Watching from the waters

The Nile crocodile, Crocodylus niloticus, is one of the most feared animals in the world and is undisputedly the most dangerous species of crocodilian to humans - being estimated to kill around 200 people each year. This is mainly due to its close proximity to our settlements and its indiscriminate diet - with it hunting anything that moves! Growing as long as 16 feet (5 metres) and weighing up to 225kg (500lb), the Nile crocodile can be found through central and south-east Africa and on the western shores of Madagascar. 

This is believed to be one of the largest specimens of Nile crocodile ever caught! Its huge size makes it no wonder why many Ancient Egyptians incorporated the beast into their belief system and worshipped Sobek, the crocodile god that lived in Crocodilopolis - a great city of crocodiles!

Probably one of the main reasons that the crocodile is such a proficient predator and is so lethal to humans is because it is a silent ambush predator - its flat body allows it to remain completely submerged, even in the shallow waters by river banks; and it has slightly raised nostrils and eyes that can be poked above the surface while keeping everything else hidden underwater, allowing it to see and breath virtually unnoticed. This allows the crocodile to get within yards of its prey (including humans), completely unnoticed and once it is ready, it lunges out of the water. Once the crocodile has lunged it is normally too late for its victim due to the speed of the attack and the animal is then crushed in the crocodile's vice-like bite and dragged into the water. After it has bitten an animal, Nile crocodiles (as with most crocodilians), have an overwhelming instinct to role - this is commonly known as 'death rolling' and, by spinning like a corkscrew, the crocodiles tear huge chunks of flesh out of their prey. This helps to compensate for their ineffective teeth, which are unusually blunt for a predator.

A Nile crocodile that has caught a gazelle. Nile crocodiles can eat up to half their body weight at a time and their bite force has been measured to be as high as 5, 000 lbf (22N), which is like being hit by a very fast-moving truck! Like most crocodiles, N. niloticus has a primary and secondary bite where an individual bites its prey once and then re-bites it without relaxing their first bite, helping to drive its blunt teeth even further into the flesh of the animal.

Ambushing their prey in this manner means that they can remain motionless in the water for very long periods of time and so, can conserve enormous amounts of energy. Crocodilians can also reduce their energy expenditure even further by slowing down their breathing and reducing their metabolism using a sophisticated cardiac shunting system that diverts blood away from their heart. Although cardiac shunting mechanisms are found in many species of reptile none have one as advanced as crocodiles. This, along with the fact that they have the most advance heart physiology in the world, has led many scientists to believe that crocodiles were once endothermic (warm blooded) like mammals and birds! Such scientists believe that their warm blooded ancestors slowly evolved back into being ectotherms (cold blooded) when they began to ambush their prey from water since a cold blooded body-plan would be much more beneficial for such a strategy; mainly because it wastes much less energy than trying to maintain a body temperature that is hotter than the surrounding water - just think about how cold you get if you spend too long in a cool bath or pool!

Thus, crocodiles can remain even in fairly cool water for long periods of time and wait for a potential meal to come to them! This is usually when an animal ventures too close to the waters edge for a drink... Nile crocodiles don't even have to use their muscles to hold their head up so can save even more energy while they wait! Their lungs act as ballast tanks and when they are inflated with air, actually push the crocodiles snout and eyes up above the water level! In fact, crocodiles can slow down their energy expenditure so much that they can hold their breath underwater for up to 2 hours when they inactive; often, lying in little 'dens' that they've dug out of the riverbed with their arms.

Certain species of bird, such as the spur-winged plover (Vanelus spinosus), have been seen picking scraps of meat from between crocodile teeth. It is not known for certain whether the birds are merely 'running the gauntlet' to obtain food at great personal risk or whether crocodiles are allowing them to this; forming a mutualistic relationship where the birds are fed while keeping the crocodile's mouth and teeth clean.

