Flying saucers

Dance fly female advertises quality by inflating her body

Feamle long-tailed dance fly advertises quality by making herself bigger

Shaped like flying saucers, long-tailed dance fly females seek the attention of males. Their wide shape indicates their quality, Jessica Browne and colleagues write.

Females of the long-tailed dance fly (Rhamphomyia longicauda), which lives in North America, possess ornaments that make them attractive to males. They have sacs on either side of their abdomen and feathery black scales on their legs. By inflating the sacs and wrapping the legs along them while flying, they become laterally expanded. In this way, they show their quality, Jessica Browne and colleagues argue.

Sex roles reversed

In most animal species, females are choosy and males try to impress them by showing off. But in long-tailed dance flies, it is just the other way around: the males are choosy, the females try to seduce them to mate.

The reason is that females are unable to gather their food on their own. They need food to produce eggs, but cannot hunt for the smaller insects on which they live. That is why they have to to be provisioned by males. A male intending to mate brings a prey as a nuptial gift. Females mate frequently, because every mating yields a meal. But males have to catch prey first. That is hard for them, and a male that has gone to all that trouble will offer his gift only to a female that deserves it.


In order to seduce males, females gather in a lek. At dawn or dusk they form a swarm of dozens of flies in a clearing in the forest and ‘dance’ about half a meter above ground level. Males that have captured a prey will approach such swarm from below and see the females silhouetted against the dimly lit sky. Upon detection of an attractive female, a male will hover just below her. She doesn’t miss the chance and immediately drops on him. Together they leave the swarm to mate. She stores his sperm to fertilize eggs with later.

Males prefer large females. To be attractive, females inflate their sacs, lift their legs and wrap them along the laterally expanded sacs, so that their silhouette becomes much wider. They look like flying saucers. The wider a female is, the greater her chance of being chosen.

But what exactly does a large silhouette signify? Why is it beneficial for males to choose such inflated female?

Magnified difference

The higher the quality of a long-tailed dance fly female is, the wider she can make herself, as Browne and colleagues show. A dance fly begins its life as a larva. After pupation, an adult fly emerges with dimensions that are fixed; also the size of the sacs and the scales on the legs of females is fixed. Probably, the size of an adult fly is an indication of quality and a result of how good conditions were during its larval stage. Now, it turns out that the larger a female is, the larger her expandable sacs and leg scales are in proportion. Because large females can make themselves relatively wider, the differences in quality that exist between females are magnified.

Males preferring inflated females are choosing quality.

Paternity not guaranteed

Their choice is a good one, because a wide female potentially produces many eggs. And because she is attractive, she will be chosen frequently and fed many meals, so she will be able to indeed develop those eggs. She also has a good chance of surviving long enough.

But a male that chooses an attractive female can only hope that he will sire some of that progeny. If he is the first to mate her, she will use his nuptial gift to initiate egg development, but by the time she is going to lay them, she has stored sperm from many more males and his chances are small. A male probably has the best chance to sire much offspring if he is the last to mate with her before she starts laying eggs, when they are almost mature.

But in what state of development the eggs of an attractive female are, a male cannot infer from her size. He must be choosy, but he must also be lucky.

Willy van Strien

Photo: Female Rhamphomyia longicauda with inflated sacs. ©Heather Proctor

Browne, J.H. & D.T. Gwynne, 2022. Deceived, but not betrayed: static allometry suggests female ornaments in the long‑tailed dance fly (Rhamphomyia longicauda) exaggerate condition to males. Evolutionary Ecology, online Jan. 7. Doi: 10.1007/s10682-021-10148-3
Murray, R.L., J. Wheeler, D.T. Gwynne & L.F. Bussière, 2018. Sexual selection on multiple female ornaments in dance flies. Proceedings of the Royal Society. B 285: 20181525. Doi: 10.1098/rspb.2018.1525
Funk, D.H. & D.W. Tallamy, 2000. Courtship role reversal and deceptive signals in the long-tailed dance fly, Rhamphomyia longicauda. Animal Behaviour 59: 411-421. Doi: 10.1006/anbe.1999.1310

Content with second place

European pied flycatcher may prefer to be a concubine

Female pied flycatcher may become secondary mate of a male

A high quality male is so desirable that a female pied flycatcher may be willing to become his secondary mate – as long as it is not too hard to take care of the young without his assistance, Simone Santoro and colleagues write.

