﻿SOCIAL 
  PARASITISM 
  IN 
  BIRDS 
  

  

  By 
  Hkrbkut 
  Friedmann 
  

   Curator, 
  Divinion 
  oj 
  Birds, 
  U 
  . 
  S. 
  National 
  Museum 
  

  

  If 
  one 
  were 
  to 
  enumerate 
  the 
  main 
  features 
  eharacteristic 
  of 
  birds, 
  

   the 
  chances 
  are 
  that 
  the 
  habit 
  of 
  nest-building 
  would 
  be 
  among 
  the 
  

   first 
  to 
  be 
  mentioned. 
  This 
  indicates 
  in 
  no 
  uncertain 
  fashion 
  the 
  

   universality 
  of 
  this 
  habit 
  in 
  this 
  large 
  group 
  of 
  vertebrates, 
  and 
  in 
  

   turn, 
  this 
  very 
  universality 
  immediately 
  focuses 
  our 
  attention 
  on 
  

   those 
  relatively 
  few 
  species 
  that 
  neither 
  build 
  nests 
  nor 
  care 
  for 
  their 
  

   eggs 
  or 
  young. 
  These 
  birds 
  lay 
  their 
  eggs 
  in 
  occupied 
  nests 
  of 
  other 
  

   species, 
  to 
  whose 
  care 
  they 
  are 
  left, 
  and 
  because 
  of 
  this 
  habit 
  are, 
  

   for 
  want 
  of 
  a 
  better 
  term, 
  said 
  to 
  be 
  parasitic. 
  The 
  habit 
  is 
  not 
  true 
  

   parasitism 
  in 
  the 
  real 
  biological 
  sense, 
  and 
  may 
  be 
  called 
  social 
  or 
  

   breeding 
  parasitism. 
  Few 
  problems 
  in 
  the 
  study 
  of 
  animal 
  behavior 
  

   have 
  aroused 
  more 
  interest 
  for 
  a 
  longer 
  period 
  of 
  time, 
  and 
  from 
  

   Aristotle 
  to 
  the 
  present 
  time 
  there 
  is 
  an 
  unbroken 
  series 
  of 
  attempts 
  to 
  

   explain 
  the 
  origin 
  of 
  this 
  peculiar 
  habit. 
  In 
  the 
  early 
  days 
  of 
  biological 
  

   science 
  this 
  question 
  was 
  limited 
  to 
  a 
  single 
  species, 
  the 
  well-known 
  

   P^uropean 
  cuckoo, 
  Cuculus 
  canorus, 
  and 
  it 
  was 
  of 
  this 
  bird 
  that 
  

   Aristotle 
  wrote, 
  ending 
  his 
  discourse 
  with 
  the 
  cautious 
  sentence, 
  

   "People 
  say 
  that 
  they 
  have 
  been 
  eyewitnesses 
  of 
  these 
  things." 
  

   Since 
  his 
  time 
  a 
  great 
  many 
  individuals 
  have 
  also 
  claimed 
  to 
  have 
  

   been 
  eyewitnesses 
  of 
  these 
  and 
  similar 
  things, 
  but 
  it 
  is 
  only 
  within 
  

   the 
  last 
  century 
  that 
  accuracy 
  and 
  precision 
  have 
  been 
  brought 
  into 
  

   play 
  in 
  these 
  observations 
  and 
  the 
  facts 
  separated 
  from 
  the 
  interpre- 
  

   tations. 
  Less 
  than 
  two 
  centuries 
  ago 
  it 
  was 
  found 
  that 
  many 
  cuckoos 
  

   in 
  Asia 
  were 
  also 
  parasitic, 
  but 
  the 
  habit 
  was 
  still 
  supposed 
  to 
  be 
  

   confined 
  to 
  the 
  one 
  family 
  of 
  birds. 
  

  

  In 
  the 
  early 
  days 
  of 
  the 
  last 
  century 
  it 
  was 
  discovered 
  that 
  the 
  

   cuckoos 
  were 
  not 
  the 
  only 
  birds 
  with 
  parasitic 
  breeding 
  habits, 
  and 
  

   that 
  the 
  cowbird 
  of 
  North 
  America, 
  Molothrus 
  ater, 
  a 
  bird 
  belonging 
  

   to 
  an 
  entirely 
  different 
  order, 
  also 
  exhibited 
  this 
  remarka?jle 
  mode 
  of 
  

   reproduction. 
  Later, 
  workers 
  in 
  southern 
  South 
  America 
  found 
  that 
  

  

  ' 
  iidpTint&l 
  by 
  permission, 
  with 
  slight 
  omissions, 
  from 
  The 
  Quarterly 
  Review 
  of 
  Biology, 
  Vol. 
  Ill, 
  No. 
  

   4, 
  December, 
  1938. 
  

  

  363 
  

  

  