Tetrapod Zoology

Gannets, most awesome of seabirds

Seabirds are undeniably cool. They often look neat, they often have very cool names (witness such examples as Macronectes, Oceanodroma and Cerorhinca), and their biology is often amazing. They include some of the largest and longest-lived of birds, the most numerous (there might be over 50 million Wilson’s storm-petrels Oceanites oceanicus in the world), and the most wide-ranging. While crossing the English Channel recently, I kept a look out above-deck for, well, whatever.

i-a6deb65b341b5bdf7e547dd86d29a2b6-Northern_Gannet_wikipedia_Dec_2008.jpg

And I was rewarded with excellent views of Northern gannet Morus bassanus [adjacent pic from wikipedia]. Together with their close kin the boobies (the six species of Sula), gannets form a bird family called Sulidae (conventionally included within Pelecaniformes, the group that also includes pelicans and cormorants). Gannets are big (their wingspans can exceed 1.7 m), and they exhibit specialisations that allow them to indulge in a pretty incredible piece of behaviour: they hurtle down to the sea like arrows, plunging deep beneath the water…

While undeniably alike, there is little question that gannets and boobies can be distinguished on the basis of overall appearance and skeletal morphology (van Tets et al. 1988), and the fossil record indicates that they diverged something like 20 million years ago. Olson (1985, p. 204) therefore stated that ‘There is no justification … for combining Morus with Sula‘. On the other hand, all the extant members of the group are pretty uniform and the differences – while obvious – are all very minor. In recent years it has become increasingly fashionable for gannets and boobies to be given separate genera, but not everyone does this [a white-phase Red-footed booby S. sula shown below, from wikipedia].

i-f00b7966cb8b095be3bc994be420a6ed-Red-footed_Booby_flight_wikipedia.jpg

Less well known is the proposal that Abbott’s booby (originally Sula abbotti) is distinct enough for its own genus, Papasula Olson & Warheit, 1988. Abbott’s booby lacks characters present in both Sula and Morus and differs from them in details of vertebral morphology, and in having its sclerotic ossicles fused together to form a ring (a totally unique – and bizarre – character). Olson & Warheit (1988) proposed that it represented the most basal sulid lineage: in a molecular analysis, Friesen & Anderson (1997) found that it was the sister-taxon to the gannets.

Sulid anatomy is highly distinctive. They’re streamlined, with long, high-aspect wings, large, totipalmate* feet, and long, pointed bills. The eyes face forwards, presumably allowing binocular vision (I say ‘presumably’ because it’s not always possible to be sure when binocular vision is present). The long bill is approximately conical, sharply pointed, and with strongly ossified walls that are covered with numerous channels made by blood vessels [skull of Northern gannet below, from Mayr (2002)]. The tip of the upper jaw is gently curved (but strongly hooked in Abbott’s booby), and in Abbott’s booby the tomial edges are deeply serrated. External nostrils are entirely absent in all species: a vertical, slit-like aperture which persists at the posterior end of the bill (just in front of the nasofrontal hinge) is covered in life by a flap of rhamphotheca that is forced shut over the aperture when the bird plunges into the water.

* Totipalmate = all four toes are united by extensive webbing.

i-6e8e347a19a46ec125d54d3d1bcfe7eb-Morus_bassanus_skull_Dec_2008.jpg

Sulids are predominantly (though not entirely) white (more on this in a later post). As is the norm among seabirds, the wing-tips are black. Some people think that black wingtips have evolved because melanin granules (which are insoluble) help provide strengthening and hence reduce damage to these extremities. That might be partly true, but it can’t be the whole story because there are of course some seabirds (mostly gulls) that have no black at the wingtips at all. As with so many other details of morphology, it is probable that black wingtips have several functions, but they probably serve predominantly as species discriminators and display structures.