Like most passerine birds, the European pied flycatcher (Fidecula hypoleuca) is mainly socially monogamous. But some males have a secondary female. This concubine gets little help from him when raising the young, but in good years, when food is abundant, that may not be a major problem, Simone Santoro and colleagues argue.

Short breeding season

The males are the first to return from the wintering area in Africa, mid-April. They look for a suitable nest hole, which can be a tree cavity or nest box, and defend a small territory around it. Once a male occupies a good place, he tries to attract a female to breed with. Females visit a number of males before making their choice.

A couple is then busy for about five weeks. She lays five or six eggs and starts breeding when the clutch is complete. Both parents feed the young until they fledge, and dad defends the family. The breeding season covers the months of May and June; only one clutch can be raised in this period. But some males want more.

Good genetic quality

To get more, an ambitious male will have to occupy a second nest site and attract another mate. If successful, he will have to divide his paternal efforts over two nests. The research group, which works in Spain, had already shown how things go.

Males that succeed in starting a second nest are birds that have arrived and started breeding early, and that are able to defend two nests against rivals. These are strong males: of high genetic quality and in good condition. Such male stays with his first mate during the week that she is laying eggs. When she starts incubating, he tries to seduce to a second female. Usually, a second nest is located close to the first one.

When the young hatch in the first nest, he goes there to help feeding them. The primary female gets his full attention. Only when that first nest has fledged does he offer his services to the second nest.

So, the secondary female is worse off, as she has to feed the kids on her own for a while: that is hard work and she will see fewer young fledge. But, on the other hand, these young inherit a good genetic quality from their father. That is why a female may prefer to be the secondary mate of a high quality male rather than the only mate of a low quality male.

Fat and lean years

Particularly later in the season – when desirable single males are not available anymore -the choice to become a secondary female can turn out fairly well, because the time interval between father’s first and second brood will be larger and he will start helping on the second nest earlier.

Now, the researchers show that the availability of food also matters.

Because secondary females have to work harder than females in a monogamous relationship, their chance of survival is lower. (That is also true for primary females. Apparently, the situation is not ideal for them either, but it isn’t their choice.)

However, the lower survival rate of secondary females is an average over years; the researchers followed the birds for 26 seasons. The survival rate varies from one year to the next. In good years, a secondary female has less difficulty raising her young and her chance to survive is almost as high as that of a female in a monogamous relationship. To assess whether a year was good or bad, the researchers considerd the percentage of young that survived and fledged. A good year probably is a year in which food is abundant. In such year, a female can more easily accept a secondary position.

And sometimes. she does, as it turns out: in fat years it is more common for a male to have two families than in lean years. But even then, monogamous relationships remain the majority.

Willy van Strien

Photo: Caroline Legg (Wikimedia Commons, Creative Commons CC BY 2.0)

Santoro, S., P. Fernández‑Díaz, D. Canal, C. Camacho, L.Z. Garamszegi, J, Martínez‑Padilla & J. Potti, 2022. High frequency of social polygyny reveals little costs for females in a songbird. Scientific Reports 12: 277. Doi: 10.1038/s41598-021-04423-0
Canal, D., L. Schlicht, J. Manzano, C. Camacho & J. Potti, 2020. Socio-ecological factors shape the opportunity for polygyny in a migratory songbird. Behavioral Ecology 31: 598–609. Doi: 10.1093/beheco/arz220

Hurry up please

Spikethumb frog males transfer messages to females by biting

Spikethumb frog males bite partner during mating

Males of three spikethumb frog species give their mate a chemical message during mating, using their upper teeth, as Lisa Schulte and colleagues show.

During mating, males of some species of spikethumb frogs (Plectrohyla) press their upper lip onto their mate’s head or back. That’s not exactly a caress, on the contrary: they scrape their teeth over it, Lisa Schulte and colleagues found. The scratches are clearly visible afterwards. Why would they do this?

