Howler monkeys’ eyes, new research


This video is called Howler Monkeys | National Geographic.

From Science News:

Howler monkeys may owe their color vision to leaf hue

Distinguishing red from green makes healthier leaves stand out

By Laurel Hamers

5:59pm, February 21, 2017

BOSTON — A taste for reddish young leaves might have pushed howler monkeys toward full-spectrum color vision. The ability to tell red from green could have helped howlers pick out the more nutritious, younger leaves, researchers reported February 19 at the annual meeting of the American Association for the Advancement of Science. That’s a skill their insect-eating close relatives probably didn’t need.

Primates show substantial variation in their color vision capabilities, both between and within species, said Amanda Melin, a biological anthropologist at the University of Calgary in Canada. Trichromatic vision (how most humans see) requires three light-sensitive proteins in the eye that can detect different wavelengths of light. Within most monkey species in Central and South America, only some individuals have trichromatic vision. Males have dichromatic vision — they’re red-green colorblind — and only some females can see the whole rainbow. Howlers are an exception — thanks to a duplicated gene on their X chromosomes, trichromatic vision is the norm for both males and females.

Howlers graze on leaves from Ficus trees and other plants when fruit can’t be found. In field observations of mantled howlers (Alouatta palliata) in Costa Rica, the monkeys preferentially munched on the younger, more nutritious leaves, Melin’s team found. The reddish hue of new leaves makes them pop more when seen with trichromatic vision than dichromatic vision, the researchers reported in a paper accepted for publication in Ecology and Evolution. Because young leaves are a fleeting treat and not a constant resource, monkeys able to spot them more quickly could have had a selective advantage.

Similar selection pressures might also help explain why Old World monkeys from Asia and Africa also have consistent trichromatic vision, Melin said. “What we might be seeing is a convergent evolution for animals who fall back on leaves when fruit isn’t around.”

On the other hand, other Central and South American monkeys usually go for insects, instead of leaves, when there’s no fruit. Dichromatic vision might be a better fit for their lifestyle, Melin said. “Color can impede ability to see patterns, borders and textures. Insects hide and camouflage.”

I was privileged to hear and see howler monkeys in Suriname and Costa Rica.

Black woodpecker on video


This 21 February 2017 video shows a black woodpecker preparing its nest for the new season.

Luuk Punt made this video in Gelderland province in the Netherlands.

Young cormorant, young shag, what’s the difference?


This 16 February 2017 Dutch video is about a young great cormorant and a young shag. They look similar. However, look around their eyes for the difference.

Red knots feeding, video


This 15 February 2017 video is about red knots feeding at the Brouwersdam causeway in Zeeland province in the Netherlands.

Otters drive away bittern, video


This 16 February 2017 video shows an otter couple swimming through partly frozen water near Kropswolde village in Groningen province in the Netherlands.

They drive away a bittern.

Both bitterns and otters are rare in the Netherlands.

Eastern black redstart video


This video is about the eastern black redstart, a black redstart subspecies from Asia.

Humphead parrotfish video


This video says about itself:

17 February 2017

A school of Humphead Parrotfish descend on the coral reef to feed and turn the age-old coral into a fine sand that, in turn, forms islands. Fascinating video from BBC natural history show Blue Planet. Narrated by Sir David Attenborough.