Mouse plagues: the terror of Australia

In 1993, south Australia was assaulted with a plague of mice. Sounds ridiculous doesn't it? But when half a billion field mice rise up in the spring to destroy your crops and eat your livestock alive, then no-one's laughing... And this is exactly what happened.

The common field mouse, Apodemus sylvaticus, is the culprit of the regular mouse plagues in Australia. The mouse, originating in Asia, was spread around the world as a stow-a-way on-board merchant trading ships.

The 1993 assault was Australia's largest recorded mouse plague and an estimated 500, 000 tons of wheat was destroyed by the rodents over the plague's 6 month duration, which is enough to feed the entire state of Utah (USA) for 4 years! The mental trauma of the plague and the loss in the livelihood of farmers was enough to drive at least 6 people to suicide and many farmers chose to abandon their livelihood and leave the at-risk areas in the south, for good.

Surprisingly, mouse plagues are fairly common in Australia and on average, happen about once a decade. (Australia suffered its most recent mouse plague last year, although it was nowhere near as large as the one in 1993). They typically erupt after a period of very wet weather that causes a 'bumper' harvest, which provides enough food for the mice to allow their populations to grow to enormous sizes. This, coupled with the fact that field mice living in Australia have very few natural predators, suffer from only a handful of the diseases that are endemic to their European cousins and have a very rampant sex life, means that their populations can grow to ridiculous sizes in a very short space of time. In fact, it has been estimated than one mouse and all of her offspring can produce 3, 000 new mice in a single year: a single pair can have babies every 3 weeks, producing an estimated 500 young in 5 months; babies that can then breed themselves at just 5 weeks old!

A pile of field mice that were poisoned by Australian farmers during the mouse plague of 1917. Although mice plagues are rare elsewhere in the world now, evidence suggests that have blighted humans throughout our history. Aristotle wrote about them 2, 351 years ago and they have even been mentioned in the Bible, in the First Book of Samuel.

As previously said, such large populations of mice are extremely destructive and consequently, farmers go to huge lengths to eradicate them in order to protect their crops and livestock. These techniques range from many simple (but not very effective) 'old-school' traps such as drowning mice in troughs full of water and leaving tarpaulins tied to the ground. During the day, field mice will hide beneath these tarpaulins, a fact that farmers have traditionally taken advantage of, using many inhumane methods like crushing and fire to kill the pests. Poisons are another, much more effective way to kill mice and are now laced over grain during mouse plagues. Poisons are usually sufficient to end mouse plagues, turning previously swarming land into killing fields. In 1993, 35 million mice were killed in just 1 month after poison was used (which reportedly hardly even dented their numbers) and one farmer claimed to be removing 70, 000 dead mice a day from his property.

Even without poisoning the plagues would eventually burn themselves out anyway, as such incredibly high numbers of field mice means that diseases spread throughout their populations like wildfire and they will eventually use up all of their available resources, meaning that they will starve to death. However, this won't be before they cause billions of dollars worth of loss to the Australian economy, so their government must still invest in expensive poisons (which also kill other native wildlife so are a last-resort weapon) in order to control the situation.

Despite being a fairly common occurrence in Australia, mice plagues cause huge amounts of damage and are very hard to control for in advance, mainly due to their unpredictability. They are incredibly damaging to the country's economy, to individual farmers' livelihoods and to local peoples' mental health! So all-in-all, are a real menace. Fortunately though, mouse plagues can be controlled and after human intervention their populations crash, with only an estimated 2 mice out of every 1, 000 surviving the cull...

Life's so short so I'm so fast

The Peregrine Falcon is a large, crow-sized bird of prey that is renown for its exceptional in-flight capabilities: the bird is incredibly agile and is the fastest known animal, entering dives of over 200mph whilst hunting! The Peregrine is also the world's most widespread raptor, being found on every ice-free landmass except New Zealand and can flourish in almost every ecosystem other than extreme polar regions, very high mountain ranges and areas of dense vegetation such as in tropical rainforests.