Swollen lips

In three species, females are found that have scratches on their head or back: Hartweg’s spikethumb frog (Plectrohyla hartwegi), Matuda’s spikethumb frog (Plectrohyla matudai), and arcane spikethumb frog (Plectrohyla sagorum). The distance between the scratches is similar to the distance between the upper teeth of the males, which are elongated and protruding. These frogs live in the South American tropics.

In addition to elongated teeth, the males have swollen upper lips during the breeding season. They turn out to contain specialized, large glands. These produce mucus and excrete it on the inside and outside of the lips. The researchers found several proteins in the mucus, including proteins known from salamanders as messenger molecules with which the animals communicate with each other.

Direct message

The conclusion is that during mating, the males transfer the mucus of the glands into their partner’s skin with teeth and lips. These proteins are probably taken up by the blood and delivered elsewhere. As a consequence, eggs are laid more quickly, the researchers think.

That would  be advantageous. When mating, a frog male clings to a female with a mating embrace or amplexus. The two stay like this for hours or even days, until she lays her eggs, and he can fertilize them. And all the while, such a joined pair is less agile than a single frog, and thus an easy prey for predators. The sooner a mating is completed, the shorter that unsafe state lasts.

The males are not very gentle. But if the mating is finished earlier because of the biting behaviour, both partners benefit. It is not yet known whether mating indeed is faster.

Anyway, the males of these frogs give off a chemical message during mating and are sure that it is received.

Willy van Strien

Photo: Plectrohyla sagorum. Ruth Percino Daniel (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Schulte, L.M., A. Martel, R. Cruz‑Elizalde, A. Ramirez‑Bautista & F. Bossuyt, 2021. Love bites: male frogs (Plectrohyla, Hylidae) use teeth scratching to deliver sodefrin precursor‑like factors to females during amplexus. Frontiers in Zoology 18: 59. Doi: 10.1186/s12983-021-00445-6

Cleaner wrasse cheats client secretly

Female knows if partner observes her behaviour

in a bluestreak wrasse pair, a conflict may arise

A bluestreak cleaner wrasse female sometimes scares a customer away by biting off a bit of its mucus layer. But if she knows that her partner can see what she’s doing, she behaves somewhat better, Katherine McAuliffe and colleagues report.

Bluestreak cleaner wrasses (Labroides dimidiatus) often work in pairs. Male and female jointly inspect their clients, fish that want to be cleaned. With their pointed snout, the cleaners pick up ectoparasites and dead skin cells. It is a textbook example of cooperation between species, called mutualism: clients get rid of their parasites, cleaners have a meal.

In cleaner wrasses that operate as a couple, a conflict sometimes arises because the female bites a client; that client then will leave, causing the male to miss his meal. A female cleaner is more likely to misbehave if she knows that her partner can’t see what she’s up to, Katherine McAuliffe and colleagues found.


When a female cleaner bites, it is for good reason. She takes a mouthful out of a client’s protective mucus layer. This is tempting, especially during breeding season, because she needs a lot of energy and mucus is more nutritious than the parasites she should be eating. But upon being bitten, a client leaves, and the male, that serves the client properly, is the victim: because she cheats, he also loses the client – without the benefit of ingesting a bit of mucus like she has done.

There is also a risk that he will lose his territory, in which several females live. This is because these fishes change sex during their lifetime. Young cleaner wrasses are always females which, after reaching a certain size, become males. A female that eats nutritious mucus grows well. If she is almost the same size as her partner, she can change sex any moment and compete with him; maybe she’ll manage to chase him off and take over his territory.

It is therefore logical for a male not to tolerate that his partner bites a client. When she does, he punishes her by chasing or biting her. It was known from previous research that he punishes more severely when the client is larger, presenting more food. The punishment is also more severe if his partner is about the same size as himself and a risk of takeover exists.

After punishment, the female delivers good service to the clients and the partners cooperate well.

Model clients

McAuliffe already knew that cleaners treat their clients better when other fishes, potential clients, are watching. That is because bystanders leave when they see clients being hurt. Now, she wanted to know whether a bluestraek cleaner wrasse female is less likely to cheat a client when she knows that her partner can see her.

