Swifts of the World
Even though many people confuse members of the two swift
families with swallows and martins, once one has understood some of the
differences, then observed these birds in action – one never forgets that
swifts are not only different but very special.
Some special experiences I have enjoyed with swifts were:
In 1854 the Common Swift (Apus apus) of Europe was also called the Black Martin, and the Chimney Swift (Chaetura pelagica) was called the American Chimney Swallow, and the Glossy Swiftlet (Collocalia esculenta) of south-east Asia was called the Esculent Swallow (Maunders 1854). At the time swifts and swallows were classified in the same family: Hirundinae. They have since been separated into their own families as we have learnt more about them. We are still learning about them, and invite you to share in the enjoyment of discovering new facts about their design and behaviour. So what type of birds are swifts?
Swifts are characterised by:
1.
A short neck & humerus.
Humerus bone.
Photo:
Common Swift skeleton copyright Jean-Christophe Theil.
2. A protective
ridge of feathers above the eye to protect the eye from damage in collisions
with 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.
Common Swift, Belgium. Photo: copyright Raymond De Smet. Common Swift, France. Photo copyright J.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 hanging
from tree-trunk, foliage or cave roof, while asleep.
Foot of White-rumped Swiftlet roosting in a Lava tube cave, Samoa. Photo copyright M. Tarburton.
Foot of White-throated Needletail, Qld, Australia. Photo copyright M. Tarburton.
7. Long wings that can be swept
back to reduce drag and increase speed, allowing them to glide without
wing-beats in any direction on the slightest of breezes.
Fork-tailed Swift
Apus pacificus
Qld 5/2/2005
Photo copyright Ian Montgomery: birdway.com.au
The distinctive scythe shaped curve of the wings leading edge generates leading edge vortices providing lift and thrust beyond that of any other birds measured so far and when supported by changing wing-shape, high levels of oxygen-carrying haemoglobin 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 air all day. They take all their food and nesting materials from the air, and they fly up to heights of three or four kilometres (Gustafson et al 1977, Tarburton 2009). They even drink, bathe, mate and can spend the night on the wing (Lack 1956, Tarburton & Kaiser 2001).
Most species have enlarged salivary glands for production of the glue-like saliva used in nest building and for holding their food boluses together until they return to the nest to feed to the nestlings, which they only do at widely spaced intervals. Some species only feed their nestling(s) two to four times a day. Tests show they can go without food for two or three days. This means that young swifts have a cyclone-proofing that most birds do not enjoy. Sexes are similar and both share in breeding activities, such as incubation and nestling provisioning.
Swift physiology combined with their morphology enables them to fly using little energy compared to other birds. Their flying metabolic rate is only 2-5 times their sleeping metabolic rates, whereas most other birds have an increase of about 12 times (Lyuleeva 1970). Lets look at how the morphology of a swifts wing works.
The
traditional method of explaining how a bird or plane wing provides lift is to
show that air flowing over the top of the wing has further to go than air
passing under the wing. So air
particles going over the wing are stretched further apart – reducing air
pressure, compared to air going under the wing which remains more dense where
the higher pressure pushes up.
Together these features provide lift.
If the angle of attack of the wing is increased, drag is
increased, slowing the wing down as well as the attached bird or plane. In fact one leading authority on the
evolution of birds (Welty 1975. p.2) referring to bird design said that birds
compared to mammals Òsimply dare not deviate widely from sound aerodynamic
design. Nature liquidates
deviationists much more drastically and consistently than does any
authoritarian dictator.Ó It is
always dangerous to make generalisations, and particularly so for
scientists.
Greater knowledge arrived in 2004 when Science journal broke the news that:
ÒThe current understanding
of how birds fly must be revised,
because birds use their hand-wings in an unconventional way to generate lift
and drag.Ó (Videler et al. 2004).
They use the lift for gliding and flapping flight and they generate high
drag 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 at
Groningen & Leiden Universities in the Netherlands.
These researchers found that the arm-wing uses the
traditional aeronautics system, but that the distal hand wing (which in swifts
is most of the wing) is much thinner in cross-section and is designed to set up
a 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 all
the way and then are released at the tapered tip without the normal amount of
drag behind the wing.
