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Tubenosed seabirds that shear the waves: of Calonectris, Lugensa, and Puffinus (petrels part VII)


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Manx shearwater (at left) and Sooty shearwater, from Naumann's 1903 Natural History of the Birds of Central Europe. A quiz: name the artist!

As a regular Tet Zoo reader (right?) you’ll be aware of the petrel series. I’m keen to finish it (hey, just as I am with all the other still-incomplete Tet Zoo series), so let’s crack on. In previous articles, we looked at gadfly-petrels, the members of Fulmarini, and also at the evolution, biology and diversity of petrels in general: see the links below. Here, we look at some (but not all) members of the next petrel clade – Puffinini, the shearwaters. These birds are well named for their stiff-winged style of gliding, their (typically) long, slender, pointed wings seeming to ‘shear’ the waves.

Highly simplified 'consensus' cladogram for Procellariidae, again. Images (top to bottom) by Mark Jobling, Bryan Harry, T. Muller and Patrick Coin. Procellaria petrel and shearwater images in public domain; other images licensed under Creative Commons Attribution-Share Alike 3.0 Unported license (fulmar) and Creative Commons Attribution-Share Alike 2.5 Generic license (gadfly-petrel).

Puffinini includes the many shearwater species included in Puffinus and the three Calonectris species: the Mediterranean or Cory’s shearwater C. diomedea, the Streaked or White-faced shearwater C. leucomelas and the Cape Verde shearwater C. edwardsii. Shearwaters tend to have longer and more slender bills than other petrels, with the Puffinus shearwaters having the longest and most slender bills of all tubenoses.

Puffinus shearwaters are famously social, often forming large feeding rafts at sea (though some are strictly solitary when foraging) and often nesting in colonies sometimes known to number in the millions. In the Great shearwater colony on Nightingale Island, Tristan da Cunha, there’s such competition for burrow space that some birds are forced to give up and lay their eggs on the surface of the ground. Apparently, about a quarter of a million eggs end up this way each year (Nelson 1980). Incidentally, there are suitable, unoccupied islands a short flight away, but even these desperate birds choose not to nest there. The choice of nesting habitats is diverse. There are shearwaters that use burrows at sea-level and on the sides, slopes and tops of cliffs, but others that dig burrows among the trees of tropical forests and yet others that use snowy mountainous places.

Short-tailed shearwater (Puffinus tenuirostris) megaflock, photographed in Unimak Pass, Alaska. Photo by USGS. This remarkable image was used on Tet Zoo in the first petrel article (March 2012).

Puffinus was found to be paraphyletic by Heidrich et al. (1998), Nunn & Stanley (1998) and Pyle et al. (2011): in these studies, Calonectris was found to be nested within Puffinus sensu lato, and the sister-taxon to the specific Puffinus clade that includes the so-called small shearwaters. Other studies have instead found Calonectris and Puffinus to be sister-groups (Kennedy & Page 2002, Penhallurick & Wink 2004) while others are ambiguous on this point (Austin et al. 2004).

So far as I know, the jury is still out on this issue and Calonectris is still widely treated as a taxon distinct from Puffinus. Heidrich et al. (1998) wondered whether the solution might be to lump the Calonectris species into Puffinus, or if it might be time to split Puffinus into distinct ‘genera’. Penhallurick & Wink (2004) recommended that we use Ardenna Reichenbach, 1853 for the larger shearwaters and that, within this clade, the Buller’s or New Zealand shearwater P. bulleri and Wedge-tailed shearwater P. pacificus represent a clade for which the name Thyellodroma Stejneger, 1888 should be used (see also Heidrich et al. (1998)).

A few additional names have been used for various hypothesised clades within Puffinus. Hemipuffinus has been used for the Pink-footed shearwater P. creatopus and Neonectris for the Christmas shearwater P. nativitatis and Short-tailed or Slender-billed shearwater P. tenuirostris. However, Neonectris doesn’t seem to be monophyletic (Heidrich et al. 1998, Kennedy & Page 2002, Penhallurick & Wink 2004).

Kerguelen petrel, as illustrated by John Gerrard Keulemans in 1909.

The extremely distinctive Kerguelen petrel Lugensa brevirostris was found to be the sister-taxon to the other shearwaters by Nunn & Stanley (1998) and Penhallurick & Wink (2004), though it had previously been suggested to be a petrodromine or a close relative of fulmars. Olson (2000) argued that the generic name Lugensa couldn’t be used for this species since early specimens associated with that name couldn’t be identified with confidence as Kerguelen petrels. He therefore proposed the new name Aphrodroma (and used the combination A. kidderi for the species). Bourne (2001) argued that this course of action was inappropriate, since the creator of the name Lugensa did specifically state that it was intended for brevirostris (Mathews 1942).

Why is this species “extremely distinctive”? It’s slate-grey overall with unusual reflective, silvery patches on the undersides of its wings and an especially stubby bill. In view of its overall shape, you can understand why people have generally not regarded it as a close relative of shearwaters.

The Calonectris shearwaters

Until recently, only two living species were recognised in Calonectris, both of which were well separated geographically. The Streaked or White-faced shearwater occurs in the north-west Pacific (though it disperses as far west as the Philippines and Borneo) while the Cory’s or Mediterranean shearwater occurs where you might guess it does, as well as in the Atlantic all the way down to South Africa. It used to breed further north than its present-day northern-most breeding limit (the Azores), since evidence for its presence as a breeding species is known from Great Britain.

Cory's shearwater, photographed on one of the Selvagem Islands of Portugal. Licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

The Mediterranean populations of Cory’s shearwater move into the Atlantic during the winter (probably due to the Mediterranean’s low productivity at this time) while those breeding further south winter off the coasts of Namibia, South Africa, Natal, and in the western Indian Ocean (Harrison 1988). As I said in one of the previous Tet Zoo petrel articles, the individuals in the Indian Ocean normally (it is thought) move back into the Atlantic before heading north, but the presence of individuals in the northern Red Sea suggests that some of these birds get back into the Mediterranean by migrating north along the east side of Africa, not the west side.

Streaked shearwater photographed on Mikura Island; image by Kanachoro, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

The resurrection of the Cape Verde shearwater from synonymy with Cory’s shearwater means that there are now two Atlantic Calonectris species. The two remaining subspecies of Cory’s shearwater (C. d. diomedea and C. d. borealis) are distinct enough that they might warrant distinction as species too (Heidrich et al. 1998). [Adjacent image of Streaked shearwater by Kanachoro.]