The cleaner fish live on coral reefs, where they occupy a ‘cleaning station’, as single or as a couple. It is difficult to observe exactly what is happening between cleaners and their clients. That is why the researchers did experiments in the lab, where they brought cleaner pairs into contact with artificial clients: plexiglass plates with food items stuck on them. Mashed prawn, which cleaner fish like, served as a model for a client’s mucus; a mixture of fish flakes and prawn, which the cleaners like less, did for parasites.

First, the cleaner fish learned to deal with the model clients. If they ate fish flake mixture, against their preference, that was seen as good cleaning service. But if they took a bite of mashed prawn, it was considered cheating, and the researchers removed the model client.

After training, the researchers first investigated how females behave when their partner was separated from them by either a transparent or an opaque barrier. As soon as a female took a bite of mashed prawn, the model client was removed, and her partner was given access.

Bad service

When their partner was visible and could see them, cleaner females ate a little more fish flake items on average before taking a bite of mashed prawn and chasing off the model client. So, in that case, the females provided a better service. If the partners were invisible to each other, females took less fish flake items. In other words, they cheated more in secret.

Males, that could punish their partner after she had eaten mashed prawn, punished less severely the more fish flake items she had consumed before. Surprisingly, it made no difference whether males had seen their partner’s behaviour or not. Apparently, they still noticed somehow how much their partner had cheated.

Choosing two times

So, it seems that females are aware whether their partner is or is not able to observe what they are doing, and that they are more inclined to cheat a client when the partner cannot see it.

A next, somewhat more complicated test affirmed this finding. In this set-up, the male was again behind a transparent or opaque partition, but now, two model clients were offered behind additional partitions. One of them was visible to the male – if the male himself was behind a transparent partition- behind a transparent partition; the other was hidden from him behind an opaque screen. The female was allowed to choose which model client to serve. She was given the choice twice; in between the male was admitted, having the opportunity to punish her.

The first time, females were more likely to choose the model client behind the opaque partition if their partner could watch them than if he couldn’t. But the second time, they went more often to the model client behind the transparent partition. This was probably because males were more likely to punish their partner after the first time if she had visited the hidden client. And, in accordance with the first experiment, they punished her whether they had been able to see that she went there or not. Apparently, she betrayed herself somehow.

Clever fish

The researchers’ main conclusion: a bluestreak cleaner wrasse female is more likely to cheat a client if she knows that her partner, who punishes bad behaviour, cannot see what she is doing. In the first trial, females more quickly took a mashed prawn item, which equated to the protective mucus layer of a client fish. In the second trial, they initially preferred to visit a model client hidden from the partner to a visible one.

That she realizes what he can see indicates impressive cognitive capacities. Such capacities were already known: the cleaners recognize themselves in a mirror.

But the question is why a female should care about whether her partner can see her bad behaviour or not, because that did not affect the punishment.

So, the story still does not have an end. But it probably will continue, as the research group has been conducting thorough research on these cleaner fish for years.

Willy van Strien

Photo: Bluestreak cleaner wrasse cleaning a blue angelfish (Pomcanthus semicirculatus). Longdongdiver (Vincent C. Chen) (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

More about the behaviour of bluestreak cleaner wrasse

McAuliffe, K., L.A. Drayton, A. Royka, M. Aellen, L.R. Santos & R. Bshary, 2021. Cleaner fish are sensitive to what their partners can and cannot see. Communications Biology 4: 1127. Doi: 10.1038/s42003-021-02584-2
Kohda, M., T. Hotta, T. Takeyama, S. Awata, H. Tanaka, J-y. Asai & A.L. Jordan, 2019. If a fish can pass the mark test, what are the implications for consciousness and selfawareness testing in animals? PLoS Biol 17: e3000021. Doi: 10.1371/journal.pbio.3000021
Raihani, N.J., A.I. Pinto, A.S. Grutter, S. Wismer & R. Bshary, 2012. Male cleaner wrasses adjust punishment of female partners according to the stakes. Proceedings of the Royal Society B 279: 365-370. Doi: 10.1098/rspb.2011.0690

Honeydew with dopamine

Japanese mugwort aphid forces ants to provide extra protection

Japanese mugwort aphid manipulates attending ants

A Japanese mugwort aphid colony makes ants more aggressive, as Tatsumi Kudo and colleagues show. As a result, enemies have less opportunity to feed on the aphids.