Although Nile crocodiles often hunt via ambushing their prey, they can also hunt with a much more proactive and energetic approach - chasing after fish and eating them underwater. It is believed that Nile crocodiles prefer to eat larger terrestrial game that they hunt with surprise attacks preferentially and switch to smaller fish when they aren't available or during then night when their mammalian prey is less active. Nile crocodiles are thought to prefer to ambush mammals for two main reasons: firstly, since it is less energetically expensive as mentioned above; and secondly, because crocodiles are far-sighted underwater due to the closure of their protective nictitating, or 'third', eyelids. Closing their third eyelid helps to protect their eye from underwater debris but also bends the light that passes through it so that the lenses in their eye can't refract the light enough to focus on close-up objects. Obviously, this will severely reduce their ability to hunt underwater and hunting in such a manner would probably be impossible if they didn't have many sensory papillae around edge of their lower jaw. These papillae act a bit like whiskers in dogs and cats and are able to detect even very minute vibrations in the water, allowing the crocs to sense fish that are close to their mouth! Crocodiles use much more energy when hunting fish in such a manner and as a result, can only hold their breath underwater for about 15 minutes since their muscles require more oxygen.

Their ruthless ability to surprise their prey and the fact that they eat humans has undoubtedly earned the Nile crocodile a fearsome reputation as a heartless monster. Oddly however, this isn't true and Nile crocodiles are one of the few crocodilians that care for their young - with mothers watching over their nests from when they lay their eggs to when they hatch! Most crocodilians abandon their nests as soon as they have lain their eggs and leave their offspring to fend for themselves. Furthermore, many crocodilians are cannibalistic and will eat juvenile crocodiles so that they may actually kill their own young unknowingly...

The gender of crocodiles is determined by the temperature that the eggs are at during their incubation, with temperatures of 32 - 33C producing males. Anything warmer or cooler than this narrow temperature range produces females, which is of great concern to conservationist biologists since global warming may result in more females being born and less males! The small size of the baby crocodiles makes them very vulnerable to predation early in life, but as they grow bigger and, if all goes well, the crocodiles can live for up to 100 years!

The Nile crocodile then, is a brutal and ruthless predator that preferentially hunts by ambushing unsuspecting animals from water. It accomplishes this using a range of physiological and behavioural adaptations and techniques which allow them to get within yards of their prey, gliding through the water causing barely a ripple... Despite their danger to man and the polluting effects that our lifestyle has on the waters of their habitats, the Nile crocodile is thriving and is classified as being of 'Least Concern' by the IUCN. This is not surprising really, since crocodilians are ancient animals that even trod the world with the dinosaurs! Their famed resilience allowed them to survive through the catastrophe that killed off the once mighty dinosaurs; and maybe, will even mean that they will survive for long after man has disappeared...

Save Peoples' Sight!

Hi everyone,

This weekend one of my friends is taking part in the Great Manchester Swim, hoping to raise money in support of the Royal National Institute for Blind People (RNIB). As you may or may not be aware, the RNIB is a charity that aims to prevent people from losing their sight unnecessarily and to support blind and partially sighted people so that they can live as independent lives as possible. Personally, I think that sight loss is one of the worst and most distressing ailments of man that sadly effects millions worldwide and any money that you could donate would be greatly appreciated by Charlotte and her brother, Malcolm, as well by the charity and the many individuals that it helps. If you are interested, more information is available on Charlotte's blog and you can sponsor their swim via their JustGiving page.

Obviously this is a very worthy cause and every penny counts! So please sponsor Charlotte and Malcolm for their efforts and help the RNIB to provide a better quality of life for many people less fortunate than ourselves.

Thanks,

David

How effective are captive breeding programs?

One of the most amazing attributes that humans have is our unprecedented ability to alter our surrounding environment so that it is more suitable for our daily needs; with the most obvious of such alterations being the clearing of land to make room for housing and agricultural crops. Whilst we are not the only animals to alter our habitat (many other species such as beavers and termites also build large structures), we are the only species to build and destroy at such a large scale. The fact is that we have now spread onto every continent - even having science stations of Antarctica - and wherever we go, deforestation soon follows. The result of this is that there is very little true 'wilderness' left on Earth and many animals have lost their habitats due to our destructive ways and face imminent extinction in the near future as a result.

