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“Meet the Flockers” – Myths of Monogamy

“Meet the Flockers” – Myths of Monogamy

By Martin Franklin

Monogamy

Monogamy can mean different things to different people, encompassing, for example:

Marital monogamy, i.e. marriages of only two people (in contrast to polygamy).
Social monogamy, i.e. two partners living together/sharing a territory and cooperating in securing basic resources (e.g. food and shelter).
Sexual monogamy, i.e. two partners having an exclusive sexual relationship.
Genetic monogamy i.e. sexual monogamy with DNA evidence of the two partners reproducing exclusively with each other.

Monogamy within human societies

It has been suggested that few human societies are monogamous, despite what many of us like to believe. For example, of 1,231 societies reviewed in one study:

186 were deemed monogamous;
453 displayed occasional polygyny (where a man has multiple wives simultaneously);
588 displayed frequent polygyny; and
4 displayed polyandry (where a woman has multiple husbands simultaneously).¹

Monogamy within mammalian societies

It is reckoned that only around 3–5% of all mammal species are socially monogamous^2,3, though around 29% of primate species are considered socially monogamous.⁴

One fairly accurate predictor as to whether males within a primate species are likely to be monogamous or have several sexual partners at one time is to look at their testicle size^5,6. I would suggest, however, that for reasons of both safety and odour, one should not look too closely.

The rule of thumb is that the smaller the testicles (relative to overall body size), the more likely that species is to be monogamous. Accordingly, for example, highly promiscuous male chimpanzees have relatively large testes (thus producing more sperm, with a corresponding impregnation advantage), whereas male gorillas have relatively small testes (as gorilla society has a polygynous mating system in which the dominant male avoids sperm competition by controlling access to females).

Monogamy within other taxa

In relation to non-mammalians, it is frequently suggested that while, for example, there are relatively few known examples of reptiles, amphibians, fish and invertebrates being socially monogamous (one fascinating example being a common parasitic fluke that lives in human blood⁷, around 90% of birds are socially monogamous.⁸

Monogamy within avian societies

By “monogamy within avian societies” I refer, of course, to the behaviour of birds of the same species, not people who belong to bird societies, not least as I assume that members of this latter group are typically lucky to engage in recreational copulation at all, let alone have the opportunity to acquire more than one sexual partner. (I may, or may not, belong myself to one or more such bird societies.)

But back to the point. “Monogamy” in birds may be considered “a prolonged pair bond with a single member of the opposite sex for purposes of raising young”.9 Unlike most reptiles and amphibians, that typically leave their eggs once laid, bird eggs (and subsequently chicks) typically need significant care from both parents (e.g. nest building, defense of the territory, incubation, and fetching food for the parent tending the egg(s)/chick(s) and/or the chick(s) themselves). Accordingly, it seems that most birds are indeed monogamous (at least socially).⁹

Exceptions within avian societies

It shouldn’t be assumed however, that such pair bonds will be “till death do us part”.

While some birds (e.g. many parrots and eagles) do indeed form life-long pairs, others will only do so if their partner from the previous mating season arrives (post winter migration) within the same week (or so) at the nesting site (e.g. black-tailed gotwits).

Others (e.g. female oystercatchers and female blue tits) will readily leave their partners if more attractive territories become offered by other suitors.

Even within socially monogamous pairs, it’s now believed that birds are only very rarely sexually monogamous.

One significant study found that in approximately 90% of the species studied there were “extra-pair offspring” (i.e. offspring fathered by a male other than the social father), and on average over 11% of offspring were not fathered by the social father.¹⁰

Such behaviour may be an insurance against a mate’s potential infertility and/or way of ensuring genetic variability and/or robust immune systems in the offspring and/or (where the extra-pair copulation is with a male superior to the social father) offspring of improved quality and diversity.⁹