The cooperation between aphids and ants is one of the best-known examples of cooperation or mutualism. Aphids, which feed on the plant saps, excrete excess sugars in a sticky substance, the honeydew. This is a great food source for ants. They collect the honeydew: they milk the lice. To secure the harvest, they protect the aphids from predators, as if it were their livestock. The parties thus exchange food for protection, and both sides benefit from this cooperation.

Such mutualism exists between the Japanese mugwort aphid (Macrosiphoniella yomogicola), which feeds on mugwort (Artemisia montana), and several ant species, of which Lasius japonicus is the most important one. This aphid manipulates the ants that protect it into becoming more aggressive against predators by excreting dopamine in their honeydew, Tatsumi Kudo and colleagues discovered. In other words: the aphids manipulate the behaviour of the ants.


Earlier, the Japanese research group had shown how the ant manipulates the aphids. Two colour morphs of the Japanese mugwort aphids exist, and the ants favour the morph that reproduces slower, but produces a better-quality honeydew. Now the team shows that, the other way round, the Japanese mugwort aphids do not quite behave like obedient livestock.

The researchers detected dopamine in the honeydew of the aphids, a substance that acts on the nervous system. The crop of ants that harvested the honeydew also contained dopamine.

And that affected the behaviour of the ants. The researchers conducted experiments to find out how aggressive ants were towards the Asian ladybird (Harmonia axyridis), a major predator of the aphids. Shortly after visiting an aphid colony, ants were more aggressive than ants that had not visited aphids. As other experiments show, this is due to the dopamine. In these experiments, administration of dopamine made the ants more aggressive than normal, whereas artificial honeydew without dopamine did not.

Extra benefit

So, both the Japanese mugwort aphid and the ant Lasius japonicus that protects it benefit from their mutualistic relationship. The aphid forces the ant to provide better protection, the ant manipulates the aphid colony so that an extra amount of high-quality food is produced.

The relationship with ants is especially important for the aphid. A colony wouldn’t survive without its ant bodyguards.

Willy van Strien

Photo: Japanese mugwort aphid. ©Ryota Kawauchiya

On YouTube: ladybird larva consuming aphids is bitten by an ant

See how the ant manipulates the aphid colony

Kudo, T., H. Aonuma & E. Hasegawa, 2021. A symbiotic aphid selfishly manipulates attending ants via dopamine in honeydew. Scientific Reports 11: 18569. Doi: 10.1038/s41598-021-97666-w


Ants translocate their larvae and pupae to a warm bird’s nest

Myrmica ruginodis translocates brood to a wood warbler's nest

In the nest of a wood warbler not only young wood warblers may grow up, but also ants, as Marta Maziarz and colleagues discovered. Ant larvae and pupae probably survive, grow and develop better in the bird’s nest than in their own nest.

Usually, nests of European forest ants, especially Myrmica ruginodis and Myrmica rubra (the European fire ant or common red ant), are so cold in spring that the larvae and pupae do not grow well. Their development only starts at 16°C, but ant nests rarely get that warm before summer. They are located on the forest floor, between fallen leaves of deciduous trees. The ants cannot produce heat, so without sunlight the nests have the same temperature as the environment. A temperature of 20 to 25°C is optimal for raising brood; the nests never reach that temperature in spring.

But warm places are available nearby, Marta Maziarz and colleagues show. On the forest floor, the wood warbler, a songbird that breeds in European forests, makes a domed nest of grasses, leaves and moss. The bodies of bird parents and, later on, their fully feathered young keep the nest warm.


When the bird parents incubate the eggs, in the second half of May, the nest temperature often reaches 16°C or more; especially on cold days, the difference with the ambient temperature is large. Once the young birds are fully feathered, in the first week of June, the nest temperature even rises to 20°C and higher.

This is a nice temperature for the ants, which indeed visit the warm wood warbler’s nest. In cold weather in May and in the first week of June, they move larvae and pupae from their own nest to a bird’s nest and put them in the sidewalls. Translocation is a lot of work, but apparently, it is worth the effort.