'Slash and burn' agriculture is an ancient way of clearing land that dates back to our earliest endeavours of farming 12, 000 years ago and involves setting blaze to, sometimes, vast acres of forest. Obviously this technique is highly destructive and displaces all of the resident organisms that were previously living there, destroying their homes. The problem is made worse by the fact that land gained in such a way is very infertile so that farmers need to create new plots of land every year.

In fact, the problem is now so bad that research undertaken during the Millennium Ecosystem Assessment (MEA) has found that in the past 50 years humans have changed ecosystems more rapidly and extensively than at any other comparable time throughout our entire history! This has resulted in a huge and irreversible loss of Earth's biodiversity and the MEA found that we have already destroyed over half of the planet's forests, 20% of its coral reefs and 35% of its mangroves - all of which are essential ecosystems for providing habitats to animals, providing ecosystem services to us and in preserving the planet's future evolutionary potential. To make matters even worse, the MEA has predicted that the degradation of ecosystems is likely to get considerably worse during the first half of this century at the very least! This loss of habitat has had profound implications on the survival of many species, which are now already extinct or are endangered and this destructive human behaviour is unlikely to change any time soon. The question then, is whether or not we should try to preserve at least some of the species and ecosystems that we are threatening and of course, many people believe that we should. As the result of this, there are countless specialised conservation organisations across the globe like the WWF and the IUCN.

One of the methods that we can use to preserve endangered species then, is via captive breeding programs in which we take animals from the wild and breed them ex-situ in institutes such as zoos and aquariums. Captive breeding programs have been very successful in the past and have been sufficient to restore the natural populations of endangered species back to relatively 'safe' numbers. A good example of this is the black-footed ferret (Mustela nigripes), which has now made a remarkable recovery after its entire population was removed from the wild and bred in captivity, with reintroduction schemes running since the early 90's. In addition to breeding rare animals in an environment that is safe from illegal poaching, captive breeding programs also allow the animals to be studied by scientists; allow the public to see foreign and exotic animals in zoos, which is both interesting and may help to raise their awareness of the importance of conservation; and furthermore, helps to maintain a 'stock' population against unforeseeable events like natural disasters (which become a huge problem if all the individuals of a particular species are only found in one place!).

These elephant tusks were seized after an anti-poaching raid in Tanzania. Sadly, despite the great efforts to protect wild elephants, illegal poaching for their highly valuable ivory tusks still goes on as is very difficult to protect wild populations. Bringing endangered species, such as elephants, into captivity however makes this much easier.

However, even though captive breeding programs sound like a good idea at first glance and definitely have their good points, are they really feasible on a large scale? The IUCN has estimated that 2, 000 - 3, 000 species of terrestrial vertebrates will have to be captive bred in the near future in order to save them from extinction and sadly, the space and money that is available globally is nowhere near sufficient enough  to cope with such an epic undertaking. Thus, we may have to decide to save some species at the expense of others - decisions that would undoubtedly be both unpleasant and controversial: why is one species more important than another?

Obviously then some animals will be more suitable for captive breeding programs than others: mainly, small creatures that can be kept and maintained cheaply in small enclosures. Amphibians are a great example of such animals and furthermore, can be easily released back into the wild because they don't have any learnt behaviours that must be taught to them in order for them to survive. This is one of the main problems with reintroduction schemes, which is particularly evident in predators - without learning how to hunt and kill their prey, captive-bred animals cannot survive in the wild and thus depend on humans for their entire lives! The fact that amphibians make such good candidates for breeding in captivity is very fortunate, as over a half of all amphibians are now endangered due to the Chytid Fungus that is killing them in large numbers across the globe and due to their extreme susceptibility to anthropogenic environmental pollutants.

The endangered black-eyed tree frog, Agalychnis moreletti, is currently being bred in captivity in Chester Zoo. The zoo is participating in an international effort called the Amphibian Ark (AArk) program that aims to preserve amphibian life and safe-guard them against their global decline.