Plus, of course, a significant minority of birds are polygynous (probably fewer than 10%). Broadly speaking, when the following occurs:

the more impressive the male’s song and more beautiful the male’s plumage (relative to the female); together with either
the ability of a male to control scarce resources (e.g. golden-backed weavers); or
there being no need for males to find food for their offspring (e.g. where there’s an abundance of fruit for frugivore species, as is the case for most birds-of-paradise)…

Southern Rockhopper Penguin pair (Source: Penguins International photo library)

…then the more likely it is to be a species where the male copulates with numerous females (or, as Iago might have put it to Brabantio, makes “the beast with two beaks”).⁹

Monogamy within penguin societies

What, then, of penguins? Given that in all penguin species, both the male and female play an essential extensive and complementary role in incubation and chick-rearing, and given that no individual can control available resources, we would expect widespread monogamy.

Available evidence confirms this to be the case: all penguin species are believed to display widespread sexually monogamous behaviour each breeding season.¹¹

Seasonal monogamy within penguin societies

That said, many individuals will choose a different mate from season to season.

Across all penguin species, it is believed that, on average, around 60-90% of pairs remain together over successive seasons, though this drops as low as 15% in Emperor Penguins.

One of the factors which seems to drive a pair to separate is the failure to find a partner that complements the often complicated nest-relief patterns of penguins (i.e. taking turns to incubate the egg/protect the chick(s) and hunt for food for the chick(s), in each case returning before the partner/chick(s) starve). Accordingly:

In species that take long turns on the nest (e.g. Adelie and Macaroni Penguins), if a pair fails to synchronise effectively and raise a chick in any given year, they are less likely to pair up again the next year.
Conversely, there seems to be no such correlation in species that take frequent short turns on the nest (e.g. Gentoo Penguins).¹¹

Humboldt Penguins copulating (© Martin Franklin/ZSL)

Penguin “cheaters”

Individual penguins are also known to “cheat” on their partners. For example, female Adelie Penguins may mate with a new male if their partner from the previous year is late returning to the nest site (following which such females have been observed returning to their former partner upon his arrival, and this cuckolded male then incubating the egg(s) fertilised by the first male).

Similarly, my colleagues at ZSL London Zoo have observed a few individual female Humboldt Penguins regularly and openly mating with more than one male in the same season, with one particular individual regularly flitting between two adjacent nest-boxes, each occupied by males with whom she copulates.

So why stay together in the long-term?

Ultimately there seems (unlike in some birds, including skuas) to be no increased breeding success rate for penguin pairs that remain together for several seasons. Researchers have suggested, therefore, that many penguin pairs simply stay together because they have had offspring, and finding (or having to compete for) a new mate would be potentially too much trouble.11 And who says we anthropomorphise penguins too much?

Martin Franklin is a bird keeper at ZSL London Zoo, and works extensively with Humboldt Penguins. Any views or opinions expressed in this article are the author’s own, and do not necessarily represent those of ZSL.

Penguins, monogamy, or cheaters…? Amazing what we have learned. Let us know what you think. And please help us to continue to provide you with penguin news articles by donating to Penguins International.

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References

1 Ethnographic Atlas, a database coded by George P. Murdock and published in 29 successive installments in the journal Ethnology, 1962-1980.

2 Kleiman, D. G. (1977). Monogamy in Mammals. The Quarterly Review of Biology. 52 (1): 39–69.

3 Lukas, D. and Clutton-Brock, T. (2012). Cooperative breeding and monogamy in mammalian societies. Proceedings of the Royal Society B: Biological Sciences. 279 (1736): 2151–6.

4 Lukas, D. Clutton-Brock, T. (2013). The Evolution of Social Monogamy in Mammals. Science. 341 (6145): 526–530.

5 Dixson, A. and Anderson, M. (2001). Sexual selection and the comparative anatomy of reproduction in monkeys, apes, and human beings. Annual Review of Sex Research. 12: 121–144.

6 Harcourt, A. H., Harvey, P. H., Larson, S.G. and Short, R. V. (1981). Testis weight, body weight and breeding system in primates. Nature. 293 (5827): 55–57.