Then these modified aerodynamic theories were shown in 2008
to be inadequate by testing, not models but the swifts themselves flying in low
turbulence wind tunnels at Lund University, Sweden (Henningsson et al 2008, 2011). The Dutch had already postulated a theory (Lentink et
al 2007) to explain how a swift can glide
and 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 the
wing produced thrust as well as lift equal to 60% of the lift of the
downstroke. Most birds do not
produce 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 swift
wing feathers, the sweep of the wing, the tapered tip, as well as a changing
wing shape. The swift wing generates clockwise leading-edge
vortices on the downstroke and anti-clockwise leading-edge vortices during the
upstroke. Put all this together
and it has the effect of increasing manoureveability in a bird that is
otherwise designed for speed. For
a bird that feeds on flying insects this would be a big help. This also answers the question insect
and swift researchers could not answer till now. How come many species of swifts and swiftlets at times catch
disproportionately more flies than other orders of flying insects, when
compared to the proportion of flies to other flying insects in the air, (Tarburton
1986) & when entomologists tell us flies are the most manoeuvrable group of
flying insects? (Hespenheide 1975).
SYSTEMATICS
Swifts are grouped into two families: the APODIDAE (Typical Swifts) and HEMIPROCNIDAE
(Tree Swifts).
Typical
Swifts Tree
Swifts
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
Telacanthura
Panyptila 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 Arctic
being 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 of
flying insects and hatchling spiders that drift through the air on strands of
web, and so may be seen over a wide range of terrestrial habitats, but for
roosting and sleeping they are dependent on cliffs, caves, hollow trees or
branches or foliage of either tall trees, or smaller trees on high ground. However, it has been shown that some
swifts 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 is
the Pygmy Swiftlet Aerodramus troglodytes
of the Philippines with a length of 90-92 mm (tip of bill to tip of tail), wing
length 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 Hirundapus
celebensis and though found in Indonesia
and 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 cannot
take off from the ground.
Even books about swifts say Òa downed swift is doomedÓ, or ÒWith long narrow wings shaped for
speed, and short weak legs, a swift that is brought down has a poor chance of
survivalÓ (Bromhall, D. 1980. Pp.
48 & 47). This is despite
David Lack stating as far back as 1956 (p. 119), that ÒContrary to popular
belief, it is not impossible for a swift to take off from a flat surfaceÓ. Yet
Campbell (1964) in The Oxford Book of Birds says ÒIf a swift lands by accident
it cannot take off againÓ I have placed White-throated Needletails on the
ground and watched them take off.
Paul Jones has also seen one of these needletails crash into his fire
lookout-tower, fall to the ground, in a stunned condition, then recover and fly
away (personal communication). In
1985 Leidgren published his observation of seeing a Common Swift tumble to the
ground in battle with a Starling.
When the Starling released itÕs grip the swift very easily flew
away. Leidgren has also seen one
crash after hitting pine branches, but it took off from the ground and entered
the nest box as if nothing unusual had taken place. Erich Kaiser & I have watched Common Swifts take off
from the floor of his house in Kronberg Germany, and Erich believes this myth
started from the observation that injured and starving swifts cannot take off
from a flat surface.
2. The legs of
Swifts have become almost useless.
Bromhall
(1980 p.8) will also provide an example for those who publish the idea that
swifts legs are small and almost useless.
It is true that they have short legs but they are not useless. They are very strong, with larger
species easily drawing blood from a human hand. I have found this to be particularly true with
White-throated Needletails. But
even at the other extreme, swiftlets feet are very strong. In fact to successfully remove nestling
swiftlets from their nests one has to learn how to get them to release their
grip on the nest or cave wall/roof, or their claws (toe-nails) (which do not
grow again) will be pulled off, so strong is their grip. It is important that swiftlets keep
their 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. Another
indicator of the importance of having strong feet & legs is that the legs
of White-rumped Swiftlets reach adult size in just 13.5 days whereas the wing
takes over 50 days to reach adult size (Tarburton 1986, 1987).
3. Australian
Swiftlets emigrate north of the equator for the Austral winter.Australian Swiftlets migrate in the winter time.
Pecotic (1974) visited three swiftlet nesting caves at
Chillagoe in the winters of 1965-1967 and not finding any birds in the caves
during daylight hours, published that Òthe birds were away, presumably north of
the equatorÓ. If he had gone back
in 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 were
any white spots of guano on the black areas. The white component disappears in one to two weeks so is a
good indicator as to whether the swiftlets are still resident in the cave or
not. I have met several people who
still thought this bird migrates north for the winter.
