6o PERIODICITY IN ORGANIC LIFE. 



this is required to account for periodic abundance and scarcity when 

 the area over which either may occur is very large. 



For some few years, on our Essex and Suffolk coasts, sprats 

 have not been in their usual abundance, and, as far as known, there 

 is nothing to account for the scarcity. Their comparative scarcity 

 has not been due to either change of locality or over-fishing, and we 

 can only surmise that this fish is now passing through its period of 

 less abundance. It is to be hoped, for the sake of our seaside 

 dwellers, its period of abundance may soon return. Fish are most 

 difficult subjects for observation, and I will therefore simply pass them 

 over, noting only as a matter of common observation, we have bad 

 years in many species, that is years when few are taken. 



Birds are much better subjects for study and observation, and 

 we find periodicity in abundance and scarcity well marked in many 

 species. 



The first I will take is the House Martin. In many, in fact in 

 most, parts of the kingdom, we hear that this bird is becoming 

 rarer ever year, and the cause is said to be that the sparrow, being 

 so abundant, takes possession of the nests of the Martin, and so 

 prevents their increase. This may be one cause of the lessening 

 numbers, but I do not believe that it is the only one, for the Martin is 

 diminishing even in those parts where the sparrow is not, and never 

 has been, numerous. There must, therefore, be other causes ; I do 

 not know that man has had anything more to do with it than have 

 the seasons. Everywhere in this kingdom the Martin is a favourite, 

 and as such is rarely interfered with ; even on the Continent, where 

 bird slaughter is so common, I do not think that it is esteemed as 

 an article of food. From some cause this most interesting little 

 creature is diminishing in numbers ; undergoing its period of scarcity, 

 one hopes, but almost fearing that the facts point to approaching 

 extinction. 



As an illustration of the opposite condition — a period of abund- 

 ance — we may take the Hawfinch {Coccothraustes vulgaris). It is 

 not many years since this species was esteemed rare, and the find 

 of a nest was almost unheard of. This was in its period of scarcity ; 

 Init now, not only do we hear of its breeding in Epping Forest, 

 where Mr. Doubleday first recorded its nest as occurring, but also 

 in every part of this county its nest is frequently found. And to those 

 who know when and where to look for it there is generally no difii- 

 culty in finding a specimen. Now, if the scarcity of .species is to be 