The lack of space that is available in zoos however, sadly makes the captive breeding of large animals much less feasible than programs that incorporate smaller species. This is particularly true for large predatory mammals such as lions and tigers, which need very large territories to thrive and do not respond well to being kept in captivity. In addition, they require so much space and cost so much to keep that zoos can only afford to keep relatively small numbers of them in captivity. This means that only a small number of individuals can be bred from so that the captive populations would become vulnerable to inbreeding depression and would suffer from low genetic diversity and have reduced fitness as a consequence. To explain this further, a small breeding population rapidly becomes inbred because simply put, there are no animals available for a individual to breed with that they are not related to. Over time the population becomes more and more inbred and deleterious alleles build up in individuals. Usually such maladaptive alleles are recessive and are masked in outbred individuals who have a 'normal' and healthy allele for the gene so that they don't suffer from its effects, even if they are carrying it. However inbreeding increases the chances of an individual having two copies of the deleterious allele (which are then are said to be homozygous for the allele) so that they suffer from its ill effects - a phenomenon known as inbreeding depression.

The lion, Panthera leo, is one of the most majestic predators in the world. Sadly however, captive lions usually have extremely low sperm counts and a very high percentage of what little sperm they do produce is abnormal. This problem, due to inbreeding depression, is very common in species of big cat and is exacerbated even further by the fact they they rarely even try to mate when in captivity! Problems that makes them very unsuitable for captive breeding programs.

As well as inbreeding depression, captive breeding programs have two other serious problems. The first is that keeping many animals of the same species in a small confined space that often has poorer than desirable hygiene means that the spread of infectious diseases becomes very likely (unless a vaccination against the disease is available). This can be disastrous for the recovery efforts of a species, which is highlighted in the case study of the before-mentioned black-footed ferrets where canine distemper killed all of the first ferrets that were taken into captivity! Sadly this could easily have led to the extinction of the species as more individuals had to be removed from the wild - an example that highlights the final disadvantage of captive breeding programs: removing individuals from an already dwindling population could actually push the species into extinction in the wild, as there may be too few left to breed successfully! Unfortunately, there is no way around this problem and all conservationist biologists can do is make a decision on what they think would be best for a species in its own specific case of circumstances and hope that it's the right one!

So in conclusion, captive breeding programs are undoubtedly very effective measures for preventing species from becoming extinct. However, due to the lack of space that is available and the unsuitability of some species for such schemes, they cannot be used to save every endangered species of animal so we must also take measures to preserve them in-situ in the wild. Often, this is accomplished by protecting animals from hunting under law and by setting up designated animal reserves or parks that specifically aim to protect them and conserve nature (click here for a recent example of a national park).

Silence of the hunter

The killer whale, Orcinus orca, is one of few species of toothed-whale and is closely related to oceanic dolphins, which first appeared around 11 million years ago. Often being called 'the wolves of the sea', killer whales are highly intelligent and are extremely successful predators that can be found throughout the world's oceans; being able to feed off a wide range of prey species that they hunt using echolocation.

The main prey that a pod of killer whales hunts appears to be culturally specific and typically, pods hunt either mammals, sharks, fish or birds. Cultures of killer whales are highly specialised and efficient at hunting their specific type of prey and use a variety of advanced and sinister tactics. These tactics can be very different depending on what animals the whales are hunting, but usually rely on the stealth or the strength and speed of the whales. Furthermore, these tactics are usually highly coordinated and individual whales have been seen to be 'talking' with each other and adjusting their behaviour accordingly!

Killer whales living at the poles can break up through ice in order to reach the surface and breathe. In order to this they swim upwards like a battering ram and strike the ice with enormous force. The power of such strikes is staggering and was highlighted by the famous British Antarctic explorer Sir Ernest Shackleton, who recorded fragments of ice being scattered for 20 - 30 feet around their holes! This behaviour is also used to knock seals off an ice floe into the water where another whale finishes it off - a fact that was of great concern for Shackleton and his expedition while they were stranded in Antarctica for nearly 2 years!

