Ground squirrels use infrared signals to fool heat-seeking rattlesnakes

Rattlesnakes can track their prey using the infrared light given off by the warm bodies. But ground squirrels can use this super sense against the snakes. By pumping blood into their tails, they give off infrared signals that fool the snakes’ heat-seekers.

Ground squirrels use infrared signals to fool rattlesnakesIt seems like an uneven match. In one corner, the unassuming California ground squirrel (Spermophilus beechyi), 30cm in length. In the other, the northern Pacific rattlesnake (Crotalus oreganos), more than twice the length of the squirrel, and armed with hinged fangs that pack a lethal venom. But thanks to a cunning adaptation, the squirrel often gets an unexpected upper hand in this bout.

Squirrels vs snakes

Ground squirrels live in a series of burrows that keep them out of reach of most predators. Snakes, however, have exactly the right body plan for infiltrating long sinuous tunnels, and it’s not surprising that they are the squirrels’ major predators. It’s equally unsurprising that the squirrels have developed ways of defending themselves against snakes.

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Attack of the killer mice – introduced rodents eat seabird chicks alive

On Gough island, introduced mice have developed a grisly appetite for seabird chicks and could well drive local species to extinction.

As Charles Darwin learned several centuries ago, islands are havens for evolution. Newcomers to these isolated worlds find themselves unshackled from the predators that dogged them on the mainland. They celebrate their freedom by diversifying into a great variety of species.

A Gough Island mice sites amid a grisly pile of chick bodies.But predators still have ways of tracking them down, and following the footsteps of sailors is one of them. By killing adults and eating eggs, introduced predators such as rats, cats and stoats are responsible for nine in ten of the bird extinctions since 1600.

Now, conservation agencies are getting serious about introduced predators. As an example, they have spent increasingly large budgets in recent years on the eradication of rats from troubled islands.

Smaller stowaways like mice typically escape the conservationists’ wrath, and between 2001 and 2005, twenty-five times less money was spent on dealing with them. After all, mice are smaller and less opportunistic than rats and pose very little threat to seabirds.

Or at least that was what scientists used to think. In 2005, Ross Wanless, Peter Ryan and colleagues from the University of Cape Town found that on Gough Island in the south Atlantic, mice had developed sinister appetites. They were eating the chicks of local seabirds alive (see image below).

Infrared footage shows mice feeding on a chick.

House mice were introduced to Gough Island, now a World Heritage Site, in 1888 and are the only introduced mammals there. They share the island with large seabird colonies including many endangered species, and the last breeding populations of the Tristan albatross and the Atlantic petrel.

The mice seemed to be co-existing peacefully until the turn of the millennium, when some of the seabirds started experiencing massive breeding losses.

Wanless investigated and by watching about 300 nests, he found video evidence that the mice have developed a taste for albatross, petrel and shearwater chicks. They were attacking and eating chicks up to 300 times their weight, and often en masse.

Albatross chicks are not defenceless and will often ward off much larger avian hunters like the sub-Antarctic skua or the southern giant petrel. But they have also been spoilt through an evolutionary history free of mammalian dangers. The chicks have no idea how to react to mice, let alone defend themselves, hapless and helpless.

To save endangered birds like the albatross, ALL introduced predators must be dealt with.In fact, Wanless describes the mice as parasites rather than predators. They often don’t kill the chicks outright but slowly feed from open wounds over the course of days.

Typically, 60-75% of Tristan albatross young survive their first year. But thanks to the voracious mice, only 27% now do so on Gough Island. As a result, the population of this already vulnerable bird has crashed by over a quarter since the 1960s.

The birds of Gough Island will clearly need some assistance. Meanwhile, Wanless is sounding the alarm for other islands where introduced mice roam free.

On islands where they are not alone, larger introduced predators like cats or rats may be helping to keep their numbers down. The danger then, is that when conservationists get rid of these larger problems, they may unwittingly unleash a smaller foe on the native animals.

This very situation seems to be playing out on Marion Island in the South Indian ocean. In the 1990s introduced cats were finally eradicated from the island, leaving mice as the only mammal aliens around.

And sure enough, Ryan has found that several wandering albatross chicks have died of wounds consistent with mouse attacks. These attacks could be much more widespread than we had realised.

The message is clear – eradication programmes for introduced animals should target all potential predators, whether big or small. As in the case of sharks and scallops dealt with elsewhere in this blog, the removal of top predators can often doom animals at the bottom of the food chain by releasing hunters in the middle tier.

Reference: Wanless, Angel, Cuthbert, Hilton & Ryan. 2007. Can predation by invasive mice drive seabird extinctions? Biology Letters doi:10.1098/rsbl.2007.0120

Rats check their own knowledge before taking a test

Scientists from the University of Georgia have found evidence of a surprising level of intelligence in rats. Like a human student, the furry creatures can reflect on their own knowledge to decide if they want to take a test.

Animals often show a keen intelligence and many species, from octopuses to crows, can perform problem-solving tasks. But humans are thought to go one step further.

Students can predict how well they do in a test before they take it - can rats do the same?We can reflect on our own thoughts and we have knowledge about our knowledge. We can not only solve problems, but we know in advance if we can (or are likely to).

In technical terms, this ability is known as ‘metacognition’. It’s what students do when they predict how well they will do in an exam when they see the questions. It’s what builders do when they work out how long a job will take them to finish.