It had also been claimed that White-rumped Swiftlets of
New Caledonia Òmust be migratory, as during the summer months we did not
observe themÓ Layard & Layard (1879).
The previous year Layard & Layard (1878) had claimed the
opposite Òcommon in the cold
weather, up to the end of SeptemberÓ
and not seen since early October [Summer] so Òwe think partially
migratoryÓ. The birds are known to
be resident on New Caledonia all year, and the historical statements are just a
further example of observers jumping to conclusions before having adequate
data.
4. No nestling
swifts have down feathers.
While
all swifts studied to date are born naked (i.e. have no natal down), it is now
known 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 eight
to nine days old (Collins 1963).
Both these swifts breed in cool damp locations and these downy branches
of the early body feathers are assumed to help keep them warm in such
locations. A third swift the
African Palm Swift Cypsiurus parvus
has also been shown to grow these downy semiplumes to help them thermoregulate
in cool nest sites during the long absences of their parents (Collins
1965). It is true that most swifts
do not grow downy feathers.
5. Swifts always
roost before dark.
Breeding Common Swifts
are almost always at their nests before dark (Lack 1956,). Erich Kaiser (pers comm) has even had
Common Swifts return ahead of bad weather to sleep in their nests, three days
after they left on migration and apparently had run into bad weather. However, Lack (1956, p. 126) has
documented a series of observations where Common Swifts have been found trying
to roost after dark in unusual places – particularly in misty
weather. Accumulated evidence
suggests these are mostly young migrating birds not familiar with good roost
sites that they can find in cold and misty weather, and so they get caught in
the open after dark. In Southern
Sweden, Holmgren (1993) has shown that migrating Common Swifts coming in to
roost in the foliage of trees 10 to 40 minutes after sunset, on both foggy and
clear nights are almost always pre-breeding birds, likely from Lapland and on
their way to Africa.
Researchers at Rancho
Grande, in Venezuela commonly observe eight species of swifts, but only one of
them the Spot-fronted Swift Cypseloides cherriei is frequently found being attracted to lights well after sunset in
dense fog (Beebe 1949, 1950).
Collins (1980) also found
the same situation continued there and concluded that this swift might be
feeding further away than the other species and on foggy nights are thus more
likely to have difficulty finding their way back to their nests. It is suggested that this species feeds
further away to partition the resource with the other swift species in the
area. This practice might get more
food, but on foggy nights they may get caught out.
The Australian Swiftlet
is 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 are
still returning 4 hours after dark.
The Fijian birds roost in larger colonies than the Australian birds, and
so resource partitioning may be occurring within the species, just because the
populations 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 from
their roost, with most birds coming into the cave 1-3 hours after sunset and
some still entering after midnight (Hamilton et al 2001, & Tarburton unpublished). Both these swiftlets are habitually
late returning, and because they echolocate, getting lost in fog is not so
likely.
6. All swifts have
four forward facing toes (pamprodactyly).
Back when it took
minutes to take photographs and prior to that, it was natural to describe birds
from museum specimens, and one of the problems arising from this methodology
was that the toes of many dead birds, shrink into the pamprodactyl
position. So it was that many
authors have described swift feet as being pamprodactyl. For example see Wildbird
1993, 1994, and Sinclair et al. 1997, 19. Problem is, this is only true in real life
for some swifts. Hartert way back in 1892 noted that some swifts (Reinarda,
Tachornis & Cypsiurus) use their toes
in opposing pairs. Collins (1983)
published a photo of the foot of a live House Swift (Apus nipalensis) clearly portraying the lateral grasping format. You
can also see that format above, in the photo of the foot of the White-throated
Needletail. Next to that photo
above you can see the foot of the White-rumped Swiftlet roosting in a lava cave
in Samoa. It has three toes
forward and the hallux backwards – the anisodactyl arrangement. The Three-toed Swiftlet (Aerodramus
papuensis) does not have a hallux or hind
toe, to point in any direction. So
swifts have at least three types of arrangement for their toes.
References
Beebe, W. 1949. The swifts of Rancho Grande, north central
Venezuela, with special reference to migration. Zoologica 34: 53-62.
Beebe, W. 1950. Home life of the Bat Falcon, Falco albigularis
albigularis Daudin. Zoologica 35: 69-86.
Bromhall, D. 1980. Devil Birds. The life of the
Swift. Hutchinson, London. 96pp.
