Tag Archives: Mammals

Do bats know the speed of sound from birth or do they have to learn it?

Kuhl’s pipistrelle bat

Most bats use echolocation to orient themselves in space. This means that they produce high-frequency sounds and can judge the distance of obstacles that reflected the sound based on the return time of the echo. However, to judge the distance based on the time the echo returns, one needs to know the speed of sound. The problem is that the speed of sound is not constant: it can vary in nature by more than 5% depending on temperature, humidity or altitude*.

What would be your guess: are bats born with the innate knowledge of the speed of sound and therefore distance judgment, or do they need to learn this?

Since the speed of sound is not constant, scientists predicted that knowledge about it is not innate in bats, but rather gained through experience. However, research on Kuhl’s pipistrelle bats (Pipistrellus kuhlii) has shown that the opposite is true.

These bats occur mainly in the Mediterranean region and in the West Asia. In their natural environment, they experience a wide range of temperatures and thus conditions with different speeds of sound.

To assess the effect of the speed of sound on bats’ echolocation and behavior, scientists conducted experiments in normal air and helium-enriched atmospheres – with a higher speed of sound and therefore a faster echo return time**. Young bats that were reared from birth in different conditions were compared to each other as well as to adult bats that had grown up in normal air.

It turned out that in the atmosphere with helium, bats, regardless of their age or rearing environment, assessed the distance to a target (feeding platform) as being closer than it actually was. Their echolocation pattern was the same as for closer objects in normal air. Additionally, in helium atmosphere, bats often slowed down and prepared for landing too early, thus landing ahead of their intended target. Even after several days in the helium atmosphere, the bats did not change their behavior and missed their target as often as at the beginning of the experiment.

This indicates that the speed of sound is encoded in the bats’ brains from birth, and the world seems to be perceived in terms of time rather than distance.

But how do bats deal with changes in the speed of sound in the wild? Firstly, these changes are usually smaller than those encountered in experiments. Secondly, as the bat approaches the prey or obstacle, the absolute error in distance judgement decreases. The error is a fraction of the distance – for example, if the speed of sound is increased by 10%, the object that is 100cm away seems to be 90cm away – error of 10 cm. But if the object is 10cm away the error is only 1cm. Lastly, bats usually don’t catch prey with their mouths, but entrap it with their wings and tail membrane, so they don’t have to be very precise. Although, even in the wild bats may miss their target.

While animals have amazing abilities to learn and adapt to their environment, in this case they seem to rely on innate skills even if they are not perfect in all conditions.

* For example, in standard air at 0°C, sound travels at about 332 m/s and at 30°C it travels at 350 m/s. So, the echo returns faster at higher temperatures.

** The experimental conditions increased the speed of sound by 10%, 15% or 27% – depending on the amount of helium.

Photo: Leonardoancillotto86 – Italy, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=15410420

Did you know that dolphins know when they do not know?

When I was younger, I watched “Who wants to be a millionaire?” on TV sometimes. You probably know this program or one like it, in which a participant has to choose a correct answer to a question from among a couple of options. When they choose the right answer, they can continue to play for an increasing prize, but when they are wrong, they lose most or all they have won so for. But there is also a third option – the participant can decide not to choose any of the answers, but to finish the game and take with them what they won so far. Of course, the last option only makes sense if the participant doesn’t know the answer to the question.

Many animals were tested in set-ups similar to “Who wants to be a millionaire?” and like humans, they more often chose to evade “answering” when the task was too difficult.

In one experiment, scientists trained a buttlenosed dolphin to press one button when it heard a high-pitched tone (2100 Hz) and another when the tone was lower (between 1200 and 2099 Hz). At the beginning the choice was easy – the sound was definitely low or high – but with time difficulty increased (with the lower sound getting closer to the border between high and low – 2099Hz).

When the dolphin pressed the appropriate button, he got a reward (praise and a fish). However, when he chose wrong, he got nothing and had to wait a while for a new sound and another chance. Then a new button was added between the original two. When the dolphin pressed it, he didn’t get a reward, but after a short delay, a new, easy trial began. However, when the dolphin chose this option too often, the delay increased.