All three Calonectris species look something like a cross between a Puffinus shearwater and a Procellaria petrel; their soaring flight is “often likened to that of a mollymawk” (Harrison 1988, p. 256). Cory’s shearwater feeds on the wing a fair bit, reaching down to grab small prey from the water or performing short surface dives; some books say that they don’t dive as frequently as do the Puffinus species (Nelson 1980). However, all of this may be inaccurate, since proficient aquaflying has now been filmed in this species: more on that below. Xavier et al. (2011) recently documented a dietary shift in members of this species living around the Azores: since 1994, they seem to have switched from a diet of boarfish, trumpetfish and saury (all small) to one consisting mostly of mackerel. This shift might be due to changes in fish distribution that are occurring in response to sea temperature, or it might be linked to the increased use of mackerel as live bait in the tuna-fishing industry.

Skull and mandible (at top) of the fossil species C. wingatei compared with that of Cory's shearwater, from Olson (2008). The arrows point to the fonticulus orbitocranialis of and depression for the m. adductor mandibulae. Both features are especially large in C. wingatei.

Calonectris has a fossil record that extends back to the Miocene, with the oldest specimens being known from the east coast of the USA (Olson 2008). One Pliocene species, C. krantzi, was about similar in size to a Procellaria petrel, and thus gigantic for a Calonectris. A fossil Calonectris from the Pleistocene of Bermuda – C. wingatei – seems to have become extinct after a catastrophic sea-level rise of about 21 m inundated the island about 400,000 years ago, probably removing the shearwater’s breeding areas (Olson 2008). The last resident albatrosses of the north Atlantic (Short-tailed albatrosses Phoebastria albatrus) became extinct at the same time, and Olson (2008) suggested that “this event would have had a major impact on seabirds worldwide” (p. 401). Modern and future sea level rise may, equally, prove catastrophic for many species.

Large-bodied shearwaters vs small-bodied shearwaters

Little shearwater, illustrated by John Gerrard Keulemans in 1876.

Finally, we come to Puffinus. Why the name Puffinus is used for shearwaters and not for puffins is rather complicated and I’m not about to cover this issue here. So far as I can tell, it mostly relates to early confusion between these birds: the term ‘puffin’ may originally have been used for shearwaters, not for auks.

How many species should be recognised within Puffinus (sensu lato) remains the topic of debate. The group seems to be divisible into distinct small-bodied and large-bodied clades: molecular data indicates that they diverged about 10 million years ago, during the middle part of the Miocene. The small-bodied clade includes the Manx shearwater P. puffinus and Little or Dusky shearwater P. assimilis while the large-bodied clade includes such species as the Great shearwater P. gravis and Sooty shearwater P. griseus. We’ll look at the large ones first.

The large shearwaters include both mostly dark petrels as well as species with a fair bit of mottling and a lot of white on the underside. Wingspans are round about 1 to 1.2 m.

Buller's shearwater in flight, showing distinctive wing pattern. Image courtesy of Cordell Bank National Marine Sanctuary; in public domain.

Buller’s shearwater, also called the New Zealand grey-backed shearwater, is one of the most distinctive shearwaters of the Pacific. It’s large, with a white belly and underwing, and a grey back and dark, V-shaped area extending across the dorsal surfaces of its wings. This recalls the ‘M-shaped’ pattern seen in some gadfly-petrels and prions.

The Wedge-tailed shearwater P. pacificus might be the sister-species of Buller’s shearwater (Nunn & Stanley 1998, Kennedy & Page 2002, Penhallurick & Wink 2004); it has a dark morph that doesn’t look much like Buller’s shearwater at all, but there’s also a pale morph where the underside is extensively white. The wedge-like shape of the tail is, unfortunately, not a reliable field characteristic (Harrison 1988). A Buller’s shearwater + Wedge-tailed shearwater clade has been recovered as the sister-group to the remaining large shearwaters (Nunn & Stanley 1998, Kennedy & Page 2002, Penhallurick & Wink 2004, Pyle et al. 2011).

Flesh-footed shearwater, image by Duncan, licensed under Creative Commons Attribution-Share Alike 2.0 Generic license.

Within that latter group, the Flesh-footed or Pale-footed shearwater P. carneipes is one of several where the plumage is mostly or wholly dark grey or brownish-grey [adjacent image of this species by Duncan]. The others are the Wedge-tailed shearwater, Sooty shearwater P. griseus and Short-tailed shearwater. Unlike those others, the Flesh-footed shearwater has a distinctly two-toned bill where the main section is yellowish and the tip is dark. It occurs throughout the Indian and eastern Pacific oceans, but individuals also wander as far as the western coast of North America. The Indian Ocean birds breed on St Paul Island (located about half-way between Madagascar and Australia) as well as on various islands off the coast of Western Australia. The Pacific ones breed on New Zealand, Lord Howe Island and surrounding islands.

The Sooty shearwater is a long-winged, mostly sooty brown species where a white region on the underwing (surrounded by dark grey feathers on the rest of the wing) is readily visible at distance. This is one of the most wide-ranging of shearwaters, occurring through the Atlantic and Pacific but having breeding bases in and around southern South America and New Zealand and south-eastern Australia.

Great shearwater; image by Patrick Coin, licensed under Creative Commons Attribution-Share Alike 2.5 Generic license.

The Great shearwater is a large, robust and distinctly patterned shearwater of the Atlantic, breeding on various southern Atlantic islands includes Tristan da Cunha, Inaccessible Island and Nightingale Island. It has a dark cap surrounded by white, a distinctive dark belly patch (also surrounded by white), and wingtips and a dorsal tail surface that are distinctly darker than the rest of the dorsal plumage. There’s a white, U-shaped band across the tail base. [Adjacent image by Patrick Coin.]

The Pink-footed shearwater of the eastern Pacific (it breeds off Chile) is also relatively easy to identify in the field, thanks to its dark-tipped but otherwise pinkish bill and mottled underwings. It’s brownish-grey dorsally and white ventrally. This species is quite similar to the Flesh-footed shearwater, both group as sister-taxa in molecular phylogenies, and there have been repeated suggestions that they should be regarded as subspecies of the same species. The Great shearwater, Sooty shearwater and Short-tailed shearwater appear to be successively more distant relatives of this Pink-footed + Flesh-footed clade (Nunn & Stanley 1998, Kennedy & Page 2002, Penhallurick & Wink 2004, Pyle et al. 2011).

The small shearwaters

The small shearwater group includes all those species close to the Little or Dusky shearwater. All are brownish, dark grey, blue-black or blackish dorsally and pale ventrally; bold demarcations between dark and white areas on their faces and proportionally short wings give some of them a superficially auk-like flight style (the overall appearance, flight style and behaviour of a bird are combined to produce the nebulous concept referred to as ‘jizz’ by birdwatchers). They occur throughout the world’s oceans but generally stay away from the poles.

Manx shearwater photographed off Iceland by Ómar Runólfsson. Note the contact with the water surface. Image licensed under Creative Commons Attribution 2.0 Generic license.