Gannets (and apparently Abbott’s booby too) are the sister-taxon to the boobies. There are three extant gannets (Morus bassanus of the Atlantic, M. capensis of the southern African coasts and M. serrator of the Australasian coasts), but they’re so similar that some workers (most notably gannet expert Bryan Nelson) regard them as only partially differentiated and still as part of the same species. Fossils show that gannets were present in the north Pacific until late in the Pleistocene (namely M. reyannus Howard, 1936), and fossil species are also known from the Miocene of California and Peru, and the Pliocene of Florida (it’s interesting to note that the present distribution of seabird groups does not necessarily reflect their distribution in the recent past, witness the recently extinct albatross populations from the North Atlantic).

i-72e987304a9f5c1901c6c7f705d4bef5-Alan_Wilson_wikipedia_gannet.jpg

Nelson (1980) thought that gannets evolved in the tropics, and became bigger and heavier as they moved north, the end result of this being M. bassanus [awesome adjacent photo from wikipedia]. This is the heaviest extant sulid (up to 3.1 kg) and the most cold-tolerant, its thick fat layer and reduced amount of naked gular skin helping to minimise heat loss. Its size and weight mean that it can dive deeper than other sulids, getting down to as deep as an astonishing 34 m (Brierley & Fernandes 2001), and it’s also able to take relatively large prey (predominantly mackerel and herring). From a starting point 30 m or so up in the air, gannets launch themselves at the water at about 24 m/s (that’s 86 km/h or 53 mp/h, I think). Using tail, wings and feet, they adjust their trajectory and angle before beginning the entire process: Nelson (1980) wrote that ‘Gannets may hustle down in one straight air-slide, corkscrew or even tip backwards of vertical before shooting their wings behind them and entering the water like an arrow’ (p. 45). The chest is well protected with an intricate network of large air sacs (all the books repeat this fact this but, frustratingly, it’s never illustrated), and the birds use their wings and large, robust feet to force themselves further beneath the surface.

Because the dive is so incredibly brief (lasting for less than two seconds), it’s difficult to study. Ropert-Coudert et al. (2004) found that gannets underwent no – or virtually no – deceleration when entering the water during a dive (a testament to extraordinary streamlining), and that they then continued under their own momentum at an average of 2.87 m/s. The bottom of the dive was determined – not by loss of momentum – but by the bird actively decelerating once the desired depth had been reached [Australian gannet shown below, from wikipedia].

i-4f73d0e3b449ec755ff910cf3880b31f-Morus_serrator_wikipedia_Dec_2008.jpg

Incidentally, none of the sulids are obligate plunge-divers: they can also make short dives from the surface, though on these occasions they cannot hunt at depth and can only take advantage of prey that are already near the surface. Ropert-Coudert et al. (2004) noted that this shallow-diving technique probably mostly occurs in situations where other marine predators, like cetaceans, seals and big scombroids (tuna and kin), have already pushed fish shoals to the surface. This brings us to another interesting issue: if their diving habits bring them into close contact with such large marine predators, are the sulids themselves in danger of predation? They probably are: Feare (1989) discussed evidence showing that Masked boobies S. dactylatra were sometimes attacked and/or eaten by big fish like groupers. In one case, a booby ringed at Boudeuse in the western Indian Ocean turned up, eleven years later and 100 km away, in the belly of a grouper. In another, a booby returned from a fishing trip with a severely bitten wing that rendered it flightless.

Much more on sulids later: incidentally, the autocorrect function in Word thinks that ‘sulid’ should be ‘solid’, how annoying.

Finally – - if you don’t get the whole ‘gannets are awesome’ thing, watch this video (sorry if it takes a while to load: it is DEFINITELY worth it though). The music is from the Stereophonics.

And happy new year!

Refs – -

Brierley, A. S. & Fernandes, P. J. 2001. Diving depths of Northern gannets: acoustic observations of Sula bassana from an autonomous underwater vehicle. Auk 118, 529-534.

Feare, C. 1989. Underwater booby-trap. BBC Wildlife 7 (3), 142.

Friesen, V. L. & Anderson, D. J. 1997. Phylogeny and evolution of the Sulidae (Aves: Pelecaniformes): a test of alternative modes of speciation. Molecular Phylogentics and Evolution 7, 252-260.

Mayr, G. 2002. A skull of a new pelecaniform bird from the Middle Eocene of Messel, Germany. Acta Palaeontologica Polonica 47, 507-512.

Nelson, B. 1980. Seabirds: Their Biology and Ecology. Hamlyn, London.

Olson, S. L. 1985. The fossil record of birds. In Avian Biology, Volume III, pp. 79-238.

- . & Warheit, K. I. 1988. A new genus for Sula abbotti. Bulletin of the British Ornithologists’ Club 108, 9-12.