What did the dolphin do? Initially, when the high and low sounds clearly differed from each other, the dolphin had no problem choosing the correct button. However, when the sound was harder to determine, he often showed signs of uncertainty – he moved more slowly to the buttons, hesitated between them, and it took him more time to decide. In addition, he chose the middle button more often – that is, he did not try to win the reward right away, but rather preferred to wait for the next attempt.

The scientists who conducted this study did the same experiment on humans (not under water, but at a computer). The human choices were practically the same as those of the dolphin. Most people said they chose the middle option when they weren’t sure if the sound they heard was low or high. Although the dolphins could not explain their choices, their behavior indicates that they may similarly evaluate their uncertainty and respond accordingly.

Similar experiments have shown that different species of monkeys, rats, pigeons, or even honey bees also avoid difficult choices, if possible. They seem to “know that they do not know”.

Photo: Pixabay

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Did you know that adoption also occurs in animals?

Female bonobo with an adopted daughter feeding on fruit from the branch that adoptive mother broke off and was holding.

Adoption – that is, the exclusive care for someone else’s offspring (especially after the mother’s death) – occurs in many mammals, such as chimpanzees, dolphins, squirrels, hyenas and polar bears. If someone else’s egg ends up in a bird’s nest, it will often take care of the hatched chick (even one of another species, such as a cuckoo). This seems to be more of an instinctive behaviour than a conscious choice on the part of the parents. Caring for others’ offspring has also been observed in some species of fish and wasps. But these are isolated cases, and the following text concerns (non-human) mammals.

In mammals, maternal care is especially important during the period when the infant still needs milk. Usually, the orphaned young will be taken care of by a female, who at the same time is feeding her own offspring, or who has just lost it. There are also cases where the female begins lactation after adoption – for example in bottlenose dolphins.

In many mammals, the mother continues to take care of the young also after weaning, by providing e.g. protection, transportation, and food. A maternal presence is also important for the development of the young’s emotional, social and cognitive skills. Therefore, adoption even at an older age is important for the survival and wellbeing of young animals.

Why do adult animals adopt someone else’s child? After all, that requires a lot of energy and time. There may be several reasons for this behaviour.

Orphans are most frequently adopted by their family, for example older siblings. From an evolutionary point of view, caring for a relative is beneficial because family members share genes, and therefore helping a relative increases the chance of passing one’s genes to the next generation.

Adoption by young females may also give them a chance to learn and develop their maternal skills, which in the future may increase the chances of survival of their own offspring.

In animals that live in groups (for example, chimpanzees), it is common for an orphan to be adopted by females who had a close social bond with its mother. In this way, the social relationships between group members are maintained, which can be beneficial for the foster mother. An adoptee can also become an ally of the adoptive parent and help to raise their social status or reputation.

There are also cases of adoption of unrelated individuals, even from entirely different social groups by experienced mothers (e.g. in bonobos). In such cases, it seems that the adoption does not bring any direct benefits to the adopted mother (although in some cases there may the potential for help from the adoptee in the future). As I wrote elsewhere, many animals show empathy, and in some cases, adoption seems to be purely empathetic behaviour (for example, in dolphins, bonobos or chimpanzees, who additionally have a soft spot for infants).

Photo from Tokuyama (2021).

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Did you know that domestic cats… ?

This time I will give some information about the behavior of domestic cats that I think is interesting and less widely known. I’ll describe the results of various scientific studies, which mostly describe general trends. Of course, your individual cat could act differently or have different preferences, due to e.g., personality, experience or breed. If that’s the case, feel free to let me know.

… are the only* cat species that uses the “tail up” signal?

A vertically raised tail is a housecat’s sign of friendly intentions. When two cats meet, often the one who is lower in the hierarchy (or feels in a weaker position) raises its tail first.

Cats also use this signal of affiliation towards people.

The wild cats from which the domestic cat is derived do not use the “tail up” signal. One theory is that it evolved in ancient Egypt, where cats were bred in large groups (an unnatural situation for wild cats), and a clear signal of friendly intentions let them avoid unnecessary conflicts.

… prefer different toys depending on whether they are hungry?

When cats are hungry, they are more likely to attack larger prey. A similar effect can be seen in the context of play – cats usually prefer mouse-sized toys, but when hungry they choose rat-like toys. In wild animals, hunger tends to lower the desire to play altogether.