By far the best known member of this group is the Manx shearwater [adjacent image by Ómar Runólfsson]. Its size is typical for a small shearwater: total length is 30-38 cm, wingspan is 76-89 cm (Harrison 1988). This is a mostly North Atlantic species and the commonest and most frequently encountered shearwater in the region. Manx shearwaters winter off the coast of South America, with some individuals travelling as far south as Cape Horn or even the southern coasts of Africa. Remember that a seabird that moves from the North Atlantic down to the far south may be quite capable of wandering as far as the eastern Indian Ocean or even Australasia, and this is exactly what a few Manx shearwaters do. It also seems that some of them travel west around Cape Horn and into the Pacific. They then end up migrating north along the western side of the Americas.

mtDNA-based shearwater phylogeny from Austin et al. (2004). Not all members of the 'Manx shearwater complex' are close relatives.

In recent years, the number of Manx shearwaters being seen off the eastern seaboard of North America has increased to the extent that the birds can now be considered common there: compare this with the situation in the early decades of the 20th century when the species was regarded as a rare vagrant to the western Atlantic, with but three records (from Greenland, Long Island and Maine, respectively) prior to 1931 (Lee 1995). The species was reported as a North American breeder in 1973 (at Massachusetts), with other confirmed cases being reported in 1977 (Newfoundland) and 2009 (Maine). Based on what we now know about the local extinctions that have affected petrel, albatross and other seabird populations, it’s certainly reasonable to wonder whether the Manx shearwater actually bred regularly in North America during prehistoric or historic times. While there are various probable Manx shearwater fossils from Florida, the Bahamas and elsewhere, their identification isn’t certain (so far as I know) and better remains are needed to confirm this possibility. A 1947 specimen from Newfoundland has been said to perhaps suggest that breeding was occurring there prior to the 1970s (Lee 1995). The situation with the Manx shearwater in the west may therefore strike a parallel with that of the Cahow Pterodroma cahow in the east. As we saw in the gadfly-petrel article, Cahows were long associated with the western Atlantic but overlooked as birds of the east, even though they were probably always there and probably ‘normal’ denizens of the area prior to modern times.

Within the small shearwater group, the Manx shearwater has often been hypothesised to be especially close to the Black-vented shearwater P. opisthomelas, Little shearwater and Aubudon’s shearwater P. lherminieri (Kennedy & Page 2002, Austin et al. 2004, Penhallurick & Wink 2004). Several populations once regarded as Manx shearwater subspecies and included within the ‘puffinus complex’ have recently been shown to be phylogenetically distinct and worthy of recognition as distinct species. In fact, some studies find them to be less closely related to the Manx shearwater proper than are other, long recognised species like the Little shearwater and Audubon’s shearwater (Heidrich et al. 1998). Austin et al. (2004), however, did find the Manx shearwater to group with the endemic Yelkouan, Levantine or Mediterranean shearwater P. yelkouan and the critically endangered Balearic shearwater P. mauretanicus, two taxa traditionally regarded as P. puffinus subspecies [Balearic shearwater image below by Govern de les Illes Balears].

Balearic shearwater, member of the 'Manx shearwater complex'. Image by Govern de les Illes Balears, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

Indeed, the number of species included in the small shearwater group has long been somewhat confused, since many are only subtly similar and might be subspecies or other populational variants or subsets of others. Furthermore, some birds that look extremely similar have different distributions and different behaviours and might not be as closely related as their appearance suggests. Harrison (1988) said of these petrels that “few groups engender such fierce arguments, even among experts, as to number of recognisable species” (p. 257). For these and other reasons I had to give up on my initial plan to discuss all of the species and subspecies within the group. [Image below of Fluttering shearwater P. gavia by JJ Harrison.]

Fluttering Shearwater, photographed off Tasmania by JJ Harrison. This is one of a few small shearwaters that may be outside the clade that includes the Manx and Little shearwaters. Licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

By the way, there might still be new species to find: the tiny Bryan’s shearwater P. bryani was named as recently as 2011 (Pyle et al. 2011)… the fact that it’s known for a single specimen collected in 1963 has led some to suggest that it might now be extinct. However, several 2012 sightings made near Japan might be of this species.

The Bryan's shearwater holotype, collected in February 1963 on Sand Island, Midway Atoll. From Pyle et al. (2011).

Austin et al. (2004) recently examined the molecular phylogeny of small shearwaters and supported the validity of 14 taxa (an additional five were suggested to be synonyms of various of these 14) that grouped into five clades. They recommended that these 14 taxa should be regarded as subspecies, with the five clades representing the units we term species (Austin et al. 2004). A full discussion of their conclusions is beyond the scope of this article, but the take-home points are that small shearwaters mostly clustered into distinct North Atlantic, Australasian-Southern and tropical Indopacific groups, that most species and subspecies do indeed represent ‘good’, independent lineages, and that populations do not always fit where they might be expected to on the basis of morphological similarity (Austin et al. 2004).

Recently extinct shearwaters

Quite a few recently extinct (or supposedly recently extinct) species are included among the Puffinus shearwaters. Several of the Canary Islands were the breeding base for the apparently endemic Lava shearwater P. olsoni, radiocarbon dating of which indicates that it was still alive about 1200 years ago, meaning that it was still around in about the 9th century (Rando & Alcover 2008). The Great auk Pinguinnus impennis is thus no longer the only seabird known to have become extinct in the north-east Atlantic in historic times. DNA analysis shows that the Lava shearwater (characterised by an especially low, gracile skull) is probably the sister-taxon of the Manx shearwater (Ramirez et al. 2010). Another Canary Islands species, the Dune shearwater P. holei, became extinct 2000-3000 years ago and also seems to have been made extinct by human hunting. Other extinct shearwaters are known from the Pliocene, Pleistocene and Holocene of Europe as well.

Bones of the extinct P. olsoni compared to those of a Manx shearwater (P. puffinus). Note the lower skull profile in P. olsoni. Image from Ramirez et al. (2010), licensed under Creative Commons Attribution 2.5 Generic license.

On Bermuda, P. parvus became extinct after human arrival in the 16th century, and P. spelaeus on New Zealand became extinct following the arrival of humans and their commensals. Other recently extinct shearwater species have been described from the south Pacific.

Deep diving and aquaflying

Aquaflying Cory's shearwaters. Image (c) BBC.

Shearwaters use several different techniques to find and catch prey. To paraphrase Keitt et al. (2000), the general assumption that petrels and other tubenoses only exploit aquatic prey from the upper 50 cm or so of the sea ignores the various pelvic and hindlimb specialisations for proficient diving present in these birds, some of which were commented on as far back as the 1950s. Some species (like the Christmas shearwater P. nativitatis) sit on the sea surface and then swim powerfully and quickly beneath the surface, powered by strong legs and large, webbed toes.