However, this behaviour has long baffled scientists who study the pods of killer whales that hunt mammals such as seals and sea lions, since all marine mammals have excellent hearing and the whiskers of these animals can detect even very subtle vibrations in water. Judging by this then, it would be expected that their prey should hear the very vocal whales coming and flee the area or climb out of the water to safety. However this isn't the case and often, their prey doesn't even know that the whales are there. New research conducted in partnership between St. Andrews University in the UK and North Carolina State University in the USA has helped to shed some light on this, finding that when they are hunting, killer whales "go into silent mode" and neither speak to each other nor use their echolocation to help them find their prey.

Instead, the whales seem to use a very sophisticated 'search and destroy' method in order to hunt where the members of a pod spread out over great distances and then close in again. This is repeated in silence until an animal is found, whereupon the whales close in on the unfortunate animal and kill it - remarkably, still in complete silence! It is only after they have killed their prey that they begin to talk again, a behaviour that Dr. Deecke from St. Andrews relates to humans: "it's a bit like us in a dinner party - they communicate while they eat then gradually wander off and go quite again".

Killer whales have a highly complex social organisation that is comparable to that of elephants and even humans. At its most basic level, their society is made up of units of closely-related females called matrilines that typically consist of 5 or 6 individuals. These matrilines then form 'pods' with around 4 other matrilines, with which they regularly interact and spend time with. Multiple pods regularly mingle with other pods to form 'clans' and finally, multiple clans interact forming larger aggregations called 'communities', which can be spread over huge areas of ocean.

Exactly how killer whales manage to conduct this very sophisticated behaviour in silence isn't definitively known, but it is believed that they rehearse their hunting tactics beforehand so that an individual whale knows exactly where they are supposed to be and what they supposed to be doing, as well as where the rest of their pod is supposed to be. Scientists at the two universities plan to continue their research by fitting sound recording devices and satellite tracking tags to killers in order to follow their behaviour much more closely and it is hoped that by implementing such technologies into their research, that they can determine for certain whether or not the whales are hunting in set patterns and conduct 'practice' runs.

Legionnaires' outbreak claims its second life

As many of you may already be aware, there has been a sudden outbreak of Legionnaires' Disease in Edinburgh that has sadly claimed lives the lives of two men. The source of the outbreak is still unknown and although scientists doubt that they will ever be able to identify it definitively due to the large size of the industrial estate in the western district of the city, it is believed that the bacteria is spreading in the steam released from the cooling towers of certain factories. The outbreak already has 41 confirmed cases* and the number of suspected cases stands at 48*.

Although Legionnaires' Disease is caused by a range of bacteria from the genus Legionella, approximately 90% of cases are due to infection with Legionella pneumophila. L. pneumophila can cause a potentially fatal form of pneumonia in 'Legion Fever' or in some forms, can produce a milder illness that resembles the flu.

Named after an outbreak of pneumonia in a conference of the American Legion in the Bellevue-Stratford Hotel in 1977, Legionnaires' Disease is caused by small bacteria  from the genus Legionella and can be fatal in severe cases. The bacteria are found in water and are spread to people when they drink or wash in water from contaminated sources - a fact that can play havoc in hotels, apartment blocks and hotels as many individuals' in such buildings use water from the same source, meaning that infection can spread very rapidly. Legionnaires' Disease is rare in the UK however, due to the enforcement of strict regulations for the control and maintenance of water control systems (e.g. heating water to at least 60C) and as such, there was only 245 reported cases of the disease in England and Wales in 2009.

Poor maintenance of the cooling systems in the factory(s) involved is believed to have allowed the bacteria to build up and divide in the steam produced and then be disseminated over large areas of land in the airborne water vapour ejected from their cooling towers; infecting people who unknowingly come into contact with it and breathe in the droplets. Symptoms of the disease includes mild headaches, muscle pains, a persistent cough and occasionally vomiting and diarrhoea - anyone in south-west Edinburgh suffering from such symptoms should contact NHS Direct or their local GP if they are concerned (although the outbreak is believed to have already reached its peak). The disease is rarely fatal however and, as in the tragic cases of the two deaths earlier this week, is usually only so when it infects individuals who already have underlying health problems.

* as of publishing this post