Full colour: Birds and their plumage

The most beautiful characteristic of birds is their different colour patterns between species, genders, ages, and even in individuals. In this post, we will discover some ecological and behavioural factors involved in the variability of colour in different individuals and how they are perceived by the bird eye.

1. COLOURS IN BIRDS

Different colours of the bird plumage are determinated by the combination of the amount of pigments (melanin and carotene) in feathers, and the specific microestructure in some parts of the feather.

Some pigments, as melanin (eumelanin for black and grey, pheomelanin for brown and beige) are synthesized by birds. There are specific pigments of particular taxa, for example the pigment synthesized by the psittacidae family  (it includes macaws, parakeets and other from Africa and America).

Macaws – http://www.toonts.com

Other substances, as carotenoids, are assimilated with food. For example, flamingos and roseate spoonbills find this pigments in small crustaceans that they eat. Thus, colours depend on habitat and season.

Roseate spoonbill (Platalea ajaja) – http://www.merindad.com

Also colours that depend on this pigments, birds have structural colours. On bird feathers can appear an effect, called “dissemination of Rayleigh“,  when rays of light hit the melanin microgranules that reflect short waves (blue) and transmit long waves.

Structure of feather barb – http://www.wikipedia.es

In some birds, as balb ibis (Geronticus eremita), iridescense is showed under certain lighting conditions with purple and blue colours. This effect is the result of the light incidence in microleaf of the feathers: melanin absorbs light and determines the black colour, and the colours of rainbow are reflected by this microleafs, when microgranules could only reflect the blue colour.

Iridescense in bald ibis (Genonticus eremita) – http://www.econoticias.com

3. HOW THIS VARIETY OF COLOURS IS PERCEIVED BY BIRDS?

Visual system of birds have anatomical differences to humans system. We are able to see in visible spectrum because we have three cone receptors in our eyes that divide light into three different spectral ranges (blue, red and green). Birds have four cone receptors and also they are able to see the ultraviolet radation.

Wavelenghts in birds and humans – http://www.todosobrelaevolucion.org.mx

On the left human vision and on the right ultraviolet vision in birds – http://www.notaculturaldeldia.blogspot.com.es

In addition, birds have special oils on the surface of the cones that improve the colour vision enabling the perception of a colorful world.

3. ECOLOGICAL FACTORS LINKED TO COLOR VARIATION

Plumage colour helps to distinguish different species, between male and female in birds with sexually dimorphic, aged, and can be different between individuals of the same species. But also, in same species,  this variety is related with ecological and ethological factors.

Some studies point out colour is key indicator of birds’ health status and could be important in mate choise. In many species, females prefer to breed with brigher colour males. These preferences are due to brigher colour males show higher quality and a greater capacity to survive. The carotenoids that influence in plumage colour must be supplied by the diet, but also are involved in other vital processes such as inmune process, precursors of vitamins and control of oxidative stress. According this theory, colour is a good indicator of the state of bird health, because if an individual uses carotenoids in plumage colour other vital processes must be covered and this individual has a good health. In a research about mate choise in blue tit (Cyanistes caeruleus) was demonstrated that in brigher colour males the probability of selection is higher and their chicks grow best.

Blue tit (Cyanistes caeruleus) – Foto: Luis Ojembarrena

On other hand, there is some species with a cryptic plumage that makes observation hard. This kind of plumage is essential in species with high rate of predation because in this way the bird can mingle with the environment and the probability of predation decreases, specially during certain sensitive periods such us females hatching or chicks. An example of cryptic plumage is the nighthawk (Caprimulgus europaeus) that uses its plumage to dissaper in waffle when female is hatching to decrease the risk of predation.

Nighthaw (Caprimulgus europaeus) hatching – Foto: Victor Guimera

4. SOME ANOMALIES

Some individuals can have anomalies in their plumages due to influence of factors such us genetic variability, environmental pressures and diet. Some of the most common include:

• Albinism: It consists on the precense of white feather rather than the usual feather due to a genetic change that inhibits the formation of tyrosinase enzyme responsible for the synthesis of the melanin. It is fully expressed when colour feather, soft parts (beak, claws, nails) and eyes reduce melanina.
• Leucism: It is characterized by reduced pigmentation. A genetic mutation prevents melanin deposited in feathers properly.

Bird with albinism has changes in its anatomy  (colour of eyes, for example), and in leucism the bird only has decreased pigment – http://www.biodiversidad-bajio-profundo.blogspot.com.es/

•  Melanism: It is a development of the dark colored pigment melanim in the feathers. It can ocurr partially, with dark marks, or completely if all plumage becames dark.

Negative factors for quality of habitats have shown to have influence in colour birds. In this way, it is possible to study colour patterns in birds to relate them with the state of a population and to promote conservation measures. This methodology will be cheaper and gives us highly valuable information.

Rural and urban birds – P.Salmon

5. REFERENCES

• J. Carranza, J. Moreno y M.Soler. “Researches about animal behaviour”. XXV años de la Sociedad Española de Etología (1984-2009)”. Universidad de Extremadura
• P. Salmón, J.F. Nilsson, A.Nord, S.Bensch, C.Isaksson. “Urban environment shortens telomere length in nestling great tits, Parus major”. The Royal Society Publishing.
• James Dale, Cody J. Dey, Kaspar Delhey, Bart Kempenaers y Mihai Valcu. “The effects of life history and sexual selection on male and female plumage colouration”. doi:10.1038/nature15509.
• Cover photo: http://www.hdfondos.es

Three felines you might not know

Cats, tigers, lions, panthers… we all know big cats, but what about the small ones? Do you know who are the caracal, the jaguarundi and the margay? Read on to meet them.

