THE PARASITIC HABIT IN THE DUCKS, A THEORETI- 

 CAL CONSIDERATION 



By Herbert Friedmann 

 Curator, Division of Birds, United States National Museum 



It has been well known for many years that a number of kinds of 

 waterfowl are rather careless in their egg-laying habits, not infre- 

 quently laying one or more eggs in a near-by nest of another bird of 

 the same or other species, but still caring for their own nests and 

 eggs. Thus, among North American birds, some of the grebet, 

 the great auk, certain of the auklets and murrelets, a number 

 of gulls and terns, pelicans, ducks, rails, herons, a few shore 

 birds, and others have been known to drop an occasional egg in 

 another bird's nest. Gallinaceous, picarian, and passerine birds 

 have been laiown to act in a similar fashion at times, and I have 

 such records for not fewer than 54 species of North American birds, 

 not counting the regularly parasitical cowbirds. Years ago Paul 

 Leverkuhn compiled a great mass of data on this and allied topics 

 in his book Fremde Eier im Nest: Ein Beitrag zur Biologie der 

 Vogel (Strange Eggs in the Nest: A Contribution to the Biology 

 of Birds), published in 1891. Since the publication of this work a 

 still greater mass of data has been put on record, while other writers, 

 such as Swynnerton,^ have attacked the problem of rejections by 

 birds of eggs unlike their own. 



Among all the groups of birds involved, the habit is met with most 

 frequently in the Anatidae. The literature is so full of records that 

 a few quotations may here be sufficient. Sheparclson ^ writes that 

 waterfowl are addicted to this carelessness, " * * * many species 

 leaving their eggs to the care of other birds. Thus the eggs of the 

 Ruddy Duck, the Redhead, the Shoveller, and others are frequently 

 found in the nests of other ducks and coots." Job ^ found " * * * 

 nests of Gadwall, Baldpate, and Scaup that had each 1 or 2 



> Ibis, 1918, pp. 127-154. 



'Condor, vol. 17, p. 100, 1915. 



« Among the wild fowl, p. 201, 1902. 



No. 2918.— Proceedinqs u. S. National Museum, Vol. 80, Art. 18. 



91547—32 1 