Ropert-Coudert, Y., Grémillet, D., Ryan, P., Kato, A., Naito, Y. & Le Maho, Y. 2004. Between air and water: the plunge dive of the Cape gannet Morus capensis. Ibis 146, 281-290.

Van Tets, G. F., Meredith, C. W., Fullagar, P. J. & Davidson, P. M. 1988. Osteological differences between Sula and Morus, and a description of an extinct new species of Sula from Lord Howe and Norfolk Islands, Tasman Sea. Notornis 35, 35-57.

Comments

  1. #1 shiva
    December 31, 2008

    Ok, i’m no expert on nomenclature, but the splitting of Sula and Morus seems odd to me, because the sula (with an accent over the U) is Norse and/or Gaelic for the Northern Gannet, which i’m guessing with about 99% certainty, being a common and well-known European bird, was the first sulid to be scientifically described (i’d be very surprised if it wasn’t Linnaeus) – so it looks as if the type species of Sula was moved to a different genus?

    Gannets are definitely awesome birds. I had no idea until this article prompted me to look on Wikipedia that the UK had 2/3 of the world’s Northern Gannet population…

  2. #2 Bob O'H
    December 31, 2008

    I love the video clip. It makes the fishing rod look so useless.

  3. #3 David Marjanovi?
    December 31, 2008

    incidentally, the autocorrect function in Word thinks that ‘sulid’ should be ‘solid’, how annoying.

    Just take it out of the autocorrect list.

  4. #4 Neil
    December 31, 2008

    I’m a bit of a gannet fan, although the only one Ive ever seen was way off shore at Dungeness. I think our massive gannet colony at Bass Rock got to be one of the best things in the UK, Ill get there at some point. In fact gannets diving was vote the no 1 natural spectacle in the UK, in the BBCs “Nature’s Top 40″ which most people missed thanks to the BBC crimnally putting it on at 2.30 in the afternoon! And they made it a bugger to find on Iplayer too.

    Interesting side note: don’t annouce that you one day want to got to the tropics to see boobies – from personal experience people get the wrong idea!!

  5. #5 Darren Naish
    December 31, 2008

    Shiva: Linnaeus (1758) originally named gannets Pelecanus bassanus (this was itself based on the Anser bassanus of Ray, 1676) and boobies Pelecanus piscator.

    Brisson (1760) later decided that boobies needed their own genus – Sula – and Vieillot (1816) coined Morus for gannets. The type species for Sula is Sula piscator: this is an objective synonym of S. sula (Red-footed booby), but I haven’t yet understood why S. sula (Linnaeus, 1766) wins out over S. piscator (Linnaeus, 1758). Linnaeus (1766) named Pelecanus sula for ‘the booby’ (described by Catesby in 1832), so it seems that type designation was shifted from Pelecanus piscator to Pelecanus sula at some stage. Does anyone know why? Finding good information on historical taxonomy is painfully difficult.

  6. #6 Roy in Nipomo
    December 31, 2008

    Neil:

    “Interesting side note: don’t annouce that you one day want to got to the tropics to see boobies – from personal experience people get the wrong idea!!”

    Would it be better to say that you wanted to go to France to look at tits?

  7. #7 Lars Dietz
    December 31, 2008

    shiva: Linnaeus indeed described the Northern Gannet, but in the genus Pelecanus. The genus Sula is attributed to Brisson 1760, and the first mentioned species was just called Sula (Brisson didn’t use binomial nomenclature), so I guess it should be considered the type species. The description is online here: http://gallica.bnf.fr/ark:/12148/bpt6k990318/f540.chemindefer
    The bird is described as greyish-brown at the top and white at the bottom, occuring on the coasts of Africa and America, and its English name is given as “Booby”. So it’s clearly not Morus bassanus, but something today included in Sula.
    I’ve tried to find out what it is exactly, but here things get extremely confusing: Brisson mentioned Linnaeus’s Pelecanus piscator as a synonym, but in the 1766 edition of the Systema Naturae, Linnaeus lists Brisson’s Sula as a synonym of Pelecanus sula, and synonymises another of Brisson’s species (Sula candida) with P. piscator. Some sources say that P. piscator is indeterminable, while others say it’s a valid description of the Red-footed Booby. Which is now called Sula sula, based on Pelecanus sula Linnaeus 1766. But the description of Brisson’s Sula (based on a specimen in Réaumur’s collection) doesn’t seem to fit this…
    You might understand that I gave up after that. But at least I hope the original question has been answered: The type species of Sula is not Morus bassanus.