However, thanks to the use of depth gauges and, more recently, underwater photography, we now know that several shearwater and other petrel species, including Cory’s shearwaters, Short-tailed shearwaters, Sooty shearwaters and White-chinned petrels Procellaria aequinoctialis are proficient wing-propelled divers, diving beneath the surface to ‘fly’ in pursuit of prey at depths of between 10 and 20 m (Skira 1979, Brown et al. 1981, Huin 1994). This behaviour is known as aquaflying. Some excellent sequences of aquaflying Cory’s shearwaters were featured in the BBC series The Blue Planet – this might have been the first time this behaviour was filmed.

Another image that's been used on Tet Zoo before: aquaflying (and diving) Cory's shearwaters. This is a still from the BBC series Blue Planet. Image (c) BBC.

It may be possible to distinguish between those petrels that dive to depth using their wings for propulsion and those that don’t since the wing-propelled diving species have much thicker-walled humeri (Kaiser 2007). Habib (2010) incorporated data on aquaflying shearwaters into his study of aquaflight in birds, mostly concluding that the species that do it aren’t much different in wing proportions or bone shape from species that only fly in air; in fact the two shearwaters he included in his study “are mechanically indistinct from albatrosses” (p. 695). Wing shape and proportions therefore don’t provide a reliable guide to the presence or absence of an aquaflying ability – thick bone walls seem to provide a clue, however, perhaps because the thicker bone helps to act as ballast (Habib 2010). We should look at fossil seabirds, and maybe pterosaurs too, with all of this in mind.

Here’s an idea: was aquaflying more common in ancient, extinct shearwaters than modern ones? Some fossil shearwaters from the Miocene are supposed to be bigger (on average) than post-Miocene ones; I’ve heard it informally suggested that a post-Miocene decline in body size might have been due to increasing competition and predation from marine mammals. As I discussed in a 2008 article on gannets, there’s evidence of occasional predation on diving seabirds from big fish. This makes it tempting to speculate that the predatory behaviour of evolving  pinnipeds, cetaceans, scombroids, sharks and even albatrosses* had an impact on the body size, diversity and diving behaviour of shearwaters: maybe aquaflying and deep-diving ones are less common today due to interaction with these other groups. I emphasise that this is shameless speculation.

* Perhaps surprisingly, some albatrosses are routine predators of small petrels. More on this another time.

There don't seem to be any photos of diving albatrosses, so I created this illustration (with help from Paulo Nicolaides), showing a sooty albatross diving in pursuit of a Galiteuthis. Sadly, the pose of the bird is copied from a photo of an albatrosses drowned by the longline fishing industry. Drawing by Darren Naish.

Incidentally, albatrosses belonging to all major lineages (mollymawks, sooty albatrosses and great albatrosses) are also capable of diving down to depths of a few metres at least, though with dives of over 7 m being recorded for species like the Shy albatross Thalassarche cauta (Hedd et al. 1997). The record for the group (held by a Light-mantled albatross Phoebatria palpebatra) is a ridiculous 12 m (Prince et al. 1994). These deeper dives involve swimming, and not just plunging into the water at speed: Tickell (2000) said that “sooty albatrosses appear to approach the underwater proficiency of shearwaters” (p. 30). Given the shape, size and proportions of albatrosses, I find all of this remarkable: not exactly the sort of behaviour you might predict. And therein we find a familiar theme. [Adjacent illustration created with kind help of Paulo Nicolaides of Ecospaces Ltd. Like the facebook page!]

Tubenose bycatch from a longline fishing trip; the sheer number of deaths are unbelievable. Image by Fabiano Perpes.

Having mentioned albatrosses, another interesting idea is that the diving abilities of shearwaters and other petrels may make albatross species more susceptible to death at the hands of the longline fishing industry. The petrels dive and thus bring bait fish (and their attached hooks) to the surface; the surface-frequenting albatrosses displace the smaller shearwaters from their catch; the albatrosses then get caught on the hooks, and die (Jiménez et al. 2012). The albatrosses do retrieve the hooked bait fish on their own, but their stealing from the petrels does increase their susceptibility to getting hooked. As I hope is well known, longline fishing is a major caught of albatross mortality, and – if you eat fish, and if you care – you should ensure that the fish you buy are not caught via this method. As you can see from the photo here (and from many articles online), the numbers of albatrosses, petrels and other marine birds killed by longline fishing are astonishing and totally unsustainable: c. 300,000 birds are estimated to be killed annually by this practice.

More petrels still to do – the series is not finished yet. For previous articles on petrels and other tubenosed seabirds at Tet Zoo, see…

And for articles about other kinds of seabirds, see…

Refs – -

Austin, J. J., Bretagnolle, V. & Pasquet, E. 2004. A global molecular phylogeny of the small Puffinus shearwaters and implications for systematics of the Little-Audubon’s shearwater complex. The Auk 121, 847-864.

Bourne, W. R. P. 2001. The status of the genus Lugensa Matthews and the birds collected by Carmichael on Tristan da Cunha in 1816-1817. Bulletin British Ornithologists’ Club 121, 215-216.

Brown, R. G. B., Barker, S. P., Gaskin, D. E., & Sandeman, M. R. 1981. The foods of Great and Sooty shearwaters Puffinus gravis and P. griseus in eastern Canadian waters. Ibis 123, 19-30.

Habib, M. 2010. The structural mechanics and evolution of aquaflying birds. Biological Journal of the Linnean Society 99, 687-698.

Harrison, P. 1988. Seabirds: an Identification Guide. Houghton Mifflin Company, Boston.

Hedd, A., Gales, R., Brothers, N. & Robertson, G. 1997. Diving behaviour of the Shy Albatross Diomedea cauta in Tasmania: initial findings and dive recorder assessment. Ibis 139, 452-460.

Heidrich, P., Amengual, J. & Wink, M. 1998. Phylogenetic relationships in Mediterranean and North Atlantic shearwaters (Aves: Procellariidae) based on nucleotide sequences of mtDNA. Biochemical Systematics and Ecology 26, 145-170.

Huin, N. 1994. Diving depths of white-chinned petrels. The Condor 96, 1111-1113.

Jiménez, S., Domingo, A., Abreu, M. & Brazeiro, A. 2012. Bycatch susceptibility in pelagic longline fisheries: are albatrosses affected by the diving behaviour of medium-sized petrels? Aquatic Conservation: Marine and Freshwater Ecosystems 22, 436-445.

Kaiser, G. W. 2007. The Inner Bird: Anatomy and Evolution. University of British Columbia, Vancouver.

Keitt, B. S., Croll, D. A. & Tershy, B. R. 2000. Dive depth and diet of the Black-vented shearwater (Puffinus opisthomelas). The Auk 117, 507-510.

Kennedy, M. & Page R. D. M. 2002. Seabird supertrees: combining partial estimates of procellariform phylogeny. Auk 119, 88-108.

Lee, D. S. 1995. The pelagic ecology of Manx Shearwaters Puffinus puffinus off the southeastern United States of America. Marine Ornithology 23, 107-119.

Mathews, G. M. 1942. New genus. Emu 41, 305.