After fledging, the vacant nest cools down again. But the ants don’t remove their brood immediately; they delay relocation for up to two weeks. There is no hurry, because the bird’s nest is no longer warm, but it is not colder than the ants’ nest either.

In the primeval forest of Białowieża in Poland, where Maziarz conducted the research, the ants use 10 to 30 percent of wood warblers’ nests as incubators. The birds do not suffer from the inhabitants, but they do not benefit from them either. Therefore, they do not specifically seek the proximity of ant colonies when starting nest building. It is the ants that start the relationship and benefit from it.

Willy van Strien

Photo: Myrmica ruginodis with brood. Jan Anskeit (Wikimedia Commons, Creative Commons CC BY 4.0)

Maziarz, M., R.K. Broughton, L.P. Casacci, G. Hebda, I. Maak, G. Trigos‑Peral & M. Witek, 2021. Interspecific attraction between ground‑nesting songbirds and ants: the role of nest‑site selection. Frontiers in Zoology 18: 43. Doi: 10.1186/s12983-021-00429-6
Maziarz, M., R.K. Broughton, L.P. Casacci, A. Dubiec, I. Maák & M. Witek, 2020. Thermal ecosystem engineering by songbirds promotes a symbiotic relationship with ants. Scientific Reports 10: 20330. Doi: 10.1038/s41598-020-77360-z

Garden or nameplate?

Why vicuñas create communal dung piles

Vicuñas use permanent latrines to defecate and urinate

Vicuñas live in arid, cold and barren areas, high in the Andes. They set up permanent places to defecate and urinate and use those latrines for decades. There is disagreement about why.

High in the South American Andes, where the soil is arid, rocky, and barren, some places stand out because they are green, overgrown with plants. The greens islands developed because vicuñas come there repeatedly to defecate and urinate. Why do they use such latrines? To create gardens with plants that they can feed on, Kelsey Reider and Steven Schmidt suggest. No, the dung piles are kind of nameplates that mark their territory, William Franklin thinks.

Unpalatable bunch grass

Vicuñas are one of the few animal species that live in the Andes at altitudes of more than 4000 meters, right up to the edge of snow. They mainly live in groups that roam over a territory of almost 20 square kilometers. Climate change is also noticeable here; glaciers dwindle and retreat to the mountain tops. Where they melt, a bare bottom appears which is poor in plant nutrients, so that it takes decades before a noteworthy vegetation is formed. Vicuñas are the first to enter the newly exposed soil at the edge of the glaciers.

With their droppings, they enrich the soil with nutrients. They defecate and urinate only on permanent latrines or dung piles which persist for decades. Consequently, fertilized places are created where vegetation can develop more quickly.

First, a vegetation appears that is dominated by the tough and little nutritious Peruvian feather grass, Stipa pichu. It is not until hundreds of years later that a grassier vegetation develops, with the grass Calamagrostis vicunarum, other grasses and herbs.


In those grassy places vicuñas forage preferentially. Because the places are still used as latrines also, the animals run the risk of picking up gastrointestinal parasites. But places with tasty vegetation are so scarce that it is worth the risk.

That is why Reider and Kelsey believe that the vicuñas maintain latrines in order to concentrate their dung and accelerate the development of nutritious vegetation locally. In other words, latrines are gardens where they grow food.

Franklin thinks otherwise, however. Vicuñas that use a young latrine at the edge of a glacier or start a new one will not be able to enjoy a tasty yield themselves, because generations will have passed before there will grow anything edible. When it comes to food breeding, it would be better for an animal to choose an older latrine where plant growth is already substantial.

Instead, he thinks that the dung piles mark the territory of a group. This is important because if an animal enters another group’s territory accidently, it will be violently attacked and chased away and is at risk of serious injury. By marking the territory at fixed places with the characteristic group scent, especially at the borders, a group manages to keep its members within their own safe territory. So, at a border, two groups may be seen peacefully grazing side by side, each in its own area.


Every group member contributes to these scent markings, and whoever contributes benefits from the fact that the nameplate is maintained.

As a result, vegetation develops on bare ground, gradually becoming more attractive. Which is a nice side-effect for future generations and other mammals that visit the grassy places: mountain viscacha (Lagidium viscacia) and Andean fox (Lycalopex culpaeus).