7 Beltran, S. and Boissier, J. (2008). Schistosome monogamy: who, how, and why? Trends in Parasitology 24 (9): 386–91.

8 Lack, D. (1968). Ecological adaptations for breeding in birds. Science. 163: 1185–1187.

9 Gill, F. B. and Prum, R. O. (2019). Ornithology. (4th edition). W. H. Freeman and Company: New York.

10 Griffith, S. C., Owens, I. P. F. and Thuman, K. A. (2008). Extra pair paternity in birds: a review of interspecific variation and adaptive function. Molecular Ecology. 11: 2195-2212.

11 Williams, T. D. (1995). The Penguins. Oxford University Press: New York.

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Have Penguins Ever Been Able To Fly?

(© Martin Franklin/ZSL)

Humboldt Penguin showing off its flippers and swimming ability.

Have Penguins Ever Been Able To Fly?

by Martin Franklin

“Swimming is normal for me. I’m relaxed. I’m comfortable, and I know my surroundings. It’s my home.” (Michael Phelps, most decorated Olympian of all time).

“Swimming is a confusing sport. Sometimes you do it for fun, but then other times you do it to not die. And when I’m swimming, sometimes I’m not sure which one it is. You have to go by the outfit. Pants – oh oh! Bathing suit – ok! Naked – we’ll see!” (Demetri Martin, comedian).

Penguin conservation is imperative!

(© Martin Franklin/ZSL)

Humboldt Penguins with a view of their flippers in the water.

In the course of my work as a zookeeper at ZSL London Zoo (a charity which supports animal conservation projects all over the world), I frequently get asked some pretty odd (often brilliant) questions. Recently two 6- or 7-year-olds asked me, “Have penguins ever been able to fly?” (A great question, I thought). Although we ended up talking about traits these children had inherited from their grandparents, I ultimately utterly failed to explain in simple enough terms to them how evolution works – entirely mea culpa. (Incidentally, for thoroughly clear and persuasive introductions to the facts and mechanisms of evolution, I’d highly recommend reading both Coyne1 and Dawkins2).

This incident did, however, prompt me to write this piece. Of course, penguins, as we understand and envisage them, have never been able to fly. But their ancestors, from whom they evolved, unquestionably could. The real question is to ask what pressures or opportunities caused that change.

Why do penguins swim instead of fly?

First, however, a quick look at flightlessness in birds generally. Although flying has proved advantageous to most bird species (and has thus been retained), a wide range (in terms of size, geographical spread and ecology) have evolved to discard the power of flight once possessed by their ancestors. These include:

“Ratites” (i.e. ostriches, rheas, emus, cassowaries and kiwis, plus the now extinct moas and elephant birds), which lack a keel (ridge) on their sterna (breastbones) onto which to attach flight muscles.
Numerous waterfowl (Anseriformes) (e.g. Aukland Teals and Campbell Teals).
Two species of grebe (Podicipediformes) (i.e. Junin Grebes and Titicaca Grebes).
One of the pelican/cormorant group (Pelecaniformes) (i.e. flightless cormorants).
One of the parrot group (Psittaciformes) (i.e. Kakapos).
Numerous rails (Gruiformes) (e.g. Calayan Rails and Pink-legged Rails).
A variety of now extinct birds, including from the: pigeon and doves (Columbiformes) (e.g. Dodos); gamebirds (Galliformes); hoopoes (Coraciiformes); birds of prey (Falconiformes); owls (Strigiformes); nightjars (Caprimulgiformes); perching birds (Passeriformes); and auks (Charadriiformes).

