292 BULLETIN 191, UNITED STATES NATIONAL MUSEUM 



opportunity offers the carrion and hooded crows are not above raiding 

 the nests of their relatives. As shown by Elton and Buckland (1928) 

 a very high percentage of young rooks may be infected with gapeworms 

 morphologically identical with Syngamus trachea of poultry. Ninety- 

 four percent of 33 young birds examined were infested, mostly rather 

 heavily, but adults appear to be only slightly parasitized, so that it is 

 probable that infected young birds gradually rid themselves of the 

 parasites as they grow older, as happens in chickens. Cram (1927) 

 records Corvus frugilegus as host to the following nematode parasites: 

 Syngamus trachea, Acuaria anthuris, A. cordata, Oxyspirura sygmoidea, 

 and Microtetrameres inermis. G. Niethammer in the Handbuch der 

 deutschen Vogelkunde (1937) gives a list of ecto- and endoparasites ob- 

 tained from the rook. 



Fall and tuinter. — Outside the breeding season rooks are as gregarious 

 as when nesting, feeding together in flocks by day and roosting collec- 

 tively at night, and their habits during this period of the year are of 

 much interest. The general outlines of their behavior are tolerably 

 constant, but details vary considerably according to local conditions and 

 other factors. Their foraging excursions are not confined to the fields, 

 for after breeding they will resort regularly to woods, more especially 

 of oak, to feed upon caterpillars, as well as to the outskirts of the moors 

 in hilly districts. 



As the season advances the scattered parties tend to fuse together 

 into larger flocks, but in most districts it is noticeable that these flocks 

 contain remarkably few young birds. It is clear from several lines of 

 evidence that from causes still not precisely determined there must be a 

 very heavy mortality among the young during July and August, Care- 

 ful observations by J. P. Burkitt (1936) in Ireland led him to place the 

 number of young birds surviving in winter at as small a figure as about 

 10 percent of the number of adults, and this figure seems to be reached 

 as early as August. But the proportion of young to adults in flocks 

 seen in the fields is commonly even less, and many flocks consist of 

 adults exclusively. Some observations of the same author suggest that 

 the birds of the year independently of the adults (though commonly in 

 company with jackdaws) tend to form parties that wander far away 

 from the rookeries, but the subject of the habits of young rooks is one in 

 need of further careful study. 



At least in some districts from early in summer until fall parties 

 of rooks are apt to roost in any convenient wood or copse near which 

 they happen to find themselves, but in other cases the birds may con- 

 tinue to roost at their own rookery or may join up into larger roosting 

 assemblies comprising the occupants of more than one breeding colony. 



