Gaping display

Sarcastic fringehead impresses with giant upper jaw

sarcastic fringehead can open its mouth extraordinary wide

Males of the blenny Neoclinus blanchardi, the sarcastic fringehead, can open their mouths extraordinary wide. They perform their gaping display for nothing but impressing each other, Watcharapong Hongjamrassilp and colleagues show.

It is an amazing scene when Neoclinus blanchardi fully opens its mouth. A huge membrane becomes visible, consisting of palate and cheeks. It is vividly coloured and has a yellow margin.

In English, the fish is called sarcastic fringehead; it lives along the coast of California. It was already known that males, that have a larger mouth than females, impress each other with it. Now, Watcharapong Hongjamrassilp and colleagues show that they perform their elaborate display for that purpose exclusively.

Wrestling

The sarcastic fringehead can open a large mouth thanks to an upper jaw that is enlarged compared to related fish species and that grows longer than the rest of the body. Its posterior part is unossified and flexible and extends beyond the head. The jaw is connected to the skull in such a way that it can be rotated laterally.

As said, males signal by gaping to scare off each other. A successful male manages to occupy an empty snail shell or a rock crevice in which he hides with only his head protruding. He tries to attract a female. When she likes him, she will lay eggs in his shelter. He fertilizes the eggs and takes care of them until the young hatch. When another male invades his territory, he approaches him, performing the gape display.

The intruder either retreats immediately, or he persists and returns the display. Then the males clash and push each other with the open mouths pressed together. The bigger a male is, the wider his gape. The smallest usually loses, sometimes after the victor had bitten him.

Apparently, suitable shelters are so scarce that the fish has developed a special weapon to defend its place.

Missed opportunity?

But the sarcastic fringehead’s exaggerated gape would also be impressive enough to scare away predators, Hongjamrassilp thought. Or enticing enough to seduce females. He scuba-dove into the water and conducted experiments in the laboratory to see whether this happens.

It did not. If a predator looms, the sarcastic fringehead chases it away by burst swimming. And when a female shows up, he rapidly shakes his head side to side to arouse her interest. He keeps his amazing mouth closed in both cases.

A missed opportunity, you might say.

Willy van Strien

Photo: Neoclinus blanchardi in its shelter. Magnus Kjaergaard (Wikimedia Commons, Creative Commons CC BY-SA 2.5)

This video shows the gaping display

Sources:
Hongjamrassilp, W., Z. Skelton & P.A. Hastings, 2022. Function of an extraordinary display in Sarcastic Fringeheads (Neoclinus blanchardi) with comments on its evolution. Ecology, online Octobre 6: e3878. Doi: 10.1002/ecy.3878
Hongjamrassilp, W., A.P. Summers & P.A. Hastings, 2018. Heterochrony in fringeheads (Neoclinus) and amplification of an extraordinary aggressive display in the Sarcastic Fringehead (Teleostei: Blenniiformes). Journal of Morphology 279: 626-635. Doi:10.1002/jmor.20798

Cuckoo duck seeks defence

Foster family protects duck eggs against birds of prey

Cuckoo duck dumps its eggs in nest of aggressive host

Young cuckoo ducks do not need any care: they are independent upon hatching. Then why does the duck burden other birds with its eggs, Bruce Lyon and colleagues wondered.

In South America a duck species occurs that, like a cuckoo, lays its eggs in nests of other bird species. The hosts then unintentionally take care of them. This is the black-headed duck, Heteronetta atricapilla, with the appropriate nickname cuckoo duck; it is a so-called brood parasite.

Bruce Lyon and colleagues wondered why the cuckoo duck dumps its eggs in other birds’ nests. They don’t require much care, apart from brooding. After hatching, the young are immediately independent. That is a big difference with all other brood parasites, such as the common cuckoo. These species have young that have to be fed and protected for weeks, so it is very profitable for parents to outsource the care. But how does the cuckoo duck profit?

Easy prey

The shedding of parental duties may have to do with the danger of predation, Lyon hypothesized. If the cuckoo duck were to make its own nest, it would be close to water. And in such nest, eggs are easy prey for avian predators, especially the chimango caracara. This was shown in experiments in which the researchers placed chicken eggs in a self-made, unguarded nest. Within a few days, all eggs were gone.

Unless they placed the nest in a colony of brown-headed gulls. In that case, hardly any egg was stolen.

