Swifts of the World

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Swifts of the World

Even though many people confuse members of the two swiftfamilies with swallows and martins, once one has understood some of thedifferences, then observed these birds in action one never forgets thatswifts are not only different but very special.

Some special experiences I have enjoyed with swifts were:

To see and hear a swiftlet echolocate its contorted route through a complex cave to its nest in total darkness, one kilometre from the cave entrance. To witness the “playful” power-dives of a needletail, from spiralling at the base of a high cumulus cloud to below head height in a few seconds. To discover the fancy streamlines of a treeswift sitting on its all-too-small nest, perched high in a tropical rainforest. To have a flock of 20-30 Common Swifts narrowly miss your head as they noisily sweep past in an evening proliferation of energy known as a screaming party. To realise after listening to the radio transmitter attached to a nestling Common Swift for 12 hours - through the night, that this fledgling’s first flight was spent thousands of feet up in the air and in darkness. To realise that the swift and swiftlets nest is built from or held together by their saliva: Natures first superglue. All of these experiences can only make one wonder at the splendid abilities and finesse of this group of birds.

In 1854 the Common Swift (Apus apus) of Europe was also called the Black Martin, and theChimney Swift (Chaetura pelagica)was called the American Chimney Swallow, and the Glossy Swiftlet (Collocaliaesculenta) of south-east Asia was calledthe Esculent Swallow (Maunders 1854).At the time swifts and swallows were classified in the same family:Hirundinae. They have since beenseparated into their own families as we have learnt more about them. We are still learning about them, andinvite you to share in the enjoyment of discovering new facts about theirdesign and behaviour. So what typeof birds are swifts?

Swifts are characterised by:

1.A short neck humerus.

Humerus bone.

Photo:Common Swift skeleton copyright Jean-Christophe Theil.

2. A protectiveridge of feathers above the eye to protect the eye from damage in collisionswith prey.

Uniform Swiftlet, Mt Diamond, PNG. Photo: copyright M. Tarburton.

3.Very small bill, but very wide mouth (gape).

Common Swift, Germany. Photo: copyright E. Kaiser.

4. Flying continuously during daylight except when nesting.

CommonSwift, Belgium. Photo: copyrightRaymond De Smet. CommonSwift, France. Photo copyrightJ.F. Cornuet.

5.Never folding their wings between wing-beats as do swallows.

6.Small but very strong feet and toes that support their full weight when hangingfrom tree-trunk, foliage or cave roof, while asleep.

Foot of White-rumped Swiftlet roosting in a Lava tube cave, Samoa. Photo copyrightM. Tarburton.

Foot of White-throatedNeedletail, Qld, Australia. Photo copyrightM. Tarburton.

7. Long wings that can be sweptback to reduce drag and increase speed, allowing them to glide withoutwing-beats in any direction on the slightest of breezes.

Fork-tailed Swift

Apus pacificus

Qld 5/2/2005

Photo copyright IanMontgomery: birdway.com.au

The distinctivescythe shaped curve of the wings leading edge generates leading edge vorticesproviding lift and thrust beyond that of any other birds measured so far andwhen supported by changing wing-shape, high levels of oxygen-carryinghaemoglobin in both blood cells and plasma (Palomeque et al.1980), swifts are able to achieve many activities while in the air. This helps because they are in the airall day. They take all their foodand nesting materials from the air, and they fly up to heights of three or fourkilometres (Gustafson et al 1977, Tarburton 2009). They even drink, bathe, mate and canspend the night on the wing (Lack 1956, Tarburton Kaiser 2001).

Mostspecies have enlarged salivary glands for production of the glue-like salivaused in nest building and for holding their food boluses together until theyreturn to the nest to feed to the nestlings, which they only do at widelyspaced intervals. Some species only feed their nestling(s) two to four times aday. Tests show they can gowithout food for two or three days.This means that young swifts have a cyclone-proofing that most birds donot enjoy. Sexes are similar andboth share in breeding activities, such as incubation and nestlingprovisioning.

Swiftphysiology combined with their morphology enables them to fly using littleenergy compared to other birds.Their flying metabolic rate is only 2-5 times their sleeping metabolicrates, whereas most other birds have an increase of about 12 times (Lyuleeva1970). Lets look at how themorphology of a swifts wing works.

Thetraditional method of explaining how a bird or plane wing provides lift is toshow that air flowing over the top of the wing has further to go than airpassing under the wing. So airparticles going over the wing are stretched further apart reducing airpressure, compared to air going under the wing which remains more dense wherethe higher pressure pushes up.Together these features provide lift.

