Discrete invitation

Arabian babbler leads partner to hidden place

Arabian babbler invites partner in an unobtrusive way

Unlike other animals, the Arabian babbler keeps its sex life private. It has a subtle way to invite another bird for a concealed copulation, as Yitzchak Ben Mocha and colleagues observed.

Animals do not seek to conceal their sexual behaviour. But the Arabian babbler, Argya squamiceps, is an exception. The birds, which live in stable kin groups of two to twenty individuals, do not want to be detected when copulating. A couple that is going to mate will take care to be out of sight of their group mates: at a certain distance or behind thick vegetation.

Yitzchak Ben Mocha and colleagues describe how the birds take a partner to such hidden place without revealing their intention to the other birds.

Arabian babblers live in open, dry landscapes across the Arabian Peninsula and Israel, where each group defends a territory. Within a group, only one pair, the dominant pair, will breed. They are the parents of nearly all young in the group. The other adult group members are subordinates and help raise the young. After hatching, the young stay in the nest for two weeks. And after fledging, it takes another eight weeks until they reach independency. During this period, they need care: protection and food.


Observing a population, the researchers witnessed that the birds have a subtle way to invite another bird to copulate. They place themselves in a location that is visible to that specific bird only while holding an object in the beak; often they slightly shake their head. The object can be anything, such as a twig, leaf, fruit, small animal or eggshell. The signalling behaviour is unobtrusive, but the partner grasps the message. When he or she accepts the invitation and approaches, the initiator moves away or hides behind the vegetation and the partner will follow. If they lose contact, the initiator comes back, places itself within the other’s visual field and repeats the invitation.

Usually, a copulation follows. But when another group member appears, the  signaller drops the object and stops the mating behaviour.

The object presented is nothing special, just something that happens to be abundant. So, it is not intended to impress. Neither is it a gift; although it may be edible, that does not affect the partner’s response. The presentation is just a subtle way to invite a mate for a concealed copulation.

Crucial help

Even dominant birds, which don’t have to fear that subordinates will dare to disturb a copulation, take great care to hide their mating behaviour. Why is that? The authors offer an explanation. The care of subordinate group members is crucial for raising the offspring. Without that care, the young have a smaller chance to reach adulthood. Moreover, they gain less weight and will be less capable to acquire food once they are independent.

The dominant pair does not want to lose that precious help. With overt mating behaviour, the researchers suggest, they would cause social tension in the group and increase the chance that subordinates leave or fight, which would be undesirable. So, the parents prefer to keep peace by keeping their love life private.

Willy van Strien

Photo: Greg Schechter (Wikimedia Commons, Creative Commons CC BY 2.0)

See invitation for concealed copulation on YouTube

Ben Mocha, Y. & S. Pika, 2019. Intentional presentation of objects in cooperatively breeding Arabian babblers (Turdoides squamiceps). Frontiers in Ecology and Evolution 7: 87. Doi: 10.3389/fevo.2019.00087
Ben Mocha, Y., R. Mundry & S. Pika, 2018. Why hide? Concealed sex in dominant Arabian babblers (Turdoides squamiceps) in the wild. Evolution and Human Behavior 39: 575-582. Doi: 10.1016/j.evolhumbehav.2018.05.009
Ridley, A.R., 2007. Factors affecting offspring survival and development in a cooperative bird: social, maternal and environmental effects. Journal of AnimalEcology 76: 750-760. Doi: 10.1111/j.1365-2656.2007.01248.x

Who dares?

Black-headed female takes the lead in Gouldian finch

Black-headed Gouldian finch is most courageous

When Gouldian finches have to drink, not every bird is willing to leave the safe trees first. There is a pattern in the order in which they venture to a waterhole, Andrias O’Reilly and colleagues show.

Drinking water is a perilous adventure for the Gouldian finch, a songbird from north-western Australia. It is a colourful species. If the birds are on the ground near a creek or pond, birds of prey will spot them easily, so they are less safe there than in the trees. But they have no choice: they have to drink. Once a day, early in the morning, they take the risk, coming in flocks. Some of them are more courageous than others, as Andrias O’Reilly and colleagues saw.