This gull is one of the hosts in whose nests the cuckoo duck dumps its eggs. In Argentina, where the study was conducted, two other important hosts occur, the red-fronted coot and the red-gartered coot. Like the brown-headed gull, they are aggressive birds that are capable to defend their nests fiercely. Is that the reason why the cuckoo duck chooses them to care for its offspring?

Safe

It seems to be. The duck eggs are indeed quite safe with these fierce foster parents, the researchers noted. Admittedly, it may happen that foster parents recognize a foreign egg and throw it out of the nest. But if they accept the egg, it almost always remains undisturbed and hatches. This very high chance of survival upon acceptance far outweighs the risk of rejection.

The researchers do not know exactly how much the cuckoo duck gains. They could not determine how many eggs would survive in a self-defended nest, because it never builds a nest. But related duck species that do incubate and guard their own eggs lose quite a lot to birds of prey.

Willy van Strien

Photo: black-headed duck couple. Cláudio Dias Timm (Wikimedia Commons, Creative Commons BY-SA 2.0).

Source:
Lyon, B.E., A. Carminati, G. Goggin & J.M. Eadie, 2022. Did extreme nest predation favor the evolution of obligate brood parasitism in a duck? Ecology and Evolution 12: e9251. Doi: 10.1002/ece3.9251

Sponge sneezes to stay clean

Stove-pipe sponge prevents clogging of filtration system

Stove-pipe sponges sneezes to keep the filtration system clean

The water from which sponges filter their food also contains oversized and inedible particles. Niklas Kornder and colleagues show how the stove-pipe sponge gets rid of this rubbish.

Sponges are one of the oldest animal groups, and perhaps the oldest. They are simple animals, without organs. Niklas Kornder and colleagues discovered that such simple organisms can keep their body clean.

To obtain food, sponges filter the water in which they live. Water is drawn in through small inlet pores – the ostia – and passes through an internal canal system, where food particles are extracted. It leaves the sponge through larger outflow openings – the oscula.

But water not only contains suitable food particles, but also large chunks and inedible stuff. It was assumed that this waste would be shed with the outflowing water. Kornder now shows that this is not true. It would be risky, as the rubbish may clog the filtration system.

Mucus highways

The researchers investigated the cylindrical stove-pipe sponge, Alpysina archeri, which lives in the Caribbean Sea, and video-recorded how it expels waste. It is a large sponge that can grow to a length of one and a half meters.

In the internal canals, waste is embedded in mucus, as it turns out. That mucus is transported to the inlet pores and exits, accumulating at the sponge surface. So, it moves against the direction of the water flow through the canals. On the sponge surface, a weblike pattern of ‘mucus highways’ can be seen, over which mucus streams travel. The streams aggregate into clumps on slightly elevated junctions.

Meal

From time to time, a wave of contractions and relaxations propagates across the sponge surface, while the inlet pores are closed: the stove-pipe sponge is sneezing. During the sneeze, the mucus clump is shed off, the sponge getting rid of the waste. And small fish and other animals that live in the vicinity of the sponge enjoy a meal.

The researchers think that other sponges also sneeze to keep themselves clean. However, it is still unknown by what mechanism waste laden mucus is transported.

Willy van Strien

Photo: Aplysina archeri, stove-pipe sponge. Nick Hobgood. (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Watch the sneezing sponge on video

Source:
Kornder, N.A., Y. Esser, D. Stoupin, S.P. Leys, B. Mueller, M.J.A. Vermeij, J. Huisman & J.M. de Goeij, 2022. Sponges sneeze mucus to shed particulate waste from their seawater inlet pores. Current Biology, online August 10. Doi: 10.1016/j.cub.2022.07.017

Colour meanings

Aegean wall lizard with white throat is more brave

Eagean wall lizard with white throat is bold

An Aegean wall lizard with striking throat colour will run off fast when a predator looms, Kinsey Brock and Indiana Madden write.

In Aegean or Erhard’s wall lizard, Podarcis erhardii, different colour morphs exist: the animals have either a white, yellow or orange throat. The lizards can be found on walls in South-eastern Europe, in a dry landscape with tough shrubs. They have several predators: snakes, birds, and mammals.

When a predator appears, a lizard will flee. But that implies that it must stop what it was doing: sunbathing or foraging for food. For that reason, it will not leave until necessary. Kinsey Brock and Indiana Madden wanted to know whether the three colour morphs have a similar flight initiation distance. They checked the distance they could approach a lizard before it ran away.