This suggests that playing and hunting are very similar for domestic cats.

… are less aggressive when given the opportunity to play?

Too little play and a non-stimulating environment can contribute to aggression in cats (and dogs).

Even adult cats need to play, although they usually only want to do so for 2-3 minutes at a time. If you would like to play with your cat longer, wait for him/her to initiate the interaction. Research suggests that when the cat, rather than a human, initiates play, the interaction usually lasts longer. Other research shows that cats prefer a man-operated “fishing rod” to unanimated toys, and of course new toys are more interesting than old ones**.

Additionally, playing with a “fishing” toy reduces cats’ tendency to hunt wild animals.

… can use catnip as mosquito repellant?

Many cats (including wild cats, such as lynx, leopard and lion) react vigorously to catnip. They rub their head against the plant and roll in it. The smell of catnip activates the reward system in cats and the secretion of endorphins, similarly to opium’s effect in humans. However, catnip is not addictive to cats and is often added to toys by manufacturers.

It seems that the reaction to catnip is not only about euphoria. Catnip contains substances that repel mosquitoes and other insects. When rubbing against the plants these substances are transferred to the cat’s fur and it becomes less attractive to mosquitoes and other insects.

Cats hunt from ambush, by slowly sneaking up to their prey and waiting for the right moment to attack. While doing that they are an easy target for mosquitoes, which is why catnip-based repellant is a great solution (by the way, substances in catnip also repel mosquitoes when applied to human skin).

 * One exception is that lions – the only wild cats that live in groups – also raise their tails in some affiliative interactions with others. Nevertheless, I never saw lion’s tail raised as highly as domestic cat’s tail. This behavior has certainly evolved independently in domestic cats.

** Small suggestion from me: to prevent kids from getting bored with all their toys, it’s a good idea to hide some of them away. After some days/weeks/months you hide different toys and return the old ones, that now become attractive. I would expect that it works for cats as well.

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Photo: EVG Culture from Pexels.com

Did you know that wild mice that live near people are better at solving problems?

House mouse

Human activity is transforming the environment so much that many animal species are losing their place to live. But there are also a minority of species that can adapt to the new reality to some extent, or even prosper in it. Although life in the city means noise, pollution and less vegetation, there are also positive sides: an additional source of food all year round (in the form of leftovers from our tables) and fewer natural enemies (although cats are a big threat for many birds).

Living around people has an impact on animal behavior – for example, many birds in cities sing at higher frequencies to distinguish themselves from traffic. Research on birds also indicates that those living in urban areas are better problem solvers.

Coping with new problems seems to be one of the most important cognitive skills needed in the rapidly changing and unnatural environment created by humans. Recently, scientists have shown that mice that live close to humans are better problem solvers and, in at least one species, this is an innate ability that is a result of evolution, instead of something they learned during life.

Urban versus rural mice

In the first experiment, scientists caught striped field mice in the city and in rural areas. After treating all mice the same for a year in the laboratory, the tests began.

The mice were given various problem-solving set-ups (including a LEGO house – I’m not the only one who comes up with such ideas) which when opened – by pulling, pushing or moving various elements – gave them access to food.

Mice that were caught in the city were more likely to solve these problems. This couldn’t be explained by a fear of strange objects in the rural mice, because they actually approached the set-ups sooner and interacted with them longer.

As I wrote above, this experiment was carried out on mice that were born and grew up in the wild and it is possible that they could develop their cognitive abilities then – differently in rural and urban areas.

Long-term coexistence with humans

To find out the importance of long-term coexistence with humans, the same scientists conducted research on another species of mice – the house mouse. It is a synanthropic species that occurs almost exclusively near humans (this species also includes laboratory mice and various breeds of domestic pets).

There are several subspecies of domestic mice that have been associated with humans for different lengths of time: the Western European house mouse (Mus musculus domesticus) – about 11-13 thousand years, the Eastern European house mouse (Mus musculus musculus) – about 8,000 years, and the southeastern Asian house mouse (Mus musculus castaneus) – between 7,600 and 3,800 years. Thus, each of these subspecies had more or less time to adapt, through evolution, to humans’ changes to the environment (even if the living environment of people also changed a lot over these thousands of years). To eliminate the influence of individual mice’s life experience on the research, scientists did not study wild mice caught in the field, but studied their descendants, after several generations in the laboratory under constant conditions.