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

Nunn, G. B. & Stanley, S. E. 1998. Body size effects and rates of cytochrome b evolution in tube-nosed seabirds. Molecular Biology and Evolution 15, 1360-1371.

Olson, S. L. 2000. A new genus for the Kerguelen petrel. Bulletin of the British Ornithologists’ Club 120, 59-62.

- . 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.

Penhallurick, J. & Wink, M. 2004. Analysis of the taxonomy and nomenclature of the Procellariiformes based on complete nucleotide sequences of the mitochondrial cytochrome b gene. Emu 104, 125-147.

Prince, P. A, Huin, N. & Weimerskirch, H. 1994. Diving depths of albatrosses. Antarctic Science 6, 353-354.

Pyle, P., Welch, A. J. & Fleischer, R. C. 2011. A new species of shearwater (Puffinus) recorded from Midway Atoll, northwestern Hawaiian Islands. The Condor 113, 518-527.

Ramirez, O., Illera, J. C., Rando, J. C., Gonzalez-Solis, J., Alcover, J. A. & Lalueza-Fox, C. 2010. Ancient DNA of the extinct Lava Shearwater (Puffinus olsoni) from the Canary Islands reveals incipient differentiation within the P. puffinus complex. PLoS ONE 5(12): e16072. doi:10.1371/journal.pone.0016072

Rando, J. C. & Alcover, J. A. 2008. Evidence for a second western Palaearctic seabird extinction during the last Millennium: the Lava shearwater Puffinus olsoni. Ibis 150, 188-192.

Skira, I. J. 1979. Underwater feeding by Short-tailed shearwaters. Emu 79, 43.

Tickell, W. L. N. 2000. Albatrosses. Yale University Press, New Haven and London.

Xavier, J. C., Magalhaes, M. C., Mendonca, A. S., Antunes, M., Carvalho, N., Machete, M., Santos, R. S., Paiva, V. & Hamer, K. C. 2011. Changes in diet of Cory’s Shearwaters Calonectris diomedea breeding in the Azores. Marine Ornithology 39, 129-134.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com!

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The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. jtdwyer 6:47 pm 02/10/2013

    Have the density of wing bones been evaluated to determine whether that might be a distinguishing feature between those birds that fly in water an those that don’t? The obviously denser media of water would put more ‘torque stress’ on wing bones and joints than would air… While the birds’ wings might appear to be structurally identical, the two activities would certainly seem to require somewhat different mechanical characteristics.

    Link to this
  2. 2. Crown House 6:47 pm 02/10/2013

    Great post as usual, thx a lot! So many avian dinosaurs, so much to learn…
    For the quiz: That seems not so hard, as there is a second picture of the artist in the article. At first I read the initials in the right corner as “JCK”, but “J.G. Keulemans in Southend on Sea (England)” is mentioned as a contributor to the book the illustration is took from. So I think its in fact “JGK” and guess the artist is John Gerrard Keulemans, like the second lithography.

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  3. 3. naishd 6:27 am 02/11/2013

    jtdwyer (comment 1): you should check out Habib (2010) for an extended discussion of this issue. In some respects (e.g., humeral strength), aquaflying taxa do NOT differ from non-aquaflying taxa, hence Habib’s argument that thick wing bones in some aquaflyers may be more to do with buoyancy regulation than required bone strength.

    Darren

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  4. 4. jtdwyer 7:05 am 02/11/2013

    Darren, Sorry – I did miss your statement in the article:
    “It may be possible to distinguish between those petrels that dive to depth using their wings for propulsion and those that don’t since the wing-propelled diving species have much thicker-walled humeri (Kaiser 2007). Habib (2010) incorporated data on aquaflying shearwaters into his study of aquaflight in birds, mostly concluding that the species that do it aren’t much different in wing proportions or bone shape from species that only fly in air; in fact the two shearwaters he included in his study “are mechanically indistinct from albatrosses” (p. 695). Wing shape and proportions therefore don’t provide a reliable guide to the presence or absence of an aquaflying ability – thick bone walls seem to provide a clue, however, perhaps because the thicker bone helps to act as ballast (Habib 2010).”

    Sorry also I’m not likely to access the Habib reference to determine what he meant by “mechanically indistinct”, but I think that the mechanical loads placed on wings during air flight and water flight are quite distinct. While I’m no engineer, it seems that thicker walled bones would likely increase bone strength… Thanks!

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  5. 5. naishd 7:52 am 02/11/2013

    jtdwyer: regarding your last statement (comment 4)… what you say is likely correct (and consistent with those comments I referred to by Kaiser); the point is that aquaflying birds do not seem to consistently possess these and other ‘key’ bony features.

    Darren

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  6. 6. Jerzy v. 3.0. 8:53 am 02/11/2013

    Interesting story about possible Lava Shearwater – not too likely, but nice read:
    http://www.britishbirds.co.uk/news-and-comment/resurrection

    Link to this
  7. 7. Gigantala 8:59 am 02/11/2013

    The existence of large aquaflying shearwaters is very interesting because it shows that the theorem that water temperatures above 16ºC rendering aquaflying predation difficult might be wrong.

    Is there any specific reason as to why petrels manage to exist in tropical seas while other aquaflyers can’t?

    Link to this
  8. 8. Heteromeles 2:09 pm 02/11/2013

    @Gigantala: one might speculate that plesiosaurs and pliosaurs should be included in speculation about temperature and aquaflying…

    Link to this
  9. 9. David Marjanović 2:58 pm 02/11/2013

    the theorem that water temperatures above 16ºC rendering aquaflying predation difficult

    …Why would that be?

    There’s generally more food in cold water, but that’s another story.

    Link to this
  10. 10. jtdwyer 3:17 pm 02/11/2013

    Darren – Thanks for further explaining, and sorry for all confusion on my part!

    Link to this
  11. 11. naishd 4:32 pm 02/11/2013

    I confess that I’ve never heard of this ’16°C rule’ – where does it come from? I wonder if it’s one of those ‘rules’ invented by people who base observations on the modern world alone and forget that there’s history. I would think that the profitability or otherwise of aquaflying would depend on the availability of prey.

    Darren

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  12. 12. Halbred 7:08 pm 02/11/2013

    I might have asked this in a previous post, but my memory has been crap ever since that brain abscess. Aquaflying immediately brings to mind penguins; penguin ancestors must have been aquafliers, right? Or did penguins develop their aquaflight differently?

    Is this even something that can be known?

    Link to this
  13. 13. Gigantala 7:41 am 02/12/2013

    Here’s the source:

    Schreiber, Elizabeth A. & Burger, Joanne (2001) Biology of Marine Birds

    Link to this
  14. 14. naishd 6:47 am 02/13/2013

    Penguins! (comment 12). The early evolution and peculiarities of penguins are fascinating and complex topics: you may know that there’s an excellent blog already devoted to penguin evolution (Dan Ksepka’s March of the Fossils Penguins). There have been suggestions that penguins evolved from flightless ancestors (not likely), but an origin from among flight-capable aquaflyers is most likely. Despite recent discoveries of more early penguins (like Waimanu), the earliest stages of penguin adaptations are still poorly known.