  8. #8 Mo Hassan
    December 31, 2008

    How recent are the recently extinct north Atlantic albatrosses?

  9. #9 Brad Bryant
    December 31, 2008

    Wonderfully informative and intriguing write-up! And the video sure is fun, too. Thanks for this.

  10. #10 Luna_the_cat
    December 31, 2008

    There are gannets near where we live.

    I love their aerodynamics.

    But the smell…… ewww.

    That, I’m afraid, kills much of the appeal for me.

  11. #11 Lars Dietz
    December 31, 2008

    Darren: I started writing the last comment before yours had appeared, so sorry for anything that has been said twice. But I don’t think you’re correct on S. sula and S. piscator being objective synonyms, Linnaeus listed both species in the 1766 edition. Source: http://gallica.bnf.fr/ark:/12148/bpt6k99004c/f217.chemindefer (P.sula is on the next page)
    I saw lots of gannets this summer on Helgoland, by the way. Great birds.

  12. #12 Carlos
    December 31, 2008

    “How recent are the recently extinct north Atlantic albatrosses?”

    I believe they disappeared at the end of the last ice age, when the rising sea levels destroyed their nesting grounds.

  13. #13 Darren Naish
    December 31, 2008

    North Atlantic albatrosses: see Olson & Hearty (2003)…

    Olson, S. L. & Hearty, P. J. 2003. Probable extirpation of a breeding colony of Short-tailed albatross (Phoebastria albatrus) on Bermuda by Pleistocene sea-level rise. Proceedings of the National Academy of Sciences 100, 12825-12829.

    The remains are Middle Pleistocene, from the Lower Town Hill Formation (radiometrically dated to c. 405,000 yrs ago). Ok, not technically ‘Recent’, but recent enough to be ‘recent’. As many as three still-extant albatrosses (short-tailed, Laysan and black-footed) were in the eastern North Atlantic during the Pliocene, and an entirely extinct species (‘D.’ anglica) is known from the Pliocene and Pleistocene of England.

    Incidentally a shearwater, Calonectris wingatei, was just described (Olson 2008) from the same deposits as the Bermudan albatrosses…

    Olson, S. L. 2008. A new species of shearwater of the genus Calonectris (Aves: Procellariidae) from a middle Pleistocene deposit on Bermuda. Proceedings of the Biological Society of Washington 121, 398–409.

    I’ll not mention cahows: more on them later :)

  14. #14 Thomas R. Holtz, Jr.
    December 31, 2008

    Personally, I’m a big fan of boobies (I know, I know, insert joke here…). I’ve been snorkeling when boobies have been diving around me: a very awesome experience, but one tinged with the fear that I was going to wind up with a sulid beak stuck in my skull or back…

  15. #15 Dartian
    December 31, 2008

    Personally, I’m a big fan of boobies (I know, I know, insert joke here…)

    A joke here, on a sulid thread? You gannet be serious.

  16. #16 Richard Carter, FCD
    December 31, 2008

    More on gannets (including a stirring poem) at:
    http://darwin.gruts.com/weblog/archive/2008/06/27/

  17. #17 Jerzy
    December 31, 2008

    BTW, how strong are forces acting on the breast of diving gannet? This creature must be extremely resilient.

    Way off – I read somewhere that breast feathers of the humble ring-necked pheasant are adapted so that can often bounce a shot from hunter’s gun. There was even a bulletproof vest made from pheasant feathers. Pheasants neither dive or evolved under hunting pressure, but presumably have convergent mechanism to take off quickly and safely in dense shrubs.

  18. #18 Graham King
    December 31, 2008

    Thomas R. Holtx, Jr,. wrote

    I’ve been snorkeling when boobies have been diving around me: a very awesome experience, but one tinged with the fear that I was going to wind up with a sulid beak stuck in my skull or back…

    …’sulid’? or ‘solid’?
    :-)

  19. #19 Graham King
    December 31, 2008

    Darren, they are indeed awesome. I watched gannets diving in the River Forth, during an RSPB-hosted boat cruise on the evening of 25th June. I was with friends from the local Friends of the Earth (Fife) group. The Forth and its islands are a great place to see various seabird species.