Many of these flightless species come/came from remote, predator-free, food-abundant islands, which helps explain why they lost the ability to fly. It is “expensive” (in terms of energy required and lost other opportunities) for birds to maintain the necessary physical attributes needed for flight (e.g. large, calcium-rich, keeled breastbones and large chest muscles). Therefore, if it’s no longer necessary to fly to avoid predation or hunt, natural selection frequently results in less investment in such “expensive” materials/attributes.3

Flightlessness exists in many birds besides penguins

Flightlessness has also evolved independently in:

large-bodied, herbivorous birds (e.g. ostriches, emus, cassowaries, moas and elephant birds), as a diet of high-volume low-quality vegetation favours developing a large body, which in turn increases the challenges of maintaining the apparatus needed for flight;
several foot-propelled diving birds (e.g. flightless cormorants), as these evolved to have powerful, paddle-like legs and feet (so their wings and chest-muscles became increasing less important for locomotion, and accordingly regressed); and
penguins (i.e. wing-propelled divers, that in water use their feet as a rudder, rather than for propulsion). These are by far the largest bird family whose entire members are flightless.4

The transition from flying birds to wing-propelled divers was a gradual process which started around 65 million years ago for penguins, and would have involved an intermediate stage whereby its ancestors could use their wings for both flying in the air and diving/swimming underwater (much as Razorbills, for example, do today). These ancestors were probably seabirds similar to modern diving petrels.

Strategies for a bird to choose swimming vs. flying

One of two strategies can be adopted once such a bird reaches a critical size of around 1kg (above which the size of wing needed for flying becomes too large for efficient swimming). Either:

(1) the wings can be kept solely for flying, and the feet/legs can be used for underwater propulsion (as observed in most modern ducks and cormorants); or

(2) aerial flight can be abandoned in return for superior underwater swimming (as happened with penguins).4,5

Gradually, therefore, as this ancestor fared better swimming underwater than flying above it:

No longer constrained by the necessity of flying as well as swimming, it was able to increase its weight. (One now-extinct penguin species, Anthropornis nordenskjoeldi, weighed around 135kg, and the modern Emperor and King Penguins are also relatively large animals).
Slim wing bones became increasingly shorter and heavier, eventually resulting in the flat, broad (and less flexible) flippers sported by modern penguins.
Other related adaptations developed, including, for example, a hydrodynamic body shape and denser bones (unlike flying birds’ air-filled bones), meaning penguins are not overly buoyant.

As a result, by 55 million years ago, penguins were completely flightless but thoroughly adapted to life in water.4,5

(© Martin Franklin/ZSL)

Streamlined bodies and rigid, flat flippers allowing strong swimming ability in penguins.

The adaptations that penguins have developed over thousands of years never ceases to be fascinating. Tell us your thoughts in the comment sections below. And please consider assisting with our conservation projects and helping us to continue to provide you this information by donating to Penguins International.

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References

1 Coyne, J. A. (2009). Why Evolution is True. Oxford University Press: Oxford.

2 Dawkins, R. (2009). The Greatest Show on Earth. Transworld Publishers: London.

3 McNab, B. K. (1994). Energy Conservation and the Evolution of Flightlessness in Birds. The American Naturalist. Vol. 144, no.4, 628-642.

4 Gill, F. B. and Prum, R. O. (2019). Ornithology. (4th edition). W. H. Freeman and Company: New York.

5 Lynch, W. (2007). Penguins of the World. A&C Black Publishers Limited: London.

Martin Franklin In Blog

Penguin Record Breakers

Penguin Record Breakers

by Martin Franklin

At 100-130cm long and 22-40kg in weight, the Emperor Penguin is by far the largest of all the penguins. (This is, incidentally, only a little smaller than champion gymnast Simone Biles, whose height is 142cm and weight 48kg). But do the Emperor Penguin’s height and weight advantages translate into record-breaking penguin performances?

