jueves, 9 de febrero de 2017

How do cheetahs defend themselves?

(Generally speaking, cheetahs run).

Although adult cheetahs are skilled predators built for speed, as we all know, they are weaker than other big cats (lions and leopards) and hyenas which are their natural competitors. They can, and often do, steal their preys and also kill their cubs. Besides, as cheethahs rely on their speed to chase, they will not risk to fight to another predators.

I don't consider cheetahs top predators in this sense, they are really vulnerable to their competitors, according to some data they can lose up to 50% of their preys due to interlopers, and what is worst, up to 90% of their cubs are killed in the first weeks of life by wild dogs, lions, leopards, hyenas and eagles..
So the best defense against these threats is to avoid it. Cheetahs tend to hunt

in the mornings and  evenings, when enemies are dormant. It also eats immediately after it  downs its prey, before intruders such as lions, leopards, hyenas,  jackals, baboons and vultures arrive.
But in some cases cheetahs fight. For example, mother cheetahs defending their young and groups of male cheetahs teaming up to chase away other predators such as servals:

Here is a video of a mother cheetah confronting a wandering lioness to defend her cubs (in this case the cheetah seems to have notice the relaxed pace of the lioness and taken advantage of it, there are also some other videos of lions and lionesses kiling cheetahs, but I have preferred this one as an example of how brave can be cheethahs in some ocassions):

A great place to know about cheetahs, and their conservation:

Cheetah Conservation Fund

lunes, 6 de febrero de 2017

Do fishes have 3D vision?

Short and tricky answer, yes. It is tricky because fish are a vast number of animals, besides a paraphyletic group of animals.
Long answer that need an explanation i´ll provide you bellow is "yes, to some degree, fishes are able to have binocular vision".

Getting into a deeper view of your point, what you are looking for is binocular vision. And it is due to the superposition of the fields of vision of both eyes and the work of the brain as you say.
And you are right, the position of the eyes have a a determining role on getting this binocular or stereovision, exactly they inceed in the width or degree of the angle where this 3d vision is possible.

  • For a start, we can take a look to a typical hervibore mammal. I choose this protoptype because they live in the same enviroment that we do, and they have similar eyes to that we have:

The Mammal Eye and Vision in Mammals
Horses can see up to 215º, but have a binocular vision field of less than 90 degrees, just in front of their head. Humans have a total vision field of 180º, 140º of binocular vision.  In fact, primates have greater binocular vision field than typical carnivores. This is a great advantage if you jumping between branches and can fell down more than 40 mtrs if you don´t see clearly how far is the next branch.

  • Let´s go to the fishes. They make stereovision the way we do, overlapping the two eyes field of vision

The Earth Life Web, the Fish Eye and Sight in Fish

  • But many fishes have an extra vertically flattered head that keep their eyes quite in the side of the head. One of the ways of improving their frontal, and thus binocular vision, is to increase the their monocular field of vision.

This chart is excerpted from The Earth Life Web, the Fish Eye and Sight in Fish

                     Visual Range in Men and Fish
 Entity Horizontal Vertical Binocular
Man              154°              150°              25°  
Fish                165°             134°               12°                          (**)

This is what many of the fishes that have extra narrow compressed head  shape do. They usually have very large eyes and they are in a very front  position in their heads, allowing a major overlaping this way.

(**) You can say now, but you telled that people had 140º of binocular vision. Yes, but here are data from another source and they make a difference between horizontal and vertical vision. And data usually varies a little depending of the source.

As usual, predators have more frontal eyes to increase distance perception and prey side eyes to increase the field of vision in spite of binocular vision.

  • There are more special adaptations to improve their vision skills as water is a more challenging enviroment to this sense that is air.

  • Some of the deeper water fish have tubular eyes with big lenses and only rod cells that look upwards. These give binocular vision and great sensitivity to small light signals. This adaptation gives improved terminal vision at the expense of lateral vision. Vision in fishes.