    Thanks for the extra info here. The biology and physics of sulid diving would make a fascinating study. I’m intrigued to know how young birds learn to do it: do they accompany their parents on increasingly ambitious plunges?

    Happy New Year when it comes!
    thanks for Tet Zoo, and (because made aware thereby) thanks for the great time I had at the Dinosaur Conference in May!

  20. #20 Zach Miller
    December 31, 2008

    I don’t know if we get gannets up here, but we have TONS of seabirds including the always-awesome puffins and oystercatchers. Lots of gulls. LOTS of gulls. Irritating birds, very loud, always nesting in places with lots of people (and then dive-bombing them). For me, you can’t beat cormorants. I have a bird book with a picture of a flightless cormorant (Phalacrocorax harrisi) with its wings spread, sunning itself. Looks just like what one might imagine an unenlagiine dromaeosaur might resemble.

  21. #21 David Kelly
    December 31, 2008

    Graham

    The parents abandon the young. When they leave the nesting colonies the young are heavier than their parents. Too heavy to fly and they jump off the nesting cliffs into the sea and start swimming. As they swim they lose weight and by the time they swim from the Firth of Forth to the Bay of Biscay they are light enough to fly and start fishing.

  22. #22 LeeB
    December 31, 2008

    There is another reason to be interested in boobies if you like mysterious living creatures.
    In his 1967 paper on the birds of Cocos Island in the east pacific, Slud discusses a mystery booby that flew inland presumably to nest.
    It was brown with khaki coloured legs.
    It could out fly the other boobies, did shallow dives to fish, and had a call like a bull frog, ie like a juvenile Abbots booby.
    And of course Abbots booby nests in trees on the centre of islands.
    Nelson in his 1978 book on sulids found this intriguing enough to mention it.
    Then in 1988 Steadman et al described fossils of Abbots booby from the Soloman Islands, and a new subspecies of Abbots booby, S. abbotti costelloi from the Marquesas which are the next island group to the west of Cocos as the booby flies.
    The authors were aware of Sluds report and mentioned it.
    More recently in 2006 Steadman has suggested that if alive today Costellos booby would probably be considered a separate species.

    Certainly if the Booby Slud saw was a living Costellos booby the call, which is a species specific recognition signal, and which sounds like a neotenic version of Abbots booby’s call, sugests it is a separate species, Papasula costelloi.

    Slud only saw a few of these boobies towards the end of his stay on Cocos island, so they are either very rare or nest in greater numbers after he left.

    Given that there are very large numbers of the brown phase of the Red Footed booby nesting on the island, and the best place to hide a brown coloured booby would be amoung other brown coloured boobies, perhaps (hopefully)there are more than a handful of them left.

  23. #23 Nathan Myers
    January 1, 2009

    LeeB: I can’t tell whether your posting is a year-end joke, or, if so, what exactly it is. Success!

  24. #24 RStretton
    January 1, 2009

    They are amazing birds. I watched three Australasian Gannets today plunge diving whilst out on a sojourn to Tiritiri Matangi Nature Reserve in the Hauraki Gulf off Auckland and they are stunning.

    Without doing any research does anyone know the difference between the Northern and Australasian Gannets? They look very similar to the untrained eye.

  25. #25 David Kelly
    January 1, 2009

    RStretton wrote “Without doing any research does anyone know the difference between the Northern and Australasian Gannets? They look very similar to the untrained eye.”

    Australasian Gannet has black primaries (ie the wingtip) and secondaries (the feathers on the trailing edge of the wing closest to the body) and a black tail with white outer tail feathers in adult plumage.

    Adult Northern Gannet has black restricted to the primaries.

  26. #26 Darren Naish
    January 1, 2009

    Thanks to LeeB for the discussion of Papasula abbotti costelloi from the Marquesas: I was going to discuss this taxon – together with another recently extinct booby (or allegedly extinct booby), the Tasman booby Sula tasmani – in the next post. That second taxon (if it is a taxon: be patient) is also of cryptozoological interest.