(1) Greatest Diving Depth – Emperor Penguin vs. Human

Alexey Molchanov holds the current human world record for the deepest single-breath dive (with fins, and without use of weights or inflation devices). He managed 130m. (Without fins, William Trubridge holds the record, at 102m). This equates to the Emperor Penguin’s preferred “average” dive depth, but it can easily dive to 400m, and has even been recorded at a depth of 564m. With a pressure at such depths of up to 30 times that at the surface, and no other penguins able to descend so deep, the Emperor Penguin is unquestionably the champion deep sea diver.^1,2

(2) Longest Time Spent Under Water for Emperor Penguins

The human record for this is currently held by Stephane Mifsud, who lasted 11m 35s. This, however, was stationary and in a shallow swimming pool, meaning his physical exertion was negligible, and he was unaffected by water pressure associated with water depth. Again, the Emperor Penguin beats this hands (or perhaps flippers) down: It prefers short dives of 3-6 minutes, but can stay under water for up to 22 minutes, which is longer than any other bird can manage.¹

Southern Rockhopper Penguins diving in the water

Southern Rockhopper Penguins diving into the water

(3) Fastest Swimming Speed of Emperor Penguins

The human world record holder in the 100m freestyle is Cesar Cielo, with a time of 46.91s, which equates to around 4.8mph (7.7kmph). The unofficial fastest recorded penguin to date (though others could be faster) is the Gentoo, at around 22mph (36kmph). That’s around 5 times faster than the fastest human.

Gentoo Penguins after a day of fishing

Penguins achieve these incredible speeds due to their unique anatomy, which includes:

A torpedo-like body shape (including legs placed far back on their bodies) which results in remarkably little drag (the legs only being used for steering when swimming);
Flattened and rigid wing bones, the arrangement of which (unlike in flying birds) create significant forward propulsion on both the up and down-stroke;
A silky outer layer of feathers; and
Heavy (non-pneumatic) bones, so the birds are not fighting buoyancy in the way flying birds would.

Penguins also have handy built-in “goggles”, meaning they can see well on both land and in water, as they possess:

Nictitating membranes (i.e. a transparent inner eyelids which can be drawn over the eyes);
Flat corneas (the transparent front part of the eyes), which reduce refraction (light changing course in different ways in different media); and
Strong focusing muscles (allowing them to change their lens shapes as required).^{1, 3}

(4) Competitive Eating (and Remarkable Egg-Care)

Penguins can eat an astonishing quantity of food very quickly, and their consumption increases markedly at particular times, i.e.:

Immediately before they moult (during a moult, which typically lasts a few weeks, they are no longer water-proof or able to thermo-regulate effectively, and thus cannot go fishing at sea);
When they have chicks to feed (which are fed regurgitated food);
In the case of Emperor Penguins, immediately before they start their long (up to 125 mile/200km) “march” to form breeding colonies. This is followed by the males taking on egg-incubation duties (which last for 62-67 days without food and in temperatures as low as minus 60^oC, unassisted by their female partners, and with only the body heat of other males with whom they huddle to help stay warm).

This feat of the Emperor Penguin breaks numerous records, including:

Being the only penguins to breed during the Antarctic winter;
This being the most intense cold experienced by any warm-blooded animal;
This being the longest continual incubation period of any bird (although kiwis and great albatrosses incubate for 71-84 days, they leave their nests to feed)²;
Males being able to regurgitate a protein-rich stomach secretion to feed their chicks for up to 10 days (if the females don’t get back to share chick-feeding duties in time);
Being the only birds (technically) never to touch land (as they generally form their breeding colonies on winter sea ice).¹

Adélie Penguins have been reported as able to eat 25g of krill per minute (which equates to around 0.5% of their body weight per minute).³This species has also been reported as eating around 800g of food per bird per day (which equates to around 16% of their body weight).⁴ In terms of weight alone (not calorific content), this is broadly equivalent to an average American man eating two 240g “Big Mac” hamburgers per minute, or 59 “Big Macs” per day.

Two colleagues tell me anecdotally that they once witnessed a chick-raising pair of Humboldt Penguins at ZSL London Zoo rival even the Adélie Penguins mentioned above. In just a few minutes, I am told that these birds (a female named Heidi and a male named Lars, pictured) each ate approximately 80-100 sprats (weighing around 840g). Given these penguins’ normal weights of around 4½kg each, this equates to them each eating around 19% of their normal body weights in one brief sitting.

Of course, Heidi and Lars were behaving naturally and appropriately, given their own nutritional requirements and those of their chicks at that particular time. I only wish I could claim a similar excuse myself in respect of my own occasional over-indulgences.