Adapting to life with humans

The descendants of the wild house mice were subjected to the same problem-solving tests as the field mice in the previous experiment. It turned out that the longer a mouse subspecies was associated with humans, the more likely it was to solve the problems. And this couldn’t be explained by the differences between subspecies in the time they took to approach the set-ups, or the differences in fear of a new environment.

Since all these experimental animals had lived under the same conditions throughout their lives, these studies show that different subspecies differ in their innate ability to deal with new problems. It seems that over the course of generations, coexistence with humans influenced the evolution of cognitive skills in wild animals.

Photo based on 4028mdk09, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11056096

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Rats in action 2 / Szczury w akcji 2

After a handful of attempts (for video of the first trials see here) my rats figured out how to open my LEGO puzzle boxes. It took them the longest to realise how to open the door of the DUPLO house. Tokyo was more interested than Stripe in the whole affair and is better at the ask.

Po paru próbach (film z pierwszych prób możesz naleźć tutaj) moje szczury nauczyły się otwierać pudełka-łamigłówki. Najtrudniejsze okazało się otwieranie drzwi do domku z DUPLO. Tokjo okazała większe zainteresowanie pudełkami i nauczyła się je otwierać szybciej.

Did you know that rats’ tails feel nice?

Many people are creeped out by rats’ tails. They think that they are grose and hairless. The former may be a matter of taste, but the latter is simply not true. A rat’s tail is covered in short delicate hairs and in my opinion feels quite pleasant: warm, dry* and slightly fuzzy.

Their tail helps rats with thermoregulation. For example, during intensive physical activity, rats don’t sweat like us, but the blood flow to the tail is increased which helps them lose heat (in humans the blood flow to the skin also increases when we overheat). At lower temperatures, the blood flow to the tail decreases.

Additionally, their tails help rats to keep their balance when climbing or running on narrow surfaces. Although not prehensile, the tail can hook onto, for example, a hand when the rat suddenly loses its balance.

Remember to never to pull on your pet rat’s tail or, even worse, use it to pick the rat up. It’s not only painful but can lead to removal of part of the skin, together with the underlying tissue (so-called degloving).

* There is also a common misconception that reptiles such as snakes are slimy, but they are actually have dry skin.

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Did you know that wolves can’t make puppy eyes?

Even if you have never had a dog you’ve probably seen one make an expression like the one in the photo above. Dogs can raise their inner eyebrows, making so-called “puppy eyes”. It seems that the dog wants to say “I messed up, but you won’t be angry, right?” Or “You really want to leave me home alone?”

However, wolves – dogs’ closest relatives – cannot make puppy eyes. The muscles of dog and wolf faces are practically identical, except for the single muscle that lets dogs raise their eyebrows. Instead, wolves only have a small tendon, which means they cannot be nearly as expressive with their eyebrows. Additionally, dogs raise their inner eyebrow more often than wolves.

But why do dogs differ from wolves in this respect? It seems that humans, consciously or not, selected for “puppy eyes muscles” and behaviour in dogs.

When dogs pull up their inner brow, they eyes look bigger, more similar to big infant eyes. This facial expression is also similar to the one made by us when we are sad. Dogs with more pronounced puppy eyes may have triggered the human nurturing response. They could have gotten more food, more care and have a higher chance of survival. Even nowadays dogs in shelters that make puppy eyes more often find a new home faster.

Pronounced facial expressions, especially around the eyes, are important in human communication. And it seems important for dog – human communication as well. Even if the dog doesn’t always understand us, its expression may at least give an impression of understanding. Also, dogs more often than other domesticated animals seek eye contact with humans and can follow the human gaze, which helps dog-human communication.

Although I’ve spoken generally here, the facial musculature of just a handful of breeds has been tested so far, but all of them had the extra muscle above the eyes. Except for the husky – the breed most closely (among the studied breeds) related to wolves.

Maybe it’s time to start our own observations? Do you know breeds (or individual dogs) that can’t make puppy eyes?