Careful

The throat colour of the Aegean wall lizard is genetically determined. Most animals, males and females alike, have a white throat; yellow and orange are less common. There are also individuals with mosaic throat colours, but they are rare. Brock and Madden investigated lizards with plain throat colour on the Greek island of Naxos.

You can get most closely to the white-throated wall lizards, they found; lizards with an orange throat run off earliest; yellow-throated animals are in between.

So, animals with an orange throat are the most careful. They also stay closest to a refuge: a crevice in a wall or dense vegetation. And once they fled, they are slower to reappear than animals with yellow or white throats.

It is in line with lab research showing that white-throated males are the most aggressive, bold, and brave.

Striking colour

An orange-throated Aegean wall lizard probably is more wary because it is more detectable. The grey-brown blotchy body has a camouflage colour, but a yellow, and especially an orange throat stands out against the background. This makes it easier for a predator to discover a lizard with an orange throat, so, in turn, it must flee earlier to escape from the enemy.

Willy van Strien

Photo: Male Podarcis erhardii with white throat. Gailhampshire (Wikimedia Commons, Creative Commons CC BY 2.0)

Source:
Brock, K.M. & I.E. Madden, 2022. Morph‑specific differences in escape behavior in a color polymorphic lizard. Behavioral Ecology and Sociobiology 76: 104. Doi: 10.1007/s00265-022-03211-8

Partnership

Young spotted bowerbird joins older male

Spotted bowerbird males collaborate

In company of a subordinate, a spotted bowerbird male stands stronger: his bower is safe, and more females are impressed, according to observations by Giovanni Spezie and Leonida Fusani.

Bowerbird males keep themselves to themselves. To seduce females, they each build their own bower with courtship platforms. They keep a far distance from each other; in the spotted bowerbird, the average distance is no less than 1 kilometre. Yet the owner of a bower often has company of a subordinate male. Giovanni Spezie and Leonida Fusani wondered what such male is doing there. Is he a younger male learning skills from an older one? Or does he actively participate in the activities, is it a form of collaboration?

The spotted bowerbird (Ptilonorhynchus maculatus or Chlamydera maculata) is one of 21 species of bowerbirds that exist, and it lives in eastern Australia. It has an erectile lilac crest on the nape.

spotted bowerbird bower is a lane with two platformsA male builds a lane of grass and twigs with a platform on both sides of mainly greyish objects, such as bones and stones. He decorates the place with berries, leaves and pieces of glass. Females will visit and enter the bower to watch the male calling and dancing next to his bower. The performance can last an hour. With his elaborate bower and energetic courtship display, he shows his quality. If she likes it, she will mate.

Males can devote all their time to show off, because taking care of the young is a females’ task. Some males attract several females, but all the effort of many others are in vain.

Adequate reaction

To find out what subordinate males are doing at bowers, the researchers made motion-activated video recordings. They analysed the footage to see if such male just watches, or also participates in bower maintenance and courtship. And if he helps, is he, like the bower owner, able to adapt his behaviour to the reaction of a visiting female, for example if she threatens to leave? Does the bower owner benefit from the help? And the helper himself?

Although subordinate males are less active than bower owners, they behave similar and respond to female behaviour in the same way (unless the researchers missed subtle differences). So, the relationship between an owner and subordinate seems unlike that of teacher and apprenticeship, the researchers suggest.

Both participants benefit

Rather, the subordinate seems to be a helper. In his presence, the bower is less likely to be plundered by competing males. Males often destroy each other’s bower or steal precious ornaments to embellish their own place. In the spotted bowerbird, marauding is less common than in other species, but the presence of an extra male even reduces the risk. That is why a bower owner may tolerate the presence of another male.

In addition, an owner with a helper has more courtship success.

The owner thus benefits from the company of a subordinate. In turn, the auxiliary male also benefits; sometimes he has an opportunity to mate with a visiting female. In addition, there is a chance that he will gain ownership of the bower. A partnership between males may last for years.

Related?

The collaboration would be most useful if the males were related, for example brothers, so that the subordinate indirectly has some reproductive success via the bower owner. But researchers have not yet investigated whether that is the case.

It is questionable. Other research had shown that males pay little attention to family relationships. They don’t necessarily place their bower near relatives, but they don’t avoid them either. And if they maraud a bower, it is the neighbour’s bower, regardless of whether the birds are relatives.