Lars and Heidi – Humboldt Penguins at ZSL London Zoo with (seasonal dependent) impressive appetites

Penguins are amazing animals with even more amazing adaptions that help them live in extreme places. Like this story? Have a story of your own? Leave a comment below. And please help us to continue to provide you with penguin news articles by donating to Penguins International.

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References

¹De Roy, T., Jones, M. and Cornthwaite, J. (2013). Penguins: Their World, Their Ways. Bloomsbury Publishing: London.

² Lynch, W. (2007). Penguins of the World. A&C Black Publishers Limited: London.

³ Williams, T. D. (1995). The Penguins. Oxford University Press: New York.

⁴ Culik, B. M. (1993). Energetics of the Pygoscelid penguins. Habilitation thesis. University of Kiel.

Martin Franklin In Blog

Penguin Fight Club

Penguin Fight Club

By Martin Franklin

As readers of a certain age will know, both the first and second rules of Penguin Fight Club are, “You do not talk about Penguin Fight Club.”

That, however, would mean an especially short and (even more than normal) disappointing blog post.

I’m therefore going to bend the rules this once, not least as penguin combatants themselves often discard the rules of Fight Club, in particular, as Brad Pitt’s character so clearly articulates, “Fourth rule: Only two guys to a fight. Fifth rule: One fight at a time, fellas.”

Numerous members of the colony at ZSL London Zoo involved in a brief squabble (© Martin Franklin/ZSL)

Fictional penguins tend to bend the rules even further. For example, Batman’s old adversary “The Penguin” used technology to fight, frequently using modified high-tech umbrellas as weapons. Similarly, the clay-animated “Feathers McGraw” disguised himself as a chicken by pulling a rubber glove over his head, used robotic “Techno Trousers” to steal a diamond, and trapped Wallace and Gromit in a wardrobe at gunpoint.

Real penguins do, however, thankfully tend to stick to a fairly well documented and more traditional set of agonistic behaviours (i.e. social behaviours related to fighting)^{1, 2, 3}. These include:

1. Visual penguin displays from a short distance

Staring. This may be a “sideways” stare (where the head is held to one side, with one eye fixed on the opponent), or “alternate staring” (where the head is moved from side to side, and opponent stared at with each eye alternately). The whites of the eyes may be exposed.
Pointing. The bird points its closed bill directly towards the opponent (sometimes with neck-rotation). This is often used by birds on nests towards other birds that venture too close.
Gaping. The bird leans towards its opponent, with neck stretched and bill open.

2. Penguin Vocalisations (combined with visual displays)

Ecstatic displays (also called trumpeting). This can either be performed by an individual or in pairs (in which latter case it is termed a “mutual” ecstatic display). It involves stretching the neck upward and flippers outward, and making one or more loud donkey-like brays (potentially also rolling the head from side to side, depending on the species). Context, however, is everything, as although such displays often indicate ownership of (or claims to) territory (particularly nest sites), and are often seen in connection with fights, they can also be used to advertise availability for mating and communicate identity (e.g. to a partner elsewhere on the beach).
Growling/hissing. This is produced during exhalation and may accompany, for example, “pointing” (particularly in the crested penguins) or “lunging” (particularly in Little Penguins).

3. Physical/Close Contact

Charging/lunging. The bird runs or lunges towards its opponent.
Pecking. The closed bill is used to make a hard, speedy jab (often following “pointing”).
Bill vibrating. Two birds rapidly and repeatedly clap their bill against the other’s bill (think of “fencing”).
Biting. A pinching grip (particularly on the opponent’s neck or back), making use of the sharp hook on the end of the bill (which is otherwise primarily useful for grasping fish), sometimes in conjunction with pulling and twisting.
Beaking (also called the tête-à-tête posture). Two birds interlock their bills, then pull and twist to try to dislodge the opponent.
Beating. During “biting”/”beaking”, the bird rapidly and repeatedly slaps its opponent with a flipper. (The author can attest that this is surprisingly painful when a bird elects to perform this on a human.)