Photo: Dominika Roseclay, Pexels.com

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Did you know that rats show empathic behaviour?

Imagine that you are walking along a lake. Suddenly you notice someone in the water, calling for help. What do you do? The answer may depend on many factors, such as how well you can swim or whether there are other people nearby. You can consciously analyse the situation but feelings are also important. Most people actually feel distressed when seeing others suffering which may push them into action.

And it seems that such empathy with others’ suffering is not restricted to humans, but occurs in many other animals.

Scientists studied empathic behaviour in rats and found that rats saved others from a water bath (not deep but still unpleasant). They did that even if the helped rat would end up in another compartment, without the possibility for social interaction which is rewarding for these animals. The rats helped not only their cage-mates but also strangers and if they experienced the bath themselves earlier, they were more willing to help the other rat.

However, when more effort was needed to help another rat – for example: multiple chain pulls were required to activate the opening mechanism – animals were less willing to help (similarly to humans).

Another experiment showed that one rat can take the time and effort to release another from a very tight and uncomfortable tube, even when it could choose to eat chocolate (which they like a lot) instead. Although in this case rats could interact with each other and eventually share the chocolate.

It seems that the willingness to help other animals, even if it brings no direct reward, or even comes at a cost (less chocolate later), stems from the fact that rats try to reduce their own empathetic discomfort. This is supported by the fact that rats which were given the anxiety-reducing drug midazolam paid no special attention to distressed companions (but they did to chocolate).

Not only rats show empathy, but also for example, dolphins, elephants and monkeys. There are even cases of chimpanzees in zoos drowning while trying to help their children or mates that had fallen into a moat surrounding their enclosure.

So, we know that animals can show empathic behaviour. Will we show empathy towards them?

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Did you know that humpback whales have seasonal hit songs?

Most likely you have heard birds singing. But have you heard whale song?

In some whale species, for example humpbacks, male sing, probably for similar reasons why birds do, to attract females or to keep other male away.

But what is whale song?

In humpback whales it consists of basic units, like moans, whoops, groans and barks. A few of these elements in a sequence form a phrase and a couple of phrases repeated together form a theme. Different themes together form a song. A male can repeat a single song for hours.

For years, scientists have recorded the songs of humpback whales breeding along Australia’s east coast and some Pacific islands (see map below). There are several separate groups that breed in these waters. The song males sing is usually the same within a group, but may differ between groups. This is an example of animal culture – a socially learned behaviour specific to a given group.

Breeding locations of the studied groups

What I find even more interesting is that the song sung by a given group can completely change from one season to the other, and new ‘hits’ move eastwards over time to other groups. Usually, the group at the East coast of Australia sings a new hit, then the next season the neighbouring group or groups eastwards copy it and with time it reaches central Pacific. While the group in the central Pacific still sings this song a couple of years later, two more new hits may have appeared at the Australian coast.

Schematic representation of changes in the song trends in humpback whales. Notes in different colours represent different songs (different shades are new songs based on the old ones).

But where do new hits come from? They may be variations on phrases and themes of the old song that finally turn into a completely different arrangement. But sometimes the new song has nothing to do with the old song. The songs were recorded during the breading season and it seems that the song transitions happened outside it.

Different humpback groups live separately in the breeding season and males rarely move between groups. However, groups do have contact with each other when travelling to and from, and eating at, the feeding grounds close to the Antarctic. It seems that this is how songs find new fans. It seems that humpbacks just like new tunes, learn them quickly, while at the same time show conformity*. And soon the whole group sings the new hit.

Why, in the west Pacific, it is the East-Australian group that starts new trends? Possibly because it is the largest one and therefore has the highest impact on what is heard in mixed groups. But where do they get their new songs from? Likely from contacts with the group from the West Coast (although this population were not thoroughly studied). I wonder whether the songs may travel around the world, slowly transforming, to come back to the same group so much changed that they are not recognisable as the old songs any more.

While one season hits and temporary trends are common in humans, the level, scale and rate of cultural change in whale songs is unique among nonhuman animals.

You can find more information and recordings of whale song here (recordings at the bottom of the page).

* You can read about the great tit conformists and their traditions here.

Humpback whale photo: Photo Elianne Dipp from Pexels.

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