That was already known from experiments in the lab. Gouldian finches have different head colours; most birds (70 percent) have a black head, others (30 percent) a red one and a few (less than 1 percent) a yellow one. Research had shown that the colour is linked to personality: animals with a red head are more aggressive, whereas black-headed birds are more explorative and more courageous. The researchers wondered if this is also the case in the wild. If it is, a difference in courage should be visible in a risky activity, such as drinking water.

So, they observed the birds at their daily drinking party and noted what type of bird descended first to the waterhole, taking the greatest risk. They conducted their research at the end of the breeding season, when the young had fledged.

Apparently, Gouldian finches are no heroes. They will not land on the ground to drink untill other birds are present at the waterhole. If no bird is there, they will remain in the trees and wait for other birds to appear.


Only in that case, they dare as well. And then, the black-headed birds are most likely to take the lead, as it turned out. That is in agreement with what was found in the lab. The black-headed birds run less risk because they are less conspicuous than the red-headed ones, the explanation is.

Young birds have not yet full colours and are even less conspicuous. Still, juveniles let the adult birds precede; probably the young birds are more cautious because they have little experience.

At the start of the research period, mainly females are the first birds to descend to the water. Fathers primarily care for the young for a while after fledging; during this period, males will stay with the cautious young, so females have to take the lead. And the black-headed females will take it.

Willy van Strien

Photo: Gouldian finch, black-headed male. Linda de Volder (via Flickr; Creative Commons CC BY-NC-ND 2.0)

O’Reilly, A.O., G. Hofmann & C. Mettke-Hofmann, 2019. Gouldian finches are followers with blackheaded females taking the lead. PLoS ONE 14: e0214531. Doi: 10.1371/journal.pone.0214531

Costs before benefits

By guarding stepkids, bee male may get the mother

In bee Ceratina nigrolabiata, the male takes care of other males' offspring

Ceratina nigrolabiata bee males guard the nest of their female partner. This seems surprising, as the brood consists mainly of other males’ offspring, as Michael Mikás and colleagues show. Still, the males have good reason.

Bee males don’t do much. Okay, they mate with females and of course that is important, but that’s it. The females construct a nest and take care of the offspring. In solitary species, such as the species that visit a bee hotel, each female makes her own nest; social species, such as the honeybee, live in groups in which queens produce eggs and workers do the work.

There is one exception, Michael Mikát and colleagues report: in the solitary bee species Ceratina nigrolabiata, males do participate in care – but, surprisingly, mainly by protecting other males’ offspring.


A Ceratina nigrolabiata female makes her nest in the hollow stem of a plant. She goes inside, lays an egg, brings food for the larva that will hatch, closes the space by building a wall and lays another egg in the next part of the stem. Ultimately, a nest consists of six to seven cells in a row, with young in a descending stage of development when viewed from the inside out. The mother leaves when the nest is completely provisioned.

In the majority of nests in which a female is active, a male is present, as the researchers observed during their studies in the Czech Republic. When the female performs foraging trips, the male stays inside the nest to protect it from predators such as ants, driving them away when they come near. He is sitting near the entrance with the head facing inwards. When she returns, she will scratch his abdomen and he will let her pass.

The benefit for her is clear: thanks to this guard, she can leave to forage without having her nest unattended.

For him, it is different. DNA analyzes show that in most cases the brood that he protects does not contain any offspring that he fathers. So he takes care of other males’ offspring, and in general, that is not a good strategy from an evolutionary point of view.

Male switches

In fact, the bee males have no interest in the brood at all; it is the mother that captivates them. A male only has a chance to mate if he finds a female and stays with her until she is willing; in Ceratina nigrolabiata, a female will mate several times in her life. So he has to stay at her nest. While he certainly participates in care by actively protecting the brood, this stepfather care is a by-product of monopolizing a female, according to the researchers.

And indeed, if they removed a female from her nest, the male abandoned the brood.

So, every female is assured of a helpful lover. If a male disappears, his place is usually taken by another within a day.

These stepfathers are not ideal helpers, because they stay on average for only seven days, while a female needs about forty days to complete her nest. As a consequence, the male inhabitant of most nests changes one or more times, and in fatherless periods the female spends less time collecting food, staying on the nest instead. The more changes, the fewer offspring she therefore can produce. But at least she gets help, which is unique among solitary bees.