  • And there are more tricks in the bag: Benthic

  • predators, like flatfish, have eyes arranged so they have a binocular view of what is above them as they lie on the bottom. Vision in fishes.

sábado, 4 de febrero de 2017

Do dolphins have eyelashes?

o, they don't. I'm not sure that eyelashes are totally unuseful for them, but as so many things in animals potential the existence or ausence of a character is not always totally correlated with its utility.

But they have whiskers or at least they had, dolphins are born with a few hairs around the tip of the beak -which is called the rostrum if you want to sound more technnical- , that they lose them shortly after birth, retaining only the roots under the skin. Only the Boto river dolphin  retains them which has persistent small hairs on the rostrum.

In the four pictures above you can see the stages of dolphin hair.  Figure A shows the hair root that all dolphins have buried in the skin.   Figures B and C show with arrows the hairs that stick out around the  time of birth.   Figure D shows the dark pits that each contain the hair  root below.
Source of these terrific photos and text: NATIONAL MARINE MAMMAL FOUNDATION, by Sam Ridgway. (Thank you Sam).

But...what I suspect, but I haven't been able to test is that embryos have more hair in earlier states of development and that those hairs are reabsobed before birth.


jueves, 2 de febrero de 2017

If Cecil the lion's death is going to lead to the death of the remaining 6 cubs from another male lion in pride, why can't the national park authorities make a move to relocate the 6 cubs or the male lion? Won't it save the 6 cubs' lives? Unfollow3 Comment Share Downvote

n spite that this was the main concern in the first moments after the killing of Cecil, today it seems that the better decission is to keep his 7 cubs in their pride.
The main reasons for this may be these:
- Cecil's comrade Jericho (presumably his brother), the amle lion you ask about, got along well with Cecil. It was very probably that Jericho didn't hurt the cubs when he took over the pride, as it has happened. Also, relocating him would have left the females alone, and any rogue male could easily take over the pride. Jericho is an ally,so to speak, not an enemy for the cubs.
- Cecil's genetics. If they relocate the cubs, they had to raise them, and hence they would not be wild lions no more, avoiding to continue this good genetic pool in the wild.
- Although the risk of an alliance of rogue males taking over the pride is a fact, Jericho (probably 11 years) is doing a good job by now.
- Economy. I don't know whether there are parks with captive lions under the responsability of Zimbabwean authorities and/or conservation organizations, but the Zimbabwe is a country with low incomes that already told about that the cost of translocating these cubs is very high to them. Also, wildlife conservation doesn't interest the general media in this country, so there has not been a internal demand of soing it so.

But, so far, these cubs are ok:

These are some of the cubs, date Aug 2. Source of the image: Safaris @ African Bush Camps

If you want to trustable
information about these cubs, the best link is Wildlife Conservation Research Unit, it is the the team that monitored Cecil. In their web they report that the cubs are healthy and secure as of Aug. 18th 2015

martes, 31 de enero de 2017

Why was Oliver the chimpanzee human-like?

I learned about Oliver the chimpanzee after answering another question and I developed a kind of sympathy towards his story.
The abstract of my answer is that Oliver was a common chimpanzee that had retained some juvenile characteristics in his face that made him appear more 'human-like' and a preference for walking upright that he could have developed as a juvenile growing with his first owners, a couple that bought him when he was about two y.o. The most peculiar trait he shoed was how upright he could walk, but this type -although very excepcional- of gait has been found in some other apes like the gorilla of the video I have added. And finally, some years of abuse resulted in muscle atrophy and loss of all teeth wich contributed to making his appeareance more slender and his face more plane.
Oliver was famed as a chimpanzee with many human like traits, but in fact many studies carried out after his death showed clearly that he was a common chimpanzee without chromosomic anomalies.
A geneticist from the University of Chicago examined Oliver's chromosomes in 1996 and revealed that Oliver had forty-eight chromosomes instead of forty-seven. This disproved the earlier claim that he did not have a normal chromosome count for a chimpanzee.
Oliver's cranial morphology, ear shape, freckles and baldness fall within the range of variability exhibited by the Common Chimpanzee.
Scientists performed further studies with Oliver, the results of which were published in the American Journal of Physical Anthropology.
However a full DNA test has never been performed. Although many requests were made for access to Oliver for medical testing during his later years at Primarily Primates and again after his death in 2012, it was the policy of PP to refuse all such requests, calling those inquiries "scientific tourism."