Willy van Strien

Photo: Dick Culbert (Wikimedia Commons, Creative Commons CC BY 2.0)

Franklin, W., 2021. Vicuña dung gardens at the edge of the cryosphere: Comment. Ecology 102: e03522. Doi: 10.1002/ecy.3522
Reider, K.E. & S.K. Schmidt, 2021. Vicuña dung gardens at the edge of the cryosphere. Ecology 102: e03228. Doi: 10.1002/ecy.3228

Crossdressing in white-necked jacobin

Male-like plumage reduces social harassment in females

in white-necked jacobin, males are brightly coloured

Most white-necked jacobin females are distinguishable from males by a less bright colour. But 20 percent of the females looks like a male. Jay Falk and colleagues wanted to know why they deviate from the normal pattern.

In hummingbirds, a bird family with more than 300 species, males tend to be more brightly coloured than females. But in one in four species, some females have a male-like plumage, as reported earlier this year by the research group that Jay Falk is part of. Now, he tried to figure out why these females dress like a male. He discovered that it enables them to forage relatively undisturbed. They experience less harassment of both conspecifics and other hummingbirds.

most white-necked jacobin females are less colourful than males, but some have male-like plumageThat hummingbird females normally are less colourful than males – though they are by no means dull compared to many other bird species – is because they raise the young. If they are on or around the nest, a dull colour provides safety: their predators detect them less easily. Hummingbird males have no such tasks and are free to seduce females. To be attractive, they have flashy colours, which females like.

White-necked jacobin

But in some hummingbird species, females may have a showy male appearance. The white-necked jacobin, Florisuga mellivora, is an example. About 20 percent of adult females has a shiny blue head, white belly and tail and white spots on the neck like males. Would this confer any benefit?

Perhaps also males prefer a brightly coloured partner, Falk thought at first. But that is not the case, as it turned out when he offered males a choice from several stuffed birds: they prefer a female with normal female plumage.


Another possibility is that brightly coloured birds are less likely to be harassed when foraging. Hummingbirds are small animals with a high metabolism that need to consume large quantities of food. So, the birds spend a large part of the day foraging, sucking nectar from flowers. Competition over food is high, and they are quite aggressive around flowers with a high nectar content. Continuously, they are trying to chase each other away.

White-necked jacobin females in female plumage lose out, according to observations. Apparently, they are not impressive. They are more often chased off than brightly coloured animals, both by conspecifics and other hummingbirds. Conversely, they are less aggressive themselves. In addition, they are likely to be sexually harassed more often. Females in male’s outfit, on the other hand, can forage relatively undisturbed.

Accordingly, male-like females were found to visit a place where nectar was offered more frequently than females in female plumage, and they stayed longer. So indeed, male plumage in females is beneficial because it reduces harassment.

A white-necked jacobin female with male plumage does not look exactly the same as a male. When the tail is fanned, a black tail band becomes visible that is wider in these females than in males. They also have some green on the tail.

Brood care

There is another indication that male plumage offers protection against aggression: all young are brightly coloured, while young of animal species usually are camouflaged. Male-like plumage also enables young white-necked jacobins to forage without too much trouble.

So, young females are brightly coloured. As they reach adulthood, 20 percent of females retains that colourful plumage, while the majority, 80 percent, switches to a less conspicuous appearance. Why don’t they all keep looking like males if that increases access to food resources?

Probably because it is still true that during the breeding period a female should not be clearly visible, favouring a less bright colour. Young females don’t have that concern yet.

Willy van Strien

Large: white-necked jacobin male. Kathy & sam (Wikimedia Commons, Creative Commons CC BY 2.0)
Small: white-necked jacobin female in female plumage. Joseph Boone (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Falk, J.J., M.S. Webster & D.R. Rubenstein, 2021. Male-like ornamentation in female hummingbirds results from social harassment rather than sexual selection. Current Biology, online August 26. Doi: 10.1016/j.cub.2021.07.043
Diamant, E.S., J.J. Falk & D.R. Rubenstein, 2021. Male-like female morphs in hummingbirds: the evolution of a widespread sex-limited plumage polymorphism. Proceedings of the Royal Society B 288: 20203004. Doi: 10.1098/rspb.2020.3004

Successful as bird dropping

Crab spider imitates fresh bird’s poo

bird-dung crab spider mimics bird's poo

It looks like bird dropping, it smells like bird dropping. But it is the bird-dung crab spider Phrynarachne ceylonica, waiting until an unsuspecting fly comes close, as Long Yu and colleagues show.