Willy van Strien

Photo: Ceratina nigrolabiata, female returns at her nest in a hollow plant stem and scratches the guarding male. ©Lukáš Janošík

Mikát, M., L. Janošík, K. Cerná, E. Matoušková, J. Hadrava, V. Bureš & J. Straka, 2019. Polyandrous bee provides extended offspring care biparentally as an alternative to monandry based eusociality. PNAS: 116: 6238-6243. Doi: 10.1073/pnas.1810092116

Care for everyone

Earwig mother tends foreign eggs and adopts orphans

earwig female cares for another female's offspring 

An earwig mother will treat another female’s eggs as caring as her own eggs, Sophie Van Meyel and colleagues write. Previously, Janine Wong and Mathias Kölliker had discovered that she is willing to accept young orphans in her family.

Earwigs are not very popular animals, but actually they are lovely creatures. The extensive and complex care that females provide to their offspring is impressive.

In late autumn, a female European earwig, Forficula auricularia, lays twenty to forty eggs in a burrow. She then remains in that nest and tends her clutch during winter. And that pays off: without her presence, almost all eggs would be lost, Sophie Van Meyel and colleagues show. A mother cleans the eggs with her mandibles to prevent growth of fungi and pathogens. She protects her clutch against predators. She ensures that the eggs will not desiccate. And she relocates them if necessary.

This nice maternal behaviour is not directed exclusively to a mother’s own clutch.

Weight loss

When the clutch of an earwig female is replaced by that of another female, she provides the same care with the same dedication, as Van Meyel witnessed when she conducted cross-fostering tests in the lab with five-day-old clutches. The eggs have their mother’s odour, so a female should be able to recognize foreign eggs. But she does not reject them. When tending eggs, a female faces a tough task, because she will not leave to forage until the young have hatched, which takes a few months. So, she will lose weight.

But strangely enough, the weight loss during winter is even greater for a female that has no eggs to tend. Apparently, food is scarce outside. A tending mother probably cannibalizes  some of her eggs to survive. This may explain that she is willing to care for a foreign clutch as well as for her own clutch, as the possession of eggs is a guarantee that she does not have to starve. She will be forgiven for consuming a small part of the clutch, since without her care almost no egg would make it through the winter months.


The young hatch in early spring. Earwigs do not go through a complete metamorphosis with larval and pupal stages, but the juveniles resemble adult animals. They are nymphs.

After hatching, the nymphs usually stay in their burrow for a week. The mother protects them, regurgitates food for them and accompanies them when foraging at night. The nymphs can do without that care; they are mobile shortly after hatching and can search for food independently. But they do better if their mother attends them during the first week.

However, not every mother survives until spring, so some nymphs are orphans from the start of their life. Many such nymphs leave their natal nest during the first night. If they survive, they often join another family. Then again something remarkable happens: the mother of that family typically accepts them, and most orphaned nymphs end up well, as Janine Wong and Mathias Kölliker have shown.

Most motherless nymphs appear to choose an adoptive family with smaller juveniles. They are safe there, because when food is scarce, nymphs may cannibalize each other, preferring nonsibling smaller nymphs. By accepting foreign nymphs, an earwig family therefore runs a certain risk. Apparently,  group augmentation confers an advantage to the adoptive family that outweighs that risk, but it is not clear yet what that advantage might be.

Willy van Strien

Photo: European earwig female with eggs. ©Joël Meunier

Watch an earwig mother tending her eggs on You Tube

Van Meyel, S., S. Devers & J. Meunier, 2019. Love them all: mothers provide care to foreign eggs in the European earwig Forficula auricularia. Behavioral Ecology, online 9 February. Doi: 10.1093/beheco/arz012
Wong, J.W.Y. & M. Kölliker M., 2013. The more the merrier? Condition-dependent brood mixing in earwigs. Animal Behaviour 86: 845-850. Doi: 10.1016/j.anbehav.2013.07.027

Young rebels

Ant larvae help to resist hostile take-over

The ant Formica fusca can resist parasites

When the nest of the ant Formica fusca is taken over by a parasitic queen of another species, the colony is lost. But the larvae help to limit the damage, according to Unni Pulliainen and colleagues.

