1942] 
Notes on Hippoboscidce 
111 
with the swifts by far the speedier of the two groups. Some 
species of swifts are possibly the fastest birds for their size, 
capable of reaching 70 to 100 miles per hour. 2 Both swallows 
and swifts are also capable of long-sustained flight, as they 
catch their food on the wing; but, again, the swifts spend much 
longer periods in the air, some species being unable to perch. 
When not nesting, some swifts must stay aloft for the major 
part of the day, at one stretch. In swallows and even more so 
in swifts, the narrow, pointed wings, very long in proportion to 
the small body, and often the more or less forked tail (the fork 
capable of opening and closing) are clearly adaptations to a 
predominantly aerial life. The body, particularly the head, is 
built so as to offer the least resistance to the air and is perhaps 
a little more “stream-lined” in the swifts than in the swallows. 
The plumage is very even and smooth at the surface. That 
of the swifts is usually coarser, stiffer, with less down on the 
bases of the body-feathers, than that of the swallows. 3 Several 
of these features explain well the peculiarities of the parasitic 
flies of these birds. The wings of the flies have become reduced 
or atrophied, because on birds travelling at high speed they in- 
crease the risk of the fly’s being blown off the host. They are, 
moreover, of little use for reaching a new host, on birds spend- 
ing so much of their life in mid-air and far away from the nest. 4 
2 Most published observations on the average and maximum speed of birds 
are unreliable, as they fail to take in account a number of important outside 
factors. The following data seem, however, to be fairly trustworthy. R. Mein- 
ertzhagen (1921, The Ibis, Ser. 11, III, pp. 232 and 237) gives the observed 
speed of a Mesopotamian swift (species?) as 68 miles per hour and estimates 
that of the alpine swift, Apus melba (Linne), as 70 to over 100 miles per hour. 
A. Magnan (1922, Ann. Sci. Nat., Zool., Ser. 10, V, p. 167) includes the Euro- 
pean swift, Apus apus (Linne), with the European swallows and martins in a 
group of high-speed birds averaging 45 to 80 miles (80 to 150 kilometers) per 
hour. E. Stresemann (1931 and 1934, in Kiikenthal, Handbuch der Zoologie, 
VII, pt. 2, pp. 584 and 837) gives the speed of the Asiatic swift, Hirundapus 
caudacuta (Latham), as 80 miles (144 kilometers) per hour. J. P. Chapin 
(1939, Bull. Amer. Mus. Nat. Hist., LXXV, p. 464) observed the Ruwenzori 
alpine swift, Apus melba maximus (O.-Grant), shooting by at a terrific speed 
and was tempted to estimate its velocity at about 100 miles per hour. 
3 These and other adaptive peculiarities of swifts and swallows were ac- 
quired independently, as the two groups are not related in the opinion of 
modern ornithologists. The Hirundinidae are placed in the order Passeres, and 
the Apodidae in the order Macrochires. Fossil Apodidae are known from the 
Oligocene to date (possibly from the Upper Eocene) (K. Lambrecht, 1933, 
Handbuch der Palaeornithologie, p. 621). 
4 The larvae of Stenepteryx and Crataerina are known to be laid in the nests 
of the host, where they hatch. In colder climates, some of the puparia remain 
unchanged through the winter, after the birds have migrated. They hatch upon 