    Darren

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  15. 15. naishd 7:17 am 02/13/2013

    Gigantala (comment 13): thanks, there’s a copy at the NOCS library, I’ll check it out. Right now, I’m sceptical of the idea that aquaflying might be constrained in the way suggested. After all, petrels capable of aquaflying (like the Calonectris species) definitely occur in waters warmer than 16° C… (around the Azores, for example, sea temperatures get above 20° C during part of the year). Then again, maybe the species concerned don’t aquafly in the warmer parts of their range, or during the warmer parts of the year? It does seem odd to me.

    Darren

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  16. 16. Gigantala 7:41 am 02/13/2013

    The reasoning provided is that fish appearently are more active at warmer temperatures, and therefore are faster than aquaflying birds under those conditions.

    But personally, I think that seems a bit illogical, given how easily endothermic some fish are.

    Also present on the Wikipedia article on Alcidae:

    “The speed at which small fish (which along with krill are the auk’s principal food items) can swim doubles as the temperature increases from 5°C to 15°C, with no corresponding increase in speed for the bird.”

    Link to this
  17. 17. naishd 8:00 am 02/13/2013

    All interesting, and definitely something to keep in mind. I shouldn’t say any more without reading the relevant section of Schreiber & Burger (2001) but… this tidy idea breaks down if aquaflying shearwaters pursue and capture fish in tropical waters. As I said above, some aquaflying species do occur in tropical regions: the question then is, do they practise aquaflying while in these warm regions? I’m not sure on that, trying to find out.

    It’s also possible that even warm-water species only aquafly in places where cold, upwelling currents keep the water temperature below the 16° C threshold. Paleogene penguins were aquaflying in warm oceans, and foraging in cool currents has been suggested.

    As discussed in one of the previous Tet Zoo petrel articles, tropical petrels are less diverse in morphology and feeding biology than cool-water ones anyway, presumably because prey is more scattered, lower in density, and often less close to the surface.

    Darren

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  18. 18. Jerzy v. 3.0. 8:24 am 02/13/2013

    Ehm, the basis seems rather weak.

    Does every fish species really swim faster than petrels above 16oC? Do petrels eat nothing but fish? Do petrels hunt only fish free to escape at maximum speed – no surprise attacks, no group hunts, no benefitting from other predators?

    It sounds that this idea depends on treating flexible ecological averages as they were immutable laws.

    In the meantime, I think a flock of Pteranodon and other pterosaurs scavenging from a mosasaur kill would be cool sight. ;)

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  19. 19. naishd 9:26 am 02/13/2013

    There may be something in this idea (the ’16° C threshold’), but I share your scepticism, Jerzy (comment 18). I keep thinking of the Blue Planet scene, where the aquaflying Cory’s shearwaters are grabbing fish that are also under attack from dolphins, sharks and a Bryde’s whale. As I said above, “I would think that the profitability or otherwise of aquaflying would depend on the availability of prey” (comment 11).

    Darren

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  20. 20. naishd 9:27 am 02/13/2013

    Oh, and as for pterosaurs… that’s an interesting one. General wisdom is that oceanic pterosaurs (Pteranodon being the ultimate example) are not built for diving or aquaflying, and just couldn’t do it. But Chris Bennett (monographer of Pteranodon) noted that the skeleton of Pteranodon isn’t notably ‘flimsier’ or less strongly built than that of, say, a Brown pelican. And given what we know about plunge-diving, deep diving and aquaflying in albatrosses and petrels.. well, can we rule out the possibility that Pteranodon and similar pterosaurs were also capable of such feats? I don’t know. Their membranous wings may well have acted very differently from bird wings underwater, and indeed there are no aquaflying or plunge-diving bats (to my knowledge). It might also be that Pteranodon and other oceanic pterosaurs were more like frigatebirds than tubenoses. Frigatebirds >can< swim, but they prefer not to, and are certainly not in the habit of diving or aquaflying.

    Darren

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  21. 21. Jerzy v. 3.0. 10:00 am 02/13/2013

    @20
    I wonder if anybody studied the range of movement of forelimbs of fish-eating pterosaurs, and if they could be used for paddling?

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  22. 22. MarkWitton 10:20 am 02/13/2013

    Yes, I think only Bennett has provide comments on diving pterosaurs in the literature (along with comments in this, coming soonish). Obviously, the meat of work on this remains to be done, but my provisional feeling is that it’s quite possible some pterosaurs dived for food. It strikes me that many ornithocheiroids – nyctosaurs and perhaps istiodactylids being exceptions – have forelimb anatomy very conducive to water launching, so probably at least landed on water fairly frequently. From that, I see no reason why some species could not engage in dives from alighted positions, even if they were only shallow. It’s of interest that the feet and pelves of some ornithocheiroids are relatively large and robust, which is at odds with the general perception that these animals weren’t particularly adept at terrestrial locomotion. Perhaps this reflects hindlimb use in diving? I don’t know if their membranous wings would be a disadvantage, either. We all seem happy that their membranes shrink down fairly well when the wings are retracted, so they probably wouldn’t be flopping about when swimming, and they are reinforced distally. Who knows: maybe they’d work fairly well as wings for aquaflying. Lots to think about here, I reckon.

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  23. 23. naishd 11:11 am 02/13/2013

    Membranous wings: while there aren’t aquaflying or plunge-diving bats, it should be noted that bats can (mostly) swim ok. A video. And another one.

    Darren

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  24. 24. naishd 11:18 am 02/13/2013

    Aaaand… hello comment # 23. Time to move on.

    Darren

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  25. 25. Andreas Johansson 11:21 am 02/13/2013

    Darren@20: Are there any birds that cannot swim, however poorly, at all?

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  26. 26. naishd 11:28 am 02/13/2013

    I think all birds can swim to some extent (provided that they don’t get their plumage soaked). I’ve heard it said that swifts and hummingbirds can’t swim, but youtube indicates otherwise. Small birds capable of rapid flapping are usually able to travel quickly across water if they find themselves submerged. Big birds can either propel themselves with leg strokes (ratites, gamebirds, herons, flamingos, rails, bustards, cranes) or flap clumsily with their wings (hawks, eagles, owls, thrushes). Plenty of videos online of all this sort of stuff. I love the swimming eagle footage.

    Darren

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  27. 27. Heteromeles 11:29 am 02/13/2013

    Actually, the more I look at that Cory Shearwater clip, the more I get confused by aquaflying.