Peregrine Falcons have long, broad wings that end in points, the physics of which allows the bird great manoeuvrability, whilst simultaneously allowing them to reach very high speeds. Their wing-span can be a large as 47 inches and their typical body length is between 13-23 inches. Like many birds of prey, Peregrines show reverse sexual dimorphism and female falcons can be as much as 30 times more massive than males. Peregrines become sexually mature when they are a year old and mate with one partner for their entire life (unless their partner is killed), which is usually around 15 years. The falcons also use the same scrape nest for many years, which unfortunately means that their breeding habits are easily disrupted by anthropogenic activities and if their nest is disturbed, it may be a few years before the pair breeds again.

The Pergrine Falcon, Falco peregrinus. This photo shows the characteristic black 'moustache' of the bird that descends either side of its beak. Their moustache is often used by birdwatchers to quickly identify the bird. The Peregrines upper beak is notches near to its tip, which is an adaptation that allows them to kill prey by severing their spinal column at their neck.

Peregrines predominately eat medium-sized birds such as pigeons and small ducks, but will also occasionally hunt small mammals, reptiles and even insects when their preferred food sources are scarce. Like all falcons, Peregrines specialise in hunting prey whilst it is in-flight, which is where their manoeuvrability becomes useful as well as their extreme speed. When hunting, the falcons will soar to an extreme height until they locate a potential meal. Once they have locked onto a bird they enter a ridiculously steep dive, called a hunting stoop, where they reach incredible speeds of over 200mph. To-date, the fastest recorded dive of a Peregrine is 242mph! Dropping like a missile, the falcon aims to clip one of the wings of its prey, the force of which often kills the unlucky bird outright. Even if the bird does survive the impact however, its fragile wing will be shattered and it will fall to its death. The Peregrine then simply finds where the bird has landed and tucks in...

A Peregrine Falcon entering its hunting stoop. The bird pulls its wings in tightly against its body and will drop at an almost vertical trajectory. Third eyelids, called nictitating eyelids, shut during the dive to protect the bird's eyes and specialised bony tubercles on its nostrils prevent much of the airflow from entering its lungs, preventing them from bursting due to the high-pressure air that is flowing into them.

The speed and spectacular hunting techniques of the Peregrine Falcon has long made the bird of interest to humans and the bird has historically been associated with aggression and martial powers. In Europe for example, Peregrines were the hierarchical bird of prey associated with princes, just below the Gyrfalcon that was used by kings, and princes often used the falcon for hunting and as a display of status. Native American Indians also used the raptor as a symbol of status, along with various other birds of prey, as a representation of celestial power and men of high status were often buried in costumes of such birds.

Man's interest in the Peregrine has also meant that it has been heavily sought after for falconry for more than 3, 000 years and the bird is frequently used in shows and by experienced falconers due to the high speeds of its dives.

A Peregrine Falcon featured on the quarter for the state of Idaho, USA.

Unfortunately, the high human interest in the bird has meant that historically, it was vulnerable to egg poaching. This, along with their persecution by farmers and their susceptibility to many pesticides such as DDT, meant that the numbers of Peregrines decreased dramatically throughout the mid- to late- 20th Century and bird was once classified as an endangered species by the IUCN. However, although the interest of humans in the Peregrine was part of its downfall, it is also the bird's saving grace and the recovery of the bird has been very successful. This is mainly due to the large numbers of the bird that were kept in captivity for their use in falconry, which enabled conservation biologists to mount a large-scale breeding program and the species has responded well, with an increase in Peregrine populations worldwide. There are now an estimated 1, 400 breeding pairs of Peregrine Falcons in the UK and in 1999, the bird was removed from the US Endangered Species List.

The world's smallest dog ever is born

About three weeks ago Beyonce, a Miniscule Dachshund cross, was born in the Grace Foundation Animal Shelter, California. Beyonce was so small when she was born that she fitted into a tablespoon and at just 10cm in length, she is smaller than a credit card or an iPhone! This makes Beyonce smaller than Boo Boo, a 10.16cm chihuahua, who currently holds the Guinness World Record for being the smallest dog ever and her application to Guinness has been submitted.

Beyonce was the last puppy to be born from a litter of five and was critically ill when she was born, which is not surprising really given her small size. Thankfully however, vets were able to help Beyonce using chest compressions and, amazingly, mouth-to-mouth resuscitation! As a result, Beyonce has cheated death 4 times and is doing fine at the animal shelter and will be available for adoption, along with her mother and siblings, within a couple of months.