If the angle of attack of the wing is increased, drag isincreased, slowing the wing down as well as the attached bird or plane. In fact one leading authority on theevolution of birds (Welty 1975. p.2) referring to bird design said that birdscompared to mammals “simply dare not deviate widely from sound aerodynamicdesign. Nature liquidatesdeviationists much more drastically and consistently than does anyauthoritarian dictator.” It isalways dangerous to make generalisations, and particularly so forscientists.

Greater knowledge arrived in 2004 when Science journal broke the news that:

“The current understandingof how birds fly must be revised,because birds use their hand-wings in an unconventional way to generate liftand drag.” (Videler et al. 2004).They use the lift for gliding and flapping flight and they generate highdrag when they want to brake or land.This finding was based on solid moulds made in the shape of the wing of the Common Swift (Apus apus)being studied in flowing water tunnels atGroningen Leiden Universities in the Netherlands.

These researchers found that the arm-wing uses thetraditional aeronautics system, but that the distal hand wing (which in swiftsis most of the wing) is much thinner in cross-section and is designed to set upa series of vortices along the front upper edge of the wing. These are called leading edge vortices(LEVs) and they travel along to the tapered tip of the wing, providing lift allthe way and then are released at the tapered tip without the normal amount ofdrag behind the wing.

Then these modified aerodynamic theories were shown in 2008to be inadequate by testing, not models but the swifts themselves flying in lowturbulence wind tunnels at Lund University, Sweden (Henningsson et al 2008, 2011). The Dutch had already postulated a theory (Lentink etal 2007) to explain how a swift can glideand make sharp turns at both low and high speed and even to sleep on the wing,by changing the shape of the wings.Now the Swedes were demonstrating it to be true.

This new research showed that in swifts the upstroke of thewing produced thrust as well as lift equal to 60% of the lift of thedownstroke. Most birds do notproduce any lift on their upstroke.They also found that the lift/drag ratio in the swift was the highest(13) of any bird measured so far.The team believes these phenomena result from the stiffness of swiftwing feathers, the sweep of the wing, the tapered tip, as well as a changingwing shape. The swift wing generates clockwise leading-edgevortices on the downstroke and anti-clockwise leading-edge vortices during theupstroke. Put all this togetherand it has the effect of increasing manoureveability in a bird that isotherwise designed for speed. Fora bird that feeds on flying insects this would be a big help. This also answers the question insectand swift researchers could not answer till now. How come many species of swifts and swiftlets at times catchdisproportionately more flies than other orders of flying insects, whencompared to the proportion of flies to other flying insects in the air, (Tarburton1986) when entomologists tell us flies are the most manoeuvrable group offlying insects? (Hespenheide 1975).

SYSTEMATICS

Swifts are grouped into two families: the APODIDAE (Typical Swifts) and HEMIPROCNIDAE(Tree Swifts).

TypicalSwifts TreeSwifts

Class Aves Aves

Order Apodiformes Apodiformes

Family Apodidae Hemiprocnidae

Sub-Family Cypseloidinae Apodinae

Tribe Cypseloidini Chaeturini Apodini Collocaliini

Genera Cypseloides Mearnsia Aeronautes Collocalia Hemiprocne

Streptoprocne Zoonavena Tachornis Aerodramus

TelacanthuraPanyptila Schoutedenapus

Rhaphidura Cypsiurus

Neafrapus Tachymarptis

Hirundapus Apus

Chaetura

Number of genera species:

19 genera; 103 species

Distribution

Almost world-wide.Main regions avoided are Antarctica and the Arctic, with the Arcticbeing given a wider berth in central and eastern Asia.. Most species live in the tropics.

Habitat

Swifts forage on aerial plankton taking a wide range offlying insects and hatchling spiders that drift through the air on strands ofweb, and so may be seen over a wide range of terrestrial habitats, but forroosting and sleeping they are dependent on cliffs, caves, hollow trees orbranches or foliage of either tall trees, or smaller trees on high ground. However, it has been shown that someswifts can spend the whole night in the sky (Tarburton Kaiser 2001).

Size

Length range = 90-250 mm; Wing Length 86-234 mm Mass range =5-205 g. The smallest species isthe Pygmy Swiftlet Aerodramus troglodytesof the Philippines with a length of 90-92 mm (tip of bill to tip of tail), winglength 86-99 mm and weight 4.5-6.8 g. (Hartert 1897, Oberholser 1906, Rand Rabor 1960, Dickinson 1989, Dunning 1993). The largest swift is the Purple Needletail Hirundapuscelebensis and though found in Indonesiaand the Philippines, very few birds have been measured. A small sample were length 229-234 mm,Wing 218-220 mm, and weight 170-203 g. (Morse Laigo 1969).