An ants’ nest contains a large workforce serving the queen, which has the exclusive task to reproduce. Worker ants feed the queen and take care of her offspring, keep the nest clean and defend it. Their diligence attracts the attention of queens of other ant species that have not yet workers and for that reason could use some help. The black ant Formica fusca often suffers from such queens, which may invade a nest to exploit the workforce – thereby destroying the colony. But the host may resist, Unni Pulliainen and colleagues report.


If a hostile queen tries to enter a nest of Formica fusca, which lives in clear-cut forest areas and along forest edges in Europe and parts of southern Asia and Africa, the workers may detect her and kill her. But that doesn’t always happen; sometimes, they accept her.

Once she’s inside, she can go on. She kills the resident queen or queens – in Formica fusca, a few queens usually live together in one colony – and she will start laying eggs. The workers have to raise her offspring as if they were the offspring of their own queen. The foreign queen, which outlives the workers, gradually acquires her own workers, while the original workers die. By temporarily parasitizing the Formica fusca colony, she founds her own.


But the enslaved workers can limit the damage by sabotaging. The workers can remove the foreign eggs. And the orphan ant larvae seem to help.

Ant larvae sometimes eat ant eggs, and Pulliainen wanted to know if Formica fusca larvae might be keen to consume the eggs of a foreign queen. In experiments, she offered larvae one egg each, either of their own queen or of a foreign queen, which belonged either to a parasitic species or to an innocent species that never invades other ants’ nests.

The larvae never consumed an egg of their own queen. But when they were given an egg from a parasitic queen, they consumed it in one in ten cases; eggs of an foreign innocent queen were consumed less often.


The feeding behaviour of the larvae, albeit not very spectacular, may help to limit the damage. The eggs are nutritious and their consumption may increase the orphan larvae’s chance of survival. Male larvae can leave to reproduce as adults. And some of the female larvae will be future queens, which may found a new colony elsewhere. Female larvae destined to become workers can be successful too. They are not able to mate, but they can produce some sons, as sons develop from unfertilized eggs. The colony may be lost, but some larvae still have a future.

Willy van Strien

Photo: Formica fusca. Mathias Krumbholz (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Pulliainen, U., H. Helanterä, L. Sundström & E. Schultner, 2019. The possible role of ant larvae in the defence against social parasites. Proceedings of the Royal Society B 286: 20182867. Doi: 10.1098/rspb.2018.2867
Chernenko, A., M. Vidal-Garcia, H. Helanterä & L. Sundström, 2013. Colony take-over and brood survival in temporary social parasite of the ant genus Formica. Behavioral Ecology and Sociobiology 67: 727-735. Doi: 10.1007/s00265-013-1496-7
Chernenko, A., H. Helanterä & L. Sundström, 2011. Egg Recognition and Social Parasitism in Formica Ants. Ethology 117: 1081-1092. Doi: 10.1111/j.1439-0310.2011.01972.x

Humboldt squid doesn’t discriminate

Sperm to both male and female partners

Humboldt squid male mates male and female partners

Males of the humboldt squid are generous with their sperm cells; male-to-male mating is as common as male-to-female mating, Henk-Jan Hoving and colleagues discovered.

The mating of the humboldt squid or jumbo squid, Dosidicus gigas, is peculiar. Males produce spermatophores, long narrow capsules in which sperm cells are packed, and deposit them around a partner’s beak, which is between the eight arms and two tentacles. Each spermatophore then turns itself inside out to form a so-called spermatangium, which attaches itself to the skin.

If the partner is a female, the sperm cells will be needed. When she is spawning, she will use the sperm cells to fertilize the eggs. But the males transfer their sperm packets not only to females, but also to other males, according to Henk-Jan Hoving and colleagues. And males can’t use them.

It is not possible for researchers to directly observe the mating behaviour of the squid, which occurs in the eastern Pacific Ocean, because the animals live at a depth of several hundred meters. Instead, in order to learn something about that behaviour, the team examined the buccal area of captive specimens, both males and females, and counted the implanted spermatangia. They found sperm packets attached to both females’ and males’ buccal tissues, the same number in both sexes. The motto of mating males seems to be: ‘deposit your spermatophores anywhere you can’.

The question is why they don’t distinguish between male and female partners, as sperm cells transferred to a male are wasted.