Crab spiders get their meals by sitting motionless and waiting for a prey to come within range. Then they may strike suddenly. It helps if they don’t look like a spider while they sit-and-wait, but are disguised. The bird-dung crab spider Phrynarachne ceylonica, for example, successfully mimics a moist bird’s dropping, Long Yu and colleagues write.

The spider not only looks like bird poo, but it also smells like it. It was already known to mislead its predators, such as larger jumping spiders, which simply don’t recognize it.

The spiders occurs in Sri Lanka, China, Japan, and Taiwan.

Leaf miner flies

Now this masquerade proves doubly useful. The sneaky spider attracts tasty insects, mainly leaf miner flies (agromyzids), as Yu notes after observing several juvenile and female crab spiders in the field. The larvae of these flies feed on plant tissue, but adults have a different diet, and to them, fresh bird droppings are a favourite source of nutrients.

Yu painted several spiders entirely white or black, and these painted spiders did not attract the flies.

As he shows, the bird-dung crab spider Phrynarachne ceylonica has the same colours as fresh bird droppings to the eyes of insects. Spinning some threads, the spider mimics a dehydrated edge. And it works out well: insects land right next to the spider. The spider attracts prey at a lower rate than a real bird’s dropping, but that isn’t much of a problem if it is satiated after only one meal.

Unfortunately, the researchers do not report whether the crab spiders do indeed capture and consume the leaf miner flies.

Willy van Strien

Photo: LiCheng Shih (Wikimedia Commons, Creative Commons CC BY 2.0)

Another crab spider mimics a flower

Yu, L., X. Xu, Z. Zhang, C.J. Painting, X. Yang & D. Li, 2021. Masquerading predators deceive prey by aggressively mimicking bird droppings in a crab spider. Current Zoology, online July 24. Doi: 10.1093/cz/zoab060


In bright sunlight, a peregrine falcon can see well thank to malar stripes

Peregrine falcon can see well in bright sunlight thanks to dark malar stripes

Solar glare can impede vision. Michelle Vrettos and colleagues make it plausible that the black malar stripes of a peregrine falcon are helpful during hunt.

With an impressive high-speed dive, a hunting peregrine falcon descends to capture a prey in mid-air. It is the fastest flier among the birds – it can reach about 350 kilometres per hour in a hunting stoop – and it hunts other birds and bats while flying. Its striking black stripes below the eyes help it to track its fast-moving, agile prey, Michelle Vrettos and colleagues write.


The idea that those black stripes, the so-called malar stripes, are important for sharp vision already existed. Light feathers would reflect sunlight from the cheeks into the eyes, blurring the image, but dark feathers absorb the light. As a consequence, a hunting peregrine falcon would suffer less from solar glare. Other falcon species and some songbirds and hunting mammals have similar dark stripes or an eye mask. And some American athletes blacken their cheeks with eye black to reduce glare and better track fast balls. Does it help?

Apparently, it does, at least in peregrine falcons. Vrettos used photos that were posted on internet of a few thousand peregrines from all over the world; except in Antarctica, the bird is found everywhere. She measured the malar stripes on each photo. And she found that the malar stripes are larger and darker as the average annual solar radiation in the area where a photo was taken is higher. Even though, in sunny areas, dark feathers have the disadvantage that they absorb heat.

Experiments are required to proof that the malar stripes really help vision by reducing solar glare. But the findings are at least striking.

Willy van Strien

Photo: A peregrine falcon with prominent malar stripes. Kevin Cole (Wikimedia Commons, Creative Commons CC BY 2.0)

Vrettos, M., C. Reynolds & A. Amar, 2021. Malar stripe size and prominence in peregrine falcons vary positively with solar radiation: support for the solar glare hypothesis. Biology Letters 17: 20210116. Doi: 10.1098/rsbl.2021.0116

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