Beyonce, the world's smallest dog ever!

The bite of a killer is unpleasant indeed

Komodo dragons, sometimes called Komodo monitors, are the largest living species of lizard and can grow to lengths of 3 metres, weighing up to 70kg. Their large size means that they dominate the island ecosystems of Indonesia where there are no other carnivorous animals for them to compete with and they prey upon invertebrates, birds and mammals alike. Komodo dragons are highly intelligent have frequently been seen hunting in packs - the only species of lizard known to do this!

The large size of the lizards is unusual and is believed to be due a phenomenon called island gigantism, which is where species that are isolated on islands can grow to much larger sizes than those on mainlands due to the lack of competition for resources and the absence of predators. Island gigantism explains the Komodo dragons huge size in part, but the species also belongs to the ancient Asian Varanus genus that contained many species of large lizard, so it likely that the dragons' should be big anyway. The genus was isolated in Australia 40 million years ago and many larger cousins of the Komodo dragon once stalked its lands. However these larger cousins, which were species of megafauna, became extinct with the arrival of humans in Australia and the changes that we caused to their environment. Thus only their smaller cousins, which are believed to have evolved in Queensland and spread into Indonesia during a period of glaciation when sea levels were lower, survive today.

The Komodo dragon, Varanus komodoensis. Like all reptiles, the lizards 'smell' by tasting the air with their forked tongues and rubbing the odorants that they pick up onto the roof of their mouth. These odorants are then detected by a specially modified organ called the vomeronasal organ.

The one the most well known facts about Komodo dragons is that they have saliva that contains an extremely high number of bacterial species, which frequently causes fatal infections in animals that they bite. However, this is a misconception and although Komodo dragons do have a large range of bacterial species in their saliva, which can be as high as 57 different species, it is not unusually high for a predator. In fact, human saliva contains many more species of bacteria than a Komodo dragon and we have one of the most infectious bites of any organism in the world! However, although Komodo saliva contains no more types of bacteria than other predators, it is still highly unusual. This is because when Komodos bite their prey, they tear off its flesh by pulling their head back in a circular motion, which works in the same way as a can opener. This twisting motion is very damaging to their teeth and as a result, their gums are prone to bleeding. Thus, their saliva often has a high blood content, which enables bacterial colonies to grow to extremely large sizes so that when they bite their prey, they overload its blood with bacteria - giving the wound a greater chance of becoming infected!

Komodo dragons have very viscous saliva that often remains hanging from their mouths for long periods of time. This allows bacteria to build up in it, since the Indonesian climate is perfect for bacterial growth; meaning that the environment is very infectious.

In addition to having incredibly infectious saliva, Komodo dragons are also poisonous. This was only recently discovered and makes Komodo dragons one of only three known poisonous species of lizard. (The other two are the American Gila monster and the Mexican beaded lizard). Its venom, secreted into its saliva from two large glands beneath its tongue, is highly toxic and works like an anti-coagulant to stop blood from clotting. Clotting is the body's normal response to a cut and basically, once the body realises it's been cut it activates certain proteins in plasma, the fluid that erythrocytes (red blood cells) are suspended in. The activated proteins, called platelets, change shape and form a 'net' that traps erythrocytes at the site of the wound, forming a scab. As I'm sure you know, scabs prevent blood loss, so anti-coagulant poisons stop this from happening. As a result of this, an animal bitten by a Komodo dragon will eventually bleed to death, whilst becoming weaker and weaker as they lose more blood. Komodos take advantage of this by biting their prey a few times and then backing off, which reduces their risk of injury from their prey. They then follow the wounded animal at a safe distance until it dies, or becomes too weak to struggle.

This allows them to bring down animals much larger than themselves and sadly, the lizards have been known to kill humans. However, despite being fearsome predators with deadly saliva and the intelligence and brute force needed for ambushes, Komodo dragons are predominately scavengers that feed off carrion, eating anything that they come across.

Unfortunately, the loss of Komodo dragons habitat due to human activity, illegal poaching and the effects of improperly managed tourism means that there are now less than 5, 000 individuals living in the wild and it is believed that there may be as few as 350 breeding females left. Consequently, the species is classified as 'vulnerable' by the IUCN and may soon disappear, being on the agency's Red List.