    Incidentally, is it true that the name ‘abbotti costelloi‘ is meant to be a joke? I haven’t seen the original description (Steadman et al. 1988) so don’t know.

    Refs – -

    Steadman, D. W., Schubel, S. E. & Pahlavan, D. 1988. A new subspecies and new records of Papasula abbotti (Aves Sulidae) from archeological sites in the tropical Pacific. Proceedings of the Biological Society of Washington 101, 487-495.

  27. #27 Andreas Johansson
    January 1, 2009

    shiva wrote:

    Ok, i’m no expert on nomenclature, but the splitting of Sula and Morus seems odd to me, because the sula (with an accent over the U) is Norse and/or Gaelic for the Northern Gannet

    In modern Swedish, sula (no accent) means any sulid, but especially the northern gannet, the only sulid you’re likely to see in Sweden. I can’t help but think Sula and Morus should be combined!

  28. #28 Martijn
    January 1, 2009

    The Dutch for gannet is ‘Jan-van-gent’ which translates to ‘John-from-Ghent’, which makes it probably the weirdest named bird in the Dutch language (according to Wikipedia the name is probably a bastardization of ‘gannet’)

  29. #29 Mike from Ottawa
    January 1, 2009

    BTW, how strong are forces acting on the breast of diving gannet? This creature must be extremely resilient.

    Darren wrote that “Ropert-Coudert et al. (2004) found that gannets underwent no – or virtually no – deceleration when entering the water during a dive (a testament to extraordinary streamlining)”, which would mean the forces acting on a diving gannet when it enters the water are low. Now, they might not be if the gannet prangs the dive, but at least normally, they wouldn’t be badly stressed.

  30. #30 Lee B
    January 1, 2009

    Darren, it is a long time since I read the paper but if I remember correctly the Abbott and Costello movies were mentioned, and as Costellos booby is heavier in build than the Abbots booby I think it was intended as a joke.

  31. #31 Tim Morris
    January 2, 2009

    I imagine no set of Gannet posts can go without appropriate Dixon-bashing about vertical cervical undulations and certain popular Speculative Zoology critters?

  32. #32 Hai~Ren
    January 2, 2009

    I was watching Wild Ocean, and seeing how pods of dolphins were driving sardines closer to the surface, while gannets were diving in from above. I can’t help but wonder if gannets ever inadvertently impale each other or other large marine creatures while diving. Like if say, one gannet was plunging in while another was heading back up towards the surface, or if a dolphin just happened to be in the wrong place at the wrong time.

  33. #33 deang
    January 2, 2009

    For some reason, I never made the connection until reading this post that mulberries and gannets share the same generic name: Morus.

  34. #34 Dartian
    January 5, 2009

    Darren:

    This brings us to another interesting issue: if their diving habits bring them into close contact with such large marine predators, are the sulids themselves in danger of predation?

    This topic is too intriguing to let go without further comment…

    I’m not aware of any records of underwater predation on gannets, but they are certainly sometimes predated on at the surface. Those of you who’ve seen the BBC documentary Wild Africa might remember the scene in episode IV where a fledgling Cape gannet was killed by a Cape fur seal Arctocephalus pusillus, during its first flight out to sea. That, incidentally, was not an unusual occurrence; fur seal predation is a significant cause of gannet chick mortality in South Africa (David et al., 2003).

    There is also a record of an adult Cape gannet being killed by a fur seal on land (Crawford & Cooper, 1996).

    References:

    Crawford, R.J.M. & Cooper, J. 1996. Cape fur seal Arctocephalus pusillus catches Cape gannet Morus capensis ashore at Malgas Island. Marine Ornithology 24, 53-54.

    David, J.H.M., Cury, P., Crawford, R.J.M., Randall, R.M., Underhill, L.G. & Meyer, M.A. 2003. Assessing conservation priorities in the Benguela ecosystem, South Africa: analysing predation by seals on threatened seabirds. Biological Conservation 114, 289-292.

  35. #35 Alton Dooley
    January 11, 2009

    Gannets are the most common fossil birds in the middle Miocene Calvert Formation of Maryland and Virginia (go here for some examples); they’re also known from the early Pliocene at the Lee Creek Mine in North Carolina.

The site is undergoing maintenance presently. Commenting has been disabled. Please check back later!