40 



THE OdLOGIST 



Bird Parasitism 



The rather elderly person whose 

 name is subscribed, hereto, has be- 

 come greatly interested in the 

 phenomena of parasitism, with many 

 birds. (One uses the term, "many 

 birds," quite soberly; for the term 

 covers a literal truth). There are now 

 two distinct kinds of Parasitism, what 

 we might call domiciliary-parasitism, 

 and ovo-parasitism. Let us glance, 

 briefly, at these, in turn. 



With birds that nest in tree-hollows, 

 it is quite natural that there should 

 be more pairs of birds of several kinds, 

 in a given locality, than there are 

 available hollows. Hence there has 

 arisen the cheerful spectacle of 

 halcyon nestings, in close contiguity, 

 of species most-unlike; and on the 

 contrary the rather repulsive 

 spectacle of bickerings without end, 

 between aspirants for a summer 

 home. Of the same character, involv- 

 ing violent usurption, is the finding of 

 eggs of sundry woodpeckers in the 

 arid south-west, within cactus hollows 

 in use by elf owls. Rarer, still, yet 

 sometimes occurring, is the case of 

 eggs of golden-eyes intruded into nest- 

 hollows occupied by hooded mergan- 

 sers. (In this connection, the writer 

 cites a rare experience of his own, il- 

 lustrating the persistence of the hom- 

 ing instinct, with many birds. Twice 

 have I found an egg of the previous 

 year with the fresh eggs in the nests 

 of hooded mergansers, blew 'em, too!) 

 Fairly incomprehensible, on any other 

 hypothesis than that of sheer laziness, 

 is the finding of intruded eggs in ex- 

 ternal nests, of various kinds. This is 

 habitual, with both species of our 

 easterly-breeding Cuckoos; and, of 

 course, with the erratic and uncaring 

 mourning dove. Often have I found 

 a nest of the latter containing three 

 eggs, one of them far less incubated 

 than the others; while just once, here 



in Kansas, did I find a nest on the 

 ground with its norm of two eggs; 

 and later turned aside to the see the 

 same nest, only to find it, to my sur- 

 prise, containing, four eggs two of 

 them quite fresh. I have also found, 

 just once, an egg of the mourning 

 dove in a nest of bronzed grackle. 

 Inexplicable, yet entirely heart-warm- 

 ing, are the rare cases when robins 

 and cuckoos have been found sitting, 

 peacefully, side by side; on a hodge- 

 podge of robin, cuckoo and, possibly, 

 brown thrasher-eggs. 



In the field of ovo-parasitism we 

 find greater diversity. Rarely enough, 

 the eggs of even three species have 

 been found in the same nest, example, 

 a cardinal nest, found by me, last 

 summer, containing, beside the normal 

 complement, an egg, each, of cowbird 

 and cat bird. Ovo-parasitism is dis- 

 tinctly common, with all the fuligin- 

 ous, and with some of the anatine, 

 ducks. The records I have compiled 

 are greatly interesting; and very vol- 

 uminous. The redhead appears to be 

 the commonest victim; and the canvas- 

 back the ordinary aggressor. Of this 

 sort of parasitism, innumerable cases 

 are on record. I here set down one 

 of my own: In a by-gone year, I 

 spent several days about the borders 

 of a grassy, meandering rush-filled 

 lake of North Dakota. In those days 

 there were ducks, a plenty. One sunny 

 June morning, for illustration, I count- 

 ed no less than seventy-five pintail 

 drakes, all sunning themselves on the 

 lake margin, amid the coverts. Mal- 

 lards, pintails, shovellers and a very 

 few green-winged teals were nesting 

 beside that lake; with an occasional 

 gadwall. Phalaropes were abundant; 

 as also were winged teal. On my 

 ways to and fro, between town and 

 lake, I noted how frequent was my 

 encounter with a very fussy female 

 canvas-back. Always, at a certain. 