But can animals do the same? Finding out is obviously difficult. No animal is going to tell us what it is thinking. To work that out, we need clever experiments.

Allison Foote and Jonathon Crystal searched for metacognition in rats by giving them a test that they could decline. If they passed, they received a big reward and if they failed, they got nothing.

But the cunning part of their study lay in giving the rats a small reward if they declined the test. If they knew they were unlikely to pass the test, they’d be better off bowing out. In this experiment, a measured attitude beats a gung-ho one.

The test asked the rat to classify a burst of noise as ‘short’ or ‘long’. Noises that were very short or very long were easy to classify, but those of intermediate length were more challenging.

Rats show metacognition just like humans.After hearing the noise, the rat was offered two holes through which it could stick its nose – one for accepting the test and one for declining it. If it was game, it was then given two levers, one for a short noise, and one for a long one.

After some initial training, the results were clear. The rats were much more likely to opt out of the test if the noise they heard was challenging. And when they accepted the test, they were much more likely to answer correctly than in trials where they were forced to take it.

To Foote and Crystal, these results show that the rats knew when they didn’t know the answer. And armed with this knowledge, they could make adaptive choices about their future.

I love experiments like this. They are elegant, clever, and ever so slightly like talking to animals directly.

While we’re never going to have Doolittle-style conversations with rats, looking inside their heads (experimentally not literally) is the next best thing. Scientists like Foote and Crystal are like lab-coated rat whisperers.



Reference: Foote & Crystal. 2007. Metacognition in the rat. Curr Biol. 17: 551-555.

Human cone cell lets mice see in new colours

While humans have three types of colour-detecting cells, mice and most other mammals have just two. But when a group of scientists gave mice the human gene for a third colour detector, they were able to detect colours that no mouse has ever seen before. This profound response to a simple genetic change may show us how our own vision evolved.

A new human receptor gives mice the ability to see into the orange and red end of the spectrumEvolution is almost synonymous with small, gradual changes, and for good reason. We might expect that large changes to an animal’s genetic code, and therefore to its body plan, simply wouldn’t work. It would be like shoving an extra cog into a finely-tuned machine and expecting it to fit in – the more likely outcome is a malfunctioning mess.

But that’s not always the case, at least not for the evolution of the human eye. To Darwin, the eye was so perfect that it made him cast serious doubts over his theory of evolution.

But new research shows that the eye and its connections to the brain are surprisingly flexible, and can incorporate major evolutionary changes with ease.

In our retinas, cone cells are responsible for giving us colour vision. Most mammals have just two types, one that is sensitive to short violet-ish wavelengths of light (S cones), and another that responds strongly to medium greenish-blue wavelengths (M cones).

But somewhere in our history, humans and many other primates picked up a third cone sensitive to longer wavelengths (L cones), that allows us to see colours near the red end of the spectrum.

You might expect that adding another type of cone cell into the eye would be a very large step, requiring substantial (and gradual) changes in the wiring of both the retina and the brain. But Gerald Jacobs from the University of California has shown that it’s as easy as installing new software into your computer.

The three human cone cells respond to different wavelengths of light.Together with Jeremy Nathans from Johns Hopkins Medical School, Jacobs genetically engineered a strain of mice that had human L cones in addition to its medium and short-wavelength ones.

Using a technique called electroretinography, they confirmed that these added cones were in full working order and were sending electrical outputs to the brain. They were clearly providing visual signals, but did this translate into any meaningful information in their brains?

Nathans and Jacobs set the mice a challenge to test their new retinal powers. They were shown three panels lit with coloured lights and had to pick out the one that was lit differently.

The normal mice failed to tell the difference between greenish-blue and yellowy-orange lights. They only chose correctly about a third of the time – the success rate you’d expect from random guesswork.

But the triple-coned mice passed with flying colours, so to speak. After lengthy training, they picked the odd panel out up to 80% of the time. Their genetic change had clearly been smoothly slotted in to their nervous system. They were seeing in three colours.

The human eye has three types of colour-detecting cone cells.The success of Nathans’s experiment is testament to the tremendous flexibility of a mammal’s nervous system. And it gives us a tantalising glimpse into how modern primate vision evolved.

At some point in our evolutionary past, one of our ancestors was born with a mutation that gave it a third and slightly different type of cone cell. This change would have brought it an instantaneous competitive edge over its two-coned peers.

Having three types of cones, rather than two, greatly expands the range of light that an animal can detect, and gives it a much broader colour palette. Such an animal would have gained a deeper appreciation of its surroundings than its peers – its eyes would quite literally have been opened to new possibilities.

Some scientists believes that the key advantage lay in being able to discern unripe green fruit from ripe ones that are typically red or orange. The bright colours of fruit may even have co-evolved with the advent of three-coned primate vision, to take advantage of these new seed-dispersing agents.

Over future generations, these new visual powers would have been honed by further genetic changes, but it is highly likely that the initial genetic jump-start would have spread like evolutionary wildfire.

The same may even apply to other senses, like taste and smell, with new genetic changes caused profound effects by adding new receptors and expanding an animal’s sensory range.

Reference: Jacobs, Williams, Cahill & Nathans. 2006. Emergence of novel colour vision in mice engineered to express a human cone photopigment. Science 315: 1723-1725.

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