Willy van Strien

Photos:
Large: spotted bowerbird. Greg Miles (Wikimedia Commons, Creative Commons CC BY-SA 2.0)
Small: bower of spotted bowerbird. Davidgregsmith (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Sources:
Spezie, G. & L. Fusani, 2022. Male–male associations in spotted bowerbirds (Ptilonorhynchus maculatus) exhibit attributes of courtship coalitions. Behavioral Ecology and Sociobiology 76: 97. Doi: 10.1007/s00265-022-03200-x
Madden, J.R., T.J. Lowe, H.V. Fuller, R.L. Coe, K.K. Dasmahapatra, W. Amos & F. Jury, 2004. Neighbouring male spotted bowerbirds are not related, but do maraud each other. Animal Behaviour, 68: 751-758. Doi: 10.1016/j.anbehav.2003.12.006

Tripedal gait

Lovebird parrot climbs on three legs

Lovebird parrot climbs on three legs

When climbing vertically, a lovebird parrot has an extra leg at its disposal: its beak, according to research by Melody Young and colleagues.

Woodpeckers, nuthatches, treecreepers, parrots, and parakeets: all these birds are able to move up against a tree trunk. Woodpeckers, nuthatches, and treecreepers do so by hopping forward, both legs briefly releasing from the ground simultaneously. Parrots and parakeets do it differently. They clamber – using their beaks as a third leg, as Melody Young and colleagues show.

Everyone has observed parrots and parakeets using their beaks when climbing up. But do they really use their beak as a leg, or just for support and balance, in the same way as birds often use their tail? To find out, Young investigated the climbing skills of the rosy-faced lovebird, Agapornis roseicollis, a parrot from Southwest Africa.

Novel function

She brought six animals into the lab and let them walk across a runway at different inclinations. She filmed their gait with a high-speed camera and measured the force that legs, beak, and tail exerted on the substrate.

The lovebirds often used their beak and tail when walking if the runway was set up steeper than 45° inclination. If it was positioned vertically, beak and tail were always necessary. In that case, the beak functioned as an extra leg, as it turned out. The animals put both legs and beak forward in turn: right leg, left leg, beak, right leg, left leg, beak. Measured forces also showed that the beak plays a similar role as the legs in propulsion.

The tail helps support and balance the bird.

Parrots have given their beak a second function as an extra leg to climb with. The neck muscles must also have been adapted to this new task.

Willy van Strien

Photo: Rosy-faced lovebird. User Nbansal4732 of the English Wikipedia (Wikimedia Commons, Creative Commons CC BY-SA 2.5)

Source:
Melody W. Young, M.W., E. Dickinson, N.D. Flaim & M.C. Granatosky, 2022. Overcoming a ‘forbidden phenotype’: the parrot’s head supports, propels and powers tripedal locomotion. Proceedings of the Royal Society B 289: 20220245. Doi: 10.1098/rspb.2022.0245

Detering owls by buzzing

Greater mouse-eared bat mimics the sound of bees and wasps

greater mouse-eared bat deludes owls by buzzing

Owls avoid the buzzes of angry bees and wasps. The greater mouse-eared bat takes advantage of that fear by mimicking the sound, Leonardo Ancillotto and colleagues show.

A greater mouse-eared bat in stress behaves weird: it buzzes like a startled group of bees or wasps. Leonardo Ancillotto and colleagues noticed this when they handled the animals during their research. They wondered whether the bats mimic the sound of alarmed bees and wasps when they feel threatened by a potential predator to deter it. It was worth a study.

The greater mouse-eared bat, Myotis myotis, occurs in most European countries. Its enemies are owls, which are nocturnal like the bats.

Larynx

To find out, the researchers first analysed sound recordings of buzzing bats and compared that to the buzzing sounds that several species of bees and wasps produce when they are harassed and defend their nests. Among those species were honeybee (Apis mellifera) and hornet (Vespa crabro). And yes: the buzzing sounds were similar, especially to the ears of an owl.

The similarity is remarkable because the sound is created in different ways. Bees and wasps buzz by beating their wings, while bats produce the sound with the larynx.

Next, the researchers conducted playback experiments in which they broadcasted the buzzing sounds of honeybee, hornet or greater mouse-eared bat to a number of barn owls and tawny owls. The buzzing of the bat was most similar to that of honeybee and hornet. In addition, these insects live in tree cavities, in which owls are interested. As control, they broadcasted the communication calls of another bat species, the European free-tailed bat (Tadarida teniotis).