    What’s confusing me is where the stresses are. Obviously aquaflying is stressful, because they beat their wings very slowly, and they also don’t have them fully extended, presumably because their primaries (and probably wrists) couldn’t stand the strain of trying to flap underwater with fully extended wings. However, I’m not sure how one could tell whether a wing was specialized for dual-mode flying, precisely because the wings change geometry, but also because the birds use their feet quite a lot too. Weak aquaflying could easily be compensated for by kicking, and I doubt anyone’s worked out the relative contributions from each component.

    As for pterosaurs, I don’t know much about their wrist joints and wing anatomy, but it seems that aquaflying puts a tremendous amount of stress on the wrist (even when bent) and it also stresses the leading edge, even when it’s retracted. You can see that in the Cory Shearwaters by how much their primaries deform with each underwater wingbeat. With pterosaurs, it might be even worse, because that would be bone and joints flexing, rather than feathers. I’d also suggest that pterosaur aquaflyers would have a wing anatomy adapted for absorbing and flexing with such stresses, so that they don’t have sprained wingfingers when they return to the surface. Perhaps this might show up in a fossil somewhere?

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  28. 28. David Marjanović 2:04 pm 02/13/2013

    But personally, I think that seems a bit illogical, given how easily endothermic some fish are.

    Very few fish, and only big ones.

    “The speed at which small fish (which along with krill are the auk’s principal food items) can swim doubles as the temperature increases from 5°C to 15°C, with no corresponding increase in speed for the bird.”

    Oh, that makes a lot of sense. Somebody just needs to quantify the speeds, see comment 18.

    Link to this
  29. 29. Gigantala 3:11 pm 02/13/2013

    It is also possible that only small birds like auks are affected by the temperature differences. Birds like shearwaters could eprhaps be faster than auks, or more resistant when pursuing aquatic prey.

    As for diving pterosaurs, I don’t think they’d have many problems. Unlike bats, they had very thick wing membranes and pycnofibrils on the wings, so heat loss would not be as much of an issue.

    Link to this
  30. 30. Heteromeles 4:02 pm 02/13/2013

    Is aquaflying and temperature about temperature per se, or is it about oceanic productivity? I’ve seen a comparison between seals and sea lions that says the former are adapted for efficient swimming (think gliders), while the latter are adapted for acrobatic swimming (think helicopter). Sea lions’ swimming skills are great when there’s a lot of food available for the taking. If food isn’t so available, they starve. Seals, being slower and possibly more streamlined, do better on more scattered prey, as well as in things like deep diving to reefs and such.

    I wonder where avian aquaflyers fall in this spectrum of energy use. Powered flight is expensive, and flying wet is even more so. It makes sense to do this where there’s a lot of food. Most tropical seas are nutrient deserts, and I suspect the dearth of food excludes most aquaflyers more than the temperature does.

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  31. 31. CS Shelton 10:53 pm 02/13/2013

    First you give me snowy peacocks, now aquaflying pterosaurs to imagine. It’s always the tossed off comments where the fun is hanging out.

    Hey, totally off topic, I never had a favorite anuran until I found out about the genus Breviceps. A quick google search turned up very little Tet Zooery to do with rain frogs. I humbly beseech thee to tell us about the cutest frogs in the world: Breviceps! Thanks!

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  32. 32. Dartian 3:20 am 02/14/2013

    Does this supposed ’16°C rule’ refer to the water temperature at the surface of the sea? If the shearwaters frequently pursue fish at such depths as 10-20 m, the water temperature there will be (even in the tropics) significantly lower than that at the surface.

    Darren:
    I think all birds can swim to some extent (provided that they don’t get their plumage soaked)

    Hm. I think we need to define ‘swimming’. Surely it takes rather more than just ‘not immediately sinking like a stone’ in order to count as swimming?

    Gigantala:
    small birds like auks

    There are several small-bodied alcid species, but I wouldn’t call guillemots (Uria species weigh about 1 kg), razorbills or puffins particularly small – at least not in comparison to shearwaters.

    Birds like shearwaters could eprhaps be faster than auks, or more resistant when pursuing aquatic prey.

    Why do you think that? The streamlined body form of alcids seems supremely well adapted for fast underwater swimming. There are data on the underwater swimming speeds of alcids (e.g., Lovvorn et al., 1999) but I do not know how these compare to those of shearwaters. However, the data on the depths to which alcids are known to regularly dive indicate that alcids (or at least the largest species; dive depth in alcids appears to be linked to body size) are capable of diving much deeper than what shearwaters are known to – down to 180 m, at least (Piatt & Nettleship, 1985).

    References:
    Lovvorn, J.R., Croll, D.A. & Liggins, G.A. 1999. Mechanical versus physiological determinants of swimming speeds in diving Brunnich’s guillemots. The Journal of Experimental Biology 202, 1741-1752.

    Piatt, J.F. & Nettleship, D.N. 1985. Diving depths of four alcids. The Auk 102, 293-297.

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  33. 33. naishd 3:56 am 02/14/2013

    CS Shelton (comment 31): interest in Breviceps duly noted (but don’t hold your breath). Sorry I didn’t answer on question about cool-climate peacocks – missed the comment until now.

    Darren

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  34. 34. naishd 4:04 am 02/14/2013

    Dartian (comment 32): for the purposes of this and other discussions, I imagine ‘swimming’ to be the process whereby an animal locomotes through water. It can be slow, ineffectual, clumsy or desperate; so long as the animal is using its limbs or body to move, and is moving with purpose, we’re dealing with swimming.

    Darren

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  35. 35. Jerzy v. 3.0. 5:08 am 02/14/2013

    @22
    Thanks! It was always strange to me if all fish-eating pterosaurs were unable to swim – given how many times birds evolved into swimmers. :D Thanks!

    @29
    I also think that lack of tropical penguins and auks is related to low ocean productivity in the tropics, not to escape speed of tropical fish.

    Link to this
  36. 36. Dartian 5:14 am 02/14/2013

    Darren:
    so long as the animal is using its limbs or body to move, and is moving with purpose, we’re dealing with swimming

    But in order to qualify as swimming, shouldn’t the animal’s propulsive body/limb movements take place in and/or under the water? Does (for example) a ‘swimming’ hummingbird really use its legs at all for propelling itself? My impression (which admittedly rests on the flimsy basis of casually watching a few YouTube videos) is that it just flaps its wings vigorously in the air – without them really making contact with water – and is thus able to move forward (kind of like a miniature hovercraft).

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  37. 37. naishd 5:18 am 02/14/2013

    Yes, we are/I am talking about propulsive movements taking place in and/or under the water. If we’re talking about hummingbirds specifically, I have a memory of a video where one has its wings flat on the water surface, and then flutters: its wings are thus in the water for part of the ‘stroke’. I’m not, however, committed to the idea of a swimming ability in hummingbirds :) It’s not as if they’re giraffes or anything.

    Darren

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  38. 38. Lars Dietz 6:36 am 02/14/2013

    What about Galapagos penguins? They appear to be an exception to the “16°C rule”. Here is a page with the water temperatures in the Galapagos, they’re clearly above 16°C during the whole year.