Judging by the pictures I have seen he looked like if he had retained some juvenile characters like a somehow flatter face (aslthough that the effect was stressed by the fact that many of the photographs were taken when he was old and had his teeth removed), bald and without beard. He also had a tendence for walking upright, strinkingly upright,  and rarely was seen knucling. He was a well developed male in spite of the juvenile traits in his appeareance. Also, reading his biography -it is very interesting- it results that Oliver was purchased by a Pensilvannia laboratory when he was about 30 years old, and that he spent nine years in a small cage what resulted in his muscles atrophying, which could give him the slender look he exhibits in the pics, apart from horrible mental and phisycal suffering. Oliver, with all his fame, was an abused chimp, and I congratulate that people of Primarly Primates finally took care of him and decided to maintain scientific analysis far from him for the rest of his life:
Oliver was purchased in 1989 by the Buckshire Corporation, a Pennsylvania laboratory leasing out animals for scientific and cosmetic testing. His entrance examination revealed some previous rough handling. He was never used in experiments, but for the next nine years, his home was a small cage, whose restricted size resulted in muscular atrophy to the point that Oliver's limbs trembled.
In 1996, Sharon Hursh, president of the Buckshire Corporation, after being petitioned by Primarily Primates, allowed his retirement to Buckshire's colony of 13 chimpanzees.
So, accordingly to the studies carried out, and in absence of a genetic study, it seems that Oliver was a common chimpanzee whose 'human-like' traits had been highly hyped by his owners who had exhibited him.
The peculiar -for a chimp- way of walking is also not unheared of in some few other non human apes (very few), like the gorilla of this video:

lunes, 30 de enero de 2017

Melancolía, pesadilla en vainilla.

Is it true that animals see colours?

- Animals see in colors thanks to a type of specialized cells located in the retina, the cones, that are sensible to the colors of the light. Humans have around 6-7 millions of those cones (and now imagine how did they manage to count them). tl; dr different type of cones respond to different wavelengths, we humans have 3 different types of cones, the majority about 64 percent of them respond most strongly to red light, while about  a third are set off the most by green light. Another 2 percent respond  strongest to blue light. (Source: How Do We See Color?). So, basically we see in red, green and blue, 3 primary colors, and the rest of them all is got by mixing these 3.

Source Taringa.net.
- The small and grumpy purple spot mantis shrimp, Onodactylus smithii, is the winner of vision in colors.
Remember we have 3 primary colors?. Well, this critter has 11 or 12 primary colors. Also, they have eyes that simultaneously measure four linear and two  circular polarisations, enabling them to determine both the direction of  the oscillation, as well as how polarised the light is. (Source: Page on sciencedaily.com).

Souce of this beautiful image: http://www.nature.com/scitable/b...
- Many birds see ultraviolet.
IN THE EARLY 1970s, A RESEARCHER testing the ability of pigeons to discriminate colors discovered by accident that the birds can see ultraviolet (UV) light.  The finding was deemed curious but not too important. “It was natural  for scientists to assume that bird vision is like human vision,” says Geoffrey Hill, an Auburn University ornithologist and the author of Bird Coloration.  “After all, birds and humans are both active by day, we use bright  colors as cues. ... No one really imagined birds might see the world  differently.”
But during the following decades, systematic testing of bird vision  revealed something unexpected: Many bird species—not just pigeons—can  see UV light. Indeed, with the exception of night-flying birds such as  owls, the eyes of most birds probably are even more sensitive to  ultraviolet light than they are to what we call visible light.  Scientists also have learned that many birds have plumage that reflects UV light. Together, these discoveries “made us realize there could be new answers to old questions,” says Drake University biologist Muir Eaton.  Birds rely on vision to choose mates, find food and scan for predators,  for example. “If you assume birds see exactly what we see, you could  have the wrong framework for understanding bird behavior,” Eaton says.
Souce (True Colors: How Birds See the World - National Wildlife Federation)

Also, many insects are able to see ultraviolet. This time you'll have to trust on me because I'm not adding links here.