Experience

The owls moved away from loudspeakers that emitted buzzes, whether these were produced by honeybee, hornet, or greater mouse-eared bat. Bat communication calls, in contrast, attracted them. Wild owls, which may have encountered angry bees or wasps and suffered painful stings, were even more averse to buzzing sounds than owls that had been raised in captivity.

Does it make sense that owls, which are nocturnal animals, are afraid of bees and wasps, which are active during the day? Yes, that fear is conceivable. Honeybees fly until late evening in summer and hornets may fly at night, under moonlight or artificial light. Barn owls appear already at dusk, and when they have hungry young to feed, tawny owls sometimes even hunt during the day.

Apparently, the owls are afraid of bees and wasps and the bats delude them. Buzzing like bees or wasps, acoustic mimicry, may be all they can do to escape from their predator.

Willy van Strien

Photo: Greater mouse-eared bat. Kovács Richárd (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Source:
Ancillotto, L., D. Pafundi, F. Cappa, G. Chaverri, M. Gamba, R. Cervo & D. Russo, 2022. Bats mimic hymenopteran insect sounds to deter predators. Current Biology 32: R408-R409. Doi: 10.1016/j.cub.2022.03.052

Food supply according to demand

Leafcutter ant prevents fungus garden from starving

Acromyrmex octospinosus also is a lefcutter ant species

The fungus-breeding ant Acromyrmex ambiguus checks its crop and intervenes if it threatens to starve, Daniela Römer and colleagues show.

Leafcutter ants grow fungus on plant material in their underground nests with chambers. The ant workers cultivate their crop with care, according to research by Daniela Römer and colleagues on Acromyrmex ambiguus: if the fungus garden in one of the nest chambers deteriorates because of lack of food, they will bring it more pieces of fresh green leaves.

Acromyrmex balzani carrying a leaf to its cropAnts are unable to digest plant leaves, but, thanks to their crop, fungus growing ants still are herbivorous. The fungus breaks down plant material and converts it into digestible, nutritious globules. The larvae are completely dependent on that food, the workers also eat it.

It was already known that leafcutter ants, which live in North, Central and South America, take excellent care of their crops. They have to, of course, because if the fungus dies, all their effort to grow it is wasted and the larvae have no food.

Even distribution

Acromyrmex ambiguus is such leaf cutter species; it lives in nests holding thousands of chambers in which fungus grows and brood is raised. Römer wanted to know how the workers distribute the leaf material they collect – i.e., food for the fungus – equally among those chambers.

The experiments she conducted once again show how skilled the small farmers are. The researchers have a colony of Acromyrmex ambiguus in the lab. It is housed in an artificial nest with a number of nest chambers that are filled with fungus, about thousand workers, and ant brood. For the experiments, they placed three of those nest chambers serially, each with its own access tube connected to a main corridor. Chambers with fresh leaf material and with water and honey for the workers were connected to one end of the main corridor. At the other end was a box to which the ants could bring waste. Video cameras recorded the workers’ behaviour.

In experiments in which the fungus in every nest chamber was in good condition, the workers distributed the pieces of leaf evenly among those three chambers: they delivered a similar amount to each one.

Undernourished

But in several trials, the researchers had starved the fungus in the center chamber by disconnecting it from chambers with pieces of leaf during two days before the experiment. The workers in that chamber had been unable to provide food for the fungus. As a result, the normal greyish-green top layer of the fungal mass had vanished.

In these experiments, the ants brought much more pieces of leaf to the center chamber than to the other two. They probably noticed that the fungus crop in this chamber was in bad condition and demanded more food because of the smell it emitted. So, they tried to save the dying fungus garden with extra care.

Workers of Acromyrmex ambiguus, and probably also those of other leafcutter ants, are farmers that monitor how their crop is doing. If its condition deteriorates, they react appropriately.

Willy van Strien

Photos: two different fungus growing Acromyrmex species
Large: Acromyrmex octospinosus. Deadstar0 (Wikimedia Commons, Creative Commons CC BY-SA 3.0)
Small: Acromyrmex balzani. Alex Wild (Wikimedia Commons, Creative Commons, Public Domain)

Source:
Römer, D., G.P. Aguilar, A. Meyer & F. Roces, 2022. Symbiont demand guides resource supply: leaf‑cutting ants preferentially deliver their harvested fragments to undernourished fungus gardens. The Science of Nature 109: 25. Doi: 10.1007/s00114-022-01797-7

Emergency leap after mating

Spider male escapes from cannibalism

Philoponella prominens male jumps away to safety after mating

With a catapult mechanism, a male of the spider Philoponella prominens manages to escape his hungry partner after copulation. Shichang Zhang and colleagues recorded it on video.