Common Myths about Swifts

1. Swifts cannottake off from the ground.Even books about swifts say “a downed swift is doomed”, or “With long narrow wings shaped forspeed, and short weak legs, a swift that is brought down has a poor chance ofsurvival” (Bromhall, D. 1980. Pp.48 47). This is despiteDavid Lack stating as far back as 1956 (p. 119), that “Contrary to popularbelief, it is not impossible for a swift to take off from a flat surface”. YetCampbell (1964) in The Oxford Book of Birds says “If a swift lands by accidentit cannot take off again” I have placed White-throated Needletails on theground and watched them take off.Paul Jones has also seen one of these needletails crash into his firelookout-tower, fall to the ground, in a stunned condition, then recover and flyaway (personal communication). In1985 Leidgren published his observation of seeing a Common Swift tumble to theground in battle with a Starling.When the Starling released it’s grip the swift very easily flewaway. Leidgren has also seen onecrash after hitting pine branches, but it took off from the ground and enteredthe nest box as if nothing unusual had taken place. Erich Kaiser I have watched Common Swifts take offfrom the floor of his house in Kronberg Germany, and Erich believes this mythstarted from the observation that injured and starving swifts cannot take offfrom a flat surface.

2. The legs ofSwifts have become almost useless.

Bromhall(1980 p.8) will also provide an example for those who publish the idea thatswifts legs are small and almost useless.It is true that they have short legs but they are not useless. They are very strong, with largerspecies easily drawing blood from a human hand. I have found this to be particularly true withWhite-throated Needletails. Buteven at the other extreme, swiftlets feet are very strong. In fact to successfully remove nestlingswiftlets from their nests one has to learn how to get them to release theirgrip on the nest or cave wall/roof, or their claws (toe-nails) (which do notgrow again) will be pulled off, so strong is their grip. It is important that swiftlets keeptheir toenails in order to roost on the cave roof. In most locations that I have studied swiftlets; cats,pythons and rats eat those that that roost near or on the cave floor. Anotherindicator of the importance of having strong feet legs is that the legsof White-rumped Swiftlets reach adult size in just 13.5 days whereas the wingtakes over 50 days to reach adult size (Tarburton 1986, 1987).

3. AustralianSwiftlets emigrate north of the equator for the Austral winter.Australian Swiftlets migrate in the winter time.

Pecotic (1974) visited three swiftlet nesting caves atChillagoe in the winters of 1965-1967 and not finding any birds in the cavesduring daylight hours, published that “the birds were away, presumably north ofthe equator”. If he had gone backin the evening he would have found the swiftlets roosting in the cave.Alternatively he could had looked at the guano pile to determine if there wereany white spots of guano on the black areas. The white component disappears in one to two weeks so is agood indicator as to whether the swiftlets are still resident in the cave ornot. I have met several people whostill thought this bird migrates north for the winter.

It had also been claimed that White-rumped Swiftlets ofNew Caledonia “must be migratory, as during the summer months we did notobserve them” Layard Layard (1879).The previous year Layard Layard (1878) had claimed theopposite “common in the coldweather, up to the end of September”and not seen since early October [Summer] so “we think partiallymigratory”. The birds are known tobe resident on New Caledonia all year, and the historical statements are just afurther example of observers jumping to conclusions before having adequatedata.

4. No nestlingswifts have down feathers.

Whileall swifts studied to date are born naked (i.e. have no natal down), it is nowknown that the Chestnut-collared Swift (Streptoprocne rutila) and probably also the American Black Swift (C. niger) start to grow a covering of downy feathers when eightto nine days old (Collins 1963).Both these swifts breed in cool damp locations and these downy branchesof the early body feathers are assumed to help keep them warm in suchlocations. A third swift theAfrican Palm Swift Cypsiurus parvushas also been shown to grow these downy semiplumes to help them thermoregulatein cool nest sites during the long absences of their parents (Collins1965). It is true that most swiftsdo not grow downy feathers.

5. Swifts alwaysroost before dark.

Breeding Common Swiftsare almost always at their nests before dark (Lack 1956,). Erich Kaiser (pers comm) has even hadCommon Swifts return ahead of bad weather to sleep in their nests, three daysafter they left on migration and apparently had run into bad weather. However, Lack (1956, p. 126) hasdocumented a series of observations where Common Swifts have been found tryingto roost after dark in unusual places particularly in mistyweather. Accumulated evidencesuggests these are mostly young migrating birds not familiar with good roostsites that they can find in cold and misty weather, and so they get caught inthe open after dark. In SouthernSweden, Holmgren (1993) has shown that migrating Common Swifts coming in toroost in the foliage of trees 10 to 40 minutes after sunset, on both foggy andclear nights are almost always pre-breeding birds, likely from Lapland and ontheir way to Africa.