Sharp teeth

The authors offer an explanation. The animals live in large mixed schools, in which they encounter many females and males. External morphological differences between the sexes are small, and a male that is about to mate has little time to check whether the individual in front of him is female. If he doesn’t manage to deliver his spermatophores quickly between the other squid’s arms and tentacles, he is in danger to be attacked. The humboldt squid is a predator; the suckers on its tentacles are lined with sharp teeth and its mouth has sharp edges. Cannibalism occurs.

That is why a male prefers a partner that is not larger, but of similar size. Because males are on average smaller than females, he will often deposit his spermatophores on a female that is not yet sexually mature. That is okay; she will store it until she needs it. But there is a chance that he accidentally transfers his sperm to a male.

Because of this strategy – be fast and stay safe – a humboldt squid male admittedly will waste sperm. But that is not a serious drawback. A male has hundreds of spermatophores available, and no more than 80 are transferred per mating. Even if he often mistakenly chooses a same-sex partner, he can still mate many females.


A female has dozens of sperm-storage organs in the buccal membrane, the seminal receptacles. Sperm cells leave the spermatangium after mating and migrate over the female skin to those storage organs, which apparently secrete an attractant.

When spawning, a female releases millions of eggs, held together in a gelatinous spherical mass. When that mass of eggs passes her mouth, the sperm cells will leave the storage organs, swim to the egg mass and fertilize the eggs.

Willy van Strien

Photo: Foto: Humboldt squid. Rick Starr. Credit: NOAA/CBNMS (Wikimedia Commons, Creative Commons CC BY 2.0)

Hoving, H-J.T. Fernández‑Álvarez, F.Á., E.J. Portner & W.F. Gilly, 2019. Same‑sex sexual behaviour in an oceanic ommastrephid squid, Dosidicus gigas (Humboldt squid). Marine Biology 166: 33. Doi: 10.1007/s00227-019-3476-6
Fernández-Álvarez, F.Á., R. Villanueva, H-J.T. Hoving & W.F. Gilly, 2018. The journey of squid sperm. Reviews in Fish Biology and Fisheries 28: 191-199. Doi: 10.1007/s11160-017-9498-6

Staying cool

Southern cassowary dissipates excess heat via its helmet

thanks to its helmet, the southern cassowary can offload excess heat

How can the tropical southern cassowary stay cool at high temperatures? Danielle Eastick and colleagues show that it uses its helmet to prevent overheating.

Just because of its size and strong legs – with a dangerous dagger-like claw that can be 10 centimetres long – the southern cassowary is an impressive bird. It also wears a prominent helmet or casque. What could be its function?

Until now, that was a mystery. Perhaps the helmet amplifies the deep sounds that the bird can produce, some people thought. Or perhaps it is a decoration to seek the attention of possible partners, next to the blue head and the blue and red wattled neck, according to another assumption. Otherwise, it may protect the head when the bird is moving through dense vegetation at high speed, or involved in a fight.

But now, Danielle Eastick and colleagues come up with a different answer.

Easily overheated

The southern cassowary lives in tropical forests of New Guinea and Australia. Being a large and dark animal, it can easily become overheated at high temperatures, so it must have the possibility to offload heat. Eastick hypothesized that the helmet might offer that possibility and set out to test this idea. It turned out that she was right.

The helmet consists of fragile, spongy bone and is partly hollow; it is covered with a horn layer and has an extensive superficial network of blood vessels. Infrared images taken by a special camera revealed that the blood vessels dilate at high temperatures, and the helmet gets warm. Heat can be offloaded to the air. But when it is cold, the blood vessel walls constrict and only a small amount of blood flows into the helmet. It cools down while the heat of the animal is preserved.

The legs and the tip of the beak contribute to temperature regulation in the same way, but the helmet plays the most important role. When it is very hot, a cassowary sometimes plunges its head into the water to lose more heat.


The possibility of thermoregulation had already been suggested earlier, but it was never studied extensively. There are some other tropical birds with a helmet that may help to offload heat; for instance, some hornbills have a helmet on the beak. And perhaps the helmet of some dinosaur species facilitated heat loss as well.

The fact that the helmet of the cassowary has a function for thermoregulation does not exclude that it also plays a role in partner choice. Although, to be honest, its design is not very impressive.

