FLEAS lOI 



and bird have evolved through the ages together, this is the rule rather 

 than the exception. Fleas having, on the other hand, only relatively 

 recently moved on to birds, there has not yet been time for many such 

 close relationships to develop. An example of strict host specificity in 

 the British fauna is provided by C. rossittensis, which has never been 

 recorded except on the crow {Corvus corone), either in this country or on 

 the continent. The rock-dove flea, the sand-martin flea and the four 

 house-martin fleas can also be considered host-specific although a 

 limited amount of straggling occurs. 



The second type of host preference is illustrated by fleas which show 

 a more or less marked predilection for certain famihes of birds. For 

 example a North American flea, C. difflnis, is essentially a parasite of the 

 thrushes, and despite its wide variety of hosts in Britain C. garei is un- 

 doubtedly partial to ducks and geese. This becomes more apparent 

 when it is surveyed throughout its range. 



Finally we have a third type consisting of a few species which 

 apparently show no host preferences and are equally at home on all 

 birds. When sufficient collecting has been done and the results properly 

 analysed it will be found that this indifference is more apparent than 

 real. No one will deny that C. gallinae, with its sixty-five diflferent 

 bird hosts in Britain alone, has cathoHc tastes, but the statement so 

 frequently met with in print that it is "common on all birds" is equally 

 false. The hen flea has not, for example, been recorded off* ducks and 

 geese (order Anseriformes) or from plovers and waders (order Chara- 

 driiformes) . 



In the chapter on distribution it has been mentioned that the three 

 commonest bird fleas in Britain can be "zoned" according to the type 

 of nesting site which they favour. Despite the considerable overlap 

 which occurs it is true to say that the highest proportion of C. gallinae 

 infestations are found in nests in tree tops or elevated situations (dry 

 aerial nests), the highest proportion of D. gallinulae in nests in lowly 

 situations such as brambles, walls and small bushes (damp nests), and 

 the highest proportion of C. garei infestations in ground nests and 

 in swampy situations (wet nests). 



At times host preference and nesting site preference must cut 

 across one another. A nest may be all that the larvae require but the 

 host prove unattractive to the adult — or vice versa. For example the 

 nesting habits of the pheasant and partridge are to all appearances 

 remarkably similar and in fact these birds not infrequently use each 