Researchers at RanchoGrande, in Venezuela commonly observe eight species of swifts, but only one ofthem the Spot-fronted Swift Cypseloides cherriei is frequently found being attracted to lights well after sunset indense fog (Beebe 1949, 1950).Collins (1980) also foundthe same situation continued there and concluded that this swift might befeeding further away than the other species and on foggy nights are thus morelikely to have difficulty finding their way back to their nests. It is suggested that this species feedsfurther away to partition the resource with the other swift species in thearea. This practice might get morefood, but on foggy nights they may get caught out.

The Australian Swiftletis almost always back into its roosting cave before dark (Tarburton pers obs)but the White-rumped Swiftlet (Aerodramus spodiopygius) in Fiji rarely returns before dark and some arestill returning 4 hours after dark.The Fijian birds roost in larger colonies than the Australian birds, andso resource partitioning may be occurring within the species, just because thepopulations are so large.The Fijian species has no competing swifts. More recently I found that Three-toed Swiftlets (A.papuensis) are also feeding a long way fromtheir roost, with most birds coming into the cave 1-3 hours after sunset andsome still entering after midnight (Hamilton et al 2001, Tarburton unpublished). Both these swiftlets are habituallylate returning, and because they echolocate, getting lost in fog is not solikely.

6. All swifts havefour forward facing toes (pamprodactyly).

Back when it tookminutes to take photographs and prior to that, it was natural to describe birdsfrom museum specimens, and one of the problems arising from this methodologywas that the toes of many dead birds, shrink into the pamprodactylposition. So it was that manyauthors have described swift feet as being pamprodactyl. For example see Wildbird1993, 1994, and Sinclair et al. 1997, 19. Problem is, this is only true in real lifefor some swifts. Hartert way back in 1892 noted that some swifts (Reinarda,Tachornis Cypsiurus) use their toesin opposing pairs. Collins (1983)published a photo of the foot of a live House Swift (Apus nipalensis) clearly portraying the lateral grasping format. Youcan also see that format above, in the photo of the foot of the White-throatedNeedletail. Next to that photoabove you can see the foot of the White-rumped Swiftlet roosting in a lava cavein Samoa. It has three toesforward and the hallux backwards the anisodactyl arrangement. The Three-toed Swiftlet (Aerodramuspapuensis) does not have a hallux or hindtoe, to point in any direction. Soswifts have at least three types of arrangement for their toes.

References

Beebe, W. 1949. The swifts of Rancho Grande, north centralVenezuela, with special reference to migration. Zoologica 34: 53-62.

Beebe, W. 1950. Home life of the Bat Falcon, Falco albigularisalbigularis Daudin. Zoologica 35: 69-86.

Bromhall, D. 1980. Devil Birds. The life of theSwift. Hutchinson, London. 96pp.

Campbell, B. 1964. The Oxford book of birds. London. OxfordUniversity Press.

Collins, C.T. 1963. The downy nestlingplumage of swifts of the genus Cypseloides. Condor 65:324-328.

Collins, C.T. 1965. The down-like nestling plumage ofthe Palm Swift Cypsiurus parvus (Lichenstein) Ostrich 36:201-202.

Collins, C.T. 1980. The biology of the Spot-frontedSwift in Venezuela. American Birds 34:852-855.

Collins, C.T. 1983. A reinterpretation of Pamprodactyly in Swifts: a convergentGrasping mechanism in Vertebrates.Auk 100: 735-737.

Dickinson, E.C. 1989. A review of smaller Philippineswiftlets of the genus Collocalia. Forktail 5: 23-34.

Dunning, J.B. 1993. CRC handbook of avian body masses. Boca Raton, Fl. CRC Press.

Gustafson, T., Lindkvist, B., Gotborn, L. Gillen, R. 1977. Altitudes and flight times for Swifts, Apus apus, L. OrnisScand. 8: 87-95.

Hamilton, S., Erico, J. Tarburton, M. 2001.Notes on the sixth specimen record of the Three-toed Swiftlet Aerodramuspapuensis in Papua New Guinea. Corella 25(1):12-14.

Hartert, E. 1892. Catalogue of the Birds of the BritishMuseum, vol 16. London. Trusteesof the Brit. Mus.

