservation plan announced for the Agami Heron

By Sanya Khetani-Shah, Wed, 21/10/2015 – 09:30

Agami Herons are a nocturnal and discreet species of birds. While their range includes a large part of Central and South America, since they are so difficult to observe, nothing is known about their diet, breeding, feeding grounds or areas frequented by them during the nonbreeding season. Nor is there much information about the species’ population size. However, a huge colony of 2,000 breeding pairs exists in the Kaw-Roura Marshes in the tropical rainforests of French Guiana, France’s largest overseas département.

One thing we do know: the Agami Heron (Agami agami) is a Vulnerable species according to the IUCN Red List assessment; the population is expected to decline rapidly over the next three generations. The colony in French Guiana represents more than 90% of the world’s known breeding population.

Mining and logging (which cause deforestation), the construction of new roads (especially in densely populated coastal regions), and lack of knowledge on the species and consequently what our conservation priorities need to be are exposing this species and its habitat to degradation. To make matters worse, the pillars of the EU’s nature laws – the Birds and Habitats Directives – do not apply in Member States’ overseas regions.

To right the situation, the French Guianan Groupe d’Etude et de Protection des Oiseaux en Guyane (GEPOG) launched a study on Agami Heron (Agamia agami) conservation from 2011 to 2015, as part of a LIFE programme (the EU’s financial instrument supporting nature conservation). Data was acquired by monitoring eight Agami Herons fitted with satellite transmitters. In September 2015, the first Agami Heron conservation plan, co-written with HeronConservation (the Heron Specialist Group of IUCN) and other contributors from around the world, was published.

The purpose of this plan is to provide a range-wide framework for the conservation and management of Agami Herons and their habitats from limited legal protection, deforestation, urbanisation, rising sea levels due to climate change and other human activities and disturbances.

The plan advocates additional research and monitoring to improve our knowledge of the species, including finding the most important colony for the species in general and for the regional populations as well as the feeding areas associated with them; determining the impact of disturbances as well as mitigation and protection measures of colony sites; better understanding the range and distribution of the species; and better understanding their feeding behaviour, prey and feeding/breeding cycles.

But the plan is not just about getting to know the species better for future protection. It also includes various conservation actions that must begin now. These include: creating an Agami Heron Working Group (AHWG) to coordinate the monitoring of the population at each important colony site ; protect breeding sites, feeding areas and migratory stop-over sites; protecting mangrove forests throughout the species’ range; determining habitat areas containing important numbers of Herons outside the nesting season; and encouraging campaigns to educate people living near known colonies about the species’ importance and protection.

Most importantly, the conservation organisations involved aim to revise this plan every 10 years, so that they can stay updated on the conservation status and needs of the Agami Heron.

Agami Herons’ Full Mating Ritual Photographed for the First Time. A couple’s trek to a hidden lagoon in Costa Rica leads to a cache of new details about a glorious, yet understudied bird: here.

North American songbird southward migration, new research


This video from the USA is called Act for Songbirds – Help Save Threatened Migratory Birds.

From the Journal of Field Ornithology in Canada:

Connecting breeding and wintering grounds of Neotropical migrant songbirds using stable hydrogen isotopes: a call for an isotopic atlas of migratory connectivity

Volume 85, Issue 3, pages 237–257, September 2014

ABSTRACT

There is an overdue and urgent need to establish patterns of migratory connectivity linking breeding grounds, stopover sites, and wintering grounds of migratory birds. Such information allows more effective application of conservation efforts by applying focused actions along movement trajectories at the population level. Stable isotope methods, especially those using stable hydrogen isotope abundance in feathers (δ2Hf) combined with Bayesian assignment techniques incorporating prior information such as relative abundance of breeding birds, now provide a fast and reliable means of establishing migratory connectivity, especially for Neotropical migrants that breed in North America and molt prior to fall migration.

Here we demonstrate how opportunistic sampling of feathers of 30 species of wintering birds in Cuba, Venezuela, Guatemala, Puerto Rico, and Mexico, regions that have typically been poorly sampled for estimating migratory connectivity, can be assigned to breeding areas in North America through both advanced spatial assignment to probability surfaces and through simpler map lookup approaches. Incorporating relative abundance information from the North American Breeding Bird Survey in our Bayesian assignment models generally resulted in a reduction in potential assignment areas on breeding grounds.

However, additional tools to constrain longitude such as DNA markers or other isotopes would be desirable for establishing breeding or molt origins of species with broad longitudinal distributions. The isotope approach could act as a rapid means of establishing basic patterns of migratory connectivity across numerous species and populations.

We propose a large-scale coordinated sampling effort on the wintering grounds to establish an isotopic atlas of migratory connectivity for North American Neotropical migrants and suggest that isotopic variance be considered as a valuable metric to quantify migratory connectivity. This initiative could then act as a strategic template to guide further efforts involving stable isotopes, light-sensitive geolocators, and other technologies.

American tanagers’ colours and songs, new study


This video is called Colombia Tanagers [various species].

From Wildlife Extra:

Study dispels Darwin’s theory to prove birds can have it all

Despite popular belief birds can have a brilliant plumage, a virtuosic singing chirp and an intricate dance routine say scientists.

The author of a new study, Nick Mason, from the the Cornell Lab of Ornithology in New York state, challenged the long-held notion, first proposed by Charles Darwin, that for a bird species to excel in one area it must give up its edge in another.

For example, male northern cardinals are a dazzling scarlet, but sing a fairly simple whistle, whereas the dull brown House Wren sings one of the most complicated songs in nature.

Mason and his colleagues tested the theory by examining a very large family of songbirds from Central and South America, the tanagers.

This group consists of 371 species and included some of the most spectacularly colourful birds in the world such as the paradise tanager as well as the more drab birds, such the black-bellied seedeater. The group also includes both accomplished and weak songsters alike.

“If there were going to be any group of birds at all that would show this trade-off, the tanagers would be a very good candidate, because there’s all this variation in song and plumage complexity,” Mason said.

“But when we dived into it and did some rigorous statistics, it turns out that there is no overall trend. Tanagers can be drab and plain-sounding, or colourful and musical, or or anything in between.”

It’s still possible that trade-offs take place at the level of genus, Mason said, or that they influence species relatively fleetingly as evolutionary pressures appear and disappear.

But as a broad effect on an entire family of birds, a voice–plumage trade off doesn’t seem to exist. One possibility is that the resources needed to develop fancy plumage are different from the ones required for complex songs, freeing tanagers to invest in both forms of showiness simultaneously.

USA: Seeing the vivid red bodies and black wings of male Scarlet Tanagers is a sure sign spring has arrived: here.