For many male spiders, mating is life-threatening. Because to a female, a male not only is a supplier of sperm that she can use to fertilize her eggs, but also a tasty snack. And when he has given his sperm, he is just a meal. Dying without siring offspring is no option. So, he has to proceed with caution, and leave immediately after finishing copulation.

A Philoponella prominens male, a spider species from woods of central China, is very accomplished. After mating, he swiftly leaps away, out of her reach, Shichang Zhang and colleagues show. They recorded mating and leaping with a high-speed camera.

High pressure

During mating, which lasts half a minute, he folds his two front legs against her, the researchers observed. By suddenly stretching them afterwards, he pushes off and shoots away. He had already secured himself before with a safety line of silk, which he had tied to the edge of her web. After leaping, he crawls back via that line to mate with her again. He is able to repeat the action up to six times.

Spiders move their legs not only with muscles, but also use hydraulics. They bend the legs by contracting flexor muscles but lack extensor muscles. Instead, they fill the joints with body fluid at high pressure, so that the legs stretch by released hydraulic power as the flexor muscles are relaxed. In this way, a male Philoponella prominens jumps from his partner. He reaches a speed of about seventy centimeters per second, spinning around at high speed. A female is unable to grasp him.

The leap is lifesaving, as the researchers showed. If they prevented a male from leaping with a fine brush, he was grabbed by his partner and eaten. As if he were just prey.

Willy van Strien

Photo: Philoponella prominens, mala above female. © Shichang Zhang

Emergency leap on video

Another spider male that has to be careful: Maevia inclemens

Source:
Zhang, S., Y. Liu, Y. Ma, H. Wang, Y. Zhao, M. Kuntner & D. Li, 2022. Male spiders avoid sexual cannibalism with a catapult mechanism. Current Biology 32: R341-R359. Doi: 10.1016/j.cub.2022.03.051

First migration trip in Caspian tern

Father teaches young bird how to travel

Caspian tern father accompanies young during first autumn migration

Young Caspian terns learn from their father how to migrate to the wintering grounds. When, in following years, they make that autumn trip independently, they remember their fathers’ lesson, Patrik Byholm and colleagues show.

A young Caspian tern that is born at the end of May along the coast of Finland or Sweden, will migrate to West Africa at the end of summer to hibernate there. Its father’s job is to guide it on that first journey, Patrik Byholm and colleagues noted.

The researchers wanted to know how information about autumn migration – route and stopover sites – is passed on from one generation to the next. To find out, they equipped birds with GPS tracking devices.

The Caspian tern, Hydroprogne caspia, is found in many places in the world. In Europe, it also breeds along the Black Sea and the Caspian Sea, and in North America along ocean coasts and the great lakes. Some birds from Finland and Sweden make a stop in the Netherlands during their migration to Africa. They travel singly or in small family groups, which are single-parent families.

Reduced tempo

The collected travel data shows that couples that started a nest with two or three eggs in spring and raised their young together, leave each other after the breeding season. They travel separately, sometimes weeks apart, to the wintering area.

Young birds travel with one of the parents, and mostly, that is the father. They cannot travel safely on their own: young terns that for one reason or another lose contact with parents, are captured by birds of prey. So, they stay close to their father during the trip. He teaches them the route and knows good stopover sites, where the birds can roost and forage during the migration. The lesson is learned: the young birds will follow the same route southwards in the years that follow, using the same stopover sites.

Fathers that accompany one or a few young, will adjust their tempo a bit. They progress less quickly than adult birds traveling alone. This is mainly because young birds take more time to rest.

After arrival, the bond between father and young loosens and parental care finishes. They gradually spend less time without each other, and after a month or two they stop seeing each other at all. Sometimes, a young travels a little further south, in the company of another congener.

Willy van Strien

Photo: Colony of Caspian tern. Dmitry Mikhirev (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Source:
Byholm, P., M. Beal, N. Isaksson, U. Lötberg & S. Åkesson, 2022. Paternal transmission of migration knowledge in a long-distance bird migrant. Nature Communications 13: 1566. Doi: 10.1038/s41467-022-29300-w