Of course, differences are observed in different species.

For example, Adélie Penguins seem also to use a “bill-to-axilla” threat posture³ (which looks a bit like they’re trying to smell their armpits). Incidentally, it has been suggested that, just like in the worst human soap-operas, the most aggressive fights between Adélie Penguins occur when a female returns to her nest after an extended absence, only to find another female has pair-bonded with her former mate⁴.

Little Penguins (in which it seems around 10% of aggressive interactions escalate to fighting) similarly possess a significant repertoire of distinct agonistic behaviours (22 in cave-nesting birds and 13 in burrow-nesting birds). Some of these actions are common to most penguins, as already described above. Others (as far as the author is aware) are yet to be widely reported upon in relation to other species. These include the “zig-zag approach”, the “breast butt” (think of an angry soccer player with his arms held rigidly by his sides squaring up to another) and a variety of nuanced flipper-spreads.⁵

So what should the reader do, should he/she find him/herself on the wrong end of any such agonistic penguin behaviour?

The author suggests (without any guarantees) that a generally sensible course of action might be to attempt the kind of “appeasement” or “displacement” behaviour deployed by penguins.

Therefore, increasing the distance between you and your aggressor is probably the best tactic. However (and the following is not meant seriously):

If stationary, try the “submissive hunch”, the “face-away”, or “look-around” (rotate your retracted neck), or start “preening” yourself (good luck with that one).
If walking through a colony, try “slender-walking” (with body stretched up, neck extended, flippers very slightly spread, and – if you can manage it – feathers sleeked down).
Alternatively, get yourself a warm coat and egg and join the male Emperor Penguins during breeding season: aggression is suppressed at this time, allowing them to huddle together for warmth³.

But please repeat nothing of this: after all, you know the first two rules of Penguin Fight Club.

Wasn’t this a great read about penguin social behaviors and “Fight Club?” Let us know what you learned, and if you’re going to watch any movies this week.

And please help us continue to bring you more information about penguins by donating to Penguins International. We greatly appreciate your support.

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References

1 Merritt, K. and King, N. E. (1987). Behavioral Sex Differences and Activity Patterns of Captive Humboldt Penguins (Spheniscus humboldti). Zoo Biology, 6(2), 129-138.

2 Eggleton, P. and Siegfried, W. R. (1979). Displays of the Jackass Penguin. Ostrich, 50, 139-167.

3 Williams, T. D. (1995). The Penguins. Oxford University Press: New York.

4 De Roy, T., Jones, M. and Cornthwaite, J. (2013). Penguins: Their World, Their Ways. London: Bloomsbury Publishing.

5 Waas, J. R. (1990). ‘An Analysis of Communication during the Aggressive Interactions of Little Blue Penguins (Eudyptula minor)’. In David, L. S. and Darby, J. T. (eds). Penguin Biology. San Diego, California: Academic Press Inc. pp. 345-376.

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Penguin Pride – Same Sex Behaviour in Penguins

Penguin Pride – Same Sex Behaviour in Penguins

by Martin Franklin

With June being LGBT+ Pride Month in many places around the world, it seems an appropriate time to write about some of the many documented examples of penguin couples that frequently display same-sex sexual behaviour (including courting displays, sexual activity and nest-building activity).

Before diving in, however, it’s worth mentioning (given the potentially misleading title above) that the generally accepted collective noun for a group of penguins is not a (leonine) “pride”, but rather a “raft” (if they are in the water), or a “waddle” (if they are on land).

Same Sex Behaviour in Penguins

Same-sex sexual behaviour has been observed in numerous penguin species, including King penguins at Berlin Zoo, African penguins at Toronto Zoo, Gentoo penguins at Sea Life Sydney Aquarium, and Chinstrap penguins at Central Park Zoo in New York. In the latter case, the relevant pair (Roy and Silo, both male) even successfully incubated another pair’s egg, resulting in a chick named Tango. This in turn even resulted in a popular children’s book called “And Tango Makes Three“.