    Link to this
  39. 39. Heteromeles 5:56 pm 02/14/2013

    The Galapagos receives the Humboldt current for up to half the year (link). This is colder water from the south. While the temperature doesn’t go below 16°C, productivity does go up when the Humboldt visits the islands. When it fails, as in an El Nino, fur seals and penguins die. This suggests the key issue is one of oceanic productivity, not directly one of temperature.

    I’d

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  40. 40. SciaticPain 10:15 pm 02/14/2013

    On the “16°C rule” thing which I think is kinda fascinating- would not a bird adapted to aqua-flying lose some ability as a flyer/glider due to a more robust build/denser bones? And in tropical oceans, with very sporadic/sparse food resources, may this burden be too much to overcome for these type of aquafliers? I disagree with calling this pattern a rule but I do think it telling that penguins don’t penetrate the northern hemi and auks don’t penetrate the south presently. Or is it more useful to think of the tropics as a bit of barrier to sea birds in general due to the paucity of resources?

    Another issue with the “16°C rule” is that from what I have watched in documentaries many of these aquafliers depend on dolphins/tunas/other predators to corral the prey into a baitball from which they can easily pluck fish. In this scenario the birds do not have to outswim the fish- they simply have to get to the right place at the right time.

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  41. 41. Dartian 3:40 am 02/15/2013

    SciaticPain:
    Or is it more useful to think of the tropics as a bit of barrier to sea birds in general due to the paucity of resources?

    There is probably some truth in that but, of course, in reality the situation is a bit more complex: the tropics are, obviously, not devoid of seabirds. Some groups (e.g., tropicbirds, frigatebirds) are even exclusively tropical. Others (e.g., sulids) are more diverse in the tropics than in temperate zones; yet others (e.g., tubenoses, cormorants, gulls) are more numerous in temperate and arctic/antarctic waters but not completely absent from the tropics. (However, apart perhaps from terns I don’t think there is any major seabird group that is about equally diverse/abundant in both the tropics and in temperate zones.)

    Rather than a general lack of resources as such, I suspect that it may also be a question of how these resources are distributed in the tropics vs. the higher latitudes. For example, perhaps fish and squid are generally more widely scattered in tropical waters, and finding them requires longer flight distances for seabirds? That kind of thing could select against certain taxa and/or ecomorphological types of seabird being successful foragers in tropical waters.

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  42. 42. Yodelling Cyclist 7:15 am 02/15/2013

    If the issue were escape speeds of fish and squid, would marine mammals not be equally affected? Long distance swimming is probably even less efficient than long distance flight for locating dispersed resources.

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  43. 43. Dartian 8:16 am 02/15/2013

    Yodelling Cyclist:
    would marine mammals not be equally affected?

    Unlike seabirds (or most seabirds, anyway), dolphins and other cetaceans don’t need to regularly return to land for resting and sleeping; cetaceans are thus not similarly restricted by distance as birds are by having to return to some specific geographic location. In contrast to cetaceans, pinnipeds do need to return to land from time to time – but, interestingly, they are also much rarer in tropical waters than they are at higher latitudes. Perhaps there’s something of a pattern here?

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  44. 44. Heteromeles 10:01 am 02/15/2013

    I’d suggest that, reefs aside, fish may swim much deeper in the tropics than they do in temperate and polar waters, at least from the perspective of air-breathers.

    The thing to remember is that the ocean isn’t a uniform water bath. Upwellings are highly local both in space and time, concentrated around things like islands, seamounts, and continental coasts (as are reefs). Similarly, the boundaries where currents meet are well known as rich zones (this is where turtles and sea snakes supposedly hunt). However, all of this stuff moves, both annually and on longer cycles like the ENSO. The oceans aren’t that different from the deserts of the land, except that they’re nutrient deserts, rather than water deserts. This doesn’t even get into the ocean’s vertical zonation, which is effectively exploited by some whales, seals, and perhaps the deepest-diving penguins.

    Species that have a relatively short cruise range are limited in where they can live. Food has to be predictably available within their range all the time. Short cruisers are also limited in how far they can colonize. For example, neither penguins, auks, nor fur seals (all semi-terrestrial aquaflyers) have done a good job colonizing the deepwater islands of the Pacific or the Atlantic. The Galapagos is the exception that proves the rule, as those islands are unusual in being on the Humboldt Current, which provides an effective highway for moving penguins and fur seals from temperate zones.

    Longer cruisers (such as albatrosses) are less limited in their horizontal search space, but I strongly suspect that they trade off the horizontal space for vertical hunting depth.

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  45. 45. Yodelling Cyclist 10:40 am 02/15/2013

    Dartian may have a good point. Are the aquaflyers known from the tropics (except the Galapagos) known to sleep on the wing?

    Also important maybe the diel vertical migration: in the tropics the most reliable food sources are around at night. Cetaceans aren’t reliant on sight to hunt at night whilst I guess it would be difficult for a penguin or a pinniped (except for the very deep divers), and even harder to out compete the sharks.

    I don’t quite buy the problem that fish swim deeper in the tropics as being an inherent problem, some penguins do some decent dives, as do many pinnipeds. Finally, there all always some fusiliers, in my experience.

    I have occasionally wondered why the penguins in SA stop just before it gets pretty in Sondwana. There are plenty of fish in the mangroves.

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  46. 46. Gigantala 11:27 am 02/15/2013

    I think it’s because of the other issue posed in the source I provided: appearently, feet propelled diving birds like cormorants are more maneuverable in shallow waters, which is why there are few aquaflyers in freshwater, where maneuverability is more relevant than speed.

    In Africa, there are many types of foot propelled diving birds, like cormorants, darters and grebes.

    Link to this
  47. 47. miguelmcminn 8:49 am 02/17/2013

    Hello Daren

    The shape and proportions of the wing bones of some of the Puffinus have also been suggested as an adaptation to a “more underwater life style” (Kuroda 1954). Humerus, ulna and radius of some Puffinus are shorter and flattened. The extreme case is the humerus of the small Puffinus (Manx and Balearic,). A more extreme case of a shorter and flattened wing limb is found in diving petrels and auks.

    Diving behaviour at sea of the Cory’s Shearwater (Calonectris – with a long, slender, and rounded Albatross type of humerus) and Balearic Shearwater (Puffinus – with a short flattered humerus) is very different. Both birds can aquafly, but Puffinus is much more agile in diving – more auk type. It would be very interesting to measure aquaflight speed of Puffinus and Calonectris. The penalty of better underwater flight is probably poorer true flight performance.

    Balearic Shearwarter is a sardine pursuit specialist, while Scopolí’s is a more generalist scavenger.

    Kuroda 1954 On the Classification and Phylogeny of the Order Tubinares….. Herald Co. Ltd. Tokyo.

    Link to this

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