372 MIGEATION OF SWALLOWS 



The species of the Old and New World, with probably the 

 single exception of Cotyle riparia, are distinct from each other. 

 Species of the genus Hirundo and its immediate allies have 

 the range of the entire family, and Cotyle is also of rery exten- 

 sive distribution, inhabiting all the great continental areas, 

 unless Australia is to be excepted, as well as the Antilles. 

 Progne and Stelgidopteryx are confined to America; Petroehe- 

 lidon and Atticora are also characteristic of the Western Hem- 

 isphere, though both are said to occur in the Old World ; Che- 

 lidon is exclusively Old World ; Psalidoprogne is confined to 

 Africa ; and the single species of Phedina inhabits Madagascar 

 and the Mascarene Islands.* 



Migration of Swallows 



Being insectivorous birds that take their prey on the wing. 

 Swallows necessarily migrate through the cold and temperate 

 zones of the northern hemisphere. Their recession from the 

 north is urged as well by the delicacy of their organization 

 and their susceptibility to cold as by the periodical failure of 

 the sources of their food-supply. The prowess of their pinion 

 is equal to the emergency of the longest journeys — no birds 

 whatsoever fly better or farther than some of the Swallows do ; 

 and their movements are pre-eminent in the qualities of ease, 

 of speed, and of regularity. These facts are matters of com- 

 mon knowledge ; the comings of Swallows have passed into 

 proverb, and their leave-takings been rehearsed in folk-lore 

 among the signs of the waning times. Swallows have long 

 been held for weather-prophets; and with reason enough in 

 the quick response of their organization to the influence of 

 atmospheric changes. Swallows have figured in augury ; their 

 appearance has been noted among auspicia ; and truly their 

 flight is barometric, for they soar on clear warm days, ami 

 skim the surface of the ground in heavy falling weather, per- 

 haps neither always nor entirely in the wake of winged insects 

 on which they prey. These mercurial birds are also thermome- 

 tric ; they are gauges of temperature, if less precise than the 

 column of the fluid metal itself. It takes but a few warm 

 days, even in our midwinters, to send Swallows trooping north- 

 ward from the orange and the cypress of the South; and the 

 uncertain days, when capricious young spring pours delicious 

 balm on the wounds of winter, are sure to lure some Swallows 

 • Wallace, Geogr. Dist. Anim. ii. 281. 