WHAT IS A FELINE?

Maybe you have a cat (Felis silvestris catus) at home, but have you ever thinked about what it has in common with a tiger? The truth is that a lot: the similarity among all species of felines is extraordinary and the classification of the smallest ones is difficult .

Felines are the most specialized carnivorous mammals. They live across Eurasia, Africa and America, from deserts to alpine heights. Most are solitary, big climbers (except the larger ones) and many good swimmers.

ANATOMY

With round face and short snout, felines have developed specialized canine teeth to cut meat. They have 5 toes on their front paws and 4 in the back paws, with a curved retractable claw in each to grab prey. Retracted in the rest position, the claws are kept well sharpened. The pads of the feet, surrounded by hair, help them to be silent while walking.

Felines have very acute senses, from a good night vision, good sense of hearing and smell and sensory whiskers .

Retracted and extended feline claw. Domestic cat’s declawing involves the amputation of the nail and the first phalanx, which can cause serious injury. In many countries it is illegal to be ethically unacceptable.

THE CARACAL: THE BEST JUMPER

The caracal (Caracal caracal) lives in Africa and western, central and southern Asia, in semi-desert areas and savannah. It is also known as desert lynx, but is more related to other cats (such as serval and the African golden cat) than with the lynx. It has medium size (60-90 cm long); its lynx appearance is mainly due to hair brushes in his ears, the longest and widest of all felines. Its usefulness is unclear, maybe they can improve hearing, ward off insects or highlight facial expressions as a system of communication between peers. Indeed, its name comes from the Turkish word Karakulak, literally “black ears”.

Their fur is usually brown or reddish and blotchy white belly, although there are melanic individuals (skin and coat with lots of black pigment melanin) as found in other felines, such as the famous black panther, which actually is a melanic leopard ( Panthera pardus ).

Caracal in South Africa. Unknown author

Their habits are mostly nocturnal and solitary. The most notable ability of the caracal is their jumps up to 3 meters vertically and catching birds in flight. It is also good climber, so it can prey on nests in trees. Its other dams are small antelopes, rabbits, rodents, etc. and poultry, so it is persecuted for this reason.

Watch a caracal jumping and catching a bird in flight:

According to the IUCN Red List is not generally considered in danger, but as “least concern”, although the Asian subspecies (Caracal caracal schmitzi) has suffered a serious setback. In addition to hunting, habitat destruction is the main threat of the caracal.

JAGUARUNDI: THE RAREST ONE

The jaguarundi or eyra cat (Herpailurus yagouarondi) is distributed throughout the southern United States to South America, in habitats such as tropical forests, wetlands and arid shrublands.

It has small size (9kg), and it seems more a puma or a weasel, with long legs and short tail and ears. The coat is uniform, without spots or stripes, with colors ranging from black, gray, light brown or reddish. Even in the same litter, the pups may have different hues. The dark furs are more common in wooded areas, while clear furs in drier environments.

Jaguarundi. Photo by Kevin Schafer

Unlike other cats of its size, its territories are quite large and are mainly terrestrial, although it moves smoothly through the trees. Their prey are small mammals and birds, but can also hunt on reptiles, amphibians and fish caught in the river banks. It can jump two meters and as the caracal, catch their prey in the air.

Watch the movements and techniques of a jaguarundi hunting from 9:55 minute:

Just like the caracal, it is considered as “least concern “by the IUCN, although populations are smaller than initially thought, since being diurnal is an easily observable species. The threats are the same: prosecution for killing poultry and habitat loss and fragmentation. Fortunately his fur has no commercial value.

MARGAY: THE BEST CLIMBER

The margay (Leopardus wiedii) is distributed throughout Central and South America in forested areas. Similar to ocelots, has a size and weight (40-60 cm long and 3.5 kg) smaller than them. The spotted coat helps them blend in with the environment. These spots are called rosettes and cover the entire body except the head . Each individual has his own pattern of spots, like our fingerprints.

Margay in a tree. Photo by Wendy Shattil and Rob Rozinski

 The most striking of margay are their big eyes and tail, very long (up to 70% of their body size). These are adaptations to their nocturnal habits and extreme agility to move through the trees, where it spends most of the time. Their prey are birds, small monkeys, small mammals, lizards, tree frogs and even insects.

The margay special ability is that it can vertically go down tree trunks, with its head down like squirrels do. This is possible because they can rotate 180 degrees the rear ankles. The only other feline able to do the same: is the clouded leopard (Neofelis nebulosa). This feature, along with special claws for climbing and clinging to the branches, allow them to move through the trees with the agility of a monkey: they can even hold on to a branch with only one leg. They are therefore the best climbers among cats.

Margay down a trunk with the head down. Photo taken from Terrarium online

Like caracals and jaguarundis, margays are solitary and they meet only when they have to mate.

The margay is classified by the IUCN as “near threatened “and their populations are declining. Unlike jaguarundi, it is hunted for its beautiful fur and for use as pets illegally. The destruction and fragmentation of habitat (forest conversion into farmland) are the other major threat to the margay, who does not tolerate humanized habitats.

We finish the post with images of margay in action from 1:22 minute:

REFERENCES

• Clutton-Brock, Juliet et al. 2002. Animal. Pearson Education
• Caracal (IUCN)
• Caracal (DeAnimalia)
• Jaguarundi (IUCN)
• Jaguarundi (EOL)
• Margay: master of the trees
• Margay (IUCN)
• International Society for Endangered Cats (Canada)
• Cover photo Aaron John Curtis