Willy van Strien

Photo: Paul IJsendoorn (Wikimedia Commons, Creative Commons CC BY 2.0)

Eastick, D.L., G.J. Tattersall, S.J. Watson, J.A. Lesku & K.A. Robert, 2019. Cassowary casques act as thermal windows. Scientific Reports 9: 1966. Doi: 10.1038/s41598-019-38780-8
Naish, D. & R. Perron, 2014. Structure and function of the cassowary’s casque and its implications for cassowary history, biology and evolution. Historical Biology 28: 507-518. Doi: 10.1080/08912963.2014.985669
Phillips, P.K. & A.F. Sanborn, 1994. An infrared, thermographic study of surface temperature in three ratites: ostrich, emu and double-wattled cassowary.  Journal of Thermal Biology 19: 423-430. Doi: 10.1016/0306-4565(94)90042-6

Frightening days

Crayfish avoid light when renewing their armour

red swamp crayfish is anxious when moulting




Process takes a month








Willy van Strien



Romantic sea

Fairytale light shows of Cypridinid ostracods

ostracod produces light to escape from predator

With an amazing show of light pulses, male cypridinid ostracods try to attract a mate. Each species has its own specific show program, with either very short lasting flashes or bulbs that glow for several seconds. Nicholai Hensley and colleagues examined the chemistry behind.

It looks like a fairytale scene: dozens of blue lights dancing in the dark waters of the Caribbean Sea. The spectacle is visible to those who dive or snorkel at the beginning of the night. The light artists are ostracods of the Cypridinidae family, tiny crustaceans (less than two millimeters long) with a carapax consisting of two valves, like a clam shell.

They are also known as sea fireflies. Nicholai Hensley and colleagues study their behaviour and the chemistry behind their light.


Ostracods produce light by expelling mucus containing a reactant, vargulin, and the enzyme c-luciferase, which react with oxygen in seawater emitting blue light. The ostracods use their light mainly to avoid predation. If a fish picks up an ostracod, the prey will produce a cloud of blue mucus that is pumped into the water via the gills of the fish. It makes the fish visible to its own predators. Startled, it will spit out the bite.

In ostracods of the family Cypridinidae that live in the Caribbean Sea, males use the same light reaction in a much more subtle way with a completely different purpose: they place luminescent slimeballs in the water in order to seduce a female into a mating. This courtship behaviour produces the fairytale scenes.

Train of lights

The light artist best known is Photeros annecohenae, one of the most abundant species off the coast of Belize. In the first dark hour of the night, when the sun is down and the moon is not shining, groups of males display above seagrass beds. They have to perform well, because competition is high. While there are as many females as males, most are unavailable. This is because they incubate fertilized eggs in a brood pouch, and during this period, they will not mate.

American biologists examined male courtship behaviour in the lab, using infrared light. A displaying male will first swim in a looping pattern just above the tips of the seagrass blades and place about three bright flashes of light, probably to draw attention. Then, while spirally swimming upward, it places weaker light pulses at regular intervals. It swims at high speed, slowing down when it releases a luminescent slime ball.

By doing so, it creates a train of about twelve consecutively flashing lights that can be 60 centimetres long. When finished, it descends to start a new series. Often other males join and start displaying in synchrony.


To choose a mate, females assess the light pulses that the males produce. If a female is attracted to a particular male, she will swim to him without producing any light herself. Thanks to his regular flashing pattern, she manages to meet him just above his last light pulse. Mission accomplished.

Sometimes males try to obtain a mate without producing light themselves. Instead, they intercept a female that is on her way to a performing male.

Starting a show, following another male’s show or sneaking to get a female are different tactics to acquire a mate and a male can easily switch among them.

Species-specific shows

In the Caribbean Sea, many other species of Cypridinidae also occur, and about ten species commonly live at the same place. Because they all have their own characteristic light show, a female has no difficulty finding a conspecific partner. The shows vary in the trajectory a courting male swims, the number of light pulses, the brightness of the light, the interpulse distance and time interval and the time that a pulse remains visible.


Hensley investigated the cause of the variation in light pulse length. For although all species perform the same chemical reaction to make light pulses, the duration of the pulses varies greatly: some species, such as Photeros annecohenae, show flashes that last only a fraction of a second, others make light bulbs that continue to glow for 15 seconds.

