530 



The Scarcity of Swallows. 



[Sept., 



As already stated, the swallows show partiality for wet ground, 

 and in Northern Europe, where insect life is abundant in the 

 swamps, these species summer in large numbers. In this coun- 

 try, the Hirundines roost in large numbers in reed beds where 

 these exist, particularly in the autumn when collecting for their 

 departure. The food supply of these marshy areas is possibly 

 the attraction which has developed this habit. 



There appears to be a tendency for the swallows to make an 

 earlier departure. During recent years, in the Tay Estuary, 

 considerable passage movements have been met with annually 

 in July, in the second week in some cases, and tlie sand martins 

 are moving sometimes in the first week. Many of these must 

 be young birds, but with them a considerable proportion of adults 

 is usual. It is clear, therefore, that in the case of these birds it 

 is scarcely likely that more than one brood has been reared, as 

 in Scotland, some districts, even in Forfarshire and Perthshire, 

 are not colonised until the second week of May, and in the glens 

 the house martin may only start building in the beginning of 

 June. 



It has been suggested in certain quarters that perhaps some 

 special dangers have arisen which confront the birds during their 

 migration, but it seems scarcely conceivable that destruction 

 could be wrought on a scale sufficient to make a marked cfiffereiice 

 over the whole area of Great Britain. It is quite possible that 

 an exceptional storm might cause a local shortage at some point 

 owing to the death of the birds building there, but it has been 

 proved that the various birds occupying a district do not neces- 

 sarily arrive or leave at the same time Consequently, in 

 general, some get through to preserve a colony. 



It is apparent that the swift, in spite of the similarity in some 

 of its habits to those of the swallow group, has not suffered so 

 groat a loss in recent years. In fact, in Scotland, the swift is 

 recorded as exceptionally numerous in 1918, pointing to the fact 

 that it is at least maintaining its footing there. In view of the fact 

 that only two young are reared in a brood and one brood only 

 is brought up during the season, the mortality in migration and 

 in its w^inter home must be very much less than that of the 

 swallows and martins, a problem itself worthy of investigation. 