Campbell, B. 1964. The Oxford book of birds. London. Oxford
University Press.
Collins, C.T. 1963. The "downy" nestling
plumage of swifts of the genus Cypseloides. Condor 65:
324-328.
Collins, C.T. 1965. The down-like nestling plumage of
the Palm Swift Cypsiurus parvus (Lichenstein) Ostrich 36:
201-202.
Collins, C.T. 1980. The biology of the Spot-fronted
Swift in Venezuela. American Birds 34:
852-855.
Collins, C.T. 1983. A reinterpretation of Pamprodactyly in Swifts: a convergent
Grasping mechanism in Vertebrates.
Auk 100: 735-737.
Dickinson, E.C. 1989. A review of smaller Philippine
swiftlets 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. Ornis
Scand. 8: 87-95.
Hamilton, S., Erico, J. & Tarburton, M. 2001.
Notes on the sixth specimen record of the Three-toed Swiftlet Aerodramus
papuensis in Papua New Guinea. Corella 25(1):
12-14.
Hartert, E. 1892. Catalogue of the Birds of the British
Museum, vol 16. London. Trustees
of the Brit. Mus.
Hartert, E. 1897. Podargidae,
Caprimulgidae und Macropterygidae.
Tierreich 1, i-viii, 1-98.
Henningsson, P., G.R. Spedding, & A. Hedenstršm.
2008. Vortex wake and flight kinematics of a swift in cruising flight in a wind
tunnel. the Journal of experimental Biology 211,
717-730.
Henningsson, P., Muijres, F.T., & A. Hedenstršm.
2011. Time-resolved vortex wake of a common swift flying over a range of flight
speeds. Journal of the Royal Society: Interface 8,
807-816.
Hespenheide, H.A. 1975. Selective predation by two
swifts and a swallow in Central America. Ibis 117: 82-99.
Holmgren, J. 1993. Young Common Swifts roosting in
foliage 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 the
avifauna 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. NŒgot om de lapplŠndska
tornsvalorna. FŒglar i Norrbotten 2: 10-15. English Translation by Jan Holmgren: Notes on the swifts of
Lapland.
Lentink, D., MŸller, U.K., Stamhuis, E.J., de Kat, R.,
van Gestel, W., Veldhuis, L.L.M., Henningsson, P., Hedenstršm, A., Videler,
J.J. & van Leeuwen, J.L. 2007. How Swifts control their glide performance
with morphing
wings. Nature 446, (26), 1082-1085.
Lyuleeva, D.S. 1970. Enyergiya polyeta u lastochyok i
strizhyei. [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 Philippine
Spine-tail Swift, Chaetura dubia McGregor,as a honey bee predator. Philippine
Entom. 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 the
Philippine Islands: Siquijor, Mount Malindang, Bohol, and Samar. Fieldiana Zool. 35(7):
221-441.
Sinclair, I. Hockey, P. & Tarboton, W. 1997. SASOL
birds of southern Africa. Struik Publishers, Cape Town.
Tarburton, M.K. 1986. Breeding of the White-rumped
Swiftlet in Fiji. Emu 86: 214-227.
Tarburton, M.K. 1987. An experimental manipulation of
clutch and brood size of White-rumped Swiftlets in Fiji. Ibis 129:
107-114.
Tarburton, M.K. & Kaiser E. 2001. Do fledgling and
pre-breeding Common Swifts Apus apus take part in
aerial roosting? An answer from a
radio-tracking Experiment. Ibis 143: 255-263.
Tarburton, M. 2009. Why are White-throated Needletails
and Fork-tailed Swifts often last observed in Southern Australia when migrating
northwards? 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. 2nd Ed. Philadelphia. W.B.
Saunders.
Wildbird
Jan 1993, Birders Quiz.
Wildbird Dec 1994, Wildbird Q & A. then Collins response in Wildbird May 1995 (Vol 9(5), 2-3.)
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If
you are interested in seeing more about individual species of swifts then click this LINK to Species details. It will take me some time to finish
them all, but I think it is worth a look to see if the one(s) you are
interested in are finished. Thanks
for your interest,
Prof.
Mike Tarburton.
ÒretiredÓ
from Dean of School of Science & Technology,
Pacific
Adventist University,
Papua
New Guinea.
If
you are interested in communicating with me then retype my e-mail address into your
e-mail program: . I am interested in new information,
photos, corrections, discussion, or even questions you might have.