Same Sex Behaviour in Wild Animals

Such behaviour is not limited to penguins, of course: same-sex sexual interaction has been observed in hundreds of animal species¹, in both zoos and in the wild. In some cases, this may be “sociosexual” behaviour designed at least in part to achieve a social goal (e.g. facilitating food sharing, forming alliances, reducing social tensions or facilitating reconciliations), as seen, for example, in bonobos². In other cases, however, such behaviour appears to have no sociosexual element. For example, around 8% of rams in particular domestic sheep breeds seem exclusively to choose to mount other males rather than females when given the option³.

But back to penguins, and, in particular, Humboldt penguins (a species I observe on a near-daily basis, in the course of my work as a bird keeper at ZSL London Zoo). Zoo am Meer Bremerhaven in Germany has reported same-sex sexual behaviour in Humboldt penguins, and the same is true of our observations at ZSL London Zoo.

In this context, it’s particularly serendipitous that the Humboldt penguin is named after the Humboldt ocean current (off the west coast of South America), which itself is named after the Prussian naturalist Alexander von Humboldt, who himself the evidence indicates to have been homosexual (or possibly bisexual).

Excluding recently hatched chicks, there are currently 93 penguins on Penguin Beach at ZSL London Zoo (77 adults and 16 juveniles). This number, along with the male/female split being broadly equal, means these birds have significant partner-choice. There are currently 34 nesting pairs, of which 3 are established same-sex pairs.

The first of these are Ronnie and Reggie (pictured, both 17 years old), a highly vocal and well-built all-male pair who certainly make their presence known on the far right-hand side of the beach, and who think little of barging other penguins out of the way at feeding time. (People with knowledge of the Kray Twins, who terrorised the East End of London in the 1950s and 60s, will appreciate the appropriateness of these birds’ names). They do, however, also have a nurturing side: recently when another pair’s egg needed incubation, Ronnie and Reggie took on the job, diligently taking it in turns to incubate the egg themselves.

Next up are Zimmer (21 years old) and Nadja (16), our only all-female pair (pictured). Zimmer also happens to be our oldest penguin: the species can live up to around 20 years in the wild, but can fare significantly better than that in zoos (due to better nutrition, better medical care, lack of predation, and the absence of negative human impact on their environment).

Martin (17) and Dev (13) are our other all-male couple (pictured), and tend to hang out on the left-hand side of the beach. We placed a new nest box in this area of the beach recently, and within a couple of hours this pair had abandoned their old nest box and established themselves inside the new one.

Finally, mention must be made of Rainbow (1) (pictured), who was named on the Pride Parade weekend around this time last year, and whose name was chosen specifically in honour of the LGBT+ community. She even sports identity beads on her wing reflecting this – the only penguin on the beach not to have a bead sequence that references its year of hatch. As Rainbow is still a juvenile, it remains to be seen with whom she may choose to form a pair-bond in the future.

Did you learn something new about penguins by reading this blog? A nice way to wrap up LGBT Pride Month. Let us know your thoughts. Also, please help us continue to learn more about penguins by donating to Penguins International.

Check out some of our other blogs, too:

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References

¹ Bagemihl, B. (1999). Biological exuberance: Animal homosexual and natural diversity. New York, NY: St. Martin’s Press.

² de Waal, F. B. M. (1987). Tension regulation and nonreproductive functions of sex in captive bonobos (Pan paniscus). National Geographic Researcher, 3, 318–338.

³ Roselli, C. E., Larkin, K., Resko, J. A., Stellflug, J. N., Stormshak, F. (2004). The volume of a sexually dimorphic nucleus in the ovine medial preoptic area/anterior hypothalamus varies with sexual partner preference. Endocrinology, 145, 478–483.

Martin Franklin is a bird keeper at ZSL London Zoo, and works extensively with Humboldt penguins. Any views or opinions expressed in this article are the author’s own, and do not necessarily represent those of ZSL.

Martin Franklin