﻿SOCIAL 
  PAEASITISM 
  IN 
  BIRDS 
  — 
  PRIEDMANN" 
  367 
  

  

  allows 
  for 
  a 
  numerical 
  increase 
  of 
  the 
  species 
  without 
  too 
  great 
  an 
  

   increase 
  in 
  egg-producing 
  individuals. 
  If 
  too 
  many 
  eggs 
  were 
  pro- 
  

   duced, 
  too 
  few 
  of 
  the 
  natural 
  foster 
  parents 
  would 
  be 
  able 
  to 
  bring 
  up 
  

   any 
  of 
  their 
  own 
  young 
  and 
  thereby 
  provide 
  an 
  adequate 
  supply 
  of 
  

   victims 
  for 
  the 
  succeeding 
  seasons. 
  The 
  numerical 
  status 
  of 
  the 
  

   parasite 
  depends 
  very 
  largely 
  on 
  those 
  of 
  the 
  common 
  host 
  species. 
  

   The 
  shiny 
  cowbird 
  is 
  an 
  early-breeding 
  species 
  and 
  is 
  parasitic 
  on 
  a 
  

   great 
  variety 
  of 
  small 
  birds; 
  in 
  fact, 
  almost 
  all 
  the 
  small 
  birds 
  breeding 
  

   in 
  the 
  range 
  of 
  this 
  cowbird 
  are 
  probably 
  parasitized. 
  Over 
  100 
  

   species 
  have 
  been 
  found 
  caring 
  for 
  its 
  eggs 
  or 
  young. 
  

  

  The 
  North 
  American 
  cowbird 
  is 
  very 
  similar 
  in 
  its 
  habits 
  to 
  the 
  

   shiny 
  cowbird. 
  In 
  song, 
  courtship 
  display, 
  relative 
  number 
  of 
  the 
  

   sexes, 
  sexual 
  relations 
  and 
  lack 
  of 
  specificity 
  of 
  host 
  species, 
  the 
  two 
  

   are 
  very 
  similar. 
  However, 
  the 
  shiny 
  cowbird 
  has 
  the 
  parasitic 
  

   habit 
  less 
  well 
  developed 
  and 
  wastes 
  large 
  quantities 
  of 
  its 
  eggs, 
  either 
  

   by 
  laying 
  them 
  on 
  the 
  ground 
  and 
  leaving 
  them 
  there 
  or 
  by 
  laying 
  too 
  

   many 
  eggs 
  in 
  one 
  nest 
  or 
  in 
  deserted 
  nests, 
  etc. 
  The 
  North 
  American 
  

   bird 
  is 
  more 
  efficient 
  in 
  the 
  disposition 
  of 
  its 
  eggs, 
  and 
  wastes 
  relatively 
  

   very 
  few 
  of 
  them. 
  About 
  two 
  hundred 
  species 
  of 
  small 
  birds 
  are 
  

   known 
  to 
  be 
  parasitized 
  by 
  this 
  cowbird. 
  

  

  The 
  red-eyed 
  cowbird 
  represents 
  another 
  branch 
  of 
  the 
  cowbird 
  

   tree 
  and 
  is 
  more 
  similar 
  to 
  the 
  screaming 
  cowbird 
  than 
  to 
  any 
  other. 
  

   It 
  is 
  parasitic 
  on 
  several 
  species, 
  usually 
  birds 
  of 
  genera 
  fairly 
  closely 
  

   related 
  to 
  itself, 
  such 
  as 
  Icterus. 
  The 
  males 
  somewhat 
  outnumber 
  the 
  

   females, 
  and 
  in 
  general 
  the 
  relations 
  of 
  the 
  sexes 
  are 
  similar 
  to 
  the 
  

   condition 
  in 
  the 
  North 
  American 
  cowbird. 
  

  

  THE 
  BREEDING 
  AREA 
  

  

  One 
  other 
  topic 
  demands 
  our 
  attention 
  before 
  we 
  can 
  piece 
  together 
  

   the 
  various 
  bits 
  of 
  evidence 
  offered 
  by 
  the 
  different 
  species 
  of 
  cowbirds. 
  

   This 
  is 
  the 
  matter 
  of 
  the 
  individual 
  breeding 
  area 
  or 
  territory. 
  Howard 
  

   (32) 
  has 
  shown 
  that 
  normally 
  each 
  pair 
  of 
  birds 
  establishes 
  an 
  individ- 
  

   ual 
  breeding 
  area 
  within 
  the 
  confines 
  of 
  which 
  they 
  tolerate 
  no 
  others 
  

   of 
  then- 
  own 
  species. 
  The 
  size 
  of 
  the 
  territory 
  in 
  most 
  cases 
  seems 
  to 
  

   depend 
  on 
  the 
  abundance 
  and 
  availability 
  of 
  food 
  for 
  the 
  young. 
  

   As 
  a 
  rule 
  (in 
  by 
  far 
  the 
  greatest 
  number 
  of 
  instances) 
  the 
  males 
  establish 
  

   the 
  territories 
  and 
  wait 
  there 
  for 
  the 
  arrival 
  of 
  the 
  females. 
  The 
  

   females 
  then 
  choose 
  the 
  exact 
  site 
  of 
  the 
  nest 
  within 
  the 
  territories 
  

   of 
  their 
  respective 
  mates. 
  The 
  establishment 
  of 
  the 
  territory 
  is 
  

   primarily 
  the 
  business 
  of 
  the 
  male, 
  and 
  his 
  main 
  task 
  during 
  the 
  early 
  

   part 
  of 
  the 
  breeding 
  season 
  seems 
  to 
  be 
  the 
  defense 
  and 
  maintainance 
  

   of 
  the 
  territory. 
  The 
  territory 
  seems 
  more 
  fundamental 
  than 
  the 
  

   nest 
  in 
  the 
  complex 
  of 
  instincts 
  of 
  the 
  male. 
  

  

  It 
  follows 
  that 
  the 
  sexual 
  relations 
  of 
  the 
  birds 
  (i. 
  e., 
  monogamy 
  

   versus 
  promiscuity, 
  etc.) 
  depend 
  largely 
  on 
  their 
  territorial 
  relations, 
  

  

  