Hartert, E. 1897. Podargidae,Caprimulgidae und Macropterygidae.Tierreich 1, i-viii, 1-98.

Henningsson, P., G.R. Spedding, A. Hedenström.2008. Vortex wake and flight kinematics of a swift in cruising flight in a windtunnel. the Journal of experimental Biology 211,717-730.

Henningsson, P., Muijres, F.T., A. Hedenström.2011. Time-resolved vortex wake of a common swift flying over a range of flightspeeds. Journal of the Royal Society: Interface 8,807-816.

Hespenheide, H.A. 1975. Selective predation by twoswifts and a swallow in Central America. Ibis 117: 82-99.

Holmgren, J. 1993. Young Common Swifts roosting infoliage of trees. British Birds 86(8): 368-369.

Lack, D. 1956. Swifts in a tower.London. Methuen. 239 pp.

Layard, E.L. Layard, E.L.C. 1878. Notes on theavifauna of New Caledonia. Ibis (4) 2:250-267.

Layard, E.L. Layard, E.L.C. 1879. Letters,announcements, c. Ibis (4) 3:107-108.

Leidgren, A. 1985. Något om de lappländskatornsvalorna. Fåglar i Norrbotten 2: 10-15. English Translation by Jan Holmgren: Notes on the swifts ofLapland.

Lentink, D., Müller, U.K., Stamhuis, E.J., de Kat, R.,van Gestel, W., Veldhuis, L.L.M., Henningsson, P., Hedenström, A., Videler,J.J. van Leeuwen, J.L. 2007. How Swifts control their glide performancewith morphingwings. Nature 446, (26), 1082-1085.

Lyuleeva, D.S. 1970. Enyergiya polyeta u lastochyok istrizhyei. [Flight energy in swallows swifts] Trans. Dokl. Akad.Sci. USSR. Nauk USSR 190:1467-1469. Transl. Transactions of the Doklady Akadamii of

Sciences, Nauk USSR

Maunders, S. 1854. The Treasury of Natural History.Longman, Brown, Green Longman. London.

Morse, R.A. Laigo, F.M. 1969. The PhilippineSpine-tail Swift, Chaetura dubia McGregor,as a honey bee predator. PhilippineEntom. 1: 138-143.

Oberholser, H.C. 1906. The status of the generic name Hemiprocne Nitzsch. Proc. Biol. Soc. Wash. 19: 67-70.

Palomeque, J., Rodriquez, J.D., Palacios, L. Planas, J. 1980. Blood respiratory properties of swifts. Comp. Biochem.Physiol. 67a: 91-95.

Rand, A.L. Rabor, D.S. 1960. Birds of thePhilippine Islands: Siquijor, Mount Malindang, Bohol, and Samar. Fieldiana Zool. 35(7):221-441.

Sinclair, I. Hockey, P. Tarboton, W. 1997. SASOLbirds of southern Africa. Struik Publishers, Cape Town.

Tarburton, M.K. 1986. Breeding of the White-rumpedSwiftlet in Fiji. Emu 86: 214-227.

Tarburton, M.K. 1987. An experimental manipulation ofclutch and brood size of White-rumped Swiftlets in Fiji. Ibis 129:107-114.

Tarburton, M.K. Kaiser E. 2001. Do fledgling andpre-breeding Common Swifts Apus apus take part inaerial roosting? An answer from aradio-tracking Experiment. Ibis 143: 255-263.

Tarburton, M. 2009. Why are White-throated Needletailsand Fork-tailed Swifts often last observed in Southern Australia when migratingnorthwards? Australian Field Ornithology 26, 19-24.

Videler, J.J., E.J. Stamhuis, G.D.E. Povel.2004. Leading-edge Vortex lifts swifts. Science 306,1960-1962.

Welty, J.C. 1975. The Life of Birds. 2^nd Ed. Philadelphia. W.B.Saunders.

WildbirdJan 1993, Birders Quiz.Wildbird Dec 1994, Wildbird Q A. then Collins response in Wildbird May 1995 (Vol 9(5), 2-3.)

Ifyou are interested in seeing more about individual species of swifts then click this LINK to Species details. It will take me some time to finishthem all, but I think it is worth a look to see if the one(s) you areinterested in are finished. Thanksfor your interest,

Prof.Mike Tarburton.

“retired”from Dean of School of Science Technology,

PacificAdventist University,

PapuaNew Guinea.

Ifyou are interested in communicating with me then retype my e-mail address into youre-mail program: . I am interested in new information,photos, corrections, discussion, or even questions you might have.

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