The structure of the enzyme c-luciferase appears to vary between species, resulting in the light reaction to proceed faster in one species than in another. This determines how soon the light extinguishes. In addition, the reaction rate depends on the amount of vargulin compared to the amount of enzyme: the more vargulin, the longer it takes before it is all converted and the light disappears.

Courting males produce far less light than an animal that avoids predation. Romantic lights don’t have to be that big and bright.

Willy van Strien

Photo: Luminous cloud around a fish that intended to consume an ostracod. It will spit it out. © Trevor Rivers & Nicholai Hensley

Fifteen-scaled worm emits light to defend itself in another way

Hensley, N.M., E.A. Ellis, G.A. Gerrish, E. Torres, J.P. Frawley, T.H. Oakley & T.J. Rivers, 2019. Phenotypic evolution shaped by current enzyme function in the bioluminescent courtship signals of sea fireflies. Proceedings of the Royal Society B 286: 20182621. Doi: 10.1098/rspb.2018.2621
Rivers, T.J. & J.G. Morin, 2013. Female ostracods respond to and intercept artificial conspecific male luminescent courtship displays. Behavioral Ecology 24: 877–887. Doi: 10.1093/beheco/art022
Rivers, T.J. & J.G. Morin, 2012. The relative cost of using luminescence for sex and defense: light budgets in cypridinid ostracods. The Journal of Experimental Biology 215, 2860-2868. Doi: 10.1242/jeb.072017
Morin, J.G. & A.C. Cohen, 2010. It’s all about sex: bioluminescent courtship displays, morphological variation and sexual selection in two new genera of Caribbean ostracodes. Journal of Crustacean Biology 30: 56-67. Doi: 10.1651/09-3170.1
Rivers, T.J. & J.G. Morin, 2009. Plasticity of male mating behaviour in a marine bioluminescent ostracod in both time and space. Animal Behaviour 78: 723-734. Doi: 10.1016/j.anbehav.2009.06.020
Rivers, T.J. & J.G. Morin, 2008. Complex sexual courtship displays by luminescent male marine ostracods. The Journal of Experimental Biology 211: 2252-2262. Doi: 10.1242/jeb.011130

Fiery character

A brave great tit probably is either big or hungry

The corage of a great tit depends on its body size and condition

How much risk is a great tit prepared to take? The answer differs greatly among individuals. Maria Moiron and colleagues show that how much the courage the birds exhibit, depends on their size and condition.

Just like humans, animals have a personality, a stable set of coherent behavioural traits. For example, animals differ from each other in how brave they are, the extremes being an aggressive, brutal, curious and enterprising character on the one hand and a shy, cautious and withdrawn nature on the other. As biologists pointed out, these personality types also occur in the great tit (Parus major). Maria Moiron and colleagues wondered if the personality of a great tit is linked to its physical characteristics.

To find out, they weighed a number of males and measured the length of leg, beak and wing. Also, they tested the animals for their willingness to take risks by assessing how aggressive the animals behaved to another male, which intruded into their territory. They also tested how quick they were to explore an unfamiliar test cage.

Fear or courage?

Great tits differ greatly from each other in all triats measured, as it turned out. After a statistical analysis of the data, the researchers conclude that large individuals on average are less anxious than smaller conspecifics. That may be, they speculate, because a large animal has a greater chance of winning when it comes to fighting and will be hurt less severely. An alternative explanation is that it will take more risk in acquiring food because it needs more energy.

Another finding is that the condition of the birds, in the sense of their energetic reserves, also determines their behaviour. An animal in need of some food generally takes more risks than an animal that is well-fed. A hungry bird cannot afford to be careful, it has to take action, the authors explain. It is also possible that a well-fed bird is more cautious because it has more difficulty taking off in case of danger.

Conclusion: the personality of a great tit is indeed related to its physical characteristics. That is not unexpected – but it had not been demonstrated before.

Willy van Strien

Photo: Tbird ulm (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Moiron. M., Y.G. Araya-Ajoy, K.J. Mathot, A. Mouchet & N.J. Dingemanse, 2019. Functional relations between body mass and risk-taking behavior in wild great tits. Behavioral Ecology, online January 18. Doi: 10